No abstract

Vibrio cholerae non O1 26/06, a non-pathogenic strain, was subjected to treatment by different concentration of paraquat (PQ) and H 2 O 2 . Exposure to PQ for 1 h caused induction of reactive oxygen species (ROS) such as superoxide anion radical ( • O 2 ‾) and H 2 O 2 . At the same time, second stress factor significantly inhibited • O 2 ‾ production and enhanced the intracellular H 2 O 2 content. The enhanced ROS generation resulted in a significant increase in the levels of oxidatively damaged proteins in comparison to the control variant. Thus, the exposure of V. cholerae cells to PQ and H 2 O 2 promoted oxidative stress. Cell response against this stress includes activation of antioxidant enzyme defence. The treatment with PQ concentrations in the range of 0 -5 mM resulted mainly in activation of SOD, but not noticeably changed CAT activity in V. cholerae non-O1 26/06. In contrast, effect of H 2 O 2 treatment on antioxidant enzyme synthesis in our Vibrio strain was still much more pronounced for CAT than for SOD. Therefore, oxidative stress responses induced by • O 2 ‾ (generated intracellularly by PQ) and H 2 O 2 demonstrated differential adaptation of Vibrio cells to different toxic agents.

Neuraminidase is a key factor in the infectious process of many viruses and pathogenic bacteria. The neuraminidase enzyme secreted by the etiological agent of cholera - Vibrio cholerae О1 - is well studied in contrast with the one produced by non-O1/non-O139 V. cholerae. Environmental non-O1/non-O139 V. cholerae isolates from Bulgaria were screened for production of neuraminidase. The presence of the neuraminidase gene nanH was detected in 18.5% of the strains. Тhe strain showing highest activity (30 U/mL), V. cholerae non-O1/13, was used to investigate the enzyme production in several media and at different aeration conditions. The highest production of extracellular neuraminidase was observed under microaerophilic conditions, which is possibly related to its role in the infection of intestine epithelium, where the oxygen content is low. On the other hand, this is another advantage of the microbe in such microaerophilic environments as sediments and lake mud. The highest production of intracellular neuraminidase was observed at anaerobic conditions. The ratio of extracellular to intracellular neuraminidase production in V. cholerae was investigated. The temperature optimum of the enzyme was determined to be 50 °C and the pH optimum to be 5.6-5.8.