Environmental factors affecting the occurrence of mycobacteria in brook sediments

The occurrence of mycobacteria was studied in aerobic brook sediments from 39 drainage areas in Finland, The culturable counts of mycobacteria were re lated to climatic conditions, characteristics of the drainage area, chemica l characteristics of the sediment and water, culturable counts of other het erotrophic bacteria, and microbial respiration rate in the sediment. The co unts of mycobacteria varied from 1.1 x 10(2) to 15 x 10(4) cfu g(-1) dry we ight of sediment. They correlated positively with the proportion of the dra inage area consisting of peatland, total content of C, content of Pb, micro bial respiration rate in the sediment, and chemical oxygen demand of the wa ter. The correlations of the mycobacterial counts with pH of sediment and a lkalinity of water were negative. The results of the present sediment study and of the forest soil study published earlier strongly suggest that an in crease in acidity increases the counts of mycobacteria and decreases the co unts and activity of other heterotrophic bacteria. Mycobacterial counts wer e 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.