Which type of bacteria thrive in environments that lack free oxygen?

well, those bacteria that are thrive in the absence of oxygen are ” anerobic bacteria “.

there are 2 types of anaerobic bacteria:

1. obligate anaerobes (they can grow in the absence of the oxygen.) e.g is clostridium and bacilli etc.
2. facultative anaerobes ( can grow in the absence or presence of the bacteria ) e.g. is salmonella, listeria, yersinia etc.

hope you got the point..

Thanks.