Characterizing microbial populations in petroleum-contaminated soils of Swat District, Pakistan

Abstract

Soil samples from petroleum-contaminated soil were collected from 25 different petroleum filling stations and automobile workshops in the district of Swat, Khyber Pakhtunkhawa, Pakistan. A total of seven bacterial genera were isolated. All of the isolates were Gram-positive bacteria. The genera identified by the culture and cell morphological characteristics were: Bacillus, Streptococcus, Staphylococcus, Micrococcus, Corynebacterium Arthrobacter, and Streptomyces. Lipolytic and saline activities of the selected isolates were studied. Among the isolates, Arthrobacter, Staphylococcus, Bacillus, Micrococcus, Corynebacterium, and Streptomyces produced lipase enzymes, while no lipase was produced by Streptococcus. Dense growth of Bacillus and Streptococcus was observed at 1% NaCl. Dense growth of Streptomyces was observed at strength of 2% NaCl. At 3% NaCl concentration, dense growth of Staphylococcus, Micrococcus, Corynebacterium, and Arthrobacter was observed, indicating that they were moderately halotolerent. In our study, Bacillus, Arthrobacter, and Streptomyces showed optimum growth at pH 8.0, and Streptococcus, Staphylococcus, and Micrococcus showed optimum growth at pH 7.0. Only Corynebacterium showed optimum growth at pH 9.0, indicating that it is tolerant of higher pH conditions.