Nitrogen and sulfur metabolisms of Pseudomonas sp. C27 under mixotrophic growth condition.

Pseudomonas sp. C27 is a facultative autotrophic bacterium that can grow mixotrophically to undergo denitrifying sulfide removal (DSR) reactions with both organic matters and sulfide as electron donors. A detailed understanding of how the C27 strain simultaneously removes nitrogen, sulfur and carbon from water is critical for optimal DSR process design and implementation. This study is the first to reveal the pathways of nitrogen and sulfur metabolisms, identifying a total of 47 proteins that are related to the nitrogen metabolism and seven proteins to the sulfur metabolism of strain C27 using iTRAQ and LC-MS/MS techniques. The proposed pathway of nitrogen metabolism for strain C27 from external nitrate to nitrogen gas and phosphate with a coupled ammonia cycle is based on the identified proteins, and suggests that nitrate was not essential for nitrogen metabolism and could be replaced by nitrite as the sole nitrogen source for C27.