Environmental, Agricultural and Industrial Microbiology
Domain 8 applies microbiology to nutrient cycling, waste treatment, agriculture and industrial fermentation. The exam favours named organisms and processes.
Environmental microbiology
Biogeochemical cycles include carbon (photosynthesis, respiration, decomposition), nitrogen (fixation, ammonification, nitrification, denitrification), phosphorus and sulphur. Nitrogen fixers include Rhizobium (symbiotic), Azotobacter and Azospirillum (free-living or associative) and cyanobacteria such as Anabaena and Nostoc. Nitrification is carried out by Nitrosomonas (ammonium to nitrite) and Nitrobacter (nitrite to nitrate). Denitrification returns nitrogen to the atmosphere. Sewage treatment uses primary settling, secondary activated sludge or trickling filters, and anaerobic digestion of sludge to produce biogas with methanogens. Biochemical oxygen demand measures biodegradable organic load; high BOD indicates pollution. Bioremediation and biomining also use microbes.
Agricultural and industrial microbiology
Biofertilisers include Rhizobium, Azospirillum, Azotobacter, phosphate-solubilising bacteria and mycorrhizae. Bacillus thuringiensis is a biopesticide. Composting recycles organic matter. Industrial fermentation produces penicillin from Penicillium chrysogenum, streptomycin from Streptomyces griseus, citric acid from Aspergillus niger, glutamic acid from Corynebacterium glutamicum, ethanol from Saccharomyces cerevisiae and vinegar from Acetobacter. Enzymes, vitamin B12, single-cell protein and biopolymers are also produced.
Worked example
A 1:10 diluted sample has dissolved oxygen 8 mg/L on day 0 and 4 mg/L after 5 days. BOD = (8 − 4) × 10 = 40 mg/L. Reasoning: the depletion is multiplied by the dilution factor; a high value means strong organic pollution and active microbial oxygen consumption.
Traps
Rhizobium is symbiotic, not free-living. Nitrification is not nitrogen fixation. BOD does not measure all pollutants. Antibiotics come from fungi and actinomycetes, not only bacteria. Biogas is mainly methane, not carbon dioxide.