Identification and characterization of plant growth-promoting properties of bacterial endophytes from selected Zingiberaceae plants

Aims: This study aims to isolate, characterize and screen the plant growth-promoting bacteria from Zingiberaceae plants. Plant promoting activities such as indole-3-acetic acid (IAA), phosphate solubilization, zinc solubilization and nitrogen-fixing capabilities are determined, and the IAA production of selected isolates are optimized Methodology and results: Endophytic bacteria were isolated from the plant samples by surface sterilization on nutrient agar (NA) plates and incubated at 30 degrees C for 2-3 days. The bacteria were identified based on their phenotypic characteristics and 16S rRNA gene sequence analyses. All isolates were identified as genera Bacillus, Lysinibacillus, Kerstersia, Klebsiella and Brucella. The isolates exhibited phosphate solubilization (1.5 +/- 0.75-37.5 +/- 8.75 Solubilization Index, SI), zinc solubilization (2.5 +/- 0-60 +/- 1.5 SI) and IAA production (0.1 +/- 0.2-115.7 +/- 1.6 mu g/mL), while 3 isolates possessed nitrogen-fixing capabilities. Five isolates (PHAS-2, PWS-2, PWR-2, PHBS-2 and SCG-2) were selected for IAA optimization. Isolate PWR-2 produced the maximum IAA at 447.7 +/- 0 mu g/mL when tryptophan concentration was maintained at 1.0%. Conclusion, significance and impact of study: Genera of bacteria included Bacillus, Lysinibacillus, Kerstersia, Klebsiella and Brucella were successfully isolated from Zingiberaceae plants. All the isolates showed the capability to produce IAA, while some isolates exhibited phosphate solubilization and zinc solubilization, and a few possessed nitrogen-fixing capabilities. The potential IAA production isolates could be applied for the enhancement of agricultural production that will be becoming a more widely accepted practice.