Lim, Chae-Hong (1995) The effect of environmental factors on the physiology of aeromonas hydrophila in lake water. PhD thesis, University of Warwick.

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Abstract

The survival and physiological responses of A. hydrophila were investigated in lake water microcosms under starvation and other stress conditions. Longer survival was shown in filtered- autoclaved water than in Whatman-filtered water than in untreated water. Longer survival also occurred at 4° than at 15° than at 25° than at 30° than at 37°C. The enhanced survival times over unamended controls suggesting that protozoa could be involved in regulating the size of the population of A. hydrophila. Nutrient amendments such as synthetic sewage, casein, ammonium sulphate, serine and glutamine also increased survival of A. hydrophila over that in unamended controls. Organic compounds released from Flavobacterium, Anacystis, and a number of algae also increased survival times of A. hydrophila in Filtered-autoclaved lake water microcosms. Cell size was reduced under starvation conditions and the numbers of cells capable of respiration also decreased but was always greater than their viable count especially if cells were starved at 37°C. This suggests that A. hydrophila is capable of entering a viable but non-culturable phase under starvation conditions. The effects of starvation on two enzymes, phosphatase and exoprotease, both important in the scavenging of nutrients were examined. The activity of alkaline phosphatase and exoprotease both increased under starvation stress with the largest increases being seen at higher starvation temperatures although the viable count often decreased below the limits of detection at the same time. Nutrient amendments, such as a variety of carbon and nitrogen sources, led to an increase in activity of both enzymes and also led to induction of alkaline phosphatase activity in cells grown in high phosphate medium to repress alkaline phopsphatase activity. This is an obvious indicator that derepression of alkaline phosphatase and synthesis of the enzyme could occur under these conditions in lake water microcosms. Exoprotease activity was also increased upon the addition of single nutrient source to the microcosms. Osmotic stress coupled with starvation stress also increased alkaline phosphatase activity and the addition of the osmoprotectant, betaine, also increased activity. In both cases activity increased although the viable count decreased, in some cases below the limits of dection. Exoprotease activity increased in osmotically shocked cells and increased further if betaine was added to the starvation medium. Plasmid transfer could still occur between A. hydrophila and Escherichia coli in unamended and lake water microcosms amended with carbon and some nitrogen sources. The transfer of the F group plasmid R1drd19 was temperature dependent with no detectable transfer occurring at temperatures below 15° C even in nutrient broth. Plasmid transfer was dependent upon the size of the donor and recipient populations with no detectable transfer occurring at low population densities but transfer at high densities shows that even under prevailing environmental conditions the transfer of F-plasmids was possible between E. coli and A. hydrophila. The changes in protein fingerprints of cell and periplasm extracts under starvation and other stresses were examined using two-dimensional gel electrophoresis. Several starvation specific proteins were identified on the gels and some proteins which were only transiently produced were noted. The N-terminal sequences of two stress proteins produced in response to starvation and ethanol and heat stress were obtained from the gels. Alkaline phosphatase one of the key proteins in the response to stress was also identified by colourimetric staining of two-dimensional gels. The survival of A. hydrophila under starvation and other stresses is dependent upon the sequential synthesis of many proteins, including alkaline phosphatase.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QR Microbiology
Library of Congress Subject Headings (LCSH):	Aeromonas hydrophila, Ecology, Fishes -- Diseases, Fishes -- Effect of water quality on, Stress (Physiology), Water quality -- Environmental aspects
Official Date:	August 1995
Dates:	Date Event August 1995 Submitted
Institution:	University of Warwick
Theses Department:	Department of Biological Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Cockshull, K. E.
Sponsors:	Korea (South).Kukpangbu
Extent:	xx, 344 leaves : illustrations
Language:	eng

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