Promiscuous Diffusible Signal Factor Production and Responsiveness of the Xylella fastidiosa Rpf System

Abstract

Cell density-dependent regulation of gene expression in Xylella fastidiosa that is crucial to its switching between plant hosts and insect vectors is dependent on RpfF and its production of 2-enoic acids known as diffusible signal factor (DSF). We show that X. fastidiosa produces a particularly large variety of similar, relatively long-chain-length 2-enoic acids that are active in modulating gene expression. Both X. fastidiosa itself and a Pantoea agglomerans surrogate host harboring X. fastidiosa RpfF (XfRpfF) is capable of producing a variety of both saturated and unsaturated free fatty acids. However, only 2-cis unsaturated acids were found to be biologically active in X. fastidiosa. X. fastidiosa produces, and is particularly responsive to, a novel DSF species, 2-cis-hexadecanoic acid that we term XfDSF2. It is also responsive to other, even longer 2-enoic acids to which other taxa such as Xanthomonas campestris are unresponsive. The 2-enoic acids that are produced by X. fastidiosa are strongly affected by the cellular growth environment, with XfDSF2 not detected in culture media in which 2-tetradecenoic acid (XfDSF1) had previously been found. X. fastidiosa is responsive to much lower concentrations of XfDSF2 than XfDSF1. Apparently competitive interactions can occur between various saturated and unsaturated fatty acids that block the function of those agonistic 2-enoic fatty acids. By altering the particular 2-enoic acids produced and the relative balance of free enoic and saturated fatty acids, X. fastidiosa might modulate the extent of DSF-mediated quorum sensing.

Microfluidics‐based liquid chromatography/mass spectrometry multiple reaction monitoring approach for the relative quantification of Burkholderia cenocepacia secreted virulence factors

“…A reversed‐phase HPLC analysis (adapted from Ionescu et al) was performed on an Ettan LC system (GE Healthcare Life Sciences) equipped with an Acclaim PepMap100 C18 column (3 μm, 250 mm × 75 μm; Thermo Scientific) with as solvent A 0.1% TFA in H 2 O (Milli‐Q; MQ) and solvent B 0.1% TFA in methanol. A 15‐min gradient starting from 25% solvent B and increasing to 100% solvent B was applied for the separation.…”

A proposed role for diffusible signal factors in the biofilm formation and morphological transformation of Helicobacter pylori

“…The studies conducted by Ionescu et al (38) showed that in X. fastidiosa cis-2-tetradecenic acid (C 14 :Δ 2 , XfDSF) and cis-2-hexadecenic acid (C 16 :Δ 2 , XfDSF2) are the strongest gene expression activators. X. fastidiosa and X. campestris were used to show the structural and isomeric effect of DSF molecules on the activation of DSF-dependent processes (the production of extracellular enzymes).…”

“…Saturated fatty acids, competing for the RpfC receptors, reduce the activation of processes conditioned by rpf genes, i.e. autoaggregative behavior and biofilm formation (35,38,39,45,46). Reduction of DSFs activity and an increase in AI-2 concentration results in the transformation of some coccoid H. pylori forms to the spiral morphotype, followed by chemorepulsion from the AI-2 source and migration in search of new niches in the gastric environment (6,17,(30)(31)(32)44).…”

“…The DSF-dependent autoinductive activity involves a classic two-component system in which DSF molecules, upon reaching a critical concentration, induce sensor kinase RpfC, which in turn phosphorylates the RpfG regulator. RpfG causes transduction of the signal and expression of the relevant genes (35,38,39). Communication via DSFs is involved in many processes that are crucial to the physiology and pathogenicity of bacteria, such as the production of extracellular enzymes (proteases, endoglucanases, chitinases), microcolony and biofilm formation, autoaggregative behavior, cell motility, resistance to toxins and biocides, and oxidative stress activation (40).…”

Sustainable Management of Plant Quarantine Pests: The Case of Olive Quick Decline Syndrome

“…Cell-to-cell signaling mediated by a fatty acid diffusible signaling factor (DSF) may also show different chemical structure according to strain [27][28][29]. Regulation of pathogenicity factors (rpf) cluster [27,[30][31][32] as well as DSF and cyclic di-guanosine monophosphate [33,34] were also critical for biofilm formation, plant virulence, and insect transmission. The complete genome of the CoDiRO strain is not currently available, while assessment of the genome diversity of CoDiRO isolates has been carried out [35][36][37].…”