[Mechanism of bacterial motility]

A Novel Inovirus Reprograms Metabolism and Motility of Marine Alteromonas

Members from the Inoviridae family with striking features are widespread, highly diverse, and ecologically pervasive across multiple hosts and environments. However, a small number of inoviruses have been isolated and studied. Here, a filamentous phage infecting Alteromonas abrolhosensis, designated ϕAFP1, was isolated from the South China Sea and represented a novel genus of Inoviridae. ϕAFP1 consisted of a single-stranded DNA genome (5986 bp), encoding eight putative ORFs. Comparative analyses revealed ϕAFP1 could be regarded as genetic mosaics having homologous sequences with Ralstonia and Stenotrophomonas phages. The temporal transcriptome analysis of A. abrolhosensis to ϕAFP1 infection revealed that 7.78% of the host genes were differentially expressed. The genes involved in translation processes, ribosome pathways, and degradation of multiple amino acid pathways at the plateau period were upregulated, while host material catabolic and bacterial motility-related genes were downregulated, indicating that ϕAFP1 might hijack the energy of the host for the synthesis of phage proteins. ϕAFP1 exerted step-by-step control on host genes through the appropriate level of utilizing host resources. Our study provided novel information for a better understanding of filamentous phage characteristics and phage-host interactions. IMPORTANCE Alteromonas is widely distributed and plays a vital role in biogeochemical in marine environments. However, little information about Alteromonas phages is available. Here, we isolated and characterized the biological characteristics and genome sequence of a novel inovirus infecting Alteromonas abrolhosensis, designated ϕAFP1, representing a novel viral genus of Inoviridae. We then presented a comprehensive view of the ϕAFP1 phage-Alteromonas abrolhosensis interactions, elucidating reprogramed host metabolism and motility. Our study provided novel information for better comprehension of filamentous phage characteristics and phage-host interactions.

Two-component system ArcBA modulates cell motility and biofilm formation in Dickeya oryzae

Phytopathogen Dickeya oryzae is a causal agent of rice foot rot disease and the pathogen has an array of virulence factors, such as phytotoxin zeamines, plant cell wall degrading enzymes, cell motility, and biofilms, collectively contributing to the bacterial pathogenesis. In this study, through deletion analysis of predicted regulatory genes in D. oryzae EC1, we identified a two-component system associated with the regulation of bacterial virulence. The two-component system contains a histidine kinase ArcB and a response regulator ArcA, and deletion of their coding genes resulted in changed phenotypes in cell motility, biofilm formation, and bacterial virulence. Electrophoretic mobility shift assay revealed that ArcA bound to the promoters of the bcs operon and bssS, which respectively encode enzymes for the synthesis of celluloses and a biofilm formation regulatory protein. ArcA could also bind to the promoters of three virulence associated transcriptional regulatory genes, i.e., fis, slyA and ohrR. Surprisingly, although these three regulators were shown to modulate the production of cell wall degrading enzymes and zeamines, deletion of arcB and arcA did not seem to affect these phenotypes. Taken together, the findings from this study unveiled a new two-component system associated with the bacterial pathogenesis, which contributes to the virulence of D. oryzae mainly through its action on bacterial motility and biofilm formation.

Involvement of N-acetylneuraminate cytidylyltransferase in Edwardsiella piscicida pathogenicity

Edwardsiella piscicida is a gram-negative bacterium that causes Edwardsiellosis in cultured fish. Edwardsiellosis is accompanied by symptoms such as skin lesions, hemorrhage, and necrosis in fish organs, which leads to significant economic losses in the aquaculture industry. Recently, we found that bacterial sialoglycoconjugates may be involved in the infectivity of E. piscicida. The more infectious strains of E. piscicida contain more sialic acid in the bacterial body, and the mRNA level of putative CMP-Neu5Ac synthase (css) is upregulated compared to that in the non-pathogenic strain. However, this putative css gene is yet to be cloned, and the involvement of CSS in E. piscicida pathogenicity remains unclear. Here, we cloned and transferred the css gene from E. piscicida into the FPC498 strain. CSS promoted infection in cultured cells originating from different fish species, and enhanced the mortality of E. piscicida-infected zebrafish larvae. CSS enhanced cell attachment and motility in E. piscicida, which differs from the decreased bacterial growth observed with the sialic acid-supplemented M9 medium. Both fractions (chloroform-methanol)-soluble and -insoluble fraction) prepared from E. piscicida pellet exhibited the increment of sialo-conjugates induced by CSS. Further, lectin blotting revealed the increment of Sia α2-3- and α2-6-, but not α2-8-, -linked glycoprotein in CSS-overexpressing E. piscicida. Overall, these findings indicate the physiological significance of CSS and the role of sialylation in E. piscicida pathogenicity.

The UhpA mutant of Edwardsiella piscicida enhanced its motility and the colonization in the intestine of tilapia

Edwardsiella piscicida (E. piscicida) is a significant bacterial pathogen of cultured fish, which infected fish meanly through the intestine. Glucose 6-phosphate (Glu6P) in the intestine is nutritious to the pathogen, Meanwhile, Glu6P was found using as a virulent regulating signal for bacteria. The UhpA, one of the Glu6P transport system regulatory proteins could down-regulate the uhpC/uhpB/uhpA system and decrease its pathogenicity. However, the motility and the colonization of E. piscicida affected by UhpA were still unclear. In this study, the motility and the colonization of E. piscicida were monitored. The result demonstrated that the motility of EIB202 was significantly stronger than that of in ΔuhpA according to fractions 4, 8 and 9. However, the motility of ΔuhpA was significantly stronger than that of EIB202 according to the total number at the whole experiment. Although, there was no difference in the number of bacteria in the posterior intestine of tilapia after infected with E. piscicida EIB202 and ΔuhpA. The number of bacteria in the anterior and the middle intestine of fish infected with ΔuhpA were significantly higher than that of in fish infected with EIB202 at the whole experiment (P < 0.05). Interestingly, both E. piscicida strains colonized in the anterior intestine than that of in the middle and posterior intestines of tilapia. Besides, the gene expression of IL-1β and TNF-α in the head-kidney of fish infected with ΔuhpA showed significantly higher (p < 0.05) than fish infected with EIB202 during the whole experimental period. Most importantly, the survival rate of E. piscicida EIB202 and ΔuhpA were 57% and 37% respectively. All results indicate that the uhpA gene mutant in E. piscicida could enhance its motility and the colonization in the intestine of tilapia, this illustrates the mechanism of UhpA decreases the pathogenesis of E. piscicida in fish.