To evaluate the impact of environmental factors on the occurrence of environmental mycobacteria, viable counts of mycobacteria were measured in samples of brook water collected from 53 drainage areas located in a linear belt crossing Finland at 63°north latitude. The numbers of mycobacteria were correlated with characteristics of the drainage area, climatic parameters, chemical and physical characteristics of the water, and counts of other heterotrophic bacteria in the water. The numbers of mycobacteria in the water ranged from 10 to 2,200 CFU/liter. The counts correlated positively (P < 0.001) with the presence of peatlands, precipitation data, chemical oxygen demand, water color, and concentrations of Fe, Al, Cu, Co, and Cr. The mycobacterial counts correlated negatively (P < 0.001) with water pH, whereas other heterotrophic bacterial counts lacked any correlation with pH. A linear regression model with four independent variables (i.e., peatlands in the drainage area, chemical oxygen demand, concentration of potassium, and pH) explained 83% of the variation in mycobacterial counts in brook waters. Our results suggest that acidification may enhance the growth of environmental mycobacteria.
E. IIVANAINEN, P.J. MARTIKAINEN, P. VÄ Ä NÄ NE N A N D M .-L . K AT I LA . 1999. The occurrence of mycobacteria was studied in aerobic brook sediments from 39 drainage areas in Finland. The culturable counts of mycobacteria were related to climatic conditions, characteristics of the drainage area, chemical characteristics of the sediment and water, culturable counts of other heterotrophic bacteria, and microbial respiration rate in the sediment. The counts of mycobacteria varied from 1·1 × 10 2 to 1·5 × 10 4 cfu g −1 dry weight of sediment. They correlated positively with the proportion of the drainage area consisting of peatland, total content of C, content of Pb, microbial respiration rate in the sediment, and chemical oxygen demand of the water. The correlations of the mycobacterial counts with pH of sediment and alkalinity of water were negative. The results of the present sediment study and of the forest soil study published earlier strongly suggest that an increase in acidity increases the counts of mycobacteria and decreases the counts and activity of other heterotrophic bacteria. Mycobacterial counts were more than 100 times higher (per dry weight) in forest soils with pH 3·5-4·3 than in sediments with pH 4·5-6·3.
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