A deeper insight into the phytoremediation of soil polluted with petroleum hydrocarbons supported by the Enterobacter ludwigii ZCR5 strain

Abstract

The Enterobacter ludwigii ZCR5 strain, isolated from the leaves of Zea mays growing in soil cocontaminated with hydrocarbons and heavy metals, was investigated under laboratory conditions for its plant growth-promoting traits, petroleum hydrocarbon (PH) degradation and biosurfactant production abilities and then used in bacterial-assisted phytoremediation. The whole genome of the ZCR5 was sequenced, and the presence of several genes encoding enzymes important for the enhancement of phytoremediation of soil polluted with PHs was detected. Next, the ZCR5 strain was introduced into polluted soil planted with Lolium perenne cv. Pinia. After inoculation, the ZCR5 strain was able to survive in polluted soil and colonized plant tissues. The highest efficacy of PHs removal (30.6 %) was observed for soil bioaugmented with living cells of the ZCR5, whereas in soil treated with bacterial necromass, it reached a value of 17.6 %. During the experimental period, the mechanisms enhancing the phytoremediation of PH-polluted soils were also tested in situ through the quantification of the expression of selected genes. The expression of genes encoding proteins involved in the biosurfactant production and promotion of plant growth by the ZCR5 strain was not detected either in the rhizosphere or in the endosphere of ryegrass. Among the genes involved in the degradation of PH, only CYP153 (in the rhizo- and endo-spheres) and nahAC (in the rhizosphere) were expressed. Despite the fact that we observed a higher efficiency of phytoremediation in the ZCR5-bioaugmented soil than in the controls, we were not able to indicate the bacterial mechanisms responsible for the observed effect of phytoremediation enhancement by the ZCR5 strain. The results obtained in our experiments indicate the necessity to study bacterial-plant interactions during assisted phytoremediation at the more detailed level. Thus the metatranscriptomic analysis of bacterial activity will be performed in the next step.