Impact of QseBC system in c-di-GMP-dependent quorum sensing regulatory network in a clinical isolate SSU of Aeromonas hydrophila.
Our earlier studies showed that AhyRI- (AI-1) and LuxS-based (AI-2) quorum sensing (QS) systems were positive and negative regulators of virulence, respectively, in a diarrheal isolate SSU of Aeromonas hydrophila. Recently, we demonstrated that deletion of the QseBC two-component signal transduction system (AI-3 QS in enterohemorrhagic Escherichia coli) also led to an attenuation of A. hydrophila in a septicemic mouse model of infection, and that interplay exists between AI-1, AI-2, and the second-messenger cyclic-di-guanosine monophosphate (c-di-GMP) in modulating bacterial virulence. To further explore a network connection between all of the three QS systems in A. hydrophila SSU and their cross talk with c-di-GMP, we overproduced a protein with a GGDEF domain, which increases c-di-GMP levels in bacteria, and studied phenotypes and transcriptional profiling of genes involved in biofilm formation and motility of the wild-type (WT) A. hydrophila and its ΔqseB mutant. Over-expression of the GGDEF domain-encoding gene (aha0701h) resulted in a significantly reduced motility of the WT A. hydrophila similar to that of the ΔqseB mutant. While enhanced protease production was noted in WT A. hydrophila that had increased c-di-GMP, no enzymatic activity was detected in the ΔqseB mutant overexpressing the aha0701h gene. Likewise, denser biofilm formation was noted for WT bacteria when c-di-GMP was overproduced compared to its respective control; however, overproduction of c-di-GMP in the ΔqseB mutant led to reduced biofilm formation, a finding similar to that noted for the parental A. hydrophila strain. These effects on bacterial motility and biofilm formation in the ΔqseB mutant or the mutant with increased c-di-GMP were correlated with altered levels of fleN and vpsT genes. While we noted transcript levels of qseB and qseC genes to be increased in the ahyRI mutant, down-regulation of the ahyR and ahyI genes was observed in the ΔqseB mutant, which correlated with decreased protease activity. Finally, an enhanced virulence of WT A. hydrophila with increased c-di-GMP was noted in a mouse model when compared to findings in the parental strain with vector alone. Overall, we conclude that cross talk between AI-1 and QseBC systems exists in A. hydrophila SSU, and c-di-GMP modulation on QseBC system is dependent on the expression of the AI-1 system.
Department of Microbiology & Immunology, Institute of Human Infections & Immunity and Sealy Center for Vaccine Development, University of Texas Medical Branch, UTMB, Galveston, TX 77555, USA.
Elena V
EV
Kozlova
Bijay K
BK
Khajanchi
Vsevolod L
VL
Popov
Julie
J
Wen
Ashok K
AK
Chopra
D016980:Aeromonas hydrophila / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000378:metabolism; D005260:Female; D015964:Gene Expression Regulation, Bacterial; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology*; D006801:Humans; D051379:Mice; D053038:Quorum Sensing; D014774:Virulence
D001426:Bacterial Proteins; C062025:bis(3',5')-cyclic diguanylic acid; D006152:Cyclic GMP