In industrial fermentation processes, carbon source is one of the crucial factors for reducing cost of production. Carbohydrates of agricultural origin have been chiefly used so far, but recently unconventional carbon sources such as normal alkanes, natural gas, and carbon dioxide have been also drawing attention. Particularly, C1 compounds are very promising feedstocks in fermentation industry. Methane, widely distributed as a main component in natural gas, is one of the most inexpensive carbon sources at present. Methanol is easily derived from methane by chemical oxidation. In recent years, the microbial production of single-cell proteins (SCP) and useful metabolites from methane and methanol has been of growing interest all over the world.