Abstract
Nitrosomonas europaea was transformed with a recombinant plasmid bearing the gene (vgb) encoding the hemoglobin (VHb) from the bacterium Vitreoscilla under control of the N. europaeaamoC P1 promoter. Vgb was maintained stably and appeared to be expressed in the transformants at VHb levels of about 0.75 nmol/g wet weight. Expression of VHb in the N. europaea transformants was correlated with an approximately 2 fold increase in oxygen uptake rate by whole cells at oxygen concentrations in the range of 75–100% saturation, but no change in oxygen uptake rate at oxygen concentrations below 25% saturation. VHb expression was also correlated with an increase of as much as about 30% in conversion of ammonia to nitrite by growing cells. The results suggest that engineering of key aerobic wastewater bacteria to express bacterial hemoglobins may be a useful strategy to produce species with enhanced respiratory abilities.
Highlights
One of the key functions of the aerobic portion of conventional waste water treatment is the efficient oxidation of ammonia to nitrate, because ammonia in the effluent is toxic to aquatic species when released to the environment
We were able to transform N. europaea using two vgbbearing plasmids which we had previously constructed. These included pUC8:16 (Dikshit and Webster 1988; Liu et al 1994), in which vgb with its native promoter is cloned into the E. coli vector pUC8 (Vieira and Messing 1982) and pRESX-vgb, vgb cloned into the Rhodococcus-E. coli shuttle vector pRESX, in which vgb transcription is driven by a Rhodococcus type promoter
Plasmid pSK2 is a derivative of the Messing vector pUC8 and has a ColEI type replication origin, native for E. coli
Summary
One of the key functions of the aerobic portion of conventional waste water treatment (activated sludge process) is the efficient oxidation of ammonia to nitrate, because ammonia in the effluent is toxic to aquatic species when released to the environment. As the nitrifying species are relatively intolerant of low dissolved oxygen (DO) levels, the activated sludge process is run at high DO levels, ranging from a low of 2 mg DO/L to as high as saturation at the ambient temperature (Rittmann and McCarty 2001). Nitrosomonas europaea is a key member of the bacteria responsible for the first step in nitrification, conversion of ammonia to nitrite. This conversion occurs in two steps, from ammonia to hydroxylamine, and hydroxylamine to nitrite. Molecular oxygen is the terminal electron acceptor in the electron transport chain of N. europaea (Rittmann and McCarty 2001)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
