Distribution of chromobacteria in a lowland river

Abstract

A selective medium was used to estimate the numbers of purple pigmented bacteria in the River Wey. Chromobacteria were never isolated from the springs at the source of the river, but they appeared within a short distance and their numbers generally increased over the first 30 km. Counts were always low but were much higher during the winter than during the summer.

Records of water temperature and turbidity, as well as daily rainfall, were maintained during the sampling period. An unweighted multiple regression analysis of some of the results has shown that much of the variability in the counts of chromobacteria was correlated with turbidity (r=0.67,P<0.001). After turbidity was allowed for, a significant inverse correlation with temperature (r=0.60,P < 0.001) became apparent and these two factors together accounted for 64.7% of the variation in counts. Allowing for these two factors revealed a significant correlation with rainfall during the previous 4 days (r=0.27,P<0.05), and the three factors together accounted for 67.2% of the variability in counts.

In an attempt to discover the source of chromobacteria, samples of silt, soil, and storm overflow effluents were studied. In general, chromobacteria were present in highest numbers in soil or silt containing substantial quantities of organic material.