Isolation and optimization of efficient indole acetic acid-producing Staphylococcus edaphicus from Saccharum officinarum rhizosphere with their influence on multiple plant growth-promoting traits

Abstract

Bacterial endophytes are microorganisms that promote plant growth and synthesize indole-acetic acid (IAA), modulating nitrogen fixation, producing phytohormones, and solubilizing some soil minerals. The microbes were isolated from the rhizosphere and root plants of Saccharum officinarum (sugar cane) and Citrus aurantifolia (lime) collected from Phetchaburi province, Thailand. Twenty-one strains of endophytic bacteria were isolated and examined for their potential IAA production. Eight isolated strains were identified as IAA-producing endophytic bacteria in the presence of L-tryptophan precursor. Three isolated strains of SR8, LR18, and LS13 were shown to produce high levels of IAA of around 126.35 µg/mL, 56.62 µg/mL, and 53.49 µg/mL, respectively. The optimized IAA production conditions were shown at 30°C, pH 7, 0.5% L-tryptophan concentration, and 48 hours incubation. Furthermore, all three isolated strains of IAA-producing bacteria exhibited the properties of potential plant growth-promoting effects such as phosphate solubilization, zinc solubilization, and ammonium production. Sequencing and evolutionary analysis of the 16S rRNA gene from SR8 isolates showed 99.6% similarity to Staphylococcus sp.; these rhizospheric bacteria were identified as Staphylococcus edaphicus, a new member of the plant growth-promoting bacteria from sugar cane and lime. Results could be useful for the application of the IAA-producing endophytic bacterium, S. edaphicus, isolated from sugar cane rhizosphere, as a biofertilizer for plant growth.