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Characterisation and application of Australian thraustochytrids


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Lewis, Thomas Eric (2001) Characterisation and application of Australian thraustochytrids. PhD thesis, University of Tasmania.

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Aspects of the taxonomy, lipid production and aquacultural application of several
new polyunsaturated fatty acid (PUFA)-producing microheterotrophs were examined
using 18S ribosomal DNA sequencing and fatty acid, sterol and lipid class analyses.
Thraustochytrid-like organisms were isolated from marine environments in southeastern
Tasmania (Australia). A high proportion of strains produced PUFA,
especially eicosapentaenoic acid (EPA, 20:5n3) and docosahexaenoic acid (DHA,
22:6n3). The phylogenetic relationships of Tasmanian and type strains were
compared, using 18S rDNA sequences and fatty acid profiles.
The effect of different extraction techniques on the recovery of fatty acids from two
Tasmanian thraustochytrid strains (ACEM 6063 and ACEM 000A) was examined.
Two procedures were used: the extraction of lipids from biomass followed by
transesterification of the fatty acids (extraction-transesterification); and the direct
transesterification of biomass to produce fatty acid methyl esters (i.e. without the
initial extraction step). Results showed that the most efficient direct
transesterification method yielded significantly more fatty acids than the most
efficient extraction-transesterification method. Production of biomass and lipid by strain ACEM 6063 under different culture
conditions was examined. Biomass production increased with increasing glucose and
sea salt concentration, culture temperature, and with low fermenter impeller speeds.
The predominant lipid classes were triacylglycerols and phospholipids. The
proportion of triacylglycerols increased, and the proportion of phospholipids
decreased, with culture age. Lipid content increased with increasing culture age,
temperature, glucose and sodium glutamate concentration and dissolved oxygen
(DO). Increasing DO levels substantially decreased the proportion of saturated fatty
acids and substantially increased the proportion of monounsaturated fatty acids.
Twenty sterols, 13 of which were identified, were detected. Predominant were:
cholest-5-en-3-ol, 24-ethylcholesta-5,22E-dien-3-ol, 24-methylcholesta-5,22E-dien-
3-ol, and two co-eluting sterols — one of which was 24-ethylcholesta-5,7,22-trien-3-
ol. Culture age, temperature and DO influenced squalene and sterol content. Total
sterols (as a proportion of total lipids) decreased with increasing culture age. The ability of PUFA-producing thraustochytrids to enrich rotifers (Brachionus
plicatilis) in these PUFA was examined, and compared to that of two previously
isolated PUFA-producing bacteria, which were rich in either EPA or DHA.
Enrichment with the EPA-producing bacterium only resulted in rotifer EPA levels
increasing from 0.1% to 1.2% of total dry weight (%dw). Similarly, following
enrichment with the DHA-producing bacterium only, rotifer DHA levels increased
from below detection to 0.1 %dw. When enriched with a mixture of the two bacterial
strains, final rotifer EPA- and DHA-levels were 0.5 %dw and 0.3 %dw respectively. When thraustochytrid strains ACEM 6063 and ACEM 000A were fed to rotifers, no
significant differences were found between the fatty acid profile of rotifers enriched
with thraustochytrids preserved by different treatments. Significant differences were
observed between rotifers fed biomass from individual thraustochytrid strains or a
mixture of the two strains. With both strains, the sum of arachidonic acid (AA,
20:4n6), EPA and DHA in rotifers enriched for 6 h reached 1.5-2 %dw in most
treatments. There was little change in fatty acid content of rotifers enriched for 24 h
compared to 6 h. Rotifers enriched with thraustochytrids contained increased levels
of PUFA compared to rotifers enriched with bacteria. Strain specific variation in the
PUFA content of the thraustochytrid strains also allowed the PUFA content of
thraustochytrid-enriched rotifers to be manipulated to a greater degree than that of
bacteria-enriched rotifers. Following 24 h post-enrichment starvation, levels of AA,
EPA and DHA in most thraustochytrid-enriched rotifers were still significantly
higher than in continuously starved and yeast-fed rotifers, indicating that rotifers had
digested and assimilated the microheterotroph fatty acids. The two thraustochytrid
strains are considered to be suitable for use in Australian aquaculture, as they provide
enrichment levels comparable to those achieved with currently available commercial
enrichment diets.

Item Type: Thesis (PhD)
Keywords: Microbial lipids, Rotifera
Copyright Holders: The Author
Copyright Information:

Copyright 2001 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:

Not available for loan/copying until 3/7/2003. Thesis (Ph.D.)--University of Tasmania, 2001. Includes bibliographical references

Date Deposited: 19 Dec 2014 02:41
Last Modified: 14 Jul 2017 02:13
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