Bacterial seeding potential of digestate in bioremediation of diesel contaminated soil

Petroleum contaminated soils constitute an environmental problem which may be solved with the help of bioremediation. Soil bioaugmentation with petroleum degrading bacteria is an efficient clean-up strategy. Currently scientific interest focuses on finding sources of microbial agents able to degrade hydrocarbons which may serve as species pools for enrichments during inoculum preparation. Seven microbial enrichments were obtained from various digestates, from a petroleum contaminated soil and from mix of both: soil and digestate. Diesel degrading capacities of microorganisms from digestates, which may serve as inoculum and nutrient source for bioremediation, were assessed. Additionally, the presence and abundance of alkane monooxygenase encoding genes (alkB) was estimated in enrichments. The highest proportion of alkB genes was found for enrichments originating from composted digestate of organic fraction of municipal solid waste and petroleum contaminated soil having the most efficient diesel removal rates (78 and 77% diesel removal, respectively). Enrichments obtained from digestate mixed with soil have a lower performance than single source enrichments. Strains belonging to Rhodococcus and Achromobacter genus were found in all enrichments, and Rhodococcus dominated in enrichment with the higher diesel degradation potential. All those results indicate a great potential of digestate as a source of diesel degraders for soil bioremediation.