Response to osmotic stress by the haloalkaliphilic bacterium Halomonas campisalis

by 1981- Aston, John

By John Aston, M.S. Washington State University May 2006 Chair: Bernard Van Wie This thesis is broken down into four parts. The first part (Chapter One) provides a background into the study of halophilic organisms. Diversity, survival mechanisms, ecological significance, and applications are all discussed. Chapter Two discusses the primary focus of my research. The response of the haloalkaliphilic microorganism, Halomonas campisalis, to changes in environmental salinity is investigated. Three phenotypic changes are examined in detail: (1) growth kinetics, (2) compatibles solute accumulation, and (3) phospholipid fatty acid (PLFA) analysis. The study was completed in parallel with aerobic and denitrifying samples. Growth kinetics were found to be v highly dependent on media salinity. Under aerobic conditions optimal growth occurred at 20 g/L NaCl (0.5 h-1). Under denitrifying conditions optimum growth occurred at 30 g/L NaCl (0.3 h-1). The compatible solute ectoine was observed in the absence of salt as well as across the entire range of salinities examined, with optimum intracellular accumulation occurring at 90 g/L NaCl for both aerobic and denitrifying conditions. In much smaller amounts, glycine betaine was found at intermediate salinities, and hydroxyectoine was found at the highest salinities (175 g/L NaCl). PLFA analysis provided insights into cell stress at varying salinities. High ratios of trans monoenoic fatty acids indicated an increase in cell membrane permeability in the absence of salinity under both aerobic and denitrifying conditions. In contrast no such physiological marker was present at 175 g/L NaCl where growth kinetics were also depressed. This suggests that another cell stressor is responsible for decreased cell growth. It is possible that high salinity in the media begins to interfere with cation transfer between H. campisalis and the surroundings, a necessary exchange in order to balance the intracellular pH.