Microbiology and Nitrogen Cycle

The bacteria are the prokaryotic organisms which are generally heterotrophic. These bacteria feed on the dead and digested matter. There are certain species of bacterium which is inclusive of the cyanobacteria. These are the blue-green algae which can perform photosynthesis due to the presence of the chlorophyll pigments. The other bacterial species can perform chemosynthesis and can utilise the organic and inorganic compounds as the source of energy. 

Bacillus subtilis are also called as hay bacillus. They are gram-positive bacteria. They are commonly found in hay or upper layer of soil. Hence, they are called as hay bacteria. They are also found in the GI tract of ruminants and humans. They are obligate aerobes. 

Monera is non-nucleated unicellular organisms. They are prokaryotes. They have a cell wall. They have no membrane-bound organelles such as mitochondria, Golgi complex. They lack a true nucleus. Instead, they have nucleoid, genetic material without a nuclear membrane. Examples include Bacteria, cyanophyceae (Blue-Green algae), Nitrogen-fixing organisms etc.

Bacteria exhibit diverse metabolic types regarding oxygen requirements. They include strictly aerobic, strictly anaerobic, facultative anaerobic, and microaerophilic forms, encompassing both aerobic and non-aerobic categories.

Bacteroids are the differentiated, non-motile form of Rhizobium bacteria found within the root nodules of legumes, where they fix nitrogen.

Rhodospirillum bacteria is facultative aerobic Photo - autotrophic bacteria use non-sulphur aliphatic organic  compound as donor of $H _{2}$  go,. Propyl alcohol .

$6CO _{2}+12CH _{3}CHOHCH _{3}\overset{Light}{\rightarrow}$

$C _{6}H _{12}O _{6}+12CH _{3}COH _{3}+6H _{2}O$

Some bacteria, such as cyanobacteria, are photosynthetic and contain chlorophyll, which led to their historical classification as plants.

Rhodopseudomonas and Rhodospirillum are photosynthetic bacteria that belong to the group of purple non-sulphur bacteria, which use organic compounds as electron donors.

Denitrifying bacteria convert nitrates in the soil to free atmospheric nitrogen, nitrogen-fixing bacteria are heterotrophs.

Bacteria can be classified into two groups based upon reaction bacteria to Gram's stain (Christian Gram, 1884. Bacteria are first stained with weakly alkaline solution of crystal violet and then treated with 0.5% iodine solution. This is followed by washing with water and then with alcohol or acetone. Bacteria which retain blue or purple colour are known as Gram (+) bacteria (e.g Bacillus subtilis). Bacteria which do not retain stain and become colourless are called Gram (-) bacteria (e.g. Escherichia coli). Washing of the stain in Gram (- ve) bacteria is due to high lipid content of their cell wall which gets dissolved in organic solvents like acetone. So, the correct answer is '(i), (ii) and (iii)'.

Cell wall of Gram +ve bacteria is made up of peptidoglycans (mucopeptide). Mucopeptide form about 50% of component of cell wall. Cell wall of Gram -ve bacteria is made up of single layer of peptidoglycans.

The mucopeptide or murein is a polymer of two amino sugars namely N-acetylglucosamine (NAG) and N-acetyl muramic acid (NAM). These NAG and NAM are derivatives of Glucose molecules.

Gram staining procedure is based on the principle of the ability of microorganisms to retain color of the stains used during the gram staining process. Gram-positive bacteria retain purple color after staining. They are not decolorized by treatment with alcohol. Whereas gram-negative bacteria are decolorized by the alcohol and lose purple color. When again stained with the second stain, they retain pink color. This major difference is due to the difference in the cell wall component of both the bacteria. Gram-negative bacteria contain additional peptidoglycan layer and a thin layer of LPS layer.