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Abstract
C-di-GMP has been well investigated to play significant roles in the physiology of many Gram-negative bacteria. However, its effect on Gram-positive bacteria is less known. In order to more understand the c-di-GMP functions in Gram-positive bacteria, we have carried out a detailed study on the c-di-GMP-metabolizing enzymes and their physiological functions in Bacillus thuringiensis, a Gram-positive entomopathogenic bacterium that has been applied as an insecticide successfully. We performed a systematic study on the ten putative c-di-GMP-synthesizing enzyme diguanylate cyclases (DGCs) and c-di-GMP-degrading enzyme phosphodiesterases (PDEs) in B. thuringiensis BMB171, and artificially elevated the intracellular c-di-GMP level in BMB171 by deleting one or more pde genes. We found increasing level of intracellular c-di-GMP exhibits similar activities as those in Gram-negative bacteria, including altered activities in cell motility, biofilm formation, and cell-cell aggregation. Unexpectedly, we additionally found a novel function exhibited by the increasing level of c-di-GMP to promote the insecticidal activity of this bacterium against Helicoverpa armigera. Through whole-genome transcriptome profile analyses, we found that 4.3% of the B. thuringiensis genes were differentially transcribed when c-di-GMP level was increased, and 77.3% of such gene products are involved in some regulatory pathways not reported in other bacteria to date. In summary, our study represents the first comprehensive report on the c-di-GMP-metabolizing enzymes, their effects on phenotypes, and the transcriptome mediated by c-di-GMP in an important Gram-positive bacterium.
Highlights
Eight proteins are believed to be membrane-associated via SMART database, while the other four are distributed in the cytoplasm, demonstrating that c-di-GMP-metabolizing enzymes may act and function in different space inside B. thuringiensis BMB171 the cell
The possible explanation for this bizarre behavior is that bacterial chemotaxis is possibly stimulated by certain sort of chemotaxis factors but not by c-di-GMP. These results indicated that an elevated intracellular c-di-GMP level can repress cell motility by impeding transcription of a part of flagellum assembly genes, which is consistent with the reports for some Gram-positive bacteria (Chen et al, 2012; Purcell et al, 2012; Gao et al, 2014; Gupta et al, 2015) and Gram-negative bacteria (Simm et al, 2004; Kuchma et al, 2007; Paul et al, 2010)
These results suggest that high c-di-GMP level did expedite biofilm formation in B. thuringiensis
Summary
Bis-(3′-5′)-cyclic dimeric guanosine monophosphate (c-di-GMP) is a second messenger playing important roles in a plethora of bacterial physiological processes to suppress motility (AlbertWeissenberger et al, 2010; Boehm et al, 2010; Krasteva et al, 2010), mediate transition from planktonic growth to biofilm formation (Newell et al, 2009, 2011; Ha and O’Toole, 2015; Chen et al, 2016), coordinate with quorum sensing (Kariisa et al, 2016; Matsuyama et al, 2016) and c-di-GMP Regulates Insecticidal Activity alter virulence gene expression (Aragón et al, 2015; Kariisa et al, 2015; Suppiger et al, 2016) in many Gram-negative species, as well as to confer resistance to antibiotics and induce host immune responses (Aldridge et al, 2003). The intracellular cdi-GMP level is controlled by diguanylate cyclases (DGCs) and phosphodiesterases (PDEs) for its synthesis and degradation, respectively. Mycobacterium smegmatis was predicted to possess one protein with a dual GGDEF-EAL domain that exhibits both DGC and PDE activities (Bharati et al, 2012). More than 60 potential genes associated with the c-di-GMP turnover were found in Vibrio cholera (Beyhan et al, 2008). These c-di-GMP-metabolizing enzymes are believed to locate at different cellular positions, responding to different environmental stimulus at different growth phases to precisely regulate the intracellular c-di-GMP level in a temporal and spatial way. Some eukaryotic strains (e.g., eukaryote Dictyostelium discoideum Chen and Schaap, 2016) secrete c-di-GMP to keep c-di-GMP homeostasis
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