Comparative study of soil bacterial flora as influenced by the application of a pesticide, pentachlorophenol (PCP)

The effects of pentachlorophenol (PCP) applications on the taxonomic composition of bacterial microflora were studied in water-logged soil (WS) and in shake cultures of suspended soil (SS). PCP applications resulted in a predominancy of Gram-negative bacteria over Gram-positive species. Members of the Acinetobacter group were the most common in PCP-treated soil although a small portion of the flora were in the Pseudomonas-Alcaligenes group or belonged to the Enterobacteriaceae. Coryneform bacteria and species of the Bacillus were the dominant forms in untreated WS; however, WS cultures treated with PCP at recommended rates (2.67 gm/m²) evidenced species oí Pseudomonas, Alcaligenes, Acinetobacter, and members of the Enterobacteriaceae as the predominant bacterial species. The dominance of Gram-negative bacteria in PCP-treated soil was evidenced for 3 months after application of the compound but was not evident after 17 months when PCP had dissipated. Gram-negative bacteria found in PCP-treated soil were highly tolerant of the phenol. In WS cultures coryneform bacteria were the most common although PCP tolerance was heterogenous in nature.