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Bioremediation technology, another strategy known for restoring degraded environments, utilizes beneficial microorganisms, including arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing bacteria (NFB). Despite its potential, the biological processes of these microorganisms in contaminated sites remain poorly understood, hindering effective pollutant toxicity reduction. Establishing a connection between plant root systems and these microorganisms is crucial for enabling plant survival in heavy metal-contaminated soils. Narra (Pterocarpus indicus Willd.), a leguminous plant, typically associates with symbiotic nitrogen-fixing bacteria, forming nodules in the roots. Additionally, Narra forms a symbiotic relationship with AMF, phosphorus-fixing microbes, making it an ideal tree species for rehabilitating mined-out areas. In this study, five microbial biofertilizers, namely: MYKORICH^®, MYKOVAM^®, newMYC, newNFB, and combined newMYC+newNFB, plus a control were used to test their root colonization potential on Narra seedlings grown in nickel (Ni) and gold (Au) mined-out soils collected from Taganito Mining Corporation (TMC) and Manila Mining Corporation (MMC) in Claver and Placer, Surigao del Norte, Philippines, respectively. The results showed that newMYC had the highest root colonization in Ni mined-out soil, while MYKORICH^® excelled in Au mined-out soil. The AMF spore count was highest in MYKORICH^® for Ni mined-out soil and newMYC in Au mined-out soil. NFB colonization was highest in newMYC-treated seedlings for Ni mined-out soil and combined newMYC+newNFB for Au mined-out soil. The microbial biofertilizers utilized in this research, such as MY-KORICH^®, MYKOVAM, newMYC, newNFB, and combined newNFB and newMYC, naturally occur in the environment and can be easily extracted. This cost-effective characteristic provides an advantage for mining companies seeking treatments for soil amelioration to rehabilitate mined-out areas. Full article

The effectiveness of heavy metal-tolerant microorganisms for supporting plant growth needs to be understood before it can be used as a soil bioremediation agent. The purpose of this study was to determine the effect of heavy metal tolerant microorganisms on the growth of “Narra” seedling (Pterocarpus indicus Wild). Three heavy metals-resistant (Pb, Cd, and Cu) rhizobacteria from a copper (Cu) mined-out site in Marinduque, Philippines showed plant growth promotion in vitro. A treatment combination of formula inoculant A (CuNFbM 4.1, MGR 333), B (CuNFbM 4.1, MGR 333, PbSM 2.1), and O (Uninoculated); compost (0%, 4%); and lime + inorganic fertilizer {without or with lime and inorganic fertilizer (LF0; LF1)} were applied to Narra seedlings planted on 445 mg/kg Cu-contaminated soil. Lime (2 mg/ha) and the recommended dose of soybean inorganic fertilizer were used as positive controls to evaluate the ability of inoculations and composts to promote the growth and used as positive controls to evaluate the ability of inoculants and composts to promote the growth and copper accumulation of narra in greenhouse experiments. All treatment combinations resulted in significant differences in plant height, leaf number, stem diameter, shoot and root dry weight, as well as, shoot, root Cu content, and plant Cu uptake of 13-week-old “Narra”. Inoculated “Narra” could thrive better in mine-degraded soil containing 445 ppm Cu with 4% compost. Inoculant B demonstrated the best plant performance while Pseudomonas synxantha (PbSM 2.1) probably increases the plant’s growth due to 1-aminocyclopropane-1-carboxylate (ACC) deaminase it produces. Accumulation of Cu was higher in the root compared other plant parts. More research is necessary to elucidate the mechanism of plant growth promotion and heavy metal re mediation by P. synxantha. Full article