Distribution and heterotrophic potential of microorganisms in a cold ocean environment

Powell, James Conrad (1980) Distribution and heterotrophic potential of microorganisms in a cold ocean environment. Masters thesis, Memorial University of Newfoundland.

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Abstract

During the period from April 3, 1979 to May 1, 1980, fourteen sets of seawater samples were collected at a single station in Conception Bay, Nfld. Each set, except for a set collected on April 3, 1979, consisted of samples from four depths (0.5, 10, 20 and 40 m). Total viable heterotrophic bacteria were estimated by the standard plate count (SPC) method and by the most probable number (MPN) method. Total bacterial numbers were determined by the acridine orange direct count (AODC) method. Oleoclastic bacteria were enumerated by an MPN method using a buffered basal salts medium to which Venezuelan crude oil had been added. Heterotrophic bacterial activity was determined by the heterotrophic potential method. -- Total numbers of bacteria fluctuated over the sampling period but generally were lower in winter. Numbers ranged from 2.5 x 10⁷ to 4.6 x 10⁸ per litre of seawater. Viable bacteria by the MPN method ranged from 3.3 x 10³ to 1.6 x 10⁶ per liter and, generally, were highest in the fall. MPN estimates represented 0.003 to 1.750% of the total bacteria determined by the AODC method. The SPC method yielded 6.0 x 10³ to 3.3 x 10⁶ viable bacteria per liter during the course of sampling, and the highest numbers by this technique were observed in June, 1979, for all depths tested. Throughout the sampling period, 0.003 to 3.370% of the total bacteria (AODC method} were detected by the SPC method. This method gave higher estimates of viable bacteria in June and July, while the MPN method gave higher results in October, November, and December. At other times of the year, numbers were approximately the same by the two methods. Oleoclasts ranged in number from 7.7 x 10² to 1.6 x 10⁶ per liter and were higher in the May to September period than at other times of the year. No pattern of distribution with depth was observed for either total, viable, or oleoclastic bacteria. -- Heterotrophic activities were determined at in situ temperatures and exhibited a seasonal trend. Vmax increased from spring to summer, decreased during the fall, and remained low during the winter. However, highest Vmax values at all sampling depths were recorded before the highest water temperature for the year was reached at each depth. Turnover time decreased with increasing temperature and the opposite was also observed. Vmax ranged from 1.3 to 121.0 ng glutamate l⁻¹h⁻¹ over the sampling period, and turnover time varied from 66 to 13,074 h. Neither Vmax nor turnover showed any pattern with depth. -- Vmax specific activity index (Vmax/ cell) was generally higher in summer than at other times of the year. The highest values at three depths also preceded the maximum water temperature. Values ranged from 0.007 to 1.235 fg glutamate h⁻¹cell⁻¹ over the sampling period. -- A thermocline was present on four of the fourteen sampling days. The thermocline appeared to have little effect on bacterial numbers but heterotrophic activity was lower below the thermocline than above. -- This project has shown that the majority of the bacterial population exists in a dormant state. -- This is the first study in which both bacterial numbers and heterotrophic potentials have been determined throughout four consecutive seasons for marine waters of the Canadian Atlantic seaboard.

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