Tag: bacteria

Clostridium botulinum is a bacterium that produces a potent neurotoxin, which causes botulism, a severe form of food poisoning.

• Citrus canker is a disease that affects citrus species caused by the bacterium Xanthomonas axonopodis.
  
• The bacteria causing diseases in humans are- Tuberculosis and cholera.
• Cholera is caused by the bacterium Vibrio cholera.
• Tuberculosis is caused by Mycobacterium tuberculosis. 

Mycoderma aceti is an aerobic acetic acid bacterium that converts ethanol into acetic acid in presence of oxygen. The ethanol is first aerobically fermented into acetaldehyde which is then oxidized into acetic acid. The Mycoderma aceti present in wine and in the surrounding air produce acetic acid (vinegar) which imparts sour taste to the wine. The requirement of oxygen for the process. Heat exposure renders the bacteria inactive and acetic acid production is stopped. Long term exposure to UV light affect the phenolic and ester component of wine and render it tasteless; since acetic acid formation is not affected by light, wine is not turned sour in light.

Sterilization refers to a technique that makes the desired material/medium/object completely free from all life forms including microbial spores and viruses. It is done by number of methods like boiling, incineration, pasteurization, hot air sterilization etc. Option A is incorrect. Pasteurization is technique wherein heat is applied to liquids (milk, beverages and dairy products) to kill potential agents of infection and spoilage while retaining the flavour and food value. It includes exposure of the liquid to 71.6°C for 15 seconds (flash method) or to 63°–66°C for 30 minutes (batch method) followed by its cooling. Option B is correct. The conversion of ammonia into nitrates is termed as nitrification and is carried out by chemolithotrophic bacteria; Nitrosomonas and Nitrobacter. Freezing refers to maintenance of bacteria under very low temperature that kill fractions of them but the survivors are maintained as dormants for longer periods as they show no metabolic activity; option D is incorrect. Thus, the correct answer is option B. 

Microorganisms that produce methane as a by-product of its metabolic activities is known as methanogens. They are classified either as bacteria or archaea, these anaerobic organisms are commonly found in wetlands creating the marsh gas, digestive tracts of human beings and animals, marine sediments and hot springs.

Gobar gas is mixture of methane (CH$ _4$), carbon dioxide (CO$ _2$), hydrogen (H$ _2$) and hydrogen sulphide (H$ _2$S) with methane as major component (65%). Methanogens are anaerobic, autotrophic, eukaryote that converts carbon dioxide and hydrogen into methane gas. The hydrogen serves as electron donor for reduction of carbon dioxide. Thus, methogens produce gober gas by anerobic fermentation of biomass in presence of water. The chemolithotrophic bacteria that reduce the organic nitrogen into ammonia are termed as ammonifying bacteria. The chemolithotropic bacteria that converts ammonia NH$ _3$ into nitrates, NO$ _3$-, are termed as nitrifying bacteria; it includes Nitrosomonas and Nitrobacter. The chemolithotrophic bacteria that reduce the nitrates into nitrogen are termed as denitrifying bacteria. Ammonifying, nitrifying and denitrifying bacteria are component of nitrogen cycle and do not serve in gober gas (methane) production. Thus, the correct answer is option A. 

Methane, also called as marsh gas, is a colourless, odourless gas that occurs abundantly in nature as the chief constituent of natural gas. The decomposition of sludge by anaerobic bacteria in sewage-treatment processes produces a gas rich in methane.

Soil is the rich source of water and organic matter. Decomposition of remains of dead organisms adds organic content to the soil. Weathering of minerals add inorganic fraction of soil. Thus, soil fulfils the nutritional requirement of bacteria with diverse feeding habits and serves as richest source of bacteria. Since, bacteria can live on the surface of soil particles in form of biofilms which can be formed on almost any surface; thus type of soil does not affect the bacterial population. Option B is correct. Poor solubility of oxygen and limited penetration of sun light in water limits the distribution of majority of bacteria in limnetic and profundal zone which makes option C incorrect. Owing to extreme temperatures, chemical contamination, and low nutrient environments, air does not serve as good habitat for bacteria and thus, only thick walled resistant bacteria/bacterial structures like endopores are present in air; option A is incorrect. Despite providing favourable nutritional condition for bacterial growth, temperature variations in milk limit their growth. Option D is incorrect. Thus, the correct answer is option B. 

Bacteria are the component of biological nitrogen fixation which included free living or non-symbiotic soil bacteria. It may be aerobic bacteria (Azotobacter spp), anaerobic bacteria (Clostridium spp), photosynthetic bacteria (Rhodospirillum spp), chemosynthetic bacteria (Thiobacillus spp) and blue-green algae. The finger-like projections on roots of legumes, termed as root nodules, carries Rhizobium bacteria which in turn are responsible for nitrogen fixation; legumes depend on of bacteria for nitrogen fixation. None of the parasitic algae or fungal species can fix nitrogen. Thus, the correct answer is option A.

Azotobacter is a free-living aerobic rod-shaped soil bacteria; it is a member of Gammaproteobacteria and fixes the atmospheric nitrogen into the useable form which makes option A correct. Rhizobium is a Gram-negative, motile, rod-shaped bacteria that forms special nitrogen-fixing organs, called as root nodules, in the roots of legumes and fix the gaseous nitrogen into ammonia. Option B is incorrect. Clostridium is an anaerobic free-living nitrogen fixer which makes option C incorrect. Streptomyces is filamentous free-living aerobic bacterium; S. thremoautotropicus have oxygen insensitive nitrogenase enzyme and ability to fix nitrogen. Since not all the Streptomyces spp can fix nitrogen, options D is incorrect.