Unlike proteins, RNA molecules have emerged lately as key players in regulation in bacteria. Most
reviews hitherto focused on the experimental and/or in silico methods used to identify genes
encoding small RNAs (sRNAs) or on the diverse mechanisms of these RNA regulators to
modulate expression of their targets. However, less is known about their biological functions and
their implications in various physiological responses. This review aims to compile what is known
presently about the diverse roles of sRNA transcripts in the regulation of metabolic processes, in
different growth conditions, in adaptation to stress and in microbial pathogenesis. Several recent
studies revealed that sRNA molecules are implicated in carbon metabolism and transport, amino
acid metabolism or metal sensing. Moreover, regulatory RNAs participate in cellular adaptation to
environmental changes, e.g. through quorum sensing systems or development of biofilms, and
analyses of several sRNAs under various physiological stresses and culture conditions have
already been performed. In addition, recent experiments performed with Gram-positive and Gramnegative
pathogens showed that regulatory RNAs play important roles in microbial virulence and
during infection. The combined results show the diversity of regulation mechanisms and
physiological processes in which sRNA molecules are key actor