Influence of metal ions and organic carbons on denitrification activity of the halotolerant bacterium, Paracoccus pantotrophus P16 a strain from shrimp pond

Abstract

The effect of metal ions, ferric ion (Fe³⁺) and molybdenum ion (Mo⁶⁺) on the denitrification process of Paracoccus pantotrophus P16 grown under saline conditions was investigated. Results revealed that the dosages of added Fe³⁺ and Mo⁶⁺ significantly accelerated nitrate utilization and nitrite accumulation. Enzymatic studies revealed that the membrane-bound nitrate reductase and the periplasmic nitrite reductase had activities of 998 ± 28 and 373 ± 18 nmol (mg protein)^-1 min^-1, respectively after growing Paracoccus pantotrophus P16 in medium supplemented with 1.5 µM Fe³⁺. If provided with 1.5 µM Fe³⁺and 2.4 µM Mo⁶⁺, the membrane-bound nitrate reductase activity increased to 6,223 ± 502 nmol (mg protein)^-1 min^-1 and the periplasmic nitrite reductase was 344 ± 20 nmol (mg protein)^-1 min^-1. The results indicated that an addition of Fe³⁺ and Mo⁶⁺ led to an overstimulation of nitrate reductase activity as compared with nitrite reductase activity. When glucose was supplied, the minimal ratio of carbon per nitrate (C/N) was 2.31 mg C/mg NO₃^--N with denitrification yield of 0.45 g NO₃^--N/g C. Addition of ethanol instead of glucose, the minimal ratio of C/N was 1.15 mg C/mg NO₃^--N with denitrification yield of 1.08 g NO₃^--N/g C.