Selection of Acid Tolerant Purple Nonsulfur Bacteria for Application in Agriculture

Abstract

To screen acid tolerant purple nonsulfur bacteria (PNSB) isolated from peat swamp forests for their abilities to produce plant growth promoting substances (aminolevulinic acid: ALA, siderophores, indole-3-acetic acid: IAA) and also release ammonium from N2 fixation. Among 10 PNSB isolates grown in basic isolation medium (BIM), pH 4.5 found that strain KKSSR91 was the most effective to release ALA and siderophores under microaerobic light conditions; while strain KTPWG11 exhibited highest production of siderophores under aerobic dark conditions. Based on ALA production in medium containing 60 mM glycine, 4 PNSB isolates were selected for further studies and found that strain KTSSR92 produced highest IAA at 36.9 mg/L. All of them were able to release NH4 + , but no activity to solubilize phosphate. In addition, maximal ALA production in the medium supplemented with glycine by strain KKSSR91 was 2.89 mg/L at 4000 lux light intensity. Seed germination index (GI) of kidney bean (Phasecolus vulgaris L.) test using strain KKSSR91 at 1 g fresh biomass/L, pH 4.5 was 68.81% compared with a control in distilled water as only 58.68%. Strain KKSSR91 was identified using 16S rRNA sequencing and found that it showed 99% similarity with Rhodopseudomonas palustris.

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“…Two other R. palustris strains, GJ-22 and KL9, have also been reported to yield 30-52 mg/L IAA in the presence of tryptophan [73,101]. It was reported that R. palustris KKSSR91, which secreted IAA (29.58 mg/L) in the presence of 3 mM tryptophan, was able to reduce the phytotoxic effects of acid on kidney bean plants [102]. Rhodobacter capsulatus PS-2, which was isolated from paddy soil, was capable of producing a large amount of IAA (197.44 ± 5.92 mg/L) in an optimal medium containing 0.3% tryptophan.…”