AMO (ammonia monooxygenase), is encoded byamo gene, is the important enzyme for the first step in nitrification. Based on putative ammonia monooxygenase gene of Pseudomonas stutzeri A1501, amol primers were designed to identify amo gene of P. stutzeri isolated from shrimp ponds in Bac Lieu and Kien Giang provinces. There are 9/66 P. stutzeri isolates were identified to harbour amo gene by PCR technique
nine isolates were able to oxidize ammonia when testing on the minimal medium supplemented 200-700 mM ammonium. Gene amo from five isolates (ATCC14405, VT-B2a, TN9, TB3, TN4) were sequenced, aligned on GenBank by BLAST N, BioEdit and built phylogenetic tree by MEGA 5.1 software. The results showed that four amo genes from isolated strain were 99 percent homology with the gene of Pseudomonas stutzeri A1501 strain. VT-B2a and TN9 isolates have closer relationship with reference strain (ATCC14405) closely while TB3 and TN4 isolates were arranged in another branche. Two isolates VT-B2a and TN4 were evaluated ammonia removal ability in domestic wastewater and piggery wastewater in bioreactor 10-L, the result showed that these isolates had high ability of ammonia removal (from 170-200 mg/l down 1 mg/l in 7-8 days).