Isolation and characterization of heterotrophic nitrifying and aerobic denitrifying Klebsiella pneumoniae and Klebsiella variicola strains from various environments

Aims We sought to isolate novel heterotrophic nitrifying and aerobic denitrifying Klebsiella pneumoniae and Klebsiella variicola strains from various natural environments and characterize their nitrogen removal processes. Methods and Results Ten novel Klebsiella strains with heterotrophic nitrification and aerobic denitrification abilities, including seven K. pneumoniae and three K. variicola, were successfully isolated from faeces, sewage, plant surfaces and sludge. A 1674-bp fragment of the hydroxylamine oxidase (hao) gene was successfully amplified from the novel strains. The removal rates of ammonium, nitrate and nitrite of the seven K. pneumoniae isolates were 9642-9738%, 6127-8278% and 100%, respectively, and the corresponding degradation ratios were 482-649 (higher than previously reported for K. pneumoniae CF-S9 and EGD-HP19-C), 115-138 and 148-333mgl(-1)h(-1), respectively. The removal rates of ammonium, nitrate and nitrite of the three K. variicola isolates were 9501-9615%,6860--7837% and 100%, respectively, and the corresponding degradation ratios were 479-95, 114-174 and 167-444mgl(-1)h(-1), respectively. The K. variicola strain sd-3 from sludge exhibited the best heterotrophic nitrification and aerobic denitrification abilities among the isolates. Meanwhile, the results of simultaneous nitrification and denitrification assays with all isolated strains showed that ammonium was removed prior to nitrate or nitrite. Conclusions Our results indicate that K. pneumoniae and K. variicola (isolated from a novel natural environment) play an important role in the Earth's nitrogen cycle in various natural environments. Significance and Impact of the Study This study is one of only a few works to successfully isolate K. pneumoniae with heterotrophic nitrification and aerobic denitrification abilities in various natural environments. The physiological characterization K. variicola as having abilities to heterotrophically nitrify and aerobically denitrify is the first to be reported. Moreover, this study may provide alternative microbial resources for the removal of nitrogen from wastewater.