Which bacteria are responsible for converting ammonium (NH4+) to nitrite (NO2-)?

The process of converting ammonium (NH4+) to nitrite (NO2-) is carried out by a specific group of bacteria known as ammonium-oxidizers. Among these, Nitrosomonas is the most widely recognized genus that plays a vital role in this conversion, an essential step in the nitrogen cycle.

During this process, Nitrosomonas oxidizes ammonium to nitrite via a series of biochemical reactions. This is important for soil health and fertility, as it helps to make nitrogen available to plants in a form that they can utilize. The conversion of ammonium to nitrite is one of the initial steps in nitrification, which is further followed by the conversion of nitrite to nitrate (NO3-) by other bacteria, such as Nitrobacter.

In contrast, other options listed focus on different roles within the nitrogen cycle. Denitrifiers, for example, are involved in the process of denitrification, where nitrate is reduced to nitrogen gas, thus completing the nitrogen cycle. Azotobacter is primarily known for nitrogen fixation, a process where atmospheric nitrogen is converted into a usable form for plants.