Spermine inhibits Vibrio cholerae biofilm formation through the NspS–MbaA polyamine signaling system

Abstract

The aquatic bacterium and human intestinal pathogen, , senses and responds to a variety of environment-specific cues to regulate biofilm formation. Specifically, the polyamines norspermidine and spermidine enhance and repress biofilm formation, respectively. These effects are relevant for understanding pathogenicity and are mediated through the periplasmic binding protein NspS and the transmembrane bis-(3'-5') cyclic diguanosine monophosphate (c-di-GMP) phosphodiesterase MbaA. However, the levels of spermidine required to inhibit biofilm formation through this pathway are unlikely to be encountered by in aquatic reservoirs or within the human host during infection. We therefore hypothesized that other polyamines in the gastrointestinal tract may control biofilm formation at physiological levels. The tetramine spermine has been reported to be present at nearly 50 μm concentrations in the intestinal lumen. Here, we report that spermine acts as an exogenous cue that inhibits biofilm formation through the NspS-MbaA signaling system. We found that this effect probably occurs through a direct interaction of spermine with NspS, as purified NspS protein could bind spermine Spermine also inhibited biofilm formation by altering the transcription of the genes involved in biofilm matrix production. Global c-di-GMP levels were unaffected by spermine supplementation, suggesting that biofilm formation may be regulated by variations in local rather than global c-di-GMP pools. Finally, we propose a model illustrating how the NspS-MbaA signaling system may communicate exogenous polyamine content to the cell to control biofilm formation in the aquatic environment and within the human intestine.

Shining the Light on Cyclic di-GMP Dark Matter

“…It is clear that the impact of GGDEF domain, EAL domain, and dual-domain proteins changed in different environments in the absence of transcriptional change or complex formation. These findings further highlight the discovery that environmental signals could be funneled into the network by acting as ligands directly binding to and changing the activity of DGCs or PDEs, and such mechanisms have previously been demonstrated (16)(17)(18). Additionally, environmental cues can also impact host-derived signals such as quorum sensing autoinducers or central metabolites that modulate the activity of DGCs and PDEs (19).…”

What bacteria want

“…There is a long list of potential HK inhibitors (Bem et al, 2015); it might make sense to examine them for the ability to decrease virulence at sub-MIC levels. Biofilm formation could also be repressed by modulating c-di-GMP pools with spermine and spermidine (Sobe et al, 2017). Furthermore, relatively low levels of nitric oxide trigger biofilm dispersal in multiple bacteria (Barraud et al, 2009;Cutruzzola and Frankenberg-Dinkel, 2016), apparently acting through cdi-GMP signalling.…”

Reduction of Spermidine Content Resulting from Inactivation of Two Arginine Decarboxylases Increases Biofilm Formation in Synechocystis sp. Strain PCC 6803

“…In Y. pestis, a mutant defective in the two main putrescine biosynthetic enzymes, arginine decarboxylase (SpeA) and ornithine decarboxylase (SpeC), shows a loss of biofilm formation (35). However, a limited number of examples for negative correlation were described: in Shewanella oneidensis, mutants deficient in ornithine decarboxylase (SpeF) show enhanced adherence and biofilm formation (36), and in V. cholerae, addition of spermine and spermidine inhibits biofilm formation (37,38). A recent report also shows an increase of biofilm formation in response to spermidine depletion in Agrobacterium tumefaciens (39).…”