Molecular Identification and Characterization of a Rice Field Cyanobacterium for Its Possible Use as Biofertilizer in Acidic Environment

Initial screening for cyanobacterial diversity in rice fields of Meghalaya revealed presence of a limited number of species predominantly belonging to heterocystous cyanobacteria such as Nostoc and Anabaena. However, based on morphological study alone, definite identification of the organisms was difficult. Hence, the identities of the organisms were established using partial sequence of 16S rRNA gene. In this work, we report the isolation, molecular identification, and characterization of a cyanobacterial species that could be a potential biofertilizer in acidic rice fields. The organism was identified as an Anabaena sp. and was characterized with respect to its growth, heterocyst frequency, nitrogen fixation, photochemical and respiratory activities, as well as various enzymes related to nitrogen metabolism to establish its potential as a biofertilizer strain under acidic conditions. Further, its rice root colonization ability as well as associative nitrogenase activity in the presence of nitrate was also assessed. This Anabaena strain was isolated from all the rice fields taken as study sites and found to be able to withstand cold environment and acidic condition of the region. It showed adequate growth, heterocyst frequency, and nitrogenase activity in the presence of nitrate in its vicinity. These features could make this organism a preferred biofertilizer strain in rice fields having lower pH as low pH usually restricts growth of most other cyanobacterial strains. In addition, this strain showed compatibility with nitrate and thus could be simultaneously used along with nitrate-based fertilizers to augment nitrogen content of the paddy fields and lower chemical fertilizer load.