Bacterial inoculant-assisted phytoremediation affects trace element uptake and metabolite content in Salix atrocinerea.

Natural plant-associated microorganisms are of critical importance to plant growth and survival in field conditions under toxic concentrations of trace elements (TE) and these plant-microbial processes can be harnessed to enhance phytoremediation. The total bacterial diversity from grey willow (Salix atrocinerea) on a brownfield heavily-polluted with lead (Pb) and arsenic (As) was studied through pyrosequencing. Culturable bacteria were isolated and in vitro tested for plant growth-promotion (PGP) traits, arsenic (As) tolerance and impact on As speciation. Two of the most promising bacterial strains - the root endophyte Pantoea sp. AV62 and the rhizospheric strain Rhodococcus erythropolis AV96 - were inoculated in field to S. atrocinerea. This bioaugmentation resulted in higher As and Pb concentrations in both, roots and leaves of bacterial-inoculated plants as compared to non-inoculated plants. In consequence, bacterial bioaugmentation also affected parameters related to plant growth, oxidative stress, the levels of phytochelatins and phenylpropanoids, together with the differential expression of genes related to these tolerance mechanisms to TE in leaves. This study extends our understanding about plant-bacterial interactions and provides a solid basis for further bioaugmentation studies aiming to improve TE phytoremediation efficiency and predictability in the field.

Methodology optimization for the analysis of phenolic compounds in chestnut (Castanea sativa Mill.).

Phenols are bioactive substances of great interest because of their involvement in plant physiology, their use in many industrial processes, and their impact on human health. This work aims to summarize the varied approaches to the phenolic analysis of chestnut (bark and wood of trunk and branches, leaves, catkins, burs, and fruit) and to collate the optimal conditions into an easy to follow and execute protocol. Phenolic compounds were extracted by solid-liquid extraction and separated by liquid-liquid extraction. Total phenols content was determined by Folin-Ciocalteu assay, condensed tannins by vanillin assay, and hydrolyzable tannins (gallotannins and ellagitannins) by high-performance liquid chromatography quantification of methyl gallate and ellagic acid following acid methanolysis. The lowest temperature for conservation (-80 ℃), lyophilization, and milling (liquid N2) were the most effective pretreatments for samples. For quantification of tannins, the use of water clearly reduced the sensitivity of the analysis of condensed tannins, whilst the more efficient degradation capacity of sulfuric acid improved the methanolysis of hydrolyzable tannins. These findings were validated using a range of chestnut tissues, and thus confirm the utility and effectiveness of this easy to implement, cost-effective, and efficient protocol.