B Vitamins and Their Congeners as Potential Drivers of Microbial Community Composition in an Oligotrophic Marine Ecosystem

Abstract

Determining the factors that influence marine microbial growth and community structure are critical for the understanding of global carbon cycling. Since the early twentieth century, it has been known that B vitamins play an important role in phytoplankton community dynamics. Limited oceanic dissolved B vitamin distributions indicate that these important coenzymes are present at picomolar levels, which could be too low to support maximal phytoplankton growth, and vast regions of the ocean exist where they are undetectable. Despite their importance, particulate B vitamin concentrations of field microbial populations are unknown. Here we report B vitamin concentrations measured in both the particulate and dissolved fractions, including multiple biochemically relevant B vitamin congeners. We establish their spatial distributions spanning distinct biogeographic and oceanographic regimes in the Mediterranean Sea and the Eastern Atlantic Ocean and show that all congeners are present both dissolved in seawater and in suspended particles. We observe that B vitamins cooccur in patches defined by regional biogeographic and oceanographic features. Additionally, distinct patterns of congener relative abundance in the dissolved and particulate pools provide insight to biological and chemical cycling of these compounds between and within the dissolved and particulate pools. Finally, linear model results demonstrate that model fits of microbial assemblages are strongest when they include both inorganic nutrients and dissolved B vitamin concentrations. We believe that these findings represent an advance in our understanding of B vitamin oceanographic distributions and point to interesting hypotheses of their influence on marine microbial ecology.

Comparative whole-genome approach to identify traits underlying microbial interactions

“…Some of the putatively auxotrophic organisms actually encode parts of their vitamin biosynthesis pathways, and therefore may depend on the uptake of a precursor rather than of the vitamin itself (Supplementary text, Supplementary Fig.s 7a-d). Our results, together with experimental observations of vitamin limitation in laboratory cultures and in nature [58,61,67], and of shifts in the capacity of marine communities to produce vitamins [68], argue for an important role of vitamins or their precursors and their exchange between organisms in shaping marine microbial communities. Supplementary Fig.…”

Spatial and temporal variability in the response of phytoplankton and bacterioplankton to B-vitamin amendments in an upwelling system

“…4c). Unfortunately we lack B1 measurements in this study, but, according to previous field studies in other oceanographic regions, a similar pattern to that observed for B12 can be expected (Cohen et al, 2017;Sañudo-Wilhelmy et al, 2012;Suffridge et al, 2018). The overall low and stable concentration of B12 at both sampling locations is consistent with the expected high turnover time of this compound in productive, well-lit waters (Bertrand et al, 2015), due to both biological uptake (Koch et al, 2012;Taylor and Sullivan, 2008) and photochemical degradation (Carlucci et al, 1969;Juzeniene and Nizauskaite, 2013;Juzeniene et al, 2015).…”

Comparative whole-genome approach to identify bacterial traits for microbial interactions

“…Some of the putatively auxotrophic organisms actually encode parts of their vitamin biosynthesis pathways, and therefore may depend on the uptake of a precursor rather than of the vitamin itself (Supplementary text, Supplementary Fig.s 7a-d). Our results, together with experimental observations of vitamin limitation in laboratory cultures and in nature (58,61,67), and of shifts in the capacity of marine communities to produce vitamins (68), argue for an important role of vitamins or their precursors and their exchange between organisms in shaping marine microbial communities.…”

“…They are metabolically expensive to produce as they often need several enzymes (e.g. about 20 for vitamin B12) (60), and their availability in the dissolved extracellular pools is extremely limited across all aquatic ecosystems (61,62). Some phytoplankton are known to require exogenous vitamins from co-occurring heterotrophic bacteria, and indeed vitamin B12 may be a co-limiting micro-nutrient for primary productivity, e.g.…”