Microbes in Human Welfare: Quick Review

Lactobacillus converts milk to curd by lactic acid fermentation and also increases the vitamin B12 content of curd.
Propionibacterium shermanii creates the characteristic large holes in Swiss cheese by releasing CO2 during cheese ripening.
Alexander Fleming discovered penicillin from Penicillium notatum in 1928, and Streptomyces species produce streptomycin, erythromycin, and tetracycline.
Streptokinase, produced by Streptococcus, is a thrombolytic enzyme used to dissolve blood clots — it is not an antibiotic.
Lovastatin from Monascus purpureus inhibits HMG-CoA reductase to lower blood cholesterol, while Cyclosporin A from Trichoderma polysporum suppresses immune rejection in organ transplants.
Primary sewage treatment is physical (screening and sedimentation) and does not significantly reduce BOD; secondary treatment is biological (aerobic microbial activity in aeration tanks) and significantly reduces BOD.
BOD (Biochemical Oxygen Demand) measures dissolved oxygen consumed by microbes to decompose organic matter in water — high BOD signals high organic pollution.
Methanogens, principally Methanobacterium, decompose sludge in anaerobic digesters to produce biogas (methane, CO2, and H2S).
Bacillus thuringiensis produces Cry proteins (Cry1Ac, Cry2Ab) toxic to lepidopteran insect larvae, forming the molecular basis of Bt crop technology.
Rhizobium fixes nitrogen symbiotically in legume nodules; Azotobacter and cyanobacteria (Anabaena, Nostoc) fix nitrogen freely; Glomus (mycorrhiza) enhances phosphorus uptake — not nitrogen fixation.