Enrichment of rhizospheres of crop plants raised in oily sand with hydrocarbon-utilizing bacteria capable of hydrocarbon consumption in nitrogen free media

The rhizospheres of the three legume crops, peas, beans and peanuts and the three nonlegume crops, sunflower, tomato and mallow raised in pristine sand were associated with between 1 and 1.4 × 106 hydrocarbon-utilizing bacteria per gram root. These values were much higher when the plants were raised in oily sand. Thus, numbers of the hydrocarbon-utilizing rhizobacteria of the legume crops ranged between 21.2 and 50.1 × 106 cells g−1 roots and of the nonlegumes sunflower and tomato only between 6.5 and 8.7 × 106 cells g−1 roots. According to their 16S rRNA gene sequences, the predominant oil-utilizing bacteria in rhizospheres of the legumes pea and beans, were affiliated with Microbacterium oxydans, Pseudomonas plecoglossicida and Acidovorax delafieldii. Other minor oil-utilizing bacteria were also identified and recorded. Pure cultures of all these bacteria could consume crude oil, n-octadecane (an aliphatic hydrocarbon) and phenanthrene (an aromatic hydrocarbon) in nitrogen containing, but also in nitrogen free media. The latter finding suggests that these organisms may be self sufficient regarding their nitrogen nutrition. It was therefore concluded that the use of legume crops for phytoremediation of oily desert soils through rhizosphere technology, saves the use of nitrogen fertilizers, making the phytoremediation process more economical and environmentally friendly.