Microbial biodegradation of pyridine by marine mangrove Bacillus aryabhattai strain NM1-A2 via a novel nitrogen metabolism pathway

Abstract

Background: Diverse microbes, such as bacteria, are of immense worth to mangrove ecosystems owing to their adaptability to salinity and variable environmental conditions. Bacteria have a crucial role in the nutrient cycling of carbon and nitrogen as well as the biodegradation of hazardous industrial waste materials. Methods: This work established the genetic-based molecular degradation of organic compounds in the mangrove ecosystem, which ultimately makes the availability of nutrients. As well as the effects of various abiotic factors on pyridine degradation to discover the pyridine degradation and the removal of ammonia nitrogen and the proposed nitrogen metabolism pathway. Results: The novel bacterial strain NM1-A2 was isolated from mangrove sediments and, after 16S rRNA gene sequence analysis identified as Bacillus aryabhattai. NM1-A2 completely degraded pyridine within a 100 h incubation period at a temperature of 35 °C, an initial pH of 7.0, glucose and a pyridine concentration of 500 mg/L. The pseudo-first-order kinetics model described the pyridine biodegradation profile of NM1-A2 well. Interestingly, the strain achieved almost 100% pyridine degradation with a total organic carbon removal rate of 87.9% (from 377.52 ± 45.65 mg/L) within 96 h. Within 96 h, the pyridine ring in the total nitrogen fraction at the maximum concentration (55.31 ± 0.17 mg/L) was converted into NH4+-N at a conversion rate of 51.3% ± 2.39%. Notably, NM1-A2 displayed remarkable stability considering that its pyridine biodegradation activity declined by only 4% after three consecutive cycles (48 h each). Moreover, NM1-A2 possessed nrt-ABCD nitrate transport family and gltABCD operons that participate in the activities of glutamine and glutamate synthetase in NH4+ conversion in the nitrogen cycle. Conclusion: This research offers a potential treatment strategy for pyridine in the mangrove ecosystem.