Date of Award

5-2-1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

The overall purpose of this study was to provide basic data regarding the influence of metals on a free-living terrestrial cyanobacterium, and to demonstrate the utility of laboratory studies for assigning biological significance to field observations on soil-algal ecology.Because Nostoc commune Vaucher is a subaerial inhabitant of soils, it did not respond favorably to traditional liquid culture techniques. Therefore, a filter-culture technique was developed whereby N. commune was grown as a surface film on membrane filters superimposed on an inorganic nutrient agar. Filter-cultures were established by inoculating sterile cellulose acetate membrane filters with a layer of N. commune. Growth rates, production of chlorophyll a, and nitrogenase activity were determined.Growth was exponential throughout the incubation period. Estimates of daily growth rates, culture doubling time, and nitrogenase activity were consistent with laboratory and field estimates reported for several planktonic species of Anabaena (Nostocaceae) and for strains of N. commune isolated from diverse locations. Therefore, the filter-culture technique may be superior to traditional liquid culture methodology for studies involving certain soil procaryotic and eucaryotic algae.The sensitivity of N. commune to mercury, aluminum, and cadmium was determined. Chronic toxicity was defined as the reduction chlorophyll a in filter-cultures which resulted from metal exposure for 12 days, while acute toxicity was defined as decreased nitrogenase activity in 4 day-old filter-cultures exposed to metals for 2 hours. Chronic toxicity was observed in cultures exposed to all 3 metals. Growth was completely inhibited by 100 ppb Hg, 600 ppb Cd, and 7000 ppb Al. The lowest concentrations which significantly reduced growth were 100 ppb Hg, 100 ppb Cd, and 1000 ppb Al. EC50 values of 270 ppb and 2400 ppb were determined for Cd and Al, respectively. Acute toxicity resulted only from exposure to mercury (300 ppb) and cadmium (600 ppb). Experiments with mercury suggested that metals were actively internalized by the cyanobacterium.This work is significant because: (i) it is the first to consider metal toxicity in the cosmopolitan species, N. commune, (ii) it is the first to consider aluminum toxicity in a cyanobacterium isolated from soil, (iii) establishes a baseline for comparison, (iv) it provides a framework within which one can study the influence of one or more chemical and/or physical properties on soil microflora. Finally, this work encourages further refinement of techniques for laboratory cultivation of soil microflora by successfully demonstrating a methodology which considers the growth form and habit of the organism under investigation.

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