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Vitamin B 12 excretion by cultures of the marine cyanobacteria Crocosphaera and Synechococcus
Author(s) -
Bonnet Sophie,
Webb Eric A.,
Panzeca Caterina,
Karl David M.,
Capone Douglas G.,
Wilhelmy Sergio A. Sañudo
Publication year - 2010
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2010.55.5.1959
Subject(s) - synechococcus , cyanobacteria , axenic , phytoplankton , diazotroph , biology , botany , bacteria , ecology , environmental chemistry , nutrient , nitrogen fixation , chemistry , genetics
Axenic cultures of the N 2 ‐fixing marine cyanobacterium Crocosphaera watsonii exhibit very high B 12 excretion rates (up to 40 times higher per cell), compared to the smaller non‐N 2 ‐fixing strain of marine Synechococcus . The effect of N availability on vitamin synthesis is also evident in the non‐diazotrophic strain, as they release five times more B 12 under N‐replete conditions relative to N‐limiting conditions, although this value is still an order of magnitude smaller than the amount produced by the diazotroph. The cyanobacterial contribution to the oceanic B 12 supply may be ~ 50 times higher than the contribution of heterotrophic bacteria. Oceanic cyanobacteria do not compete for exogenous B 12 with other prokaryotes and eukaryotes, but instead are obligate producers, thereby defining a unique dual ecological role for N 2 ‐fixing cyanobacteria in the oligotrophic ocean. They provide both a source of “new” bioavailable nitrogen and the B 12 needed to support the growth of larger auxotrophic eukaryotic phytoplankton important for the biological carbon pump.