Bacterial exopolysaccharide promotes acid tolerance in Bacillus amyloliquefaciens and improves soil aggregation
In this paper we report the isolation and taxonomic characterization of exopolysaccharide (EPS) producing bacteria followed by the role of EPS in conferring acid tolerance to the soil bacteria Bacillus amyloliquefaciens p16. The role of EPS in promoting soil aggregation is also presented. A total of 75 isolates were tested for acid tolerance and biofilm production under acid stress of which, 54 isolates were further tested for EPS production. Out of the 54 isolates, 28 isolates produced EPS in the range of (67.88 and 219.96 µg/ml) with B. amyloliquefaciens p16 showing the highest production. The 28 isolates characterized for phenotypic and molecular traits mostly belonged to the members of the genera Bacillus, Brevibacillus, Brevibacterium, Paenibacillus, Serretia, Pseudomonas, Arthrobacter and Lysinibacillus. The monosaccharide components of the EPS produced by B. amyloliquefaciens p16 shifted from galactose to arabinose under acid stress as revealed through HPLC analysis. Inactivation of the epsB gene encoding putative bacterial protein tyrosine kinase (BY-kinases) in B. amyloliquefaciens p16 resulted in significantly less EPS (33.23 µg/ml) production compared to wild-type (WT) (223.87 µg/ml). The mutant (B. amyloliquefaciens 6A5) was barely able to survive in pH 4.5 unlike that of the WT. Further, inoculation of the WT and mutant B. amyloliquefaciens 6A5 in the soil resulted in formation of small sized soil aggregates (42.41 mm) with less water holding capacity (27.67%) as compared to the soil treated with WT that produced larger soil aggregates of size 80.59 mm with higher 53.90% water holding capacity. This study indicates that EPS produced by acid-tolerant B. amyloliquefaciens p16 can not only impart acid tolerance to the bacteria but also aids in promoting soil aggregation when applied to the soil.
KeywordsBacillus amyloliquefaciens Soil aggregation Exopolysaccharide Acid tolerance pMUTIN4
The authors wish to acknowledge the Department of Biotechnology (DBT), Govt. of India, for financial assistance for the Project, “Screening of soil microbes for acid tolerance gene” under DBT-AAU Centre for Agricultural Biotechnology, Assam Agricultural University, Jorhat, India. The authors are grateful to Dr. M. K. Modi, Head, Department of Agricultural Biotechnology and Dr. B. K. Sarmah, Director DBT-AAU Centre, AAU, Jorhat for providing the necessary facilities. The authors also wish to thank Dr. Deniel R. Zeigler, Director, Bacillus Genetic Stock Centre, USA for providing the pMUTIN4 vector as a generous gift.
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Conflict of interest
The authors have no conflict of interests.
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