Abstract
Abstract. We experimentally evaluated the temporal (interday and interseason) and spatial variability in microbial plankton responses to vitamin B12 and/or B1 supply (solely or in combination with inorganic nutrients) in coastal and oceanic waters of the northeast Atlantic Ocean. Phytoplankton and, to a lesser extent, prokaryotes were strongly limited by inorganic nutrients. Interday variability in microbial plankton responses to B vitamins was limited compared to interseason variability, suggesting that B-vitamin availability might be partially controlled by factors operating at seasonal scale. Chlorophyll a (Chl a) concentration and prokaryote biomass (PB) significantly increased after B-vitamin amendments in 13 % and 21 %, respectively, of the 216 cases (36 experiments × 6 treatments). Most of these positive responses were produced by treatments containing either B12 solely or B12 combined with B1 in oceanic waters, which was consistent with the significantly lower average vitamin-B12 ambient concentrations compared to that in the coastal station. Negative responses, implying a decrease in Chl a or PB, represented 21 % for phytoplankton and 26 % for prokaryotes. Growth stimulation by B1 addition was more frequent on prokaryotes than in phytoplankton, suggesting that B1 auxotrophy in the sampling area could be more widespread in prokaryotes than in phytoplankton. Negative responses to B vitamins were generalized in coastal surface waters in summer and were associated with a high contribution of Flavobacteriales to the prokaryote community. This observation suggests that the external supply of B12 and/or B1 may promote negative interactions between microbial components when B-vitamin auxotrophs are abundant. The microbial response patterns to B12 and/or B1 amendments were significantly correlated with changes in the prokaryotic community composition, highlighting the pivotal role of prokaryotes in B-vitamin cycling in marine ecosystems.
Highlights
Phytoplankton accounts for almost half of the global net primary production (Field et al, 1998) and may eventually cause toxic episodes, such as those caused by harmful algae blooms of Alexandrium spp. or Gymnodinium spp., entailing human health problems and large economic losses (Hallegraeff, 1993; van Dolah et al, 2001)
Samples for chlorophyll a (Chl a); prokaryotic biomass (PB); dissolved nutrient concentration, including vitamin B12; and microbial plankton community were collected at the beginning of each enrichment experiment
Upwelling index (UI) values were computed by the Instituto Español de Oceanografía in a 2◦ × 2◦ geostrophic cell centered at 42◦ N, 10◦ W, using data from atmospheric pressure at sea level, derived from the WXMAP model (GonzalezNuevo et al, 2014)
Summary
Phytoplankton accounts for almost half of the global net primary production (Field et al, 1998) and may eventually cause toxic episodes, such as those caused by harmful algae blooms of Alexandrium spp. or Gymnodinium spp., entailing human health problems and large economic losses (Hallegraeff, 1993; van Dolah et al, 2001). B vitamins act as cofactors for enzymatic reactions and are involved in many important metabolic pathways (Madigan et al, 2005; Koch et al, 2011; Monteverde et al, 2017). Vitamin B12 (B12 ), which is exclusively synthesized by some bacteria and archaea (Roth et al, 1996; Martens et al, 2002; Warren et al, 2002), acts as a cofactor of three enzymes in eukaryotes (methionine synthase, methylmalonyl-coA mutase and ribonucleotide reductase type II) (Helliwell et al, 2011; Bertrand and Allen, 2012). Vitamin B1 (B1 ) plays a pivotal role in intermediary carbon metabolism and is a cofactor for a number of enzymes involved in primary carbohydrate and branchedchain amino acid metabolism (Croft et al, 2006)
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