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- Discuss fungi that act as antibiotics
Many secondary metabolites of fungi are of great commercial importance. Psilocybin is a compound found in fungi such as Psilocybe semilanceata and Gymnopilus junonius, which have been used for their hallucinogenic properties by various cultures for thousands of years.
At the start of the 21st century, fungi were engaged in the development of more than 10 of the 20 most money-making products utilized in human medicine. Two anti-cholesterol statins, the antibiotic penicillin and the immunosuppressant cyclosporin A are amidst the peak 10. Each of these has a turnover in surplus of $1 billion annually. As pharmaceutical breakthrough extends, the following have lately been accepted for human use: micafungin is an antifungal agent; mycophenolate is used to avert tissue rejection; rosuvastatin is used to decrease cholesterol; and cefditoren as an antibiotic.
As simple eukaryotic organisms, fungi are important model research organisms. Many advances in modern genetics were achieved by the use of the red bread mold Neurospora crassa. Additionally, many important genes originally discovered in S. cerevisiae served as a starting point in discovering analogous human genes. As a eukaryotic organism, the yeast cell produces and modifies proteins in a manner similar to human cells, as opposed to the bacterium Escherichia coli, which lacks the internal membrane structures and enzymes to tag proteins for export. This makes yeast a much better organism for use in recombinant DNA technology experiments. Like bacteria, yeasts grow easily in culture, have a short generation time, and are amenable to genetic modification.
7 Fascinating Facts About Fungi
What do you think of when you think of fungi? Do you think of the mold growing in your shower or mushrooms? Both are types of fungi as fungi can range from unicellular (yeasts and molds) to multicellular organisms (mushrooms) that contain spore-producing fruit bodies for reproduction.
Fungi are eukaryotic organisms that are classified in their own Kingdom, called Fungi. The cell walls of fungi contain chitin, a polymer that is similar in structure to glucose from which it is derived. Unlike plants, fungi don't have chlorophyll so are not able to make their own food. Fungi typically acquire their nutrients/food by absorption. They release digestive enzymes into the environment that assist in this process.
Fungi are very diverse and have even contributed to improvements in medicine. Let's explore seven interesting facts about fungi.
Microorganisms: Friend and Foe Class 8 Extra Questions Science Chapter 2
Microorganisms: Friend and Foe Class 8 Extra Questions Very Short Answer Questions
Name the groups in which microorganisms are broadly classified.
Microorganisms are broadly classified in four groups:
Name the type of microorganism that is smaller than bacteria.
Write the name of a bacterium that helps in the formation of curd.
Write a use of yeast.
Yeast is used in the production of alcohol, wine, beer and other beverages.
What does yeast produce during respiration?
Yeast produces carbon dioxide gas during respiration.
What are pathogens? Write another name of pathogens.
Disease-causing microorganisms are known as pathogens. They are also called germs.
Define food preservation.
Food preservation is the method of preserving food from being spoiled by the microbes.
Write the names of any two antibiotics.
Who discovered the vaccine for small pox?
What is fermentation?
Fermentation is the process of conversion of food into alcohol.
The storing of food products at the temperature of 0°C to 5°C is known as refrigeration.
What is vaccine?
A substance which is used in the production of immunity against various diseases in the living body is termed as vaccine.
Name any two human diseases caused by viruses.
Name any three common plant diseases.
Rust of wheat, citrus canker and wilt
Name a microorganism which helps in nitrogen fixation.
Name a disease caused by food poisoning.
What is the difference between refrigeration and freezing?
In refrigeration, the storing of the food is done at a temperature of 0°C to 5°C, whereas freezing is used to store food at -18°C of temperature.
What is decomposition?
Decomposition is the process in which organic materials are broken down into simple inorganic sub-stances by the microorganisms.
Name the two microbes that are involved in the process of decomposition.
Bacteria and fungi
Name the first antibiotic discovered.
Microorganisms: Friend and Foe Class 8 Extra Questions Short Answer Questions
What are microorganisms? Give four examples.
Small organisms that cannot be seen through the naked eyes and can only be seen under a microscope are called microorganisms or microbes e.g., Amoeba, Paramecium, Volvox, Spirogyra, etc.
Classify bacteria on the basis of their shapes.
On the basis of their shapes, bacteria are classified into four categories:
- rod-shaped bacteria (bacilli)
- spherical-shaped bacteria (cocci)
- curved-shaped bacteria (vibrios)
- spiral-shaped bacteria (spirilla)
Define communicable diseases. Give some examples.
Communicable diseases are microbial diseases that can spread from an infected person to a healthy person through air, water, or other physical contacts e.g., cholera, chicken pox, tuberculosis, common cold, etc.
Differentiate between viruses and other microorganisms.
|(i) They show the characteristics of living organisms or reproduce only by entering the host organisms.||(i) They do not need to enter any host organism to reproduce or show any characteristics of life.|
|(ii) They are non-cellular microbes.||(ii) They are cellular microbes.|
What do you mean by food spoilage?
The process in which food is deteriorated to such extent that it does not remain fit for human consumption is known as food spoilage.
What role does sugar play in the preservation of food?
The role of sugar in food preservation is significant. By adding sugar in the food item, we reduce its moisture content and hence, it stops the growth of the microorganisms.
How are carriers harmful to us?
Carriers take with them many harmful microorganisms or pathogens. They play a great role in transferring these pathogens to a healthy person, by sitting on the food items, or directly transferring the pathogens inside the body of a person. Hence they are harmful to us.
What is vaccination?
The process of putting a vaccine inside the body of a person in order to produce immunity against some disease is called vaccination.
What do you mean by immunity?
Immunity is the ability of a body to develop resistance against diseases.
Give two examples of each of the following types of microorganisms:
(a) Algae – Spirogyra, Chlamydomonas
(b) Fungi – Aspergillus, yeast
(c) Protozoa – Paramecium, Amoeba
What are antibodies?
Whenever any harmful disease-causing microorganism enters the human body, the body produces substances to fight with the entered microbe. These substances are called antibodies.
What is the role of bacteria in increasing the soil fertility?
Some bacteria, which are present in the root nodules of leguminous plants or free-living fix the atmospheric nitrogen in the soil which is ultimately used up by the plants. Hence they increase the fertility of the soil. For example, Rhizobium, Azotobacter, Azospirillum, etc.
Define Ohmic heating.
Ohmic heating is the process in which electric current of high voltage is passed through the food items to kill the microbes that cause the spoilage of food.
What is sterilisation?
The process of killing all the microorganisms above the temperature of 100°C is known as sterilisation. It is one of the widely used methods to preserve food, and is often used for various food items.
What is pasteurisation?
Pasteurisation can be defined as the partial sterilisation of foods at a temperature that destroys harmful microorganisms without major changes in the chemical property of the food.
Microorganisms: Friend and Foe Class 8 Extra Questions Long Answer Questions
Explain why antibiotics do not work against flu or any infection caused by viruses.
Viruses cannot be killed by using antibiotics as their cell pathways are different from that of bacteria. It means taking antibiotics to get rid of flu or any other viral infection is useless, because it does not re-duce the strength of the virus, nor does it reduce the duration of the infection. But, however, antibiotic will work if we get attacks of viral infection and bacterial disease at the same time. Even then, it will cure bacterial disease only but not the viral infection.
Mention any three ways through which pathogens are transmitted.
Three ways because of which pathogens are transmitted are as follows:
- When a person sneezes or coughs, tiny droplets containing a number of disease-causing microorganisms come out of the mouth, and are released in the air. They are transmitted to a healthy person while breathing.
- By making direct contacts with an infected person, pathogens are transferred to a healthy person.
- Carriers of pathogens also help in their transmission. For instance, when a fly sits on animal excreta or garbage, harmful disease-causing microbes stick to its legs. And when this fly sits on the food items, pathogens get transferred to them. This contaminated food items cause serious diseases when it is eaten by a healthy person.
Canning is a process used for food preservation. Heat, at a certain temperature and for a limited period of time, is used to kill the harmful microorganisms as well as enzymes. This method also involves the removal of oxygen gas, and to avoid post-process contamination by airtight sealing of food items.
Explain how malaria is transmitted to humans.
A protozoan called Plasmodium is responsible for malaria. It lives in the liver and blood of the person who has been infected by this disease. A female Anopheles mosquito when sucks blood from the infected person, Plasmodium along with blood, is taken into its stomach. The Plasmodium, here, multiplies itself and reaches the salivary gland of the mosquito. Now, when this mosquito bites a healthy person, it injects Plasmodium along with saliva to him. The healthy person then gets an attack of malaria.
In this way, malaria is transmitted to humans.
Explain various types of bacteria.
Bacteria are classified on the basis of their shapes into the following categories:
- Rod-shaped bacteria (bacilli):
These are aerobic rod-shaped, spore-producing bacteria. They are often occurring in chain-like formations, and they are found primarily in soil e.g., Lactobacillus.
- Spherical-shaped bacteria (cocci):
They are spherical or nearly spherical bacteria e.g., Streptococcus.
- Curved-shaped bacteria (vibrios):
They are curved-shaped bacteria e.g., Vibrio.
- Spiral-shaped bacteria (spirilla):
They are flagellated, aerobic bacteria, having a spirally twisted rod-like form e.g., Treponema.
Microorganisms: Friend and Foe Class 8 Extra Questions Higher Order Thinking Skills
Unscramble the jumbled words underlined in the following statements
(a) Curbossulite is an air-borne disease caused by a bacterium.
(b) Xanrhat is a dangerous bacterial disease.
(c) Yeasts are used in the wine industry because of their property of meronettinaf.
(d) Cells of our body produce santiidobe to fight pathogens.
(e) Aeeessrrwtip are added to food to prevent growth of microorganisms.
What is the difference between Rhizobium and cyanobacteria in the way of fixing nitrogen for the plants?
Rhizobium lives in the root nodules of leguminous plants in a symbiotic relationship whereas cyanobacteria lives freely in the soil and fixes nitrogen.
It is always suggested that not to eat anything from street hawkers. Why?
Most of street hawkers sells food items in an open area which always get contaminated with the dust and flies carrying germs with them. Such an unhygienic condition lead to spoilage of food which when consumed can lead to serious illness.
Why oil is added while making pickle?
Oil seals off the air from the item that is being pickled and thus inhibit the growth of most of the microorganisms.
Ria thought of making curd. For this, she took lukewarm milk, mixed some curd into it and stir well. She kept the mixture in fridge. Next day she observed that curd was not set. Can you tell why the curd did not set?
Curd did not set because she kept the mixture in fridge. Lower temperature of fridge retarded the growth of Lactobacillus in the mixture.
Why do idli and dosa maker add some yeast or old batter of pervious day to the newly-made batter and keep it for one day?
For fermentation of idli and dosa yeast or old batter is added. Fermentation makes idli fluffy and dosa crispy, and change the flavour.
Microorganisms: Friend and Foe Class 8 Extra Questions Value-Based Questions
Seema got cough and cold badly. Her teacher asked her to take rest at home and use handkerchief while sneezing and coughing. She obeyed her teacher.
(a) Why should we keep a handkerchief on nose and mouth while sneezing or coughing?
(b) What are the modes of transfer of diseases from infected to healthy person?
(c) Do you think Seema’s teacher decision was right? Why?
(d) What value of Seema is shown here?
(a) We should keep a handkerchief on nose and mouth while sneezing or coughing because fine drop¬lets carrying thousands of viruses or bacteria spread in the air.
(b) Air, water, food, carriers and physical contact.
(c) Yes, because cough and cold spreads through air and there are chances that other students may also get infected.
(d) Seema is an obedient girl.
On Rahul’s birthday, his mother prepared many dishes for him. After having their meal, they found that many food items were left over. Rahul’s mother kept these leftovers in a air-tight container and refrigerate them.
(a) What is food preservation?
(b) What will happen to the food if it is not refrigerated?
(c) What is the role of refrigeration in food preservation method?
(d) What value of Rahul’s mother is shown here?
(a) The methods used for prevention of spoiling of food by the action of microbes is called food preservation.
(b) The food will get spoil and emit bad smell with changed colour or taste.
(c) Refrigeration retards or slow down the growth of microorganisms and enzyme activity on food. Thus, it prevents spoilage of food.
(d) Rahul’s mother is intelligent, economical, have scientific aptitude towards preservation of food.
Activities and Projects
Pull out a gram or bean plant from the field. Observe its roots. You will find round struc¬tures called root nodules on the roots. Draw a diagram of the root and show the root nod¬ules.
Collect the labels from the bottles of jams and jellie on the labels.
Do it yourself.
Visit a dcotor. Find out why antibiotics should not be overused. Prepare a short report.
To kill or stop the development of the disease-causing microbes, antibiotics are the medicines which are majorly used.
It’s very important to keep in mind that antibiotics must be taken only on the advice of a qualified doctor. Also, one should finish the prescribed course of antibiotics given by the doctor. If one takes an an¬tibiotic when not required or overuse it, then it will help bacteria in one’s body to develop resistance to the given antibiotic. Next time when one falls sick and needs that antibiotic, it will be less effective. Excess dose of antibiotics also kills friendly microbes inside our body and thus helps to flourish patho-genic microbes.
Project: Requirements 2 test tubes, marker pen, sugar, yeast powder, 2 balloons and lime water.
Take two test tubes and mark them A and B. Clamp these tubes in a stand and fill them with water leaving some space at the top. Put two spoonfuls of sugar in each of the test tubes. Add a spoonful of yeast in test tube B, Inflate the two balloons incompletely. Now tie the balloons on the mouths of each test tube. Keep them in a warm place, away from sunlight. Watch the setup every day for next 3-4 days. Record your observations and think of an explanation.
Now take another test tube filled 1/4 with lime water. Remove the balloon from test tube B in such a manner that gas inside the balloon does not escape. Fit the balloon on the test tube and shake well. Observe and explain.
It was observed that the balloon fitted on test tube B is completely inflated but balloon fitted on test tube A is not inflated. When the inflated balloon of test tube B is fitted on test tube filled with lime water, lime water turns milky. This is because yeast celj releases C02 during respiration which inflates the balloon and C02 present inside the balloon changes lime water milky.
I. Multiple Choice Questions (MCQs)
Choose the correct option.
Tiny organisms which cannot be seen with the naked eyes are called
Microorganisms are also known as
Fungus can be seen with a
(c) magnifying glass
(d) both (a) and (c)
Microorganisms that causes disease are also kn
Pathogens are also called
Bacteria are organisms.
Bacilli are the bacteria that are
Spherical-shaped bacteria are called
Simple, plant-like microorganisms are called
(c) both (a) and (b)
Medium that transmits pathogens from an infected person to a healthy one is called
(d) none of these
Medicine that kills or stops the growth of harmful disease-causing microbes is known as
The process in which sugar in the food is transformed into alcohol and carbon dioxide by using microorganisms is known as
The fungus that is commonly used in bakery and beverage industries is
Giardia is listed under the category of
Substance used to produce immunity against diseases in the living body is called
II. Fill in the Blanks
Fill in the blanks with suitable word/s.
1. Bacteria, fungi, protozoa and _______ are the major four groups in which microorganisms are classified.
2. Two microorganisms which live in symbiotic association in lichens are _______ and _______.
3. We use a _______ to see the microorganisms.
4. _______ are considered different from other microorganisms because they can multiply only by entering the host organisms.
5. The gas released during the preparation of bread is _______.
6. The disease caused by a protozoan and spread by an insect is _______.
7. _______ are curved-shaped bacteria.
8. Saprophytes and _______ are the two main categories of fungi.
9. _______ are the threads of the multicellular fungi.
10. Yeast is a _______ fungus.
11. Protozoa are _______ in nature.
12. Flu, cough and cold are caused by _______.
13. The first antibiotic discovered was _______.
14. _______ are the microorganisms that help in the process of decomposition.
15. The process of formation of curd from milk is known as the _______ of milk.
2. algae, fungus
5. carbon dioxide
III. Match the following
Match the items given in column I suitably with those given in column II.
IV. True or False
State whether the given statements are true or false.
1. Microbiology is the science of study of microbes.
2. All the microorganisms are harmful.
3. An instrument called microscope is required to see the microorganisms.
4. Bacteria have an organised nucleus.
5. Microorganisms are found in large number around us.
6. Viruses are the most useful microbes.
7. Anabaena is listed in the category of algae.
8. Algae tend to develop on wet surfaces.
9. Amoebic dysentery is caused by algae.
10. A fungi is used in the production of alcohol.
11. Jellies, jams and squashes are preserved by adding vinegar to them.
12. Salt is used as a food preservative.
13. Oxygen alone constitutes 78% of air.
Fungi are rich, underexploited reservoirs for natural products that may serve as medicines, commodity chemicals, insecticides, pesticides and other valuable chemicals. Moreover, the biochemistry of natural product formation may be repurposed with emerging synthetic biology tools to make valuable non-natural compounds such as biofuels. However, the pathways that lead to these products are poorly understood and frequently inactive under lab conditions making discovery challenging. Recent advances in -omics approaches and synthetic biology tools provide powerful new methods to elucidate and tap this wealth of novel chemistry. In this review, we describe cutting-edge approaches to activate and characterize natural product formation, and discuss the potential of established and emerging fungal systems for natural product discovery.
Fungal infections that resist treatment are a challenge to the public&rsquos health.
Medical illustration of Candida spp., presented in CDC&rsquos Antibiotic Resistance Threats in the United States, 2019.
Antifungal drugs treat fungal infections by killing or stopping the growth of dangerous fungi in the body. Fungi, like bacteria, can develop antibiotic resistance, when germs like bacteria and fungi develop the ability to defeat the drugs designed to kill them. Antifungal resistance occurs when fungi no longer respond to antifungal drugs.
Only three types of antifungal drugs currently exist, so antifungal resistance can severely limit treatment options. Some types of fungi, like Candida auris, can become resistant to all three drug types. 1 Resistance is especially concerning for patients with invasive fungal infections&mdashsevere infections that affect the blood, heart, brain, eyes, or other parts of the body&mdashbecause these are serious infections that may be more difficult to treat if they are resistant and if antifungal treatment is limited. For example, bloodstream infections with the fungus Candida (a yeast) that are resistant to treatment can cause serious health problems, including disability and death.
What causes antifungal resistance?
Some species of fungi are naturally resistant to treatment with certain types of antifungal drugs. For example, the drug fluconazole does not work against infections caused by the fungus Aspergillus, a type of mold. Resistance can also develop over time when fungi are exposed to antifungal drugs. This resistance can occur when antifungal drugs are used improperly to treat sick people (e.g., when dosages are too low, or when treatment courses are not long enough), or even when antifungal drugs are used properly. 2,3 Use of fungicides in agriculture to prevent and treat fungal diseases in crops can also contribute to resistance in people exposed to those fungicides.
Some studies have indicated that antibiotics &mdashwhich include antifungal drugs&mdashmay also contribute to antifungal resistance in Candida. This resistance could occur in a variety of ways. For example, antibiotics can reduce good and bad germs in the gut, which creates favorable conditions for Candida growth. 4 It is not known if decreasing the use of all or certain antibiotics can reduce Candida infections, but appropriate use of antibiotics and antifungal drugs is one of the most important factors in fighting drug resistance.
Types of resistant fungi
Fungi that have shown resistance to antifungal drugs are Aspergillus and certain Candida species. Candida auris is a new species that is particularly resistant to antifungal drugs and can spread in healthcare settings. Learn more:
How do penicillins work?
Penicillins are a group of antibacterial drugs that attack a wide range of bacteria. They were the first drugs of this type that doctors used. The discovery and manufacture of penicillins have changed the face of medicine, as these drugs have saved millions of lives.
Penicillium fungi are the source of penicillin, which people can take orally or via injection.
People across the globe now widely use penicillins to treat infections and diseases.
- Penicillins were the first antibiotic that doctors used.
- There are several antibiotics in the penicillin class.
- Experts credit Alexander Fleming with discovering penicillins.
- Penicillin works by interfering with bacteria cell walls.
- Less than 1 percent of people are dangerously allergic to penicillin.
Drugs in the penicillin class work by indirectly bursting bacterial cell walls. They do this by acting directly on peptidoglycans, which play an essential structural role in bacterial cells.
Peptidoglycans create a mesh-like structure around the plasma membrane of bacterial cells, which increases the strength of the cell walls and prevents external fluids and particles from entering the cell.
When a bacterium multiplies, small holes open up in its cell walls as the cells divide. Newly-produced peptidoglycans then fill these holes to reconstruct the walls.
Penicillins block the protein struts that link the peptidoglycans together. This prevents the bacterium from closing the holes in its cell walls.
As the water concentration of the surrounding fluid is higher than that inside the bacterium, water rushes through the holes into the cell and the bacterium bursts.
People generally attribute the discovery of penicillins to Alexander Fleming. The story goes that he returned to his laboratory one day in September 1928 to find a Petri dish containing Staphylococcus bacteria with its lid no longer in place.
The dish had become contaminated with a blue-green mold called Penicillium notatum. Fleming noted that there was a clear ring surrounding the mold where the bacteria had been unable to grow.
By discovering this mold and recognizing its use, Fleming set the wheels in motion to create one of the most useful drugs in medical history.
In March 1942, Anne Miller became the first civilian to receive successful treatment with penicillin. She narrowly avoided death following severe infection after a miscarriage.
Although Fleming technically discovered the first antibiotic, scientists had to do a lot of work before penicillins could become available for general use.
Scientists with a superior laboratory and a deeper understanding of chemistry than Fleming carried out the bulk of the work. Howard Florey, Norman Heatley, and Ernst Chain performed the first in-depth and focused studies on the drug.
In Fleming’s Nobel Prize acceptance speech, he warned that the overuse of penicillins might, one day, lead to bacterial resistance. This has since become a problem.
Contrary to popular opinion, it is not the person who develops resistance to penicillins but the bacteria itself.
Bacteria have been around for billions of years. During this time, they have endured extreme environments and, as a result, are highly adaptable. They also regenerate very rapidly, making relatively quick genetic changes possible across a population.
There are three common ways in which bacteria can develop an immunity to penicillin:
What are the possible side-effects?
It is not possible in this leaflet to list all the possible side-effects of each antibiotic. However, as with all medicines, there are a number of side-effects that have been reported with each of the different antibiotics. If you want more information specific to your antibiotic then you should read the information leaflet that comes with the medicine.
Most side-effects of antibiotics are not serious. Common side-effects include soft stools (faeces), diarrhoea, or mild stomach upset such as feeling sick (nausea). Less commonly, some people have an allergic reaction to an antibiotic and some have died from a severe allergic reaction - this is very rare.
Antibiotics can kill off normal defence bacteria which live in the bowel and vagina. This may then allow thrush or other bad bacteria to grow.
You should tell your doctor if you have any of the following side-effects:
- Severe watery diarrhoea and tummy (abdominal) cramps: signs of a serious bacterial infection of the gut - Clostridium difficile infection.
- Shortness of breath, hives, rash, swelling (of the lips, face, or tongue), fainting: signs of an allergic reaction.
- Vaginal itching or discharge: signs of vaginal thrush.
- White patches on the tongue: signs of oral thrush.
- Being sick (vomiting).
Some antibiotics may interact with other medicines that you might take. This may cause reactions, or reduce the effectiveness of one or other of the treatments. So, when you are prescribed an antibiotic you should tell a doctor if you take other medicines.
Oral contraceptive pill
In the past it was recommended that, if you were taking antibiotics and were also taking the pill, you should use additional contraception. This is no longer the current recommendation after more recent evidence has been reviewed.
Antibiotics (other than one called rifampicin) do not interfere with the effectiveness of the pill. You should continue taking your pill as normal if you also need to take any antibiotics.
Side effects of antifungal medicines
Antifungal medicines may cause side effects. These are usually mild and do not last long.
- itching or burning
- feeling sick
- tummy (abdominal) pain
- a rash
Occasionally, antifungal medicines may cause a more severe reaction, such as:
- an allergic reaction – your face, neck or tongue may swell and you may have difficulty breathing
- a severe skin reaction – such as peeling or blistering skin
- liver damage (very rarely) – you may have loss of appetite, vomiting, nausea, jaundice, dark pee or pale poo, tiredness or weakness
Stop using the medicine if you have these severe side effects, and see a GP or pharmacist to find an alternative.
If you're having difficulty breathing, go to A&E or call 999.
These are also referred to as blue-green algae. Though they are capable of conducting oxygen-producing photosynthesis and live in many of the same environments as eukaryotic algae, cyanobacteria are gram-negative bacteria, and therefore are prokaryotes. They are also capable of independently conducting nitrogen fixation, the process of converting atmospheric nitrogen to usable forms of the element such as ammonia.
The prefix "cyano" means blue. These bacteria have pigments that absorb specific wavelengths of light and give them their characteristic colors. Many cyanobacteria have the blue pigment phycocyanin, a light-harvesting pigment (it absorbs red wavelengths of light). Cyanobacteria all have some form of the green pigment chlorophyll, which is responsible for harvesting light energy during the photosynthetic process (Current Biology, 2014). Some others also have the red pigment phycoerythrin, which absorbs light with the green region and bestows the bacteria with a pink or red color.
The eukaryotic algae are polyphyletic, meaning that they did not evolve from a single common ancestor. This is clearly demonstrated in our current understanding of the tree of life &mdash a family tree of all living organisms organized by their various evolutionary relationships. Eukaryotic algae are found distributed among many different groups, or major branches of the tree.
In a 2014 review article published in the journal Cold Spring Harbor Perspectives in Biology, author Fabien Burkilists five supergroups of eukaryotic organisms: Ophiskontha, Amoebozoa, Excavata, Archaeplastida and SAR (which comprises three groups, Stramenopiles, Alveolata and Rhizaria).
Archaeplastida includes plants and a variety of photosynthetic algal species such as the chlorophytes (a subset of green algae), charophytes (mainly freshwater green algae) and glaucocystophytes (unicellular freshwater algae). Chlorophytes are the green algae that commonly form lichen partnerships with fungi.
Dinoflagellates are found within Alveolata. These are primarily unicellular marine and freshwater organisms. Many dinoflagellates have lost their plastids &mdash the site of photosynthesis &mdash through the course of evolution and are phagotropic or live as parasites. Still other algal species are found distributed amongst Alveolata, Excavata, Rhizaria and Chromista (Current Biology, 2014).
3 Answers 3
I agree with @Chris that this is mostly a matter of definitions -
According to the Biocides Directive (98/8/EC), biocidal products are those that are intended to destroy, render harmless, prevent the action of, or otherwise exert a controlling effect on any harmful organism by chemical or biological means. Examples include disinfectants, preservatives, antiseptics, pesticides, herbicides, fungicides and insecticides.
Antibiotics are widely used as medication against disease-causing bacteria. However, bacteria can acquire resistance to particular antibiotics through mutation or gene transfer.
So the key difference is that antibiotics act more specific and may induce resistance. Antiseptics such as alcohol stay active, even after repeated use, because they act broadly. Now that triclosan is argued to have a specific molecular target, it may have to be re-defined from a general biocide to antibiotic. This means that its widespread use may be alarming, and I quote from your linked article (Schweizer, 2001):
[Triclosan is used in a] multitude of health care and consumer products [and has] germicidal properties [and has] flooded the market in recent years in response to the public's fear of communicable bacteria.
Triclosan binds to bacterial enoyl-acyl carrier protein reductase (ENR) enzyme, which is encoded by the gene FabI. This binding increases the enzyme's affinity for nicotinamide adenine dinucleotide (NAD+). This results in the formation of a stable, ternary complex of ENR-NAD+-triclosan, which is unable to participate in fatty acid synthesis.
If you notice, you would see that this mechanism is attributed to low concentrations of triclosan when it acts as a bacteriostatic. Disinfectants, IMO cause direct chemical damage to cell (denaturation of proteins/destruction of the membrane etc) unlike antibiotics which inhibit some vital metabolic processes. Triclosan is generally used in the form of a disinfectant (at high concentrations). Even though its enzyme inhibitory properties have been studied, it is not systemically administered in the form of an antibacterial drug.
The terms antibiotics and bactericidal were coined when mechanisms were not really known. Even then, antibiotic is traditionally known as a substance that is produced by one organism (a fungus in case of penicillin) to prevent the growth of the other.
I would like to differ from Christiaan's opinion that antibiotics are substances against which resistance can be developed. It is possible to acquire resistance towards a conventional, broad spectrum, direct damage agent. For instance there are bacteria that can survive heat/UV/γ-rays (which are physical disinfectants). Microbes can also develop resistance to chemical agents and though I cannot cite an example at the moment, I can think about how the cell can achieve it. One way is to develop a stronger cell wall.
Also note that alcohol is not considered a disinfectant at concentrations < 70%. At much lower concentrations alcohol can actually serve as an energy source.
So I think this is the tacitly accepted definition:
Disinfectants are usually synthetic chemicals that inflict direct damage whereas antibiotics are primarily natural chemicals that inhibit some vital metabolic process.
The term bactericidal or biocidal denotes the consequence rather than the nature of the mechanism. Antibiotics can be bactericidal too. Many herbicides are inhibitors of chloroplastidial metabolism.