Differential Regulation of c-di-GMP Metabolic Enzymes by Environmental Signals Modulates Biofilm Formation in Yersinia pestis.

Gai-Xian Ren,Xiao-Peng Guo,Sai Fan,Shiyun Chen,Shiyun Chen,Yi-Cheng Sun

doi:10.3389/fmicb.2016.00821

Abstract

Cyclic diguanylate (c-di-GMP) is essential for Yersinia pestis biofilm formation, which is important for flea-borne blockage-dependent plague transmission. Two diguanylate cyclases (DGCs), HmsT and HmsD and one phosphodiesterase (PDE), HmsP are responsible for the synthesis and degradation of c-di-GMP in Y. pestis. Here, we systematically analyzed the effect of various environmental signals on regulation of the biofilm phenotype, the c-di-GMP levels, and expression of HmsT, HmsD, and HmsP in Y. pestis. Biofilm formation was higher in the presence of non-lethal high concentration of CaCl2, MgCl2, CuSO4, sucrose, sodium dodecyl sulfate, or dithiothreitol, and was lower in the presence of FeCl2 or NaCl. In addition, we found that HmsD plays a major role in biofilm formation in acidic or redox environments. These environmental signals differentially regulated expression of HmsT, HmsP and HmsD, resulting in changes in the intracellular levels of c-di-GMP in Y. pestis. Our results suggest that bacteria can sense various environmental signals, and differentially regulate activity of DGCs and PDEs to coordinately regulate and adapt metabolism of c-di-GMP and biofilm formation to changing environments.

Highlights

Yersinia pestis, the causative agent of plague, is a unique Gram-negative bacterium that adopts an arthropod-borne route of transmission
To determine the effect of different environmental signals on biofilm formation, we investigated the effect of 12 different environmental conditions on the growth and biofilm formation of Y. pestis KIM6+ in vitro (Figure 1 and Supplementary Figure S1)
Neither the promoter activity of hmsC (Figure 4C) nor the HmsD protein level (Figure 5C) were significantly affected by the temperature, HmsC and HmsE expressions were markedly decreased by an increase in temperature (Figures 5B,D). These results suggest that the protein levels of HmsC and HmsE are more likely to be regulated than that of HmsD at the posttranscriptional level by environmental signals. These results suggest that HmsT, HmsP, and HmsCDE are differentially regulated by environmental signals, which might at least be partially responsible for changes in the intracellular c-di-GMP level and biofilm formation in Y. pestis in different environments

Summary

Introduction

The causative agent of plague, is a unique Gram-negative bacterium that adopts an arthropod-borne route of transmission. The bacteria can form a biofilm in the proventriculus (a valve between the midgut and esophagus), which interferes with and can eventually block the ingestion of blood (Hinnebusch et al, 1996; Jarrett et al, 2004; Hinnebusch and Erickson, 2008). As a result of this blockage-induced starvation, fleas with complete or partial blockage will repeatedly try to feed on hosts, resulting in regurgitation of ingested blood and bacteria into the bite site to infect the mammal (Bacot and Martin, 1914; Bacot, 1915). Y. pestis biofilm formation requires the hmsHFRS operon, which is responsible for biosynthesis of a polymeric β-1, 6-N-acetyl-D-glucosamine-containing extracellular polysaccharide (EPS; Hinnebusch et al, 1996; Darby, 2008).

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Results

Conclusion