Proteins of two-component systems (TCS) have essential functions in the sensing of external and selfgenerated signals in bacteria and in the generation of appropriate output responses. Accordingly, in Myxococcus xanthus, TCS are important for normal motility and fruiting body formation and sporulation. Here we analyzed the M. xanthus genome for the presence and genetic organization of genes encoding TCS. Two hundred seventy-two TCS genes were identified, 251 of which are not part of che gene clusters. We report that the TCS genes are unusually organized, with 55% being orphan and 16% in complex gene clusters whereas only 29% display the standard paired gene organization. Hybrid histidine protein kinases and histidine protein kinases predicted to be localized to the cytoplasm are overrepresented among proteins encoded by orphan genes or in complex gene clusters. Similarly, response regulators without output domains are overrepresented among proteins encoded by orphan genes or in complex gene clusters. The most frequently occurring output domains in response regulators are involved in DNA binding and cyclic-di-GMP metabolism. Our analyses suggest that TCS encoded by orphan genes and complex gene clusters are functionally distinct from TCS encoded by paired genes and that the connectivity of the pathways made up of TCS encoded by orphan genes and complex gene clusters is different from that of pathways involving TCS encoded by paired genes. Experimentally, we observed that orphan TCS genes are overrepresented among genes that display altered transcription during fruiting body formation. The systematic analysis of the 25 orphan genes encoding histidine protein kinases that are transcriptionally up-regulated during development showed that 2 such genes are likely essential for viability and identified 7 histidine protein kinases, including 4 not previously characterized that have important function in fruiting body formation or spore germination.A fundamental property of cells is their ability to sense and respond to external stimuli and self-generated signals. In the case of bacteria, this ability maximizes their chances of survival. Signal transduction proteins have essential functions in stimulus sensing, information processing, and the generation of output responses. Despite the multitude of cues that bacteria need to monitor, the signal transduction schemes involved center on a few types (11, 65): ligand-regulated one-component systems, which consist of single protein molecules containing both a sensing domain and an output domain; cyclic-di-GMP synthetases, phosphodiesterases, adenylate and guanylate cyclases, which act by modifying the level of secondary messenger molecules; methyl-accepting chemotaxis proteins that modulate the activity of chemosensory systems; and systems in which information transfer depends on covalent modification by phosphorylation/dephosphorylation by means of either Ser/ Thr/Tyr protein kinases or histidine protein kinases (HPKs). HPKs are the more common type of protein kinase in bacte...

Legionella pneumophila, the Gram-negative pathogen causing Legionnaires’ disease, infects host cells by hijacking endocytic pathways and forming a Legionella-containing vacuole (LCV) in which the bacteria replicate. To promote LCV expansion and prevent lysosomal targeting, effector proteins are translocated into the host cell where they alter membrane traffic. Here we show that three of these effectors [LegC2 (Legionella eukaryotic-like gene C2)/YlfB (yeast lethal factor B), LegC3, and LegC7/YlfA] functionally mimic glutamine (Q)-SNARE proteins. In infected cells, the three proteins selectively form complexes with the endosomal arginine (R)-SNARE vesicle-associated membrane protein 4 (VAMP4). When reconstituted in proteoliposomes, these proteins avidly fuse with liposomes containing VAMP4, resulting in a stable complex with properties resembling canonical SNARE complexes. Intriguingly, however, the LegC/SNARE hybrid complex cannot be disassembled by N-ethylmaleimide-sensitive factor. We conclude that LegCs use SNARE mimicry to divert VAMP4-containing vesicles for fusion with the LCV, thus promoting its expansion. In addition, the LegC/VAMP4 complex avoids the host’s disassembly machinery, thus effectively trapping VAMP4 in an inactive state.

Mu transposition complexes were used for transposon mutagenesis of Pseudomonas aeruginosa strain PA68. Mu DNA transposition complexes were assembled with MuA transposase and an artificial mini-Mu transposon in vitro, and introduced into Pseudomonas aeruginosa by electroporation. Eight mutants deficient in twitching motility were isolated. Southern blotting confirmed that the insertions had occurred as single events. DNA sequencing of the region flanking the insertion in the twitching-motility mutants revealed that the mini-Mu transposon had inserted into six different genes, PAO171, PA1822, PAO413, PA4959, PA4551 and PA5040. Four of these have previously been proven to be needed for twitching motility, whereas the PA1822 and PA0171 genes have not previously been shown to be required for twitching motility. The twitching-motility defect in the PA1822 mutant was partially complemented by providing the PA1822 gene in trans, and the defect in the PA0171 mutant was fully complemented when PA0171 was provided. A PA0171 mutant and a PA1822 mutant were constructed by gene replacement in the P. aeruginosa PAO1 strain. These mutants were deficient in twitching motility, showing that both the PA1822 and the PA0171 gene are involved in twitching motility.

Aims:  To evaluate the diversity of phenotypic characteristics among isolates of Edwardsiella tarda from various origins. Methods and results:  A total of 10 E. tarda strains were investigated on biological characteristics including flagella formation, bacterial motility, biofilm formation, extracellular protein and plasmid profiles. All the E. tarda strains (including two previous recognized as nonflagellation strains) were proven to have an average of 1–7 peritrichous flagella with the precise number positively correlated with motility and biofilm formation. All the E. tarda strains exhibited similar protein profiles except ET2034, LMG2793 and ET080814, which lacked the three major bands of approximately 18, 21 and 55 kDa. E. tarda with the same geographic location shared similar plasmid profiles. Conclusions:  Edwardsiella tarda strains exhibited diversities in phenotypic characteristics that may be linked to differences in geographic location or host origin. In addition, the number of flagella is essential for bacterial motility and biofilm formation. Significance and Impact of the Study:  This is the first report demonstrating the difference in flagella formation between E. tarda strains, which may broaden the understanding of flagellation trait at intra‐species level. Furthermore, evaluation of virulence‐associated characteristics can provide useful information for unveiling the diverse pathogenic mechanisms of E. tarda.

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