A Researsh On The Role Of Arctic Sea-ice Bacteria Fatty Acid System In Environment Adaptability

The arctic is a special ecosystem for its permanent coldness and high salinity andhas unique climate characteristics.The microorganisms must have special physiologicalmetabolic pathways to adapt to the extreme environment. The study towards arcticsea-ice bacteria will be helpful to the adaptation mechanisms of low temperature andhigh salinity and to the exploitation of microbial resources in arctic.Three bacteria strains having strong tolerance for low temperature and highsalinity were isolated from the sea-ice samples collected during the fourth ArcticScientific Expedition of China. We analyzed the influence of culture temperature andsalinity on the growth of three strains, drawed the growth curves and determined itsoptimal growth conditions. The optimal growth temperature and salinity of threestrains were10℃and30respectively, suggesting that they were psychrotrophic andhalophilic. Molecular identification and phylogenetic analysis indicated that threestrains were members of Pseudoalteromonas.The effects of temperature and salinity on membrane fatty acids composition andcell membrane fluidity were studied by using GC-MS and fluorescence polarization.we analyzed the growth situations and fatty acids composition by adding cerulenin atlow temperature and high salinity. The results showed that cell membrane fluidity werenot affected by low temperature treatments, the amount of total unsaturated fatty acidsand branched chain fatty acids were increased, and the monounsaturated fatty acidC16:1played a key role by low temperature and high salinity treatments. Themembrane fluidity under high salinity treatment was basically the same as control, butthe amounts of C16:1and branched-chain fatty acid were increased significantly.The results of quantitative real-time PCR (qRT-PCR) showed that the expressionof delta9-fatty acid dehydrogenase gene obviously increase and peaked at2-4h afterlow temperature treatments. The expression of target gene increased and peaked at8-12h after high salinity treatments. It is supposed that arctic sea-ice bacteria canproduce more fatty acids with low melting point, such as C16:1, through the increasedsynthesis of delta9-fatty acid dehydrogenase under low temperature and high salinitystresses to maintain cell membrane fluidity, thus their growth and reproduction.