Comparative Study of Bacterial Populations in a Grassland Soil in 1987 and 1992.

Abstract

Bacterial population in grassland soil (sampled in 1992) was studied in terms of component colony-forming curves (cCFCs) to be compared with that in soil sampled in 1987. The simulated colony-forming curve (CFC) pattern was essentially similar to that of the former study; that is, four cCFCs were observed during 163h of incubation time. Bacterial isolates were picked up from colonies appearing along each cCFC and clustered according to their morphological and physiological characteristics (biotypes). The histograms of the frequency distribution of tr value for the isolates corresponding to cCFC groups I, II and III showed a similar pattern as previously. The trend of appearing of oligotrophic bacteria among the isolates of cCFCs groups was also similar to that of the former study although the percent of oligotrophic bacteria differed; that is, oligotrophic bacteria were not found among isolates of cCFCs groups I and II, appeared at 30% in cCFC group III and increased to 68% in cCFC group IV; as the oligotrophic bacteria increased, the sensitivity to 1% NaCl also increased. The bacterial population of the grassland soil is considered to be comprised of at least four component groups (cCFC groups) through yearly variations, although the biotype composition of the respective groups varies either widely or narrowly.