Yersinia pestis cells were grown in vitro at 26 and 37 °C, the ambient temperatures of its flea vector and its mammalian hosts, respectively, and subjected to subcellular fractionation. Abundance changes at 26 vs 37 °C were observed for many outer-membrane (OM) proteins. The cell adhesion protein Ail (y1324) and three putative small b-barrel OM proteins (y1795, y2167 and y4083) were strongly increased at 37 °C. The Ail/Lom family protein y1682 (OmpX) was strongly increased at 26 °C. Several porins and TonB-dependent receptors, which control small molecule transport through the OM, were also altered in abundance in a temperature-dependent manner. These marked differences in the composition of the OM proteome are probably important for the adaptation of Y. pestis to its in vivo life stages. Thirteen proteins that appear to be part of an intact type VI secretion system (T6SS) were identified in membrane fractions of stationary-phase cells grown at 26 °C, but not at 37 °C. The corresponding genes are clustered in the Y. pestis KIM gene locus y3658-y3677. The proteins y3674 and y3675 were particularly abundant and co-fractionated in a Mr range indicative of participation in a multi-subunit complex. The soluble haemolysin-coregulated protein y3673 was even more abundant. Its release into the extracellular medium was triggered by treatment of Y. pestis cells with trypsin. Proteases and other stress-response-inducing factors may constitute environmental cues resulting in the activation of the T6SS in Y. pestis.
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