pathogens, so are intensively studied. [64] Endospores Further information: Endospores Bacillus anthracis (stained purple) growing in cerebrospinal fluid Certain genera of Gram-positive bacteria, such as Bacillus , Clostridium , Sporohalobacter , Anaerobacter and Heliobacterium , can form highly resistant, dormant structures called endospores . [65] In almost all cases, one endospore