Effects of exogenous short-chain N-acyl homoserine lactone on denitrifying process of Paracoccus denitrificans.

N-acyl-homoserine lactones (AHLs) serve as quorum-sensing signals, which control a number of bacterial processes in many proteobacteria. Here we report the effects of exogenous short-chain AHL on the denitrifying process of Paracoccus denitrificans, which are capable of aerobic and anaerobic growth by utilizing nitrate. The denitrification activity of these cells was monitored by measuring denitrification products (including nitrate, nitrite, and nitrous oxide), and the individual messenger ribonucleic acid (mRNA) levels of nitrate, nitrite, nitric oxide and nitrous oxide reductases. The results indicated that 2μmol/L C6-homoserine lactone (HSL) has little effect on cell density under either anaerobic or aerobic culture conditions, and the nitrate reduction activity appeared slightly affected by N-hexanoyl-DL-homoserine lactone (C6-HSL). However, exogenous C6-HSL significantly affected the transcription of nitrite reductase and nitric oxide reductase genes in P. denitrificans regardless of the presence of oxygen, and NO accumulation activity in P. denitrificans was suppressed by C6-HSL under aerobic condition. In contrast, exogenous C6-HSL stimulated the production of NO under anaerobic condition, suggesting that the regulation of denitrification by quorum sensing may be important in NO release.