However, microaerophiles metabolise energy aerobically, and obligate anaerobes metabolise energy anaerobically. Some Bacteria and Archaea can aerobically oxidize elemental sulfur to sulfuric acid. Without them, a cell ceases to respire aerobically and quickly dies. With very few exceptions, animals respire aerobically. Some strains are capable of oxidizing carbon monoxide aerobically. Improved mitochondria enzyme activity and increased capillary density likely accommodate more aerobically produced ATP. The organism aerobically degrades the compound. Some strains (for example, USDA 6 and CPP) are capable of oxidizing carbon monoxide aerobically. The bacterium is a saprophyte deriving its nutrition from cellulose aerobically. The lower rate of fermentation aerobically became known as the Pasteur effect. When the organism is grown aerobically, a red color is produced. Azotobacter vinelandii is Gram-negative diazotroph that can fix nitrogen while grown aerobically. In breadmaking, the yeast initially respires aerobically, producing carbon dioxide and water. This organic material can break down further, aerobically in soil. They increase the rate at which ATP is produced aerobically.