Physiological Responses of Bacteroides and Clostridium Strains to Environmental Stress Factors

Abstract

The two genera—namely, Bacteroides (non-spore-forming Gram-negative bacilli) and Clostridium (endospore-forming Gram-positive bacilli), comprise important groups of obligate anaerobic bacteria. Studies on the responses of anaerobes to environmental stress are limited, and within the Bacteroides group they are virtually restricted to one strain of B. fragilis (Bf-2). This strain has been shown to exhibit a variety of physiological responses and to induce new proteins in response to various stress factors and DNA-damaging agents. However, available evidence suggests that B. fragilis lacks a recA controlled error-prone SOS processing system that is characteristic of E. coli . In E. coli, the regulatory networks controlling the SOS response and the heat-shock response are interconnected. In addition, in B. fragilis there is no connection between the regulatory networks controlling the heat-shock response and the responses to UV irradiation, oxygen, and H 2 O 2 . The absence of any overlap between heat-shock response and the responses to oxygen and H 2 O 2 is particularly interesting because heat shock and oxidative stress have been shown to be linked in aerobic bacteria. In B. fragilis , the response to DNA-damaging stress factors and other environmental stress factors, such as heat shock, involve separate regulatory networks.