Role of the Five RNA Helicases in the Adaptive Response of Bacillus cereus ATCC 14579 Cells to Temperature, pH, and Oxidative Stresses

Abstract

In this study, growth rates and lag times of the five RNA helicase-deleted mutants of Bacillus cereus ATCC 14579 were compared to those of the wild-type strain under thermal, oxidative, and pH stresses. Deletion of cshD and cshE had no impact under any of the tested conditions. Deletion of cshA, cshB, and cshC abolished growth at 12°C, confirming previous results. In addition, we found that each RNA helicase had a role in a specific temperature range: deletion of cshA reduced growth at all the tested temperatures up to 45°C, deletion of cshB had impact below 30°C and over 37°C, and deletion of cshC led mainly to a cold-sensitive phenotype. Under oxidative conditions, deletion of cshB and cshC reduced growth rate and increased lag time, while deletion of cshA increased lag time only with H 2 O 2 and reduced growth rate at a high diamide concentration. Growth of the ⌬cshA strain was affected at a basic pH independently of the temperature, while these conditions had a limited effect on ⌬cshB and ⌬cshC strain growth. The RNA helicases CshA, CshB, and CshC could participate in a general adaptation pathway to stressful conditions, with a stronger impact at low temperature and a wider role of CshA.The DEAD-box RNA helicases are encoded by viral, archaeal, eukaryotic, and prokaryotic genomes (9) and play an important role in RNA processing, transport, and degradation and in many other processes involving RNA (4, 19, 26), such as translation or ribosome biogenesis (10,11,22). DEAD-box RNA helicases act as molecular motors that unwind doublestranded RNA, thereby affecting the rearrangement of RNA secondary structures (9, 21). RNA helicases could also be implicated in rearrangement of ribonucleoprotein (RNP) complexes by removing protein from RNA or by the combination of both RNA-unwinding and RNA-annealing activity to promote RNA strand exchange through a potential branch migration (5,13,17,24). Bacterial cells often encounter stressful conditions that tend to decrease the cellular fitness. Consequently, bacteria have to maintain RNA pathway functionalities and control their RNA turnover. Most of the synthesized mRNA is rapidly degraded to allow adaptation to environmental changes (14). RNA helicases could be involved in stress adaptation by maintaining and regulating RNA functions.Studies reporting the involvement of prokaryotic RNA helicases in the adaptation to abiotic stress mainly deal with response to cold, light, and salt conditions (17). The RNA helicase CrhC maintains the photosynthetic capacity of the cyanobacterium Synechocystis. Its expression is regulated by the changes on the redox potential of the electron transport chain caused by variations in light, temperature, and salt concentrations (12). CrhC catalyzes the unwinding of RNA secondary structures but also ensures rearrangements in RNA complexes (5,25). A Bacillus subtilis CshA homolog of Clostridium perfringens is involved in the adaptation to oxidative stress, with the corresponding null mutant strain showing better survival under oxidative stress cond...

DEAD-Box RNA Helicases in Bacillus subtilis Have Multiple Functions and Act Independently from Each Other

“…The latter finding is consistent with results obtained with Bacillus cereus: the deletion in the corresponding cshA homolog results in a severe growth defect at lower temperatures in this species as well (19,20). A further analysis of the CshA and CshB homologs of B. cereus revealed that the RNA helicases are also required for growth at a basic pH and under oxidative conditions (21).…”

Roles of Four Putative DEAD-Box RNA Helicase Genes in Growth of Listeria monocytogenes EGD-e under Heat, pH, Osmotic, Ethanol, and Oxidative Stress Conditions

“…Understanding the mechanisms behind tolerance to stresses caused by food processing, additives, preservatives, sanitizers, and disinfectants may provide new insights into the control of L. monocytogenes in the food chain. In this study, the role of DEAD-box RNA helicase-encoding genes, so far linked mainly to cold stress tolerance of bacteria (4,7,11,37,(43)(44)(45)59), in tolerance of L. monocytogenes to various stress conditions the bacterium may meet in the food chain was examined. Single deletions of the putative DEAD-box RNA helicase-encoding genes lmo0866 and lmo1450 were found to significantly alter the tolerance of L. monocytogenes EGD-e to heat, alkali, ethanol, and oxidative stresses.…”

“…Recently, DEAD-box proteins were linked with cold stress tolerance in L. monocytogenes (4,37), Bacillus subtilis (25), Bacillus cereus (44), Escherichia coli (11), and Yersinia enterocolitica (43) by mutational analyses. DEAD-box RNA helicases also contribute to heat, alkali, and oxidative stress tolerance in B. cereus (45), whereas in the anaerobic Clostridium perfringens, a DEAD-box protein was associated with decreased tolerance to oxidative stress (7). In addition, exposure to salt and light resulted in altered transcription of the DEAD-box RNA helicase gene in the cyanobacterium Synechocystis sp.…”

A Listeria monocytogenes RNA Helicase Essential for Growth and Ribosomal Maturation at Low Temperatures Uses Its C Terminus for Appropriate Interaction with the Ribosome

“…Also, its B. subtilis orthologue, YfmL, is an RNA helicase that is not well characterized and is probably not part of the RNA degradosome, given that it was not able to interact with RNA degradosome components or other helicases in a bacterial two-hybrid system assay (38). The lmo1722 orthologue cshC in B. cereus was among three RNA helicase genes out of five that were required for cold growth and involved in adaptation to several stress conditions (50,51). Lmo1722 has a core region similar to those of other DExD-box RNA helicases but also harbors a unique lysine-rich 72-aminoacid-long C terminus that is not present in the B. subtilis orthologue YfmL (see Fig.…”

“…Most studies have focused on the roles of these RNA helicases in vitro and not in their natural context in vivo (8,10,40,49). One exception is Bacillus cereus, where the physiological functions of five RNA helicase genes were examined with regard to their roles in cold growth and response to various stresses (50,51). In this study, we investigated the function of an RNA helicase in a cold-growing bacterium, L. monocytogenes.…”