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Assessment of rhizospheric culturable bacteria of Phragmites australis and Juncus effusus from polluted sites

Publication . Pereira, Sofia I. A.; Pires, Carlos; Henriques, Isabel; Correia, António; Magan, Naresh; Castro, Paula M. L.

This study aimed at the isolation and characterization of metal(loid)-tolerant bacteria from the rhizosphere of Phragmites australis and Juncus effusus plants growing in two long-term contaminated sites in Northern Portugal. Site 1 had higher contamination than Site 3. Bacteria were isolated using metal(loid)-supplemented (Cd, Zn, and As) media. Isolates were grouped by random amplified polymorphic DNA and identified by 16S rRNA gene sequencing. Strains were also examined for their metal(loid) tolerance. The counts of metal(loid)-tolerant bacteria were higher in Site 1 and ranged between log 7.17 CFU g(-1) soil in As-containing medium and log 7.57 CFU g(-1) soil in Zn-containing medium, while counts at Site 3 varied between log 5.33 CFU g(-1) soil in Cd-containing medium and log 6.97 CFUg(-1) soil in As-containing medium. The composition of bacterial populations varied between locations. In Site 1, the classes Actinobacteria (36%) and Bacilli (24%) were well represented, while in Site 3 strains were mainly affiliated to classes Actinobacteria (35%), 'y-Proteobacteria (35%), and 13-Proteobacteria (12%). The order of metal(loid) toxicity for the isolated strains was Cd > As > Zn. Overall, 10 strains grew at 500 mg Cd L-1, 1000 mg Zn L-1, and 500 mg As L-1, being considered the most metal(loid)-tolerant bacteria. These strains belonged to genera Cupriavidus, Burkholderia, Novosphingobium, Sphingo bacterium, Castellaniella, Mesorhizobium, Chryseobacterium, and Rhodococcus and were mainly retrieved from Site 1. The multiple metal(loid)-tolerant strains isolated in this study have potential to be used in bioremediation/phytoremediation.

2015Journal article

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The response of Betula pubescens to inoculation with an ectomycorrhizal fungus and a plant growth promoting bacterium is substrate-dependent

Publication . Sousa, Nadine R.; Franco, Albina R.; Ramos, Miguel A.; Oliveira, Rui S.; Castro, Paula M. L.

The combination of ectomycorrhizal (ECM) fungi and plant growth promoting bacteria (PGPB) has considerable potential in forestry. Here we report on the combined effects of PGPB Mesorhizobium sp. and the ECM fungus Paxillus involutus on the growth of Betula pubescens in two different substrates, a forest soil and an alkaline anthropogenic sediment. Growth, nutrient concentration and mycorrhizal formation of B. pubescens were determined at the end of the experiment and the fungal and bacterial communities were assessed by denaturing gradient gel electrophoresis. The combined effects of ECM and PGPB enhanced root and shoot growth most in the forest soil with Mesorhizobium appearing to stimulate mycorrhizal formation. However, in the alkaline sediment, an antagonistic interaction was detected between P. involutus and Mesorhizobium sp., with Mesorhizobium sp. alone stimulating growth. The significant interaction between the ECM and the PGBP across the two substrates is discussed.

2015Journal article

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