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Abstract

There exists a unique and characteristic bacterial biota in Antarctic
hypersaline lakes and 15 new bacterial species have been described from
the lakes of the Vestfold Hills, Antarctica. In this study, antibodies were
raised against the type strains of the four bacterial species which have
been most consistently isolated from the oxylimnion of the hypersaline
lakes of the Vestfold Hills. The abundance of these serogroups was
measured throughout the austral spring and summer in four hypersaline
lakes and a seawater site by indirect immunofluorescence microscopy.
Maximum abundances of Halomonas serogroups (up to 40% of the total
bacteria) and the Flavobacterium gondwanense serogroup (up tO 10% of
the total bacteria) were observed at discrete depths within the water
column in the two most hypersaline lakes at about midsummer,
coincident with the time of maximum sunlight and the commencement
of the summer thaw. Change in species abundance was not reflected in
the total bacterial count, indicating compositional change of the total
bacterial population. Concurrently, radioisotope incorporation methods were used to estimate
heterotrophic bacterial productivity and metabolism. In the coastal
marine site, incorporation rates were within the range previously
reported for Antarctic ecosystems, ranging up to 2.1 pM thymidine h⁻¹
and 11.0 pM leucine h⁻¹ . Incorporation rates in the hypersaline lakes
ranged up to 4.6 pM thymidine h⁻¹ and 94 pM leucine h⁻¹ . Generation
times throughout all sample sites were fastest after the summer thaw at a
depth of 2 m. Even at these peak times productivity in the hypersaline
lakes was more than 100 times lower than average productivity in
temperate aquatic environments. Optimum temperature for radioisotope
incorporation was close to in-situ temperature in most cases, confirming
the adaption of in-situ bacteria to the low water temperatures.
Dissolved organic carbon (DOC) concentrations reflected the strong
stratification and seasonal variation of other lake parameters. The ratio
of [³H]leucine incorporation to [³H]thymidine incorporation (a measure
of bacterial physiological state or species composition) correlated with
DOC concentrations. DOC concentrations correlated well with total
bacterial numbers but not with changes in species composition. In the meromictic hypersaline lakes, reduction of sulphur compounds is
also an important means of energy generation. The Halomonas and
Flavobacterium species isolated so far do not appear to be involved in
sulphur cycling. However, a novel species of Brevibacterium, isolated
and partly described in this study, reduces dimethylsulfoxide to
dimethylsulphide and utilises methionine and cysteine as sole energy
sources.

Item Type:	Thesis - PhD
Authors/Creators:	James, SJ
Keywords:	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 151-177)
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