The effect of combined pollution by PAHs and heavy metals on the topsoil microbial communities of Spolic Technosols of the lake Atamanskoe, Southern Russia.

The contamination with organic and inorganic pollutants changes significantly soil microbial community structure. These shifts indicate anthropogenic pressure and help to discover new possibilities for soil remediation. In this study, the microbial community structure of Spolic Technosols formed at the territory of a former industrial sludge reservoir near the Kamensk-Shakhtinsky (Southern Russia) was studied using a metagenomics approach. The studied soils contain high concentrations of heavy metals (HM) (up to 72,900 mg kg-1) and 16 priority polycyclic aromatic hydrocarbons (PAHs) (up to 6670 mg kg-1). Its microbial communities demonstrate an excellent adaptability level reflected in their complexity and diversity. As shown by the high values of alpha diversity indices (Shannon values up to 10.1, Chao1 values from 1430 to 4273), instead of decreasing quantitatively and qualitatively on the systemic level, microbial communities tend to undergo complex redistribution. Regardless of contamination level, the share of Actinobacteria and Proteobacteria was consistently high and varied from 20 to 50%. Following the results of the Mann-Whitney U test, there were significant changes of less abundant phyla. The abundance of oligotrophic bacteria from Gemmatimonadetes and Verrucomicrobia phyla and autotrophic bacteria (e.g., Nitrospira) decreased due to the high PAH's level. And abundance of Firmicutes and amoebae-associated bacteria such as TM6 and soil Chlamydia increased in highly contaminated plots. In the Spolic Technosols studied, the influence of factors on the microbial community composition decreased from PAHs concentration to soil characteristics (organic carbon content) and phylum-phylum interactions. The high concentrations of HMs influenced weakly on the microbial community composition.

Effect of Heavy-Metal-Resistant PGPR Inoculants on Growth, Rhizosphere Microbiome and Remediation Potential of Miscanthus × giganteus in Zinc-Contaminated Soil.

Microbial-assisted phytoremediation is considered a more effective approach to soil rehabilitation than the sole use of plants. Mycolicibacterium sp. Pb113 and Chitinophaga sp. Zn19, heavy-metal-resistant PGPR strains originally isolated from the rhizosphere of Miscanthus × giganteus, were used as inoculants of the host plant grown in control and zinc-contaminated (1650 mg/kg) soil in a 4-month pot experiment. The diversity and taxonomic structure of the rhizosphere microbiomes, assessed with metagenomic analysis of rhizosphere samples for the 16S rRNA gene, were studied. Principal coordinate analysis showed differences in the formation of the microbiomes, which was affected by zinc rather than by the inoculants. Bacterial taxa affected by zinc and the inoculants, and the taxa potentially involved in the promotion of plant growth as well as in assisted phytoremediation, were identified. Both inoculants promoted miscanthus growth, but only Chitinophaga sp. Zn19 contributed to significant Zn accumulation in the aboveground part of the plant. In this study, the positive effect of miscanthus inoculation with Mycolicibacterium spp. and Chitinophaga spp. was demonstrated for the first time. On the basis of our data, the bacterial strains studied may be recommended to improve the efficiency of M. × giganteus phytoremediation of zinc-contaminated soil.