The Bacillus species is facultative anaerobic. This means they can grow in the presence of oxygen (aerobic) but they can also grow in the absence of oxygen (anaerobic).

Here's why:

* Aerobic Respiration: Many Bacillus species can use oxygen as their final electron acceptor in cellular respiration, which is the most efficient way to generate energy.

* Anaerobic Respiration: When oxygen is not available, they can switch to anaerobic respiration, using other molecules like nitrate or sulfate as their final electron acceptor.

* Fermentation: Some Bacillus species can also carry out fermentation, which does not require oxygen.

Therefore, Bacillus species are versatile in their metabolic capabilities and can adapt to different environments with or without oxygen.