Indole intercepts the communication between enteropathogenic E. coli and Vibrio cholerae.

Reported numbers of diarrheal samples exhibiting co-infections or multiple infections, with two or more infectious agents, are rising, likely due to advances in bacterial diagnostic techniques. Bacterial species detected in these samples include Vibrio cholerae (V. cholerae) and enteropathogenic Escherichia coli (EPEC), which infect the small intestine and are associated with high mortality rates. It has previously been reported that EPEC exhibit enhanced virulence in the presence of V. cholerae owing to their ability to sense and respond to elevated concentrations of cholera autoinducer 1 (CAI-1), which is the primary quorum-sensing (QS) molecule produced by V. cholerae. In this study, we examined this interspecies bacterial communication in the presence of indole, a major microbiome-derived metabolite found at high concentrations in the human gut. Interestingly, we discovered that although indole did not affect bacterial growth or CAI-1 production, it impaired the ability of EPEC to enhance its virulence activity in response to the presence of V. cholerae. Furthermore, the co-culture of EPEC and V. cholerae in the presence of B. thetaiotaomicron, an indole-producing commensal bacteria, ablated the enhancement of EPEC virulence. Together, these results suggest that microbiome compositions or diets that influence indole gut concentrations may differentially impact the virulence of pathogens and their ability to sense and respond to competing bacteria.

Glycosylation of N-hydroxy-pipecolic acid equilibrates between systemic acquired resistance response and plant growth.

N-hydroxy-pipecolic acid (NHP) activates plant systemic acquired resistance (SAR). Enhanced defense responses are typically accompanied by deficiency in plant development and reproduction. Despite of extensive studies on SAR induction, the effects of NHP metabolism on plant growth remain largely unclear. In this study, we discovered that NHP glycosylation is a critical factor that fine-tunes the tradeoff between SAR defense and plant growth. We demonstrated that a UDP-glycosyltransferase (UGT76B1) forming NHP glycoside (NHPG) controls the NHP to NHPG ratio. Consistently, the ugt76b1 mutant exhibits enhanced SAR response and an inhibitory effect on plant growth, while UGT76B1 overexpression attenuates SAR response, promotes growth, and delays senescence, indicating that NHP levels are dependent on UGT76B1 function in the course of SAR. Furthermore, our results suggested that, upon pathogen attack, UGT76B1-mediated NHP glycosylation forms a "hand brake" on NHP accumulation by attenuating the positive regulation of NHP biosynthetic pathway genes, highlighting the complexity of SAR-associated networks. In addition, we showed that UGT76B1-mediated NHP glycosylation in the local site is important for fine-tuning SAR response. Our results implicate that engineering plant immunity through manipulating the NHP/NHPG ratio is a promising method to balance growth and defense response in crops.

Synthesis and Evaluation of Indole-Based Autoinducers on Quorum Sensing in Vibrio cholerae.

Vibrio cholerae (V. cholerae) uses the autoinducer CAI-1 (cholera autoinducer 1) and several linked quorum sensing systems in order to efficiently sense its ever-changing environment and optimally coordinate population-wide gene expression. Indole has been reported as an important signal that is sensed by V. cholerae, and here, we report the synthesis and evaluation of a focused library of synthetic indole-CAI-1 derivatives as tools to probe quorum sensing (QS) in this human pathogen. Our results show interesting and diverging effects for several conjugates, as compared to CAI-1, on virulence factor production and biofilm formation.

Silver-doped laser-induced graphene for potent surface antibacterial activity and anti-biofilm action.

Previously, laser-induced graphene (LIG) coated surfaces were shown to resist biofilm growth, although the material was not strongly antibacterial. Here, we show LIG surfaces doped with silver nanoparticles (Ag0 or AgNPs) as highly antibacterial surfaces. Starting from AgNO3 polyethersulfone (PES) polymer substrates, silver nanoparticles between 5-10 nm were generated in situ during the lasing process and stably embedded in the fibrous and porous structure of LIG in a single step. These silver doped LIG (Ag@LIG) surfaces were highly toxic to bacteria via a mechanism of both Ag+ ion release and possible surface toxicity of the AgNPs. The added antibacterial function of Ag-nanoparticles expands the functionality of LIG coated surfaces and might lead to highly effective point of use/entry devices in rural areas or in disaster situations with contaminated water sources.