Stenotrophomonas: a versatile diazotrophic bacteria from the rhizospheric soils of Western Himalayas and development of its liquid biofertilizer formulation

Abstract

Rhizosphere is a rich repository of plant growth promoting rhizobacteria (PGPR) which is a sustainable tool to increase crop productivity and maintain soil health. In this context, 43 isolates were obtained on Jensen’s medium from the rhizosphere of Triticum aestivum, Zea mays, Solanum tuberosum, Aloe barbadensis and Bacopa monnieri grown in Palampur, (Himachal Pradesh) India. Out of these isolates, only six isolates (WT-A2, WT-A1, MZ-A2, PT-A1, PT-A3 and BM-A3) exhibited significantly higher nitrogenase activity (451.45, 441.58, 440.91, 444.02, 383.64 and 374.44 nmole C2H4 h−1 mg−1 protein) as compared to the reference strain of Azotobacter chroococum MTCC 446 (372.85 nmole C2H4 h−1 mg−1 protein). The isolate WT-A2 was the most efficient with respect to nitrogenase activity (451.45 nmole C2H4 h−1 mg−1 protein), indole acetic acid production (17.45\xa0μg ml−1), ammonia production and siderophore production. Isolate WT-A2 was identified as Stenotrophomonas rhizophila on the basis of morphological, biochemical and 16S rRNA sequence analysis. In order to prepare liquid bioinoculant formulation, survivability studies on S. rhizophila was carried out in four different liquid carriers (Compost Tea, Biogas slurry, Vermiwash and Minimal Growth Medium) at room temperature (average maximum temp. was 23.83\xa0°C and average minimum temp. was 11.91\xa0°C). The results showed that S. rhizophila survived better in different liquid carriers (9.873 log cfu ml−1 in biogas slurry; 9.843 log cfu ml−1 in vermiwash; 9.163 log cfu ml−1 in minimal growth medium), and Compost Tea was the best carrier to support higher bacterial load (9.907 log cfu ml−1) on 180th day of storage. The results are of practical importance as this (compost tea) liquid carrier could be used to produce liquid biofertilizer formulation. Also, S. rhizophila could be a potential biofertilizer candidate as it posses multifarious plant growth promoting traits.