Response to UVB radiation and oxidative stress of marine bacteria isolated from South Pacific Ocean and Mediterranean Sea.

Marine bacterial strains isolated from South Pacific and Mediterranean Sea were studied for their resistance to UVB radiation, their repair capacity under photoreactivating light, as well as their oxidative stress response using concentrated hydrogen peroxide (H(2)O(2)), as an oxidizer. A total of 30 marine bacteria were isolated from the hyper-oligotrophic waters of the South Pacific Gyre to the eutrophic waters of the Chilean coast during the BIOSOPE cruise (2004), and 10 strains from surface Mediterranean coastal waters. One third of bacteria presented a high resistance to UVB and almost all isolates presented an efficient post-irradiation recovery. Only few strains showed cell survival to high concentration of H(2)O(2). No correlation between the sampling sites and the bacterial UVB resistance was observed. Two marine bacteria, Erythrobacter flavus and Ruegeria mobilis, were of particular interest, presenting a good response to the three parameters (UVB and H(2)O(2) resistance/efficient repair). Unexpectedly, two resistant strains were again identified as Ruegeria species underlining that this geographically widespread genus, resist to UVB regardless the environment from which the isolates originate.

Laser scanning detection of FISH-labelled Escherichia coli from water samples.

The development of rapid and accurate methods for the detection and quantification of bacteria without cultivation is of increasing importance for water monitoring. The aim of this study was to develop a solid phase cytometry detection method for DVC-FISH labelled Escherichia coli cells. In order to allow Stomatic detection with ChemScan RDI, the fluorescein-tyramide was combined with an oligonucleotide probe directly labelled with horseradish peroxidase to increase the fluorescence intensity. The method developed was tested for the enumeration of pure cultures, for GAC-filtered and drinking water samples. The method, which appeared to be equivalent to the culture method, was less sensitive than the DVC-FISH method followed by microscopic analysis. Research is underway to further optimise the labelling conditions.