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Some factors affecting the survival of faecal bacteria in estuarine water

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McCambridge, J (1981) Some factors affecting the survival of faecal bacteria in estuarine water. PhD thesis, University of Tasmania.

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Abstract

A seasonal variation in the numbers of faecal indicator
bacteria in the Derwent Estuary was not observed, although a decrease
in numbers along the Estuary associated with a decrease in human
population was noted. There were no consistent significant correlations
between the numbers of indicator bacteria and predacious microorganisms,
temperature, salinity, solar radiation or rainfall. The survival of
E. coli in estuarine water samples, however, exhibited a marked
seasonal variation. This variation was not correlated with changes in
salinity or microbial predators, but appeared to be associated with
changes in water temperature with greater survival during the colder,
winter months (April-July) than in the warmer, summer months (December-February).
There was no significant variation in E. cal: survival or
the growth of predators from sites subject to previous sewage pollution
to sites free from previous sewage pollution.
The introduction of faecal bacteria into estuarine water samples
produced a homeostatic response from a sequence of the indigenous microbial
predators. These organisms increased markedly in numbers, bringing about
a marked decrease and often complete destruction of the prey bacteria.
Following the exhaustion of food supply, the predacious microorganisms
gradually returned to their original level. In pure culture studies
involving individual predator and prey species, a similar pattern of
predator growth and prey destruction also occurred. Once prey numbers
had been reduced to a certain level, predator numbers also declined as
the food supply declined, until the predatory pressure was removed
from the prey population, resulting in the cryptic growth of the prey
species.
Bacterial decline following the inhibition of protozoan predators
indicated that bacterial predators also contributed to prey destruction, but in natural estuarine water samples were maintained at lower levels due to "grazing" by predacious protozoa. The periodic inhibition of
protozoan predators revealed that their major effect on the prey
population and on bacterial predators was exerted during the first 2
days of a 10 day decline period. The initial concentration of E. coli
prey present influenced the size of the predator population and the
sequence of microbial predators which developed.
The survival of faecal indicator bacteria in separate estuarine
water samples varied from one organism to another as follows:
Enterobacter aerogenes, Streptococcus faecium > E. coli, Salmonella
typhimurium > Klebsiella pneumoniae. When incubated together, prey
resistance and prey selection by microbial predators resulted in
different prey survival patterns: S. typhimurium > E. coli, E. coli >
K. pneumoniae and E. coli > S. faecium.
E. coli and S. typhimurium exhibited similar survival curves
and their presence resulted in the growth of comparable numbers of
predacious microorganisms at a range of incubation temperatures.
Bacterial decline was found to be dependent on the presence of both
bacterial and protozoan predators, the latter having a temperature
optimum of 15-20°C and the former becoming more important as the
incubation temperature increased.
The decline of E. coIi cells in estuarine water samples was
found to be significantly greater in the presence of both . naturally occurring
microbial predators and solar radiation than when each of
these factors was acting independently. The effect of solar radiation
on microbial. predators was negligible, while the resistance of bacteria
to light-induced decay varied from one organism to another as follows:
S. typhimurium, S. faecium, E. aerogenes, E. herbicola >E. coli >
K. - pneumoniae.

Item Type: Thesis (PhD)
Keywords: Feces, Estuarine ecology, Tasmania, Derwent River Estuary, Microbial ecology
Copyright Holders: The Author
Copyright Information:

Copyright 1981 the author

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1981. Bibliography: l. 211-231

Date Deposited: 19 Dec 2014 02:24
Last Modified: 11 Jul 2016 23:05
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