Impact of tropical plants on microbial activity and diversity in soil contaminated with petroleum hydrocarbons

Abstract

The effect of plants (milo, oleander and buffelgrass) and a hexadecane and phenanthrene mixture (1 g and 200 mg/kg soil, respectively) on the diversity and activity of hydrocarbon-degrading bacteria in a sandy coastal soil was investigated. Two/third of hexadecane was degraded after 56 days. Hydrocarbon depletion was not plant-enhanced but was retarded slightly by milo and buffelgrass. Lipase activity, an a1kane-metabolism indicator, increased during rapid hexadecane depletion (days 0-56). The diversity of the dominant hexadecane-degrading bacteria was based on partial sequencing of 168 rDNA. On day 0, mainly Alphaproteobacteria were found By day 56, Gammaproteobacteria dominated the contaminated samples whereas similar numbers of Alphaproteobacteria and Gammaproteobacteria genotypes dominated the uncontaminated samples. Alcanivorax was found in all contaminated samples except for buffelgrass rhizospheres, which harbored only Pseudomonas sp. IMT40. With little hexadecane left by day 114, similar abundances of Alphaproteobacteria and Gammaproteobacteria genotypes occurred in all samples. Alcanivorax had virtually disappeared.