Assessment and functional genomic investigation of methane and nitrogen metabolizing pathways in Pseudomonas aeruginosa strain AAK/M5.

Pseudomonas aeruginosa has been reported to degrade C1 and inorganic nitrogen compounds through multiple metabolic pathways. This study aims to shed light on the uncharted CH4 and NH4 oxidation pathways in P. aeruginosa strain AAK/M5 for utilization of C1 and N1 compounds in syntrophic nitrifying denitrifying medium. Around 9% and 11% higher NH4+–N and NO3––N removal respectively was observed in presence of CH4 as carbon source. Similarly, CH4 removal was 3.6-fold higher in the set supplemented with NO3–-N as nitrogen source than the set with NH4+-N. Intermediates of methane oxidation viz., CH3OH, HCOOH, and that of nitrate reduction viz., NO2––N were also detected. Induction of methane/ammonia monooxygenase in presence of CuSO4 revealed highest NH4+–N removal (84.89 mg/L) and CH4 removal (30%) at 10 µM CuSO4. Degradation kinetics using high density resting bacterial cells in phosphate buffer resulted in µmax (min− 1) of 0.0018, 0.0049, 0.0034, 0.0038, and 0.0012, for NH4+–N, NH2+–N, NO3––N, NO2––N and CH3OH respectively. Additionally, affirmation of CH4/NH3 oxidizing enzyme was done via in silico analysis which revealed the presence of two enzymes sharing 38.3% and 31.4% homology with ammonia monooxygenase subunit C and soluble methane monooxygenase subunit C, respectively. Furthermore, a quinoprotein methanol dehydrogenase was detected in the genome. The results thus suggested the CH4 metabolizing capacity of P. aeruginosa AAK/M5 in presence of ammonical/nitrate nitrogen by virtue of key enzymes sharing homology with ammonia monooxygenase and soluble methane monooxygenase.