The vitamin B requirement of Phaeocystis globosa (Prymnesiophyceae)

In batch cultures of flagellates and non-flagellate cells of Phaeocystis globosa, the biomass yield was significantly enhanced by the addition of a mixture of the vitamins thiamine (B1), cyanocobalamin (B12) and biotin (H). A bioassay with B1 and B12 using the non-flagellate cells of P.globosa showed that this prymnesiophyte is a B1 auxotroph. The bioassay also indicated a significant difference in growth rate between culture medium with 10 nmol l(-1) B1 (mu = 0.80 day(-1)) and culture medium with 10 nmol l(-1) 1312 (mu = 0.52 day(-1)). These findings are discussed in relation to the hypothesis that centric diatoms, through vitamin B1 excretion or B12 depletion, initiate Phaeocystis blooms. It is concluded, however, that an alternative hypothesis, that diatoms provide a solid substrate for colony initiation, has more experimental support.