Amino acid deprivation and central carbon metabolism regulate the production of outer membrane vesicles and tubes by Francisella Francisella

摘要

Summary Francisella tularensis is a highly virulent Gramnegative bacterial pathogen that causes the zoonotic disease tularemia.F. novicida , a model tularemia strain, produces spherical outer membrane vesicles (OMV), as well as novel tubular vesicles and extensions of the cell surface. These OMV and tubes (OMV/T) are produced in a regulated manner and contain known virulence factors. Mechanisms by which bacterial vesicles are produced and regulated are not well understood. We performed a genetic screen inF. novicida to decipher the molecular basis for regulated OMV/T formation, and identified both hypo and hypervesiculating mutants. Mutations infumA andtktA , involved in central carbon metabolism, and in FTN_0908 and FTN_1037, of unknown function, resulted in severe defects in OMV/T production. Cysteine deprivation was identified as the signal that triggers OMV/T formation inF. novicida during growth in rich medium. We also found that fully virulentF. tularensis produces OMV/T in a similarly regulated manner. Further analysis revealed that OMV/T production is responsive to deprivation of essential amino acids in addition to cysteine, and that the hypovesiculating mutants are defective in responding to this signal. Thus, amino acid starvation, such as encountered byFrancisella during host cell invasion, regulates the production of membranederived structures.