The type III secretion system (T3SS) of Edwardsiella tarda plays an important role in infection by translocating effector proteins into host cells. EseB, a component required for effector translocation, is reported to mediate autoaggregation of E. tarda. In this study, we demonstrate that EseB forms filamentous appendages on the surface of E. tarda and is required for biofilm formation by E. tarda in Dulbecco's modified Eagle's medium (DMEM). Biofilm formation by E. tarda in DMEM does not require FlhB, an essential component for assembling flagella. Dynamic analysis of EseB filament formation, autoaggregation, and biofilm formation shows that the formation of EseB filaments occurs prior to autoaggregation and biofilm formation. The addition of an EseB antibody to E. tarda cultures before bacterial autoaggregation prevents autoaggregation and biofilm formation in a dose-dependent manner, whereas the addition of the EseB antibody to E. tarda cultures in which biofilm is already formed does not destroy the biofilm. Therefore, EseB filament-mediated bacterial cell-cell interaction is a prerequisite for autoaggregation and biofilm formation. Edwardsiella tarda is a Gram-negative bacterium with a wide range of hosts, including fish and humans. E. tarda causes hemorrhagic septicemia in fish and gastrointestinal and extraintestinal infections in humans (1-3). The type III secretion system (T3SS) of E. tarda plays a pivotal role in infection and enables the bacteria to survive and replicate in phagocytes and epithelial cells (4-7).The bacterial T3SS nanomachine, delivering effector proteins directly from the bacterial cytosol to host cells (8, 9), consists of three parts: the basal body, needle, and translocation pore (10). The gene cluster of the T3SS in E. tarda contains 34 genes, which encode secretion apparatus, chaperones, translocators, effectors, and regulators (5, 11). The esrA-esrB (5) and esrC (12) genes in the T3SS gene cluster together with phoP-phoQ (13) and phoB-phoR (14) outside the T3SS gene cluster control the virulence of E. tarda. Deletion of esrB abolished the secretion of the translocon proteins EseB, EseC, and EseD (5), which can form a protein complex after secretion (5, 15, 16). Mutation of eseB led to an E. tarda replication defect in host cells (5). EseB is required not only for translocating effectors into host cells (11) but also for bacterial autoaggregation in a T3SS-inducing medium, Dulbecco's modified Eagle's medium (DMEM) (5).EseB is homologous to EspA of enteropathogenic Escherichia coli (EPEC) or enterohemorrhagic Escherichia coli (EHEC), and it has been reported that EspA forms a sheath-like structure on the bacterial surface, as revealed by immunofluorescent staining and immunogold labeling, and is required for effector translocation (17-19). EspA of EPEC or EHEC also functions as an adhesin in microcolony formation on epithelial cells and is involved in bacterial aggregation during biofilm formation on abiotic surfaces or salad leaves (19,20). The contribution of the T3SS to biofilm ...
Neosalanx taihuensis were sampled from the Tian-e-zhou Oxbow from March 2006 through November 2007. Two separate spawning seasons were identified based on the annual reproductive cycles of the females, designated as the autumn-spawning season and the spring-spawning season. Lifespan of the offspring of the spring-spawning fish was 1 year, with them dying after the subsequent spring spawning. Autumn-spawned females seem to be the offspring of the spring-spawning fish, based on monthly changes in the length-frequency distributions. Springmature females had higher absolute fecundity, gonadosomatic index, and relative condition factor in 2007 than in 2006. Relative condition factor of the immature female offspring of spring-spawning fish was higher in 2007 than in 2006, portending a further increase in reproductive investment during the spring spawning of 2008. The increasing reproductive investment suggests that the population of N. taihuensis in the Tian-e-zhou Oxbow may be recovering from its recent decline.
Otolith microstructure was used to distinguish specimens of Neosalanx taihuensis born in spring and autumn. Increment width during the early life stage was significantly narrower for spring-born than autumn-born juveniles, and the frequency distributions of the width of the first 5 increments were distinctive and diagnostic. Otolith growth trajectories and frequency distribution of the first 5 increments of spring-spawning adults displayed similar patterns to spring-born juveniles. Otolith growth trajectories of autumn-spawning adults were intermediate between those of spring-and autumn-born juveniles, and the frequency distribution of the width of the first 5 increments showed two modes, one similar to spring-born juveniles and the other similar to autumn-born juveniles. Populations of N. taihuensis have previously been shown to be dominated by spring-spawning fish. Thus, the putative life history of N. taihuensis can be summarized as: (1) a small part of the spring-born fish mature and spawn in autumn of the year of their birth, (2) the majority of the spring-born cohort matures and spawns in spring of the next year, and (3) offspring of the autumn-born fish mature and spawn in autumn of the following year. This stockstructure information should be considered in fisheries management for this species.
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