Type VI Secretion Systems: Environmental and Intra-host Competition of Vibrio cholerae

Case report: Characterization and bioinformatics analysis of non-O1/O139 Vibrio cholerae strain isolated from a choledochoduodenal fistula patient with septicemia

The gram-negative bacterium Vibrio cholerae (VC) is divided into multiple serogroups, with groups O1 and O139 responsible for cholera. Conversely, Vibrio cholerae belonging to the non-O1/non-O139 group (NOVC) does not produce cholera-causing toxins. Insufficient understanding of the frequency of NOVC causes fear during the early detection phase. Acute gastroenteritis is often caused by NOVC, while extra gastrointestinal infections are less common. In the case described here, the patient had a postoperative choledochoduodenal fistula due to prior choledochotomy. In August 2023, he was hospitalized with fever and diarrhea. The gram-negative bacilli Vibrio cholerae was isolated from a blood specimen using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The strain was identified as non-O1/O139 by serum agglutination tests. Subsequent whole-genome sequencing and database analysis revealed that the strain possessed resistance genes such as CRP, varG, almG, and QnrVC4, as well as various virulence factors such as RTX, hlyA, VAS, and T3SS. The phylogenetic tree analysis indicated that CQ23-0008VC had close relationship with cholerae strains isolated from aquatic environments. The patient was treated promptly and discharged after being admitted with severe symptoms. However, Bioinformatics analysis indicated that the virulence factors that were identified in the bacteria were significant; thus, these virulence factors can indicate to medical professionals that a patient could have a septicemia caused by NOVC.

The role of the type VI secretion system in the stress resistance of plant-associated bacteria

The type VI secretion system (T6SS) is a powerful bacterial molecular weapon that can inject effector proteins into prokaryotic or eukaryotic cells, thereby participating in the competition between bacteria and improving bacterial environmental adaptability. Although most current studies of the T6SS have focused on animal bacteria, this system is also significant for the adaptation of plant-associated bacteria. This paper briefly introduces the structure and biological functions of the T6SS. We summarize the role of plant-associated bacterial T6SS in adaptability to host plants and the external environment, including resistance to biotic stresses such as host defenses and competition from other bacteria. We review the role of the T6SS in response to abiotic factors such as acid stress, oxidation stress, and osmotic stress. This review provides an important reference for exploring the functions of the T6SS in plant-associated bacteria. In addition, characterizing these anti-stress functions of the T6SS may provide new pathways toward eliminating plant pathogens and controlling agricultural losses.