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 96·42-97·38%, 61·27-82·78% and 100%, respectively, and the corresponding degradation ratios were 4·82-6·49 (higher than previously reported for K. pneumoniae CF-S9 and EGD-HP19-C), 1·15-1·38 and 1·48-3·33 mg l h , respectively. The removal rates of ammonium, nitrate and nitrite of the three K. variicola isolates were 95·01-96·15%,68·60--78·37% and 100%, respectively, and the corresponding degradation ratios were 4·79-9·5, 1·14-1·74 and 1·67-4·44 mg l h , 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.