Nitrogen fixation in acacias

Abstract

The genus Asaia (family Acetobacteraceae) was first introduced with a single species-Asaia bogorensis and later six more species were described namely A. siamensis, A. krungthepensis, A. lannaensis, A. platycodi, A. prunellae, and A. astilbes. Acetobacteraceae family has been divided into ten genera but, only three of them include nitrogen fixing species: Gluconacetobacter, Acetobacter, and Swaminathania. This article originated from our study primarily aimed to isolate new endosymbiotic nitrogen fixer among Acetobacteraceae during which we have isolated, for the first time in India, four different strains of Asaia sp. from three different sources: Michalia champaca flower, Anopheles mosquito, and ant Tetraponera rufonigra. All the endosymbiotic strains isolated possess the ability to fix nitrogen. Evidence for both nitrogenase activity and the presence of nifH gene in isolated Asaia sp. is presented. Asaia bogorensis (MTCC 4041(T)) and A. siamensis (MTCC 4042(T)), two of the validated type strains available from the repository, were tested positive for the presence of functional nitrogenase. The nifH gene sequences from these type strains were also confirmed and compared with other nitrogen fixing members of the family Acetobacteraceae. Our result corroborate with the previous reports that Asaia sp. are indeed widely distributed in nature but this is the first time demonstration of their functional nitrogenase activity. This study shows Asaia sp. as fourth genera of nitrogen fixing bacteria in the family Acetobacteraceae.