Quantification of recA gene expression as an indicator of repair potentialin marine bacterioplankton communities of Antarctica

Marine bacteria in surface waters must cope daily with the damaging effects of exposure to solar radiation (containing both W-A and UV-B wavelengths), which produces lesions in their DNA. As the stratospheric ozone layer is d epleted, these coping mechanisms are likely to play an even more important role in the viability of marine bacterial communities. The recA gene is ubi ciuitous among eubacteria and is highly conserved both in nucleotide and am ino acid sequence. Besides its role in generalized recombination, the gene' s translational product, RecA, is the regulator of 'dark repair' activity ( DNA-repair mechanisms that do not require visible light as a cofactor). We have taken advantage of this function and used recA gene expression as a ba rometer of the DNA-damage repair capacity of bacterial assemblages in the S outhern Ocean. Studies were conducted in the Gerlache Strait, Antarctica, i n the austral springs of 1995 and 1996. Analysis of both recA mRNA and RecA protein extracted from natural communities indicated that the level of exp ression of this gene varied in a diel fashion, suggesting an increased repa ir capacity in these organisms. These included an early morning rise in Rec A levels followed by a plateau or even a reduction in RecA concentration du ring the remainder of the day. A much greater increase in RecA was consiste ntly observed after sunset. followed by a constant decrease during the nigh t. Microcosm experiments with a RecA(+) Gerlache Strait gamma -proteobacter ia isolate, RM11001, demonstrated a similar diel pattern of expression. The se studies demonstrate the usefulness of RecA as a biological indicator of DNA repair capacity in natural bacterial assemblages. They indicate that 'd ark repair' of DNA damage is an important coping mechanism for bacteria in the marine environment of Antarctica.