Poster: Plant-symbiont interactions

Abs # 582: Vitamin B₁₂ in Algae

Presenter:	Croft, Martin T, mtc29@cam.ac.uk
Authors	Croft, Martin T (A)   Warren, Martin J (B)   Smith, Alison G (A)
Affiliations:	(A): Department of Plant Sciences, University of Cambridge (B): Department of Biological Sciences, Queen Mary University of London

Vitamin B₁₂ (cobalamin) is a cofactor of several essential enzymes, and is synthesized by a plethora of bacteria. It is a tetrapyrrole derived molecule that is not thought to be synthesized by any eukaryotic organism. Higher plants neither synthesize nor require cobalamin, but many algae, and in particular the Rhodophyta (red algae), are known to be extremely rich in the vitamin. We have demonstrated that vitamin B₁₂ is an essential growth factor for Porphyridium purpureum (Rhodophyta), Lobomonas rostrata (Chlorophyta) and Monochrysis sp. (Heterokontophyta). However, the concentration of the vitamin in their natural environment is too low to support their growth. Monochrysis sp. can be grown in co-culture with a vitamin B₁₂-synthesizing bacterium in the absence of vitamin B₁₂, suggesting that a syntrophic relationship between the bacteria and the algae maybe a source of this vitamin. A range a molecular and biochemical approaches are being used to investigate the interaction in more detail. We are also interested in identifying the enzymes in algae for which vitamin B₁₂ is a cofactor. Preliminary results with vitamin B₁₂ dependent Chlorophyta (green algae) suggest that cobalamin is required for only one enzyme, vitamin B₁₂ dependent methionine synthase. The lack of a vitamin B₁₂ independent isoform in these species may confer vitamin B₁₂ dependence upon them.