Leucine, starch and bicarbonate utilization by specific bacterial groups in surface shelf waters off Galicia (NWSpain)

Abstract

The capability of different bacterial populations to degrade abundant polymers, such as algal-derived polysaccharides, or to utilize preferentially polymers over monomers, remains largely unknown. In this study, microautoradiography was combined with fluorescence in situ hybridization (MAR-FISH) to evaluate the ability of Bacteroidetes, SAR11, Roseobacter spp., Gammaproteobacteria and SAR86 cells to use bicarbonate, leucine and starch under natural light conditions at two locations in shelf surface waters off NW Spain. The percentage of cells incorporating bicarbonate was relatively high (mean 32% ± 4%) and was positively correlated with the intensity of solar radiation. The proportion of cells using starch (mean 56% ± 4%) or leucine (mean 47% ± 4%) was significantly higher than that using bicarbonate. On average, SAR11, Roseobacter spp. and Gammaproteobacteria showed a similarly high percentage of cells using leucine (47%-65% of hybridized cells) than using starch (51%-64% of hybridized cells), while Bacteroidetes and SAR86 cells preferentially used starch (53% of hybridized cells) over leucine (34%-40% of hybridized cells). We suggest that the great percentage of bacteria using starch is related to a high ambient availability of polymers associated to algal cell lysis, which, in turn, weakens the short-term coupling between phytoplankton release and bacterial production.

100 Days of marine Synechococcus–Ruegeria pomeroyi interaction: A detailed analysis of the exoproteome

“…Interestingly, it is between days 21 and 60 when R. pomeroyi shows an increased production of proteases (i.e., AAV95890 and AAV97448) and amidohydrolases (AAV97448 and AAV94260). Members of the Roseobacter group are known to preferentially target small nitrogen‐rich DOM (Bryson et al ., ; Teira et al ., ), and hence, it is not surprising that these organisms will specialize in using these compounds when they are present. While the abundance of organic matter in ASW allows R. pomeroyi to shift its targeted polymeric DOM, in SW it shows a more sTable production of hydrolases throughout the 100‐day co‐culture, with only the increase of the pectate lyase AAV93776 (from 1.4% to 3.6%) and the protease AAV95890 (from < 0.01% to 0.13%) over time.…”