VITAMIN B12‐BINDER AND OTHER ALGAL INHIBITORS1

Abstract

ABSTRACT Euglena gracilis Klebs, Poterioochromonas malhamensis (Pringsheim) Peterfi, Monochrysis lutheri Droop, Isochrysis galbana Parke and Phaeodactylum tricornutum Bohlin are known to release into the medium a substance which binds free vitamin B12. The binder, apparently a glycoprotein, makes vitamin B12 unavailable and inhibits growth of vitamin B12‐requiring microorganisms. Culture filtrates of selected marine diatoms, chrysophytes, cryptophytes, dinoflagellates and green algae contained the binder, indicating that binder release was not restricted to any algal group. However the three prokaryotic bluegreens tested do not produce B12‐binder. Production is also independent of the nutritional requirements of the donor, being produced by autotrophs and auxotrophs. The binders produced by these marine species have similar properties: they are heat labile; inhibition is not species‐specific; it is competitive, being reversed by adding B12. Production increases with density of the culture and is not restricted to stationary or scenescent cells. The marine species tested produced much less B12 than the freshwater Euglena and Poterioochromonas; the inhibition is reversed by 20–50 ng · 1−1 of B12 for marine species which reach moderate densities and by 150–300 ng · 1−1 B12 for the densely growing species. Consequently the binder may affect the growth of B12‐requiring species only in environments like the open ocean poor in B12. By contrast, the marine algae produce other inhibitors which are often heat stable and very inhibitory. These inhibitors, being species‐specific and less labile, may be more important in affecting the succession of algal species in natural waters.