Impact of petroleum hydrocarbon contamination on the indigenous soil microbial community

Changes in the microbial community structure in agricultural soils and soils contaminated with hydrocarbons were evaluated using the culture-independent method of 16S rRNA gene sequence analysis. The bacterial composition was more diverse in the agricultural soil (AS) samples in terms of number of species and Shannon diversity index [6.6 vs. 1.94 for the hydrocarbon-contaminated soil (HCS)]. Twelve known bacterial groups were identified in the AS: Proteobacteria (41 % of bacterial community), Actinobacteria (34 %), Acidobacteria (5 %), Firmicutes (4 %), Chloroflexi (4 %), Bacteroidetes (3 %), Gemmatimonadetes, Planctomycetes, Verrucomicrobia, Armatimonadetes, Cyanobacteria, TM7 and Archaea (the latter 7 each accounting for 1-2%) . In comparison, the clonal library from the HCS samples included members from only five groups: Proteobacteria (85 %) and Bacteriodetes, Actinobacteria, Chloroflexi and Verrucomicrobia (the latter four collectively accounting for 15 %). The family Ectothiorhodospiraceae was the most dominant family within the Proteobacteria isolated from the HCS. These microbes are known to synthesize a number of biotechnologically useful products, such as polyhydroxyalkanoates and ectoines, and their dominance in the sampled area suggests the possibility of discovering better adapted novel genes of commercial importance, especially since the site had high alkaline and saline characteristics. Soils (arid, alpine and polar) which are nutrient and moisture limited are typically often dominated by Actinobacteria that are well adapted to low-resource environments and do not show major changes in community structure as a result of hydrocarbon contamination.