Enhanced Arsenic Tolerance in Triticum aestivum Inoculated with Arsenic-Resistant and Plant Growth Promoter Microorganisms from a Heavy Metal-Polluted Soil

In soils multi-contaminated with heavy metal and metalloids, the establishment of plant species is often hampered due to toxicity. This may be overcome through the inoculation of beneficial soil microorganisms. In this study, two arsenic-resistant bacterial isolates, classified as Pseudomonas gessardii and Brevundimonas intermedia, and two arsenic-resistant fungi, classified as Fimetariella rabenhortii and Hormonema viticola, were isolated from contaminated soil from the Puchuncaví valley (Chile). Their ability to produce indoleacetic acid and siderophores and mediate phosphate solubilization as plant growth-promoting properties were evaluated, as well as levels of arsenic resistance. A real time PCR applied to Triticum aestivum that grew in soil inoculated with the bacterial and fungal isolates was performed to observe differences in the relative expression of heavy metal stress defense genes. The minimum inhibitory concentration of the bacterial strains to arsenate was up to 7000 mg·L−1 and that of the fungal strains was up to 2500 mg·L−1. P. gessardi was able to produce siderophores and solubilize phosphate; meanwhile, B. intermedia and both fungi produced indoleacetic acid. Plant dry biomass was increased and the relative expression of plant metallothionein, superoxide dismutase, ascorbate peroxidase and phytochelatin synthase genes were overexpressed when P. gessardii plus B. intermedia were inoculated.

Expression and Functional Analysis of BjMT-2, a Metallothionein Type-2 from Brassica juncea, in E. coli

The expression and functional analysis of plant metallothionein type 2 from Brassica juncea were achieved in E. coli. The BjMT-2 cDNA was cloned into the pETM-20 vector fused to the Thioredoxin gene and induced to E. coli. Northern blot and SDS PAGE analysis showed, respectively, that the transcription of the TrxA::BjMT-2 fusion gene and the expression of the fusion protein were predominately in E. coli cells after IPTG induction. The BjMT-2 in the crude extraction prepared from the E. coli cells bearing TrxA::BjMT-2 vector were reacted with the antibody directed against BjMT-2. The E. coli cells exhibited an increased tolerance against Cu2+ and Cd2+ after BjMT-2 expression.