Vibrio vulnificus is a bacterium responsible for severe gastroenteritis, sepsis and wound infections. Gastroenteritis and sepsis are commonly associated with the consumption of raw oysters, whereas ...wound infection is often associated with the handling of contaminated fish. Although classical virulence factors of this emerging pathogen are well characterised, there remains a paucity of knowledge regarding the general biology of this species. To investigate the presence of previously unreported virulence factors, we applied whole genome sequencing to a panel of ten V. vulnificus strains with varying virulence potentials. This identified two novel type 6 secretion systems (T6SSs), systems that are known to have a role in bacterial virulence and population dynamics. By utilising a range of molecular techniques and assays we have demonstrated the functionality of one of these T6SSs. Furthermore, we have shown that this system is subject to thermoregulation and is negatively regulated by increasing salinity concentrations. This secretion system was also shown to be involved in the killing of V. vulnificus strains that did not possess this system and a model is proposed as to how this interaction may contribute to population dynamics within V. vulnificus strains. In addition to this intra-species killing, this system also contributes to the killing of inter bacterial species and may have a role in the general composition of Vibrio species in the environment.
Summary
With the rapid increase of aquaculture contributing to sustainable food security, comes the need to better understand seafood associated diseases. One of the major aquatic bacterial genera ...responsible for human infections from seafood is Vibrio, especially from oysters. Currently, in vivo study of bacterial interactions within oysters is limited by the inability to promote high‐level uptake of bacteria by oysters. This study has therefore evolved current natural marine snow protocols to generate ‘artificial’ marine snow, into which bacteria can be incorporated to facilitate extensive uptake by oysters. This presents an adaptable model for bacterial study within filter‐feeding shellfish. Using this model, we demonstrate for the first time the antibacterial activity of Vibrio vulnificus Type 6 secretion systems in vivo, revealing an important role for the T6SS in V. vulnificus ecology.
Summary
Sulphur is essential for some of the most vital biological activities such as translation initiation and redox maintenance, and genes involved in sulphur metabolism have been implicated in ...virulence. Mycobacterium tuberculosis has three predicted genes for the prototrophic acquisition of sulphur as sulphate: cysA, part of an ABC transporter, and cysA2 and A3, SseC sulphotransferases. Screening for amino acid auxotrophs of Mycobacterium bovis BCG, obtained by transposon mutagenesis, was used to select methionine auxotrophs requiring a sulphur‐containing amino acid for growth. We have characterized one of these auxotrophs as being disrupted in cysA. Both the cysA mutant and a previously identified mutant in an upstream gene, subI, were functionally characterized as being completely unable to take up sulphate. Complementation of the cysA mutant with the wild‐type gene from M. tuberculosis restored prototrophy and the ability to take up sulphate with the functional characteristics of an ABC transporter. Hence, it appears that this is the sole locus encoding inorganic sulphur transport in the M. tuberculosis complex
Based on our N -terminal amino acid sequence of MPT53 and a deduced DNA sequence, we searched for the corresponding gene in the Mycobacterium tuberculosis genomic sequence at the Sanger centre, ...localizing mpt53 close to mpt70 and mpt83. The gene was cloned and expressed, followed by purification of MPT53 to homogeneity from recombinant M. smegmatis culture fluid. In MPT53 there is 60 % identity with the active site of thioredoxin of M. tuberculosis (MPT46) with two cysteins in a CXXC motif, but MPT53 could not serve as an alternative substrate for thioredoxin reductase. Testing for IgM and IgG1 anti-MPT53 in cattle sera showed that MPT53 is immunogenic following natural and experimental infection with M. bovis. Cloning of mpt53 represents cloning of the last of the 10 proteins originally defined as "secreted proteins" of M. tuberculosis and M. bovis based on determination of their "Localization index" (LI) (J Gen Microbiol 1991;137 : 875-84). The need for a precise definition of the term "secreted protein" is discussed. So far we have observed full concordance between occurrence of an LI value indicating secretion of a protein and occurrence of a signal sequence in the corresponding gene. Signal sequence independent protein secretion in mycobacteria may occur for a limited number of proteins and remains to be established.
Based on ourN-terminal amino acid sequence of MPT53 and a deduced DNA sequence, we searched for the corresponding gene in theMycobacterium tuberculosisgenomic sequence at the Sanger centre, ...localizingmpt53close tompt70andmpt83. The gene was cloned and expressed, followed by purification of MPT53 to homogeneity from recombinantM. smegmatisculture fluid. In MPT53 there is 60 % identity with the active site of thioredoxin ofM. tuberculosis(MPT46) with two cysteins in a CXXC motif, but MPT53 could not serve as an alternative substrate for thioredoxin reductase. Testing for IgM and IgG1 anti-MPT53 in cattle sera showed that MPT53 is immunogenic following natural and experimental infection withM. bovis. Cloning ofmpt53represents cloning of the last of the 10 proteins originally defined as «secreted proteins» ofM. tuberculosisandM. bovisbased on determination of their «Localization index» (LI) (J Gen Microbiol1991;137: 875–84). The need for a precise definition of the term «secreted protein» is discussed. So far we have observed full concordance between occurrence of an LI value indicating secretion of a protein and occurrence of a signal sequence in the corresponding gene. Signal sequence independent protein secretion in mycobacteria may occur for a limited number of proteins and remains to be established.
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