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Physiology of psychrophilic bacteria from Antarctic sea ice

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Nichols, David S 1996 , 'Physiology of psychrophilic bacteria from Antarctic sea ice', PhD thesis, University of Tasmania.

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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.

Item Type: Thesis - PhD
Authors/Creators:Nichols, David S
Keywords: Psychrophilic bacteria
Copyright Holders: The Author
Copyright Information:

Copyright 1996 the author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1997. Includes bibliographical references (leaves 187-214)

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