Erickson, D. L. | Search bioRxiv

bioRxiv2020

A link between zinc uptake, bile salts, and a capsule required for virulence of a mastitis-associated extraintestinal pathogenic Escherichia coli strain

Extraintestinal pathogenic Escherichia coli (ExPEC) are major causes of urinary and bloodstream infections. ExPEC reservoirs are not completely understood. Some mastitis-associated E. coli (MAEC) strains carry genes associated with ExPEC virulence, including metal scavenging, immune avoidance, and host attachment functions. In this study, we investigated the role of the high-affinity zinc uptake (znuABC) system in the MAEC strain M12. Elimination of znuABC moderately decreased fitness during mouse mammary gland infections. The {Delta}znuABC mutant strain exhibited an unexpected growth delay in the presence of bile salts, which was alleviated by the addition of excess zinc. We isolated {Delta}znuABC mutant suppressor mutants with improved growth of in bile salts, several of which no longer produced the K96 capsule made by strain M12. Addition of bile salts also reduced capsule production by strain M12 and ExPEC strain CP9, suggesting that capsule synthesis may be detrimental when bile salts are present. To better understand the role of the capsule, we compared the virulence of mastitis strain M12 with its unencapsulated {Delta}kpsCS mutant in two models of ExPEC disease. The wild type strain successfully colonized mouse bladders and kidneys and was highly virulent in intraperitoneal infections. Conversely, the {Delta}kpsCS mutant was unable to colonize kidneys and was unable to cause sepsis. These results demonstrate that some MAEC may be capable of causing human ExPEC illness. Virulence of strain M12 in these infections is dependent on its capsule. However, capsule may interfere with zinc homeostasis in the presence of bile salts while in the digestive tract.

microbiology↗

bioRxiv2020

A trimeric autotransporter enhances biofilm cohesiveness in Yersinia pseudotuberculosis but not in Yersinia pestis

Cohesion of biofilms made by Yersinia pestis and Yersinia pseudotuberculosis (Yptb) has been attributed solely to an extracellular polysaccharide matrix encoded by the hms genes (Hms-ECM). However, mutations in the Yptb BarA/UvrY/CsrB regulatory cascade enhance biofilm stability without dramatically increasing Hms-ECM production. We found that treatment with proteinase K enzyme effectively destabilized Yptb csrB mutant biofilms, suggesting that cell-cell interactions might be mediated by protein adhesins or extracellular matrix proteins. We identified an uncharacterized trimeric autotransporter lipoprotein (YPTB2394), repressed by csrB, which has been referred to as YadE. Biofilms made by a {Delta}yadE mutant strain were extremely sensitive to mechanical disruption. Overexpression of yadE in wild-type Yptb increased biofilm cohesion, similar to biofilms made by csrB or uvrY mutants. We found that the Rcs signaling cascade, which represses Hms-ECM production, activated expression of yadE. The yadE gene appears to be functional in Yptb but is a pseudogene in modern Y. pestis strains. Expression of functional yadE in Y. pestis KIM6+ altered the production of Hms-ECM and weakened biofilms made by these bacteria. This suggests that although the YadE autotransporter protein increases Yptb biofilm stability, it may be incompatible with Hms-ECM production that is essential for Y. pestis biofilm production in fleas. Inactivation of yadE in Y. pestis may be another instance of selective gene loss in the evolution of flea-borne transmission by this species. IMPORTANCEThe evolution of Yersinia pestis from its Y. pseudotuberculosis (Yptb) ancestor involved gene acquisition and gene losses, leading to differences in biofilm production. Characterizing the unique biofilm features of both species may provide better understanding of how each adapts to its specific niches. This study identifies a trimeric autotransporter YadE that promotes biofilm stability of Yptb but which has been inactivated in Y. pestis, likely because it is not compatible with Hms polysaccharide that is crucial for biofilms inside fleas. We also reveal that the Rcs signaling cascade, which represses Hms expression in Y. pestis, activates YadE in Yptb. The ability of Yptb to use polysaccharide or YadE protein for cell-cell adhesion may help it produce biofilms in different environments.

microbiology↗