B12 bitamin ne mai ruwa-ruwa bitamin da aka hannu a cikin metabolism na kowane cell na jikin mutum. Yana da wani cofactor a DNA kira, da kuma a duka biyu mai kitse da kuma amino acid metabolism, Yana da muhimmanci musamman a cikin al'ada aiki na juyayi tsarin via da rawar da a cikin kira na myelin. Akwai yawanci miliyan 40 kwayoyin kwayoyin a gram na ƙasa da miliyan kwayoyin kwayoyin a cikin wani millilitre na ruwa. Akwai kimanin 5×1030 kwayoyin kwayoyin halitta a kan mutum Duniya, samar da wani biomass cewa cinyewa dukan dabbobi da shuke-shuke a ko'ina. Bacteria suna da muhimmanci a matakai da yawa na abinci mai gina jiki da kuma samar da shi ta hanyar da abinci sarkar. Bincike da aka yi a watan Maris na 2013 ya nuna cewa kwayoyin halitta suna da alhakin samar da makamashi mai yawa daga matattun kwayoyin halitta a cikin matattarar ruwa mai zurfi, kamar su hydrogen, sunadarin hydrogen, sunadarin sulfur da sauran sinadarai masu amfani da kwayoyin cuta da aka sani a matsayin matattari na kwayoyin cuta
shekarun 1990s