Examples of bacteria containing intracellular membranes are phototrophs, nitrifying bacteria and methane-oxidising bacteria. Aerobic bacteria such as the nitrifying bacteria, "Nitrobacter", utilize oxygen to oxidize nitrite to nitrate. This group of organisms includes sulfur oxidizers, nitrifying bacteria, iron oxidizers, and hydrogen oxidizers. Some nitrogen may also be fixated by species of nitrifying bacteria and the cyanobacteria. Biological filters provide a medium specially designed for colonization by the desired nitrifying bacteria. High surface area provides more space for the growth of nitrifying bacteria. He was responsible for the first isolation and description of both nitrifying and nitrogen-fixing bacteria. "Nitrosococcus" belongs to the nitrifying bacteria. Nitrifying bacteria are chemoautotrophs that convert ammonia into nitrite then nitrate. Nitrifying bacteria capture ammonia from the water and metabolize it to produce nitrite. Nitrifying organisms are chemoautotrophs, and use carbon dioxide as their carbon source for growth.