Research on feasible methods for the enhancement of bioremediation in soil contaminated by crude oil is vital in oil-exporting countries such as Kuwait, where crude oil is a major pollutant and the environment is hostile to biodegradation. This study investigated the possibility of enhancing crude oil bioremediation by supplementing soil with cost-effective organic materials derived from two widespread locally grown trees, Conocarpus and Tamarix. Amendments in soils increased the counts of soil microbiota by up to 98% and enhanced their activity by up to 95.5%. The increase in the biodegradation of crude oil (75%) and high levels of alkB expression substantiated the efficiency of the proposed amendment technology for the bioremediation of hydrocarbon-contaminated sites. The identification of crude-oil-degrading bacteria revealed the dominance of the genus Microbacterium (39.6%), Sphingopyxis soli (19.3%), and Bordetella petrii (19.6%) in unamended, Conocarpus-amended, and Tamarix-amended contaminated soils, respectively. Although soil amendments favored the growth of Gram-negative bacteria and reduced bacterial diversity, the structures of bacterial communities were not significantly altered.

The planning of cities must insure a balance between human consumption and natural resources that should be preserved and if needed should be used minimally and efficiently following plans of sustainability. The current study investigated the possibility of recycling natural waste product "plants leaves" that usually fall off, are collected, dumped and burnt. In counties like Kuwait where crude oil constitutes a major pollutant and the environment is hostile for microbial activity rendering bioremediation to be a trivial option. Thus, in the present study, the leaves of Conocarpus and Tamarix were used to enrich the low organic content soils that showed the potential of soil supplementation with organic matter to enhance the growth and activity of soil indigenous microbiota. The amendments of soils with 20 mg g -1 soil significantly increased the counts of crude oil-degrading bacteria in crude oil-contaminated and uncontaminated soils to 999.4 x 10 -3 CFU g -1 and 358.8 x 10 -3 CFU g -1 soil, respectively. The identification of isolated bacteria revealed the dominance of the genus Microbacterium (39.6%), Sphingopyxis soli (19.3%), and Bordetella petrii (19.6%) in unamended, Conocarpus-amended and Tamarix-amended contaminated soils, respectively. The 16S rRNA analyses showed the high diversity of isolated bacteria. Also, the diversity of the majority of isolated bacteria decreased after soil amendments with plant-derived material. Therefore, the recycling of plant-derived materials could be an excellent option under conditions tested and confirm the commandments of sustainable planning.