Although the actual numbers in existence in the environment for this species has not been determined, bacilli occur at population levels of 10 to 10 per gram of soil (Alexander, 1977).
However, unless a soil has been recently amended with organic matter providing readily utilizable nutrients, the bacilli exist in the endospore stage.
It is thought that 60 to 100% of soil bacilli populations exist in the inactive spore state (Alexander, 1977).
Like most members of the genus, B. subtilis is aerobic, except in the presence of glucose and nitrate, some anaerobic growth can occur (Claus and Berkeley, 1986).