How haptophytes microalgae mitigate vitamin B 12 limitation
2019
Vitamin B12(
cobalamin) can control phytoplankton development and community composition, with around half of microalgal species requiring this vitamin for growth. B12 dependency is determined by the absence of
cobalamin-independent
methionine synthaseand is unrelated across lineages. Despite their important role in carbon and sulphur
biogeochemistry, little is known about
haptophytesutilization of
vitamin B12and their ability to cope with its limitation. Here we report the first evaluation of B12
auxotrophyamong this lineage based on molecular data of 19 species from 9 families. We assume that all species encode only a B12-dependent
methionine synthase, suggesting ubiquitous B12
auxotrophyin this
phylum. We further address the effect of different B12 limitations on the molecular physiology of the model
haptophyteTisochrysis lutea. By coupling growth assays in batch and
chemostatto
cobalaminquantification and expression analyses, we propose that
haptophytesuse three strategies to cope with B12 limitation.
Haptophytesmay assimilate dissolved
methionine, finely regulate genes involved in
methioninecycle and B12 transport and/or limit B12 transport to the
mitochondrion. Taken together, these results provide better understanding of B12 metabolism in
haptophytesand represent valuable data for deciphering how B12-producing bacteria shape the structure and dynamics of this important phytoplankton community.
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