isolation and identification of crude oil degrading and biosurfactant producing bacteria from the oil-contaminated soils of gachsaran

background and objectives: petroleum hydrocarbons are harmful to the environment, human health, and all other living creatures. oil and its byproducts in contact with water block sunshine to phytoplanktons and thus break the food chain and damage the marine food source. this study aims to isolate the crude oil degrading and biosurfactant producing bacteria from the oil contaminated soils of gachsaran, iran.   materials and methods: isolation was performed in peptone-water medium with yeast extract. oil displacement area, emulsification index and bacterial phylogeny using 16s rrna analysis were studied.   results and conclusion: three isolates were able to degrade the crude oil. in the first day, there were two phases in the medium; after a few days, these three bacteria degraded the crude oil until there was only one phase left in the medium. one strain was selected as a superior strain by homogenizing until the medium became clear and transparent. this method confirmed that the strain produces biosurfactant. according to the morphological and biochemical tests, the strain isolated from the oil contaminated soils is a member of bacillus subtilis , so to study the bacterial phylogeny and taxonomy of the strain, an analysis of 16s rrna was carried out, and the phylogenic tree confirmed them. the results verified that oil contaminated soils are good source for isolation of the biosurfactant producing bacteria.