Spore germination and mycelial growth of streptomycetes at different humidity levels

This study is the first to show the ability of streptomycetes to develop at a very low humidity level. All of the streptomycetes studied produced growth at low humidity (a(w) 0.86 and 0.67). This capacity was most markedly pronounced in Streptomyces odorifer, whose spores were capable of germinating, and mycelial germs increased in length, at the air humidity a(w) 0.50. The formation of lateral branches (mycelium branching) at this humidity was noted only in single S. odorifer germs and only after 72 h of incubation. Study of streptomycete growth on an agarized medium with different osmotic pressures, created by various glycerol concentrations in the medium, showed that, at a(w) 0.67, the spores of all the streptomycetes studied germinate, producing mycelial germs but not microcolonies. The ecological significance of'mycelial prokaryotes in soil microbial communities that develop and function under conditions of extremely low humidity is discussed.