AUTHOR=Terceti Mateus S. , Vences Ana , Matanza Xosé M. , Barca Alba V. , Noia Manuel , Lisboa Johnny , dos Santos Nuno M. S. , do Vale Ana , Osorio Carlos R. 

TITLE=The RstAB System Impacts Virulence, Motility, Cell Morphology, Penicillin Tolerance and Production of Type II Secretion System-Dependent Factors in the Fish and Human Pathogen Photobacterium damselae subsp. damselae

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.00897

DOI=10.3389/fmicb.2019.00897

ISSN=1664-302X

ABSTRACT=<p>The RstB histidine kinase of the two component system RstAB positively regulates the expression of damselysin (Dly), phobalysin P (PhlyP) and phobalysin C (PhlyC) cytotoxins in the fish and human pathogen <italic>Photobacterium damselae</italic> subsp. <italic>damselae</italic>, a marine bacterium of the family <italic>Vibrionaceae</italic>. However, the function of the predicted cognate response regulator RstA has not been studied so far, and the role of the RstAB system in other cell functions and phenotypes remain uninvestigated. Here, we analyzed the effect of <italic>rstA</italic> and <italic>rstB</italic> mutations in cell fitness and in diverse virulence-related features. Both <italic>rstA</italic> and <italic>rstB</italic> mutants were severely impaired in virulence for sea bream and sea bass fish. Mutants in <italic>rstA</italic> and <italic>rstB</italic> genes were impaired in hemolysis and in Dly-dependent phospholipase activity but had intact PlpV-dependent phospholipase and ColP-dependent gelatinase activities. <italic>rstA</italic> and <italic>rstB</italic> mutants grown at 0.5% NaCl exhibited impaired swimming motility, enlarged cell size and impaired ability to separate after cell division, whereas at 1% NaCl the mutants exhibited normal phenotypes. Mutation of any of the two genes also impacted tolerance to benzylpenicillin. Notably, <italic>rstA</italic> and <italic>rstB</italic> mutants showed impaired secretion of a number of type II secretion system (T2SS)-dependent proteins, which included the three major cytotoxins Dly, PhlyP and PhlyC, as well as a putative delta-endotoxin and three additional uncharacterized proteins which might constitute novel virulence factors of this pathogenic bacterium. The analysis of the T2SS-dependent secretome of <italic>P. damselae</italic> subsp. <italic>damselae</italic> also led to the identification of RstAB-independent potential virulence factors as lipoproteins, sialidases and proteases. The RstAB regulon included plasmid, chromosome I and chromosome II-encoded genes that showed a differential distribution among isolates of this subspecies. This study establishes RstAB as a major regulator of virulence and diverse cellular functions in <italic>P. damselae</italic> subsp. <italic>damselae</italic>.</p>