Genetic basis for denitrification in Ensifer meliloti

BMC Microbiology

María J Delgado¹  Eulogio J Bedmar¹  José J Pueyo²  Teodoro Coba de la Peña²  Maria I Rubia¹  Maria J Torres¹ 

[1] Estación Experimental del Zaidin, Consejo Superior de Investigaciones Científicas (CSIC), P.O. Box 419, 18080 Granada, Spain;Instituto de Ciencias Agrarias, Consejo Superior de Investigaciones Científicas (CSIC), Serrano 115-bis, 28006 Madrid, Spain

关键词: Periplasmic nitrate reductase;    Nitrous oxide reductase;    Nitric oxide reductase;    Nitrate respiration;    Cu-containing nitrite reductase;   

Others  :  1140990
DOI  :  10.1186/1471-2180-14-142

 received in 2014-02-19, accepted in 2014-05-28,  发布年份 2014

【 摘 要 】

Background

Denitrification is defined as the dissimilatory reduction of nitrate or nitrite to nitric oxide (NO), nitrous oxide (N₂O), or dinitrogen gas (N₂). N₂O is a powerful atmospheric greenhouse gas and cause of ozone layer depletion. Legume crops might contribute to N₂O production by providing nitrogen-rich residues for decomposition or by associating with rhizobia that are able to denitrify under free-living and symbiotic conditions. However, there are limited direct empirical data concerning N₂O production by endosymbiotic bacteria associated with legume crops. Analysis of the Ensifer meliloti 1021 genome sequence revealed the presence of the napEFDABC, nirK, norECBQD and nosRZDFYLX denitrification genes. It was recently reported that this bacterium is able to grow using nitrate respiration when cells are incubated with an initial O₂ concentration of 2%; however, these cells were unable to use nitrate respiration when initially incubated anoxically. The involvement of the nap, nirK, nor and nos genes in E. meliloti denitrification has not been reported.

Results

E. meliloti nap, nirK and norC mutant strains exhibited defects in their ability to grow using nitrate as a respiratory substrate. However, E meliloti nosZ was not essential for growth under these conditions. The E. meliloti napA, nirK, norC and nosZ genes encode corresponding nitrate, nitrite, nitric oxide and nitrous oxide reductases, respectively. The NorC component of the E. meliloti nitric oxide reductase has been identified as a c-type cytochrome that is 16 kDa in size. Herein, we also show that maximal expression of the E. meliloti napA, nirK, norC and nosZ genes occurred when cells were initially incubated anoxically with nitrate.

Conclusion

The E. meliloti napA, nirK, norC and nosZ genes are involved in nitrate respiration and in the expression of denitrification enzymes in this bacterium. Our findings expand the short list of rhizobia for which denitrification gene function has been demonstrated. The inability of E. meliloti to grow when cells are initially subjected to anoxic conditions is not attributable to defects in the expression of the napA, nirK, norC and nosZ denitrification genes.

【 授权许可】

   
2014 Torres et al.; licensee BioMed Central Ltd.

【 图 表 】

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