Behavior of PCP-tolerant Bacteria in Water-logged Soil Supplied with PCP

Effects of PCP on Bacterial Flora in Water-logged Soil (Part 3)

Abstract

To clarify the effects of Pentachlorophenol (PCP) on the changes of soil bacterial flora, classification was carried out in generic level for all bacterial isolates from reduced layer of water-logged soil. Tolerance of each isolate to PCP was also examined. The isolates were obtained from soil applied with recommended rate of PCP (2.67g/m² soil, Plot RR) and with a hundred times of the recommended rate of PCP (267g/m² soil, Plot 100RR), and also from the soil without PCP application (control plot). Before the application of PCP, gram-positive bacteria such as Bacillus and coryneform bacteria predominated. By the application of PCP, the predominancy of Bacillus was partly replaced with such kinds of gram-negative bacteria as Pseudomonas, Alcaligenes, Acinetobacter and Enterobacteriaceae after 1 month in Plot RR. The increase in the gram-negative bacteria in the bacterial flora lasted until 3 months but disappeared after 17 months. This means that the bacterial flora in Plot RR was recovered to the same pattern as in control plot after disappearance of PCP in Plot RR. Most gram-negative isolates which predominated by PCP application were highly tolerant to PCP. The coryneform bacteria maintained their dominancy throughout the experimental period but PCP-tolerance of the strains differed depending on the presence or the absence of PCP: In the presence of PCP the strains tolerant to PCP predominated over PCP-sensitive ones and vice versa. In Plot 100RR, bacterial succession similar to that in Plot RR was also observed meagerly.