Pseudomonas consortium improves soil health and alleviates cadmium (Cd) toxicity in Brassica juncea L. via biochemical and in silico approaches

Abstract

The exponential rise in Cd in the environment has raised concerns for its adequate remediation worldwide. Its non-biodegradable nature and highly migratory feature make it more toxic. Plant growth-promoting rhizobacteria (PGPR) have shown great potential in the remediation of Cd-polluted agricultural lands. PGPR is comparatively efficient, convenient and economical. PGPR application enhances plant growth and development by conferring direct and indirect benefits. This study aimed to evaluate bacterial strains, Pseudomonas putida (Pp) and Pseudomonas fluorescens (Pf), for their PGPR traits, soil physiochemical analyses, and physiological and anatomical traits of B. juncea under Cd stress. Results showed that both microbial strains shared positive interaction and had minimum inhibitory concentration (MIC) ranging from 0.8mM and 0.6mM values for Pp and Pf respectively. P. fluorescens displayed better anti-phytopathogenic activity against pathogenic fungal strains (Alterneria brassicae, Alterneria brassicola, Verticillium longisporum, Fusarium oxysporum) than P. putida. They also synthesised plant growth regulators (PGRs) such as IAA (0.146,0.156μg/ml) and GA (2.062, 2.074 μg/ml). The co-inoculation of strains improved soil organic C, P, N, and K by 283.01 %, 100.42 %, 8.89 % and 40.38 %. Also, the interactive effect of Pp and Pf recovered dry matter content (DMC) by 18.13 % in comparison to Cd-stressed plants. Moreover, the strains reduced Cd-induced H₂O₂ production by DAB (340.38’-3’ diaminobenzidine) staining and hence restored membrane integrity. Also, in Cd-treated B. juncea plants, the anatomical characteristics were negatively affected. However, inoculated strains induce maximum recovery as indicated by well-developed vascular elements. Genes associated with PGPR traits were mined from the NCBI database. The information compiled thereafter indicated that the genes, galU, CadR, and pgl were responsible for biofilm formation, Cd resistance and lactone synthesis. In conclusion, we reported a promising consortium having PGPR traits, that improve soil and B. juncea health under Cd toxicities. Hence, the use of such bioinoculants can be a safer substitute for chemical fertilizers.