Bioremediation of Atmospheric Hydrocarbons via Bacteria Naturally Associated with Leaves of Higher Plants.

Bacteria associated with leaves of sixteen cultivated and wild plant species from all over Kuwait were analyzed by a culture-independent approach. This technique depended on partial sequencing of 16S rDNA regions in total genomic DNA from the bacterial consortia and comparing the resulting sequences with those in the GenBank database. To release bacterial cells from leaves, tough methods such as sonication co-released too much leaf chloroplasts whose DNA interfered with the bacterial DNA. A more satisfactory bacterial release with a minimum of chloroplast co-release was done by gently rubbing the leaf surfaces with soft tooth brushes in phosphate buffer. The leaves of all plant species harbored on their surfaces bacterial communities predominated by hydrocarbonoclastic (hydrocarbon-utilizing) bacterial genera. Leaves of 6 representative plants brought about in the laboratory effective removal of volatile hydrocarbons in sealed microcosms. Each individual plant species had a unique bacterial community structure. Collectively, the phyllospheric microflora on the studied plants comprised the genera Flavobacterium, Halomonas, Arthrobacter, Marinobacter, Neisseria, Ralstonia, Ochrobactrum. Exiguobacterium, Planomicrobium, Propionibacterium, Kocuria, Rhodococcus and Stenotrophomonas. This community structure was dramatically different from the structure we determined earlier for the same plants using the culture-dependent approach, although in both cases, hydrocarbonoclastic bacteria were frequent.

The potential of oil-utilizing bacterial consortia associated with legume root nodules for cleaning oily soils.

The surfaces of root nodules of Vicia faba and Lupinus albus (legume crops), were colonized with bacterial consortia which utilized oil and fixed nitrogen. Such combined activities apparently make those periphytic consortia efficient contributors to bioremediation of oily nitrogen-poor desert soils. This was confirmed experimentally in this study. Thus, cultivating V. faba, L. albus and, for comparison, Solanum melongena, a nonlegume crop, separately in oily sand samples resulted in more oil attenuation than in an uncultivated sample. This effect was more pronounced with the legume crops than with the nonlegume crop. Furthermore, in flask cultures, V. faba plants with nodulated roots exhibited a higher potential for oil attenuation in the surrounding water than plants with nodule-free roots. Denaturation gradient gel electrophoresis (DGGE) of polymerase chain reaction amplified 16S rRNA coding genes revealed that periphytic bacteria had DGGE bands not matching those of the oil-utilizing rhizospheric bacteria. Legume nodules also contained endophytic bacteria whose 16S rDNA bands did not match those of Rhizobium nor those of all other individual periphytic and rhizospheric strains. It was concluded that legume crops host on their roots bacterial consortia with a satisfactory potential for oil phytoremediation.

Enhancing the growth of Vicia faba plants by microbial inoculation to improve their phytoremediation potential for oily desert areas.

Two experiments were conducted to investigate the effect of inoculating Vicia faba plants (broad beens) raised in clean and oily sand with nodule-forming rhizobia and plant-growth-promoting rhizobacteria (PGPR) on growth of these plants in sand and to test whether this can improve the phytoremediation potential of this crop for oily desert areas. It was found that crude oil in sand at concentrations < 1.0% (w/w) enhanced the plant heights, their fresh and dry weights, the total nodule weights per plant, and the nitrogen contents of shoots and fruits. Similar enhancing effects were recorded when roots of the young plants were inoculated with nodule bacteria alone, PGPR alone, or a mixture of one strain of nodule bacteria and one of the PGPR. Such plant growth effects were associated with a better phytoremediation potential of V. faba plants for oily sand. The total numbers of oil-utilizing bacteria increased in the rhizosphere and more hydrocarbons were eliminated in sand close to the roots. The nodule bacteria tested were two strains of Rhizobium leguminosarum and the PGPR were Pseudomonas aeruginosa and Serratia liquefaciens. The four strains were found to use crude oil, n-octadecane, and phenanthrene as sole sources of carbon and energy. It was concluded that coinoculation of V. faba plant roots in oily sand with nodule bacteria and PGPR enhances the phytoremediation potential of this plant for oily desert sand through improving plant growth and nitrogen fixation.