Physiology of psychrophilic bacteria from Antarctic sea ice

Abstract

Eighty seven psychrophilic bacterial strains, representing 85% of the total isolates, were isolated from eleven sea ice cores collected from the region of Prydz Bay near the Vestfold Hills, Eastern Antarctica during October-December 1993. The melt water of a further seven sea ice cores, which had been stored at 4°C until return to Australia, yielded only twelve psychrophilic strains (29% of total isolates). The storage of sea ice samples prior to bacterial isolation therefore appears to effect the survival and/or viability of psychrophilic isolates. Chemotaxonomic investigation of selected strains, based on cellular fatty acid composition, identified isolates of the Genera Flavobacterium-Cytophaga, Vibrio, Shewanella and Psychrobacter. Two chemotaxonomic groups of Shewanella sp. were found to contain eicosapentaenoic acid [20:5(03; EPA] while one group of Vibrio sp. produced docosahexaenoic acid [22:6(.03; DHA]. The temperature-growth characteristics of three psychrophilic strains (ACAM 456, JS6P2OrZB, JS3PST) and one psychrotolerant strain (ACAM 457) are described, with the water activity-growth characteristics of ACAM 456. The theoretical temperature range for growth of the strains appeared to be a function of T MIN. Current definitions of the term psychrophile were found to be inadequate when applied to the cardinal growth temperatures determined for the strains examined. ACAM 456 demonstrated a very low T miN (-27°C) but a narrow range of water activity for growth (0.976 to 0.995). The potential effects of variations in environmental temperature and salinity on psychrophilic growth are discussed. De novo fatty acid synthesis of ACAM 456 was investigated using sodium [1- 14C]acetate, L[U-14C]leucine and L[U-I4C]serine as radioactive precursors. ACAM 456 produced acyl components that constitute three different carbon chain types: even-chain, odd-chain and iso-branched odd-chain fatty acids. The proportions of these chain types varied according to growth temperature, nutrient stress and growth on sole carbon sources. ACAM 456 manipulated the utilisation of fatty acid primer molecules as an adaptive response to changes in environmental conditions. In particular, the regulation of odd-chain length fatty acids is described as a novel adaptational response. Investigation of polyunsaturated fatty acid (PUFA) metabolism indicated that ACAM 456 tightly regulated the conversion of fatty acid intermediates through the desaturation process. In particular, the conversion of monounsaturated to diunsaturated fatty acids, and the conversion of triunsaturated components to tetraunsaturated acyl residues appeared as two controlling mechanisms for the biosynthesis of the long-chain PUFA EPA. - The effect of culture conditions (such as temperature, culture volume, aeration and sole carbon sources) on the fatty acid composition of ACAM 456 were investigated, together with the effect of salinity on the fatty acid composition of a psychrophilic halophile strain EAS1. The fatty acid composition of the major phospholipid classes of ACAM 456 was determined, and the phospholipid speciation of ACAM 456, ACAM 459 and EAS1 was investigated by fast atom bombardment-mass spectrometry (FAB-MS) and fast atom bombardment-tandem mass spectrometry (FAB-MS-MS). The non-saponifiable lipid compositions of twenty three bacterial strains isolated from Antarctic sea ice were analysed. Eleven strains produced a novel highly unsaturated straight chain hydrocarbon as the major non-saponifiable lipid component. The compound was identified as hentriacontanonene (n-C3 1:9) and its occurrence correlated with the production of PUFA by the bacterial strains. Strain ACAM 456 was trialed as a feed for cultures of the rotifer Brachionus plicatilis. Incorporation of EPA, along with bacterial fatty acid "markers", was evidenced from ACAM 456 feed to the rotifers. ACAM 456 represents a potential alternative enrichment feed for the rotifer Brachionus plicatilis under culture conditions similar to those employed in many Australian mariculture operations

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