The ability of bacteria from legume plant roots grown on former coal mining soil to produce Indole-3-Acetic Acid (IAA)

Abstract

In general, coal mining is carried out openly using heavy equipment to take and move soil in the topsoil area until coal mining is possible to be conducted. As a consequence, the nutrient level is low because there is physical, chemical, and biological soil damage. Bioremediation is one of the alternatives to improve former coal mining land by utilizing soil microorganisms that have a role in soil plant hormone levels, such as auxin-produced root rhizosphere bacteria. This study aimed to isolate and characterize rhizosphere bacteria of legume plant roots grown on former coal mining soil, and to determine qualitatively and quantitatively its ability to produce IAA hormones. The characterizations include gram properties, colony morphology, arrangement of isolate, and cell shape. Then, the bacterial ability to produce IAA qualitatively and quantitatively respectively using the Salkowski method and spectrophotometry were tested. The results revealed that there were eleven isolates of legume plant root rhizosphere bacteria grown on the former coal mining soil that were able to produce IAA hormones with an average concentration of 15.949 ppm (2IA4); 10.762 ppm (4IIE3); 9.700 ppm (ID3); 9.422 ppm (3IB4); 7.970 ppm (2IA3); 7.847 ppm (6IIB3); 7.268 ppm (8IIIB4); 6.804 ppm (IIID5); 6.459 ppm (IE5); 5.379 ppm (7IIIB3); and 5.086 ppm (5IB3). Isolates of rhizosphere bacteria with the highest concentration have the potential to be chosen as a growth booster for legume plants grown on former coal mining soil to increase legume crop productivity.