Screening of salt tolerant endophytic bacteria with plant growth promoting characters isolated from Acanthus ilicifolius L., a species of mangrove ecosystem located at Corangi wildlife sanctuary, Andhra Pradesh

Mangroves harbour many beneficial microorganisms in their rhizosphere, phyllosphere and endophytically, which forms an ideal ecological habitation for isolating halotolerant endophytic bacteria with unique characteristics. Endophytes can produce numerous bioactive secondary metabolites and phytohormones, which may be directly or in some way beneficial to the host plant. The present study aimed to identify novel endophytes capable of producing plant growth-promoting substances. The mangrove plants Acanthus ilicifolius L. at Corangi Wildlife Sanctuary were selected, and their leaves and roots were collected for endophyte isolation. Eight isolates from the leaves and roots were collected, purified and preserved. All these isolates were subjected to morphological, phenotypical and biochemical studies. Isolates were grown best at 3% NaCl nutrient agar and could tolerate salinity upto 8%NaCl. Most of them could grow upto 42°C. The majority were gram’s positive, motile, aerobic, rod-shaped and some were gram’s negative, rod-shaped organisms. Many of the endophytic organisms had the ability to synthesize Indole-3-acetic acid(IAA) varied from 0.7 µg/ml (AIL1) to 51.0 µg/ml (AIL2) and the highest phosphate solubilizing ability was recorded with AIR3 (3.71 ppm) followed by AIR4 (3.00 ppm) and lowest was recorded by AIL4 (1.80 ppm). Among total isolates, AIL2 (51µg/ml) showed promising potential in producing IAA and had phosphate solubilization ability. Based on 16S ribosomal RNA molecular method the isolate AIL2 was identified as Bacillus altitudinis. This is the first to report that B.altitudinis strain AIL2 isolated from A.ilicifolius L. could produce IAA, which can be used as a bioinoculant in agriculture and allied sector.