Abstract
Vitamin B1, or thiamin, can limit primary productivity in marine environments, however the major marine environmental sources of this essential coenzyme remain largely unknown. Vitamin B1 can only be produced by organisms that possess its complete synthesis pathway, while other organisms meet their cellular B1 quota by scavenging the coenzyme from exogenous sources. Due to high bacterial cell density and diversity, marine sediments could represent some of the highest concentrations of putative B1 producers, yet these environments have received little attention as a possible source of B1 to the overlying water column. Here we report the first dissolved pore water profiles of B1 measured in cores collected in two consecutive years from Santa Monica Basin, CA. Vitamin B1 concentrations were fairly consistent between the two years ranging from 30 pM up to 770 pM. A consistent maximum at ~5 cm sediment depth covaried with dissolved concentrations of iron. Pore water concentrations were higher than water column levels and represented some of the highest known environmental concentrations of B1 measured to date, (over two times higher than maximum water column concentrations) suggesting increased rates of cellular production and release within the sediments. A one dimensional diffusion-transport model applied to the B1 profile was used to estimate a diffusive benthic flux of ~0.7 nmol m−2 d−1. This is an estimated flux across the sediment-water interface in a deep sea basin; if similar magnitude B-vitamin fluxes occur in shallow coastal waters, benthic input could prove to be a significant B1-source to the water column and may play an important role in supplying this organic growth factor to auxotrophic primary producers.
Highlights
Vitamin B1 is a soluble, biotically synthesized, heterocyclic sulfur, and nitrogen-containing catalyst required in trace amounts by all organisms (Jurgenson et al, 2009)
Pore water concentrations ranged from 330 to 770 pM in 2011 and 30–480 pM in 2012 as compared to water column concentrations of 30– 280 pM previously reported by Sañudo-Wilhelmy et al (2012) for the same station location (Supplementary Material Table S3)
Vitamin B1 Pore Water Profiles The pore water depth profiles of B1 from two sampling years showed high maximum concentrations compared to previous field measurement as well as a consistent profile shape, especially considering the vitamin is present in such trace concentrations
Summary
Vitamin B1 (thiamin) is a soluble, biotically synthesized, heterocyclic sulfur, and nitrogen-containing catalyst required in trace amounts by all organisms (Jurgenson et al, 2009). In the 1950s and 60s it was discovered that some species of marine phytoplankton are unable to synthesize B1 de novo (B1 auxotrophs) and instead must acquire the coenzyme from an exogenous source (Droop, 1957; Provasoli, 1958; Carlucci and Silbernagel, 1969) This included many of the major marine primary producers (Croft et al, 2006; Bertrand and Allen, 2012; Sañudo-Wilhelmy et al, 2014) as well as some ubiquitous marine bacteria (Giovannoni et al, 2005) and picoeukaryotic algae (Paerl et al, 2015). The sources of this organic growth factor have not been clearly identified and research in the area has mainly focused on B-vitamin production within the water column (e.g., Koch et al, 2012)
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