Abstract

While alternating between insects and mammals during its life cycle, Yersinia pestis, the flea-transmitted bacterium that causes plague, regulates its gene expression appropriately to adapt to these two physiologically disparate host environments. In fleas competent to transmit Y. pestis, low-GC-content genes y3555, y3551, and y3550 are highly transcribed, suggesting that these genes have a highly prioritized role in flea infection. Here, we demonstrate that y3555, y3551, and y3550 are transcribed as part of a single polycistronic mRNA comprising the y3555, y3554, y3553, y355x, y3551, and y3550 genes. Additionally, y355x-y3551-y3550 compose another operon, while y3550 can be also transcribed as a monocistronic mRNA. The expression of these genes is induced by hyperosmotic salinity stress, which serves as an explicit environmental stimulus that initiates transcriptional activity from the predicted y3550 promoter. Y3555 has homology to pyridoxal 5'-phosphate (PLP)-dependent aromatic aminotransferases, while Y3550 and Y3551 are homologous to the Rid protein superfamily (YjgF/YER057c/UK114) members that forestall damage caused by reactive intermediates formed during PLP-dependent enzymatic activity. We demonstrate that y3551 specifically encodes an archetypal RidA protein with 2-aminoacrylate deaminase activity but Y3550 lacks Rid deaminase function. Heterologous expression of y3555 generates a critical aspartate requirement in a Salmonella entericaaspC mutant, while its in vitro expression, and specifically its heterologous coexpression with y3550, enhances the growth rate of an Escherichia coli ΔaspC ΔtyrB mutant in a defined minimal amino acid-supplemented medium. Our data suggest that the y3555, y3551, and y3550 genes operate cooperatively to optimize aromatic amino acid metabolism and are induced under conditions of hyperosmotic salinity stress.IMPORTANCE Distinct gene repertoires are expressed during Y. pestis infection of its flea and mammalian hosts. The functions of many of these genes remain predicted or unknown, necessitating their characterization, as this may provide a better understanding of Y. pestis specialized biological adaptations to the discrete environments of its two hosts. This study provides functional context to adjacently clustered horizontally acquired genes predominantly expressed in the flea host by deciphering their fundamental processes with regard to (i) transcriptional organization, (ii) transcription activation signals, and (iii) biochemical function. Our data support a role for these genes in osmoadaptation and aromatic amino acid metabolism, highlighting these as preferential processes by which Y. pestis gene expression is modulated during flea infection.

Highlights

  • Plague, caused by Yersinia pestis, is a severe zoonotic disease infamous for having caused the death of millions of people in three major pandemics

  • The y3555 gene product exhibits homology to uncharacterized pyridoxal 5'-phosphate (PLP)–dependent transaminases, including aromatic and aspartate aminotransferases encoded in some bacteria

  • In this work we have determined that the coordinated expression of an uncharacterized cluster of low GC content genes, y3555-y3554-y3553-y355x-y3551-y3550, that show exceptionally robust expression during flea infection, is accounted for by their co-transcription as a single polycistronic mRNA transcript

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Summary

Introduction

Plague, caused by Yersinia pestis, is a severe zoonotic disease infamous for having caused the death of millions of people in three major pandemics. This disease primarily affects rodents which become infected mainly through blood feeding by rodent-associated infected fleas. Central to the biological mechanism of transmission via flea bite is Y. pestis biofilm blockage of the flea foregut proventriculus [4,5,6]. After acquisition from the blood of a highly bacteremic host, Y. pestis must adapt to the insect gut environment to multiply and form biofilm-mediated blockage by seven days postinfection [7]. The various physicochemical stresses Y. pestis encounters in the flea gut such as low pH, reactive oxygen species (ROS), hyperosmolarity, nutrient-limitation and the immune response are slowly being uncovered along with how Y. pestis overcomes such stresses [8, 9]

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