Vitamin B12-producing bacteria as a nutritive complement for a culture of the rotifer Brachionus plicatilis

Out of 31 bacterial strains isolated from culture tanks of the rotifer Brachionus plicatilis, only 8 strains which were vitamin B12 producers supported the growth of germ-free rotifer when they were added into yeast suspension. Of the 6 strains which were taxonomically examined, they were identified as Pseudomonas. Their vitamin B12 productivity was measured by Euglena bioassay method. The concentrations of vitamin B12 in the bacterial suspension were measured daily and the higbest levels of B12 were estimated to be 1.2-16.5ng/ml during 8 day culture. Most (98.1-99.3%) of the vitamin B12 which was produced accumulated inside the bacterial cells. The rotifer growths were tested in batch cultures under germ-free condition, provided with vitamin B12-producing bacteria as the sole food source, and with these bacteria as a complement of Nannochloropsis oculata or baker's yeast Saccharompces cerevisiae. The rotifer showed rapid growth when vitamin B12 producing bacterial cells were supplied in a range of 107-1011cells/ml. The results imply that in mass production tank of the rotifer vitamin B12-producing bacteria might play an important role as vitamin B12 supplier.