Abstract
In this study we established the B1 and B12 vitamin requirement of the dinoflagellate Lingulodinium polyedrum and the vitamin supply by its associated bacterial community. In previous field studies the B1 and B12 demand of this species was suggested but not experimentally verified. When the axenic vitamin un-supplemented culture (B-ns) of L. polyedrum was inoculated with a coastal bacterial community, the dinoflagellate’s vitamin growth limitation was overcome, reaching the same growth rates as the culture growing in vitamin B1B7B12-supplemented (B-s) medium. Measured B12 concentrations in the B-s and B-ns cultures were both higher than typical coastal concentrations and B12 in the B-s culture was higher than in the B-ns culture. In both B-s and B-ns cultures, the probability of dinoflagellate cells having bacteria attached to the cell surface was similar and in both cultures an average of six bacteria were attached to each dinoflagellate cell. In the B-ns culture the free bacterial community showed significantly higher cell abundance suggesting that unattached bacteria supplied the vitamins. The fluorescence in situ hybridization (FISH) protocol allowed the quantification and identification of three bacterial groups in the same samples of the free and attached epibiotic bacteria for both treatments. The relative composition of these groups was not significantly different and was dominated by Alphaproteobacteria (>89%). To complement the FISH counts, 16S rDNA sequencing targeting the V3–V4 regions was performed using Illumina-MiSeq technology. For both vitamin amendments, the dominant group found was Alphaproteobacteria similar to FISH, but the percentage of Alphaproteobacteria varied between 50 and 95%. Alphaproteobacteria were mainly represented by Marivita sp., a member of the Roseobacter clade, followed by the Gammaproteobacterium Marinobacter flavimaris. Our results show that L. polyedrum is a B1 and B12 auxotroph, and acquire both vitamins from the associated bacterial community in sufficient quantity to sustain the maximum growth rate.
Highlights
Culture-based (Tang et al, 2010) and field studies (Bertrand et al., 2007; Gobler et al, 2007; Koch et al, 2011, 2012) have supported long standing hypothesis that vitamin availability can have an impact on phytoplankton growth and community composition (Droop, 2007)
We found no increase in bacteria attached to L. polyedrum, the interaction between the free-bacterial community and L. polyedrum still constitute a form of symbiosis between vitamin producing bacteria in suspension and
Non-axenic cultures of L. polyedrum can acquire both vitamins from the associated bacterial community in sufficient quantity to sustain the maximum growth rate defined by culture conditions
Summary
Culture-based (Tang et al, 2010) and field studies (Bertrand et al., 2007; Gobler et al, 2007; Koch et al, 2011, 2012) have supported long standing hypothesis that vitamin availability can have an impact on phytoplankton growth and community composition (Droop, 2007). A majority of eukaryotic phytoplankton requires exogenous B vitamins, being B vitamin auxotroph. They are lacking the biosynthetic pathways to produce them or alternative pathways to bypass the need for the vitamin as in the case of B12. B12 is essential for the synthesis of amino acids, deoxyriboses, and the reduction and transfer of single carbon fragments in many biochemical pathways. B1 plays a pivotal role in intermediary carbon metabolism and is a cofactor for a number of enzymes involved in primary carbohydrate and branched-chain amino acid metabolism. B7 is a cofactor for several essential carboxylase enzymes, including acetyl coenzyme
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