Abstract
The colony-forming process of bacteria in a paddy field soil on 100-fold diluted nutrient broth (DNB) plates containing As(III) (250-1, 000ppm) was analyzed by the first-order reaction (FOR) model. The process on plates with 250ppm As(III) was simulated by a superimposition of three FOR model curves, which are respectively referred to as component colony-forming curve (cCFC) I, II, or III. Bacterial isolates from the 250 ppm As(III) plates were divided into three groups according to cCFC, along which each respective bacterium produced its colony. The three cCFC groups showed different trends of physiological properties: (1) the range of tr, which is the waiting time for the appearance of the first colony of each single population in the presence or absence of As(III), (2) the range of the maximal tolerant As(III) concentration for each isolate and some of its taxonomic properties. Twelve out of 72 strains examined harbored one or more plasmids, suggesting location of As(III)-tolerant genes on the chromosomal DNA.
