The population and potential of nitrogen-fixing bacteria from sandalwood (Santalum album L.) rhizosphere as a producer of phytohormones and stress resistance indicators.

Nitrogen-fixing bacteria (NFB) are a group of functional bacteria widely used as biostimulant agents to increase soil's nitrogen availability and revegetate critical lands. Information on their population and potential can determine soil health and fertility. Therefore, this research aims to determine the population, potential, and identity of NFB from sandalwood (Santalum album L.) rhizosphere as a producer of phytohormones and stress resistance indicators, namely nitrogenase, IAA, ACC-deaminase, siderophores, and cellulase. The research was conducted in the laboratory of Applied Microbiology – National Research and Innovation Agency of Indonesia. Furthermore, four soil samples were collected randomly from the rhizosphere of healthy and dead mature sandalwood plants, as well as healthy and dead seedlings. NFB was isolated on specific media, namely Caceres, Mannitol Ashby, YEMA Congo red, and nitrogen-free bromothymol blue, using a total plate count (TPC) technique and color indicators. Analysis of potential as producers of IAA, ACC-deaminase, siderophore, cellulase, and nitrogenase was used to characterize functional NFB. The results showed a low NFB population (1.7 x 106 CFU mL−1) in sandalwood rhizosphere with positive nitrogenase, IAA, ACC-deaminase, siderophore, and cellulase activities. The highest yields of IAA, ACC-deaminase, and cellulase were produced by isolates of 1.3 (5.70 ppm, 26.52 ppm, 1.91 ppm) and 2.4 (7.75 ppm, 27.12 ppm, 2.61 ppm) and identified as Bacillus niacini and Rossellomorea vietnamensis. [ABSTRACT FROM AUTHOR]