A Small Regulatory RNA Generated from the malK 5' Untranslated Region Targets Gluconeogenesis in Vibrio Species.

Vsr217 is a small RNA from Vibrio tasmaniensis LGP32, a pathogen associated with mortality events affecting juvenile oysters. The vsr217 gene is located within the 5' untranslated region (UTR) of malK, encoding the ATPase component of the maltose importer, and is conserved within the genus Vibrio. In the presence of maltose, vsr217 is regulated by MalT, the positive regulator of the maltose regulon. vsr217 is required in cis for the full expression of malK. In addition, Vsr217 acts in trans to downregulate the expression of fbp encoding fructose-1,6-bisphosphatase, an enzyme involved in gluconeogenesis. Thus, in the presence of maltose, the induction of Vsr217 is expected to promote glycolysis by negatively regulating the expression of a key enzyme of gluconeogenesis. IMPORTANCE Juvenile pacific oysters have been subject in recent years to summer mortality episodes with deep economic consequences. The pathogen Vibrio tasmaniensis has been associated with such mortality events. For bacterial pathogens, survival within the host requires profound metabolic adaptations according to available resources. All kinds of regulatory elements, including noncoding RNAs, orchestrate this response. Oysters are rich in glycogen, a precursor of maltose, and we previously reported that V. tasmaniensis maltose-regulated genes are strongly induced during oyster infection. Here, we report the dual mechanism by which a small regulatory RNA, generated from the 5' untranslated region of a gene belonging to the maltose regulon, acts both in cis and trans. In cis, it stimulates growth on maltose, and in trans, it downregulates the expression of a gene associated with gluconeogenesis, thus coordinating maltose utilization with central carbon metabolism.