Vitamin B1 (thiamine) Physiology of Marine Plankton
Expanding upon initial interests in bacterial picophytoplankton interactions, we are investigating vitamin B1 ecology of marine microbes, in particular the physiology of vitamin B1 auxotrophs (phytoplankton and bacterioplankton) that must obtain the thiamine or its forms/fragments from an external source.
In collaboration with B. Palenik (SIO), we have established two model systems (two vitamin B1 auxotrophic axenic cultures) for learning more about the B1 physiology of marine microbes: one, the picoeukaryotic phytoplankton O. lucimarinus (CCE9901) (Fig.4) and two, a motile alphaproteobacterium named OUnk1.
Focusing on CCE9901, we confirmed it as a B1 auxotroph and then determined its ability to grow on varying concentrations of B1 (specifically, its half saturation growth constant, Ks) (Fig.5). Interestingly, its Ks is in the upper range of B1 concentrations found in euphotic coastal waters where Ostreococcus spp. persist (e.g. Scripps Pier, Carlucci et al. 1970) (Fig.6) . Based on this result, our working hypothesis is that CCE9901 experiences B1 growth limitation in coastal CA waters where Ostreococcus cells are endemic.
Figure 5: Growth Kinetics Data for CCE9901. The Michaelis Menten fit parameters are: R2 = 0.92, Df =19. At the 95% CI, Ks= 24.94 to 59.10 pM.
Figure 6: A comparison of published dissolved B1 concentrations from surface or upper euphotic zone marine waters alongside the determined Ks range (at a 95% C.I.) for CCE9901. Presented symbols and abbreviations represent the following: ^ = B1 estimated from bioassay; # = B1 estimated via HPLC (Okbamichael and Sañudo-Wilhelmy, 2005); all other values were determined by LC/MS. LIS = Long Island Sound, NY (Koch et al., 2012); La Jolla, CA (Carlucci, 1970); SCCS = Southern California Current System off Baja, Mexico (Sañudo-Wilhelmy et al., 2012); SBHC = Stony Brook Harbor (Okbamichael and Sañudo-Wilhelmy, 2005); WTNA = Western North Atlantic (Barada et al., 2013); NA = North Atlantic (Panzeca et al., 2008).
Microbial ‘producers’ of thiamine in the ocean
De novo synthesis by organisms is the source of vitamin B1 in the ocean. It remains unclear if B1 becomes available largely through ‘active’ or ‘passive’ processes (e.g. continual exudation versus cell death). We are investigating potential differences in vitamin B1 ‘production’ by B1 autotrophic bacteria. Preliminary results indicate that B1 autotrophic bacteria vary in how much vitamin B1 they make available to CCE9901 (Fig. 7). In particular, D. shibae supported the most CCE9901 biomass in co-culture. Co-cultures with TW7 (Alteromonas representative) or SWAT3 (Vibrio representative) supported amount of CCE9901 biomass over the 13 day incubation.
We are further utilizing CCE9901 as a system to examine if certain conditions facilitate or dampen B1 production by the tested non-auxotrophic bacteria (D. shibae, TW7, SWAT3).
Figure 7: Fluorescence (FL) data for CCE9901 during co-culture experiments with B1 autotrophic bacteria. Positive controls (1nM final B1 added at the start of the experiment) are noted with solid lines. Cultures without a co-cultured bacterium are noted by Ost (O. lucimarinus, CCE9901): DSHI = Dinoroseobacter shibae; TW7 = Alteromonadales TW-7, SWAT3 = Vibrionales bacterium SWAT3. Equal amounts of CCE9901 and bacteria were combined at the start of the experiment.
Genome data publicly available via NCBI:
Bacteria-cyanobacteria associations are phylogenetically diverse