Answer to Question #207360 in Microbiology for Nani

Question #207360

Submission date:20/06/2021


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1. Describe in detail how abiotic factors affect the distribution of microorganisms in the aquatic ecosystem.

2. Explain about all the organisms which are used as indicators of water pollution.

3. Write a synopsis (general information) about bacteria which are found in surface waters and the diseases caused by them.

4. Describe the phenotypic approaches which are being used to assess the diversity of microorganisms in water.

Expert's answer


An aquatic ecosystem refers to an ecosystem that exists in water environments. It’s divided into two i.e. marine ecosystem and freshwater ecosystem. An ecosystem is largely determined by biotic (living organisms) and abiotic factors (non-living organisms). Abiotic factors are mainly the non-living part of the ecosystem which interplay with the biotic factors to generate a particular ecosystem suitable for a given organism(s). Micro-organisms are tiny and mostly invisible (with naked eyes) communities of organisms affected by these factors. They include bacteria, fungi, protozoa, algae, phytoplankton, periphyton, and microfilm. Abiotic factors such as sunlight, temperature, turbidity, salinity, amounts of oxygen dissolved, nutrients availability, and water PH mostly affect the distribution of these microbial communities.Sunlight provides heat energy needed to increase temperature, keeps harmful bacteria from dominating the ecosystem; provides light energy for photosynthesis to occur in phytoplankton and aquatic plants, influences algae growth. Too many UV rays damage cells and decrease the survival of some bacteria.

Temperature, a product of radiant heat, influences the amount of dissolved oxygen and dissolution of toxic chemical substances. At high temperatures, low amounts of oxygen are dissolved thus adversely affecting the survival of microbes; some chemicals are toxic, too, at high temperatures to aquatic life.

High salinity results in poor growth of plants and low microbial activities osmotic stress and toxic ions; bacteria are mostly affected by elevated saline conditions.

Turbidity, the measure of water clarity, determines the amount of light penetration in water and temperature; increased cloudiness of water decreases the amount of light for photosynthesis and increases water temperature since suspended particles absorb more heat. This mostly affects algae growth.

Nutrients are necessary for microbial growth and play a vital role in the proper cultivation of microorganisms.

PH is essential since it affects the various physiological process in the bodies of organisms; some such as bacteria, are sensitive to the hydrogen ions concentration, large proteins such as enzymes are affected by PH. Their shapes change or are denatures and often bring about alteration of ionic charges on the molecules. The PH of 2.6 and 4 (acidic) kills bacteria; E. Coli can grow in the condition of acidity between a range of 4.0 – 4.5.


Indicator organisms are used as a proxy to monitor conditions in a particular environment, ecosystem, area, habitat, or consumer product. Certain bacteria, fungi, and helminth eggs are being used for various purposes.

Indicator bacteria; certain bacteria can be used as indicator organisms in particular situations, such as when present in bodies of water. Indicator bacteria themselves may not be pathogenic but their presence in waste may indicate the presence of other pathogens. Similar to how there are various types of indicator organisms, there are also various types of indicator bacteria. The most common indicators are total coliforms, fecal coliforms, E. coli, and enterococci. The presence of bacteria commonly found in human feces, termed coliform bacteria (e.g. E. coli), in the surface water is a common indicator of fecal contamination.

Coliform bacteria selected as indicators of fecal contamination must not persist in the environment for long periods following efflux from the intestine, and their presence must be closely correlated with contamination by other fecal organisms. Indicator organisms need not be pathogenic. Non-coliform bacteria, such as Streptococcus bovis and certain clostridia may also be used as an index of fecal contamination.

Indicator fungi; Penicillium species, Aspergillus niger, and Candida albicans are used in the pharmaceutical industry for microbial limit testing, bioburden assessment, method validation, antimicrobial challenge tests, and quality control testing When used in this capacity, Penicillium and A. niger are compendial mold indicator organism.

Indicator helminth eggs; Helminth eggs (or ova) are a good indicator organism to assess the safety of sanitation and wastewater reuse systems for resource recovery because they are the most environmentally resistant pathogens of all pathogens (viruses, bacteria, protozoa, and helminths) and can in extreme cases survive for several years in the soil.[19] Typically, helminth eggs are found in water, soil, and food sources that are contaminated with fecal matter which comes from wastewater and sludge.


Bacteria are the most abundant and ancient microorganisms in water; when ingested, they cause several conditions some mild while some serious. Some of these harmful bacteria and the adverse effects (disease) they caused are outlined below.

Escherichia Coli; Escherichia Coli (also known as E. Coli) can cause nausea, vomiting, abdominal pain, and diarrhea if consumed in contaminated water. Symptoms usually appear within one to eight days.

 Campylobacter jejuni; drinking water contaminated with Campylobacter jejuni can cause infections with symptoms of cramping, diarrhea, fever, and pain. Symptoms of infection appear between two and ten days after exposure.

Hepatitis A; Hepatitis A is a serious infection and can be present in your drinking water. Symptoms include dark urine, jaundice, stomach pain, fever, and fatigue. Hepatitis A has a lengthy incubation period and symptoms might not appear until 28 days after exposure.

Giardia Lamblia; Giardia Lamblia is a parasite that causes the infection, giardiasis. Symptoms include nausea, cramps, gas, and diarrhea. The incubation period for giardiasis is two weeks.

Salmonella; Salmonella is a common pathogen that causes chills, fever, headache, diarrhea, and pain. Salmonella contaminates water and food and symptoms occur in one to three days after consumption.

Legionella Pneumophila; Legionella pneumophila can cause serious bacterial infections known as Legionnaires disease. Some symptoms of legionnaires infection are fever, shortness of breath, cough, and muscle aches. Legionnaires are very serious and usually involve hospitalization or can even result in death.

Cryptosporidium; Cryptosporidium is a protozoan that works similarly to a parasite. It causes severe and painful diarrhea and spreads through contaminated drinking water. Cryptosporidium can occur even in a city with clean water, and testing services are required to determine water quality and if these protozoa are thriving in your drinking water.


Conventional Phenotypic Identification; may involve several methods, including observation of growth and colony morphology on various media, analysis of manual biochemical reactions, and the use of automated and nonautomated commercially available biochemical panels. The most reliable methods are the direct plate count method and membrane filtration method. mEndo Agar is used in the membrane filtration while VRBA Agar is used in the direct plate count method. VRBA stands for violet red bile agar. A media that contains bile salts that promote the growth of gram-negative and have an inhibitory characteristic to gram-positive although not complete inhibitory.

These media contain lactose which is usually fermented by lactose fermenting bacteria producing colonies that can be identified and characterized. Lactose fermenting produces colored colonies while non-lactose fermenting produces colorless ones. Because the analysis is always based on a very small sample taken from a very large volume of water, all methods rely on statistical principles.

Multiple tube method; one of the oldest methods is called the multiple tube method. In this method, a measured sub-sample (perhaps 10 ml) is diluted with 100 ml of sterile growth medium and an aliquot of 10 ml is then decanted into each of ten tubes. The remaining 10 ml is then diluted again and the process repeated. At the end of 5 dilutions, this produces 50 tubes covering the dilution range of 1:10 through to 1:10000. The tubes are then incubated at a pre-set temperature for a specified time and at the end of the process, the number of tubes with growth in is counted for each dilution. Statistical tables are then used to derive the concentration of organisms in the original sample. This method can be enhanced by using an indicator medium that changes color when acid-forming species are present and by including a tiny inverted tube called a Durham tube in each sample tube. The Durham inverted tube catches any gas produced. The production of gas at 37 degrees Celsius is a strong indication of the presence of Escherichia coli.

ATP testing; An ATP test is a process of rapidly measuring active microorganisms in water through the detection of adenosine triphosphate (ATP). ATP is a molecule found only in and around living cells, and as such it gives a direct measure of biological concentration and health. ATP is quantified by measuring the light produced through its reaction with the naturally occurring enzyme firefly luciferase using a luminometer. The amount of light produced is directly proportional to the amount of biological energy present in the sample.

Plate count; The plate count method relies on bacteria growing a colony on a nutrient medium so that the colony becomes visible to the naked eye and the number of colonies on a plate can be counted. To be effective, the dilution of the original sample must be arranged so that on average between 30 and 300 colonies of the target bacterium are grown. Fewer than 30 colonies make the interpretation statistically unsound whilst greater than 300 colonies often result in overlapping colonies and imprecision in the count. To ensure that an appropriate number of colonies will be generated several dilutions are normally cultured. This approach is widely utilized for the evaluation of the effectiveness of water treatment by the inactivation of representative microbial contaminants such as E. coli.

Membrane filtration; most modern laboratories use a refinement of total plate count in which serial dilutions of the sample are vacuum filtered through purpose-made membrane filters and these filters are themselves laid on nutrient medium within sealed plates. The methodology is otherwise similar to conventional total plate counts. Membranes have a printed millimeter grid printed on them and can be reliably used to count the number of colonies under a binocular microscope.

Pour plate method; when the analysis is looking for bacterial species that grow poorly in air, the initial analysis is done by mixing serial dilutions of the sample in liquid nutrient agar which is then poured into bottles which are then sealed and laid on their sides to produce a sloping agar surface. Colonies that develop in the body of the medium can be counted by eye after incubation. The total number of colonies is referred to as the total viable count (TVC). The unit of measurement is cfu/ml (or colony-forming units per milliliter) and relates to the original sample. Calculation of this is a multiple of the counted number of colonies multiplied by the dilution used.



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