Exploration and Screening of Biostimulant-Producing Bacteria from Red Calliandra (Calliandra calothyrsus) Rhizosphere to Support Sustainable Wood Energy Production

Abstract

This research investigates the microbial communities associated with the roots of Red Calliandra grown in an energy plantation in Cilacap, Central Java. Samples of soil and root nodules were taken from three separate places. Then, three groups of plant-beneficial functional microorganisms were isolated and purified. These groups included Azotobacter sp., Rhizobium sp., and phosphate-solubilizing bacteria. Morphological evaluation encompassed colony structure and cellular characteristics. Functional assessment included the conversion of atmospheric nitrogen utilizing the bromothymol blue indicator, biochemical profiling, such as catalase, oxidase, carbohydrate fermentation, and the detection of phytohormone synthesis. The first round of isolation produced nine Rhizobium sp. isolates, nine Azotobacter sp. isolates, and four phosphate-solubilizing isolates. Seven Rhizobium sp. isolates, six Azotobacter sp. isolates, and three phosphate-solubilizing isolates were still alive after subculturing. The color change to blue showed that all of the chosen candidates had positive nitrogenase activity. Biochemical investigations reduced the candidates to six superior isolates, whereas phytohormone evaluation ultimately identified three ideal strains, labeled FK R 1.1, FK A 4.2, and FK BPF 351. These results show that the natural rhizosphere bacteria of Red Calliandra can help plants grow, which makes them good candidates for consortium formulations that are meant to improve host resilience and vegetative productivity when plants are under mechanical stress. Additional validation in controlled and open-field scenarios is presently in progress.