Cobalt

Cobalt has long been known to be a micronutrient for animals, including human beings, where it is a constituent of vitamin B₁₂ (1). However, its presence and function has not been recorded to the same extent in higher plants as in animals, leading to the suggestion that vegetarians and herbivorous animals need to ingest extra cobalt or vitamin B₁₂ in diets to prevent deficiency. Vitamin B₁₂ is synthesized in some bacteria, but not in animals and plants (1). Intestinal absorption and subsequent plasma transport of vitamin B₁₂ are mediated by specific vitamin B₁₂ proteins and their receptors in mammals. Vitamin B₁₂, taken up by the cells, is converted enzymatically into methyl and adenosyl vitamin B₁₂, which function as coenzymes. Feeding trials of cattle (Bos taurus L.), which also suffer from vitamin B₁₂ deficiency, show that the normal diet is deficient in cobalt to the extent that supplemental provision of the element can improve their performance, something that could also be achieved by feeding them feedstuffs grown in cobalt-rich soil (2). The only physiological role so far definitely attributed to cobalt in higher plants has been in nitrogen fixation by leguminous plants (3).