Isolation, identification, and bioprospection of endophytic bacteria from medicinal plant Mikania glomerata (Spreng.) and the consortium of Pseudomonas as plant growth promoters

Abstract

Brazil is the largest exporter of soybeans in the world, and it is of great socio-economic importance to the country. Plants, including soybeans, benefit significantly from endophytic bacteria, some of which are able to promote plant growth and stimulate cell development. In this study, we isolated endophytic bacteria from Mikania glomerata, a medicinal plant commonly known as ‘guaco,’ carried out molecular identification analyses, assessed their biological activities (inorganic phosphate solubilization, biological nitrogen fixation, indolic compounds, and siderophore production), and investigated the potential of the most promising isolates as growth promoters of soybean. Taxonomic analysis identified 31 endophytic bacteria, including Acidovorax, Acinetobacter, Bacillus, Chryseobacterium, Comamonas, Curtobacterium, Delftia, Kurthia, Microbacterium, Micrococcus, Pseudomonas, Serratia, Stenotrophomonas, and Streptomyces. Strains of Pseudomonas japonica and Pseudomonas tolaasii were tested for their ability to promote soybean growth under greenhouse conditions in association with a coating polymer for seed treatment. Plant height (43.67 cm), trifoliate leaf number (9.25), root length (108.4 cm), root fresh weights (15.7 g), root dry weights (1.06 g), shoot fresh weights (5.7 g) and shoot dry weights (1.39 g) were positively influenced by combined treatment of soybean seeds with two endophytic isolates and the polymer, compared to the control group (35 cm, 8 leaves, 91.42 cm, 10.93 g, 0.70 g, 3.41 g, and 0.87 g, respectively), with only the shoot dry weight showing statistical significance. This results in improved seedling development and plant growth, indicating a promising option for reducing chemical fertilizers.