There are several examples of microbial granules produced in nature. The best-known example is kefir grains, which are the aggregates of lacto-bacilli, acetobacteria, and yeasts, used in milk fermentation from ancient times. Diameter of these granules range from 1 to 5 mm. It is considered that the main mechanism of their aggregation is the formation of polysaccharide slime connecting the cells together. There are also known soil aggregates, which are the clumps of soil particles, microbial slime, bacterial cells, and fungal hyphae. These aggregates are formed due to the frame binding by the hyphaes of fungi and slime production binding the particulates together. Microbial granule, called mycetoma or sclero-tia, can be formed inside the body of human or animal. It is spherical or ellipsoidal aggregate of slow-growing bacterial cells or fungal mycelium in the infected body part. Probably, these spherical granules are formed due to microbial growth in dense tissue, which is pressing aggregate of microbial cells evenly from all directions. Hypothetically, it would be possible to find granular microbial aggregates in all viscous and stagnant aquatic environments, where the mechanical dispersion of microbial cells from aggregate is weak.
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