Research Description:

Aerobic and Anoxic Growth in Denitrifiers

As urban population has increased, more efficient ways of wastewater treatment have been developed. Nitrogen is one of the pollutants contained in wastewater and if not treated properly it causes eutrification of receiving waters with the concomitant effects of fish kills and odors.

The most widely used method for eliminating nitrogen from domestic wastewater is biological nitrogen removal through the activated sludge process. Biological nitrogen removal is achieved through a process that involves exposing a mixed culture of bacteria to alternating aerobic (water aerated) and anoxic (no dissolved oxygen in the water) conditions. Under aerobic conditions, nitrifying bacteria oxidize ammonium to nitrite and then nitrate. Under anoxic conditions, denitrifying bacteria reduce nitrate to nitrogen gas, which is then released to the atmosphere.

The enzyme that enables growth under anoxic conditions is a membrane bound nitrate reductase, which is inhibited by the presence of oxygen. However, some denitrifiers have a second enzyme located in the periplasm and also involved in the denitrification process. The function of this second enzyme has not been completely elucidated. Microbiologists believe that this periplasmic reductase cannot result in growth. Nevertheless, some growth has been detected while the membrane bound reductase is inhibited. Our group has isolated various cultures of denitrifiers and I will be conducting growth experiments trying to determine how does these bacteria grow under aerobic and anoxic conditions. I will also test for the presence and activity of the periplasmic reductase enzyme by performing enzyme assay tests. All the techniques and procedures will be performed under aseptic conditions. The equipment used involves:

• Biosafety cabinets.
• C24 Incubator Shaker
• Marathon 21,000R Centrifuge
• Anaerobic chamber
• Spectrophotometer