Bacterial carbon demand and growth efficiency in a coastal upwelling system

Eleven culture experiments were conducted in the coastal upwelling ­system of the Ría de Vigo (NW Iberian Peninsula) by inoculating GF/C filtrated (10%) in 0.2 µm filtrated (90%) surface seawater collected under contrasting hydrographic conditions. Short-term (4 d) laboratory incubations were performed in the dark at 15°C. Dissolved organic carbon (DOC) concentration, bacterial biomass (BB), bacterial production (BP) and electron transport system (ETS) activity were then monitored to: (1) study the course of bacterial carbon demand (BCD) and growth efficiency (BGE) during the incubation period; and (2) determine how BCD and BGE were linked with changing environmental conditions. Following the 4 d incubation, BP decreased by <4 times its initial values (range from 3 to 11 times) and ETS activity increased by 6 times its initial values (range from 1 to 75 times). As a result, BCD increased by 5 times (range from 1 to 16 times) and the BGE decreased by 15 times (range from 2 to 55 times) over the same period. BGE integrated over the 4 d incubation period ranged from 7 ± 1% to 55 ± 11% (mean ± SD: 27 ± 15%); integrated BGE increased significantly (R2 = 0.64, p < 0.003) with the initial concentration of dissolved inorganic nitrogen (DIN), and decreased significantly (R2 = 0.55, p < 0.01) with the C:N ratio of the bioavailable dissolved organic matter (BDOM). A multiple linear regression with DIN and the C:N ratio of BDOM explained 89% of the observed variability in the integrated BGE, demonstrating the strong dependence of growth efficiency on nutrient conditions and the quality of the organic substrate feeding the community of this coastal embayment.This study was funded by fellowships to C.L. from the early-stage training site ECOSUMMER (MESTCT-2004-020501) and the Carlsberg Foundation.Peer reviewe

Effects of the photochemical transformation of dissolved organic matter on bacterial physiology and diversity in a coastal system

8 páginas, 2 tablas, 1 figuraThe effect of solar radiation on dissolved organic matter (DOM) and the subsequent impact of photo-altered DOM on bacterial activity and community structure were assessed during two experiments in the coastal system of the Ría de Vigo (NW Iberian Peninsula). After exposure of 0.2 μm filtered seawater for 3.5 days to dark and full sunlight, an inoculum of the bacterial community collected at the same time as the exposed water was added and the mixture was incubated for 4 days in the dark at 15 °C. Changes in bacterial production (BP), diversity (assessed by Fluorescence in situ hybridization) and electron transport system (ETS) activity, dissolved organic carbon (DOC) and nitrogen (DON) and DOM humic-like absorption and fluorescence were followed. The exposure to sunlight had no effect on DOM concentrations while an average (±SD) decrease in DOM humic fluorescence of 45 ± 10% was found. The incubations with photo-altered DOM had lower BP (57 ± 11%), ETS (42 ± 9%) and bacterial carbon demand (BCD) (42 ± 8%) compared with the dark incubations, while bacterial growth efficiency (BGE) was unaffected. This suggests that DOM photo-alteration had a negative effect on bacterial metabolism in the study system. The bacterial growth on irradiated DOM resulted in a significant enrichment of the Gammaproteobacteria group compared with the dark control, indicating that solar exposure of DOM led to rapid changes in the bacterial community composition of the Ría de Vigo.This study was funded by fellowships to C.L from the early stage training site ECOSUMMER (MEST-CT-2004-020501) and the Carlsberg FoundationPeer reviewe

Dissolved inorganic carbon fixation of Thaumarchaeota vs. Bacteria in the meso- and upper bathypelagic waters of the world’s oceans differentiated with the use of metabolic inhibitors

Recent studies suggest that the dark ocean prokaryotes fix inorganic carbon at rates substantially higher than assumed. We have studied the contribution of Archaea vs. Bacteria to total prokaryotic fixation of dissolved inorganic carbon (DIC) in the meso- and upper bathypelagic waters of the world’s oceans during the Malaspina circumnavigation expedition carried out between December 2010 and July 2011. We used the metabolic inhibitor Erythromycin, an antibiotic specifically inhibiting growth of Bacteria but not affecting Archaea. Bacteria dominated throughout the water column in the three major ocean basins (54% of the total DAPI counts), decreasing in their relative contribution to total prokaryotic abundance from the surface to the meso- and bathypelagic waters. By contrast, the relative contribution of Thaumarchaeota was generally higher in the meso- and bathypelagic layers than in the surface waters (up to 29% of the total DAPI counts in the Pacific Ocean). Averaged over the entire water column, Thaumarchaeota contributed 8%, 33% and 18% to the total prokaryotic DIC fixation in the Indian, Pacific and Atlantic Ocean, respectively. The contribution of Thaumarchaeota to total prokaryotic DIC fixation increased with depth, particularly in the Atlantic below 1000 m depth and in the lower mesopelagic zone of the Pacific Ocean. Preliminary results from an station in the Atlantic Ocean, combining microautoradiography and fluorescence in situ hybridization (MICRO-CARD-FISH), confirmed that both Thaumarchaeota and some bacterial groups such as SAR 324 take up DIC. Thaumarchaeota and SAR 324 accounted for 7 % and 12% of DIC-positive DAPI-stained cells, respectively, as revealed by MICRO-CARD-FISH. Our results suggest that some phylogenetic groups may be significant contributors to the dark ocean chemoautotrophy

Role of bacterial community composition as a driver of the small-sized phytoplankton community structure in a productive coastal system

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGWe present here the first detailed description of the seasonal patterns in bacterial community composition (BCC) in shelf waters off the Ría de Vigo (Spain), based on monthly samplings during 2 years. Moreover, we studied the relationship between bacterial and small-sized eukaryotic community composition to identify potential biotic interactions among components of these two communities. Bacterial operational taxonomic unit (OTU) richness and diversity systematically peaked in autumn–winter, likely related to low resource availability during this period. BCC showed seasonal and vertical patterns, with Rhodobacteraceae and Flavobacteriaceae families dominating in surface waters, and SAR11 clade dominating at the base of the photic zone (30 m depth). BCC variability was significantly explained by environmental variables (e.g., temperature of water, solar radiation, or dissolved organic matter). Interestingly, a strong and significant correlation was found between BCC and small-sized eukaryotic community composition (ECC), which suggests that biotic interactions may play a major role as structuring factors of the microbial plankton in this productive area. In addition, co-occurrence network analyses revealed strong and significant, mostly positive, associations between bacteria and small-sized phytoplankton. Positive associations likely result from mutualistic relationships (e.g., between Dinophyceae and Rhodobacteraceae), while some negative correlations suggest antagonistic interactions (e.g., between Pseudo-nitzchia sp. and SAR11). These results support the key role of biotic interactions as structuring factors of the small-sized eukaryotic community, mostly driven by positive associations between small-sized phytoplankton and bacteria.Xunta de Galicia | Ref. EM2013/023Xunta de Galicia | Ref. ED481A-2019/290Xunta de Galicia | Ref. ED431I 2020/03Ministerio de Economía y Competitividad | Ref. CTM2017-83362-RMinisterio de Ciencia e Innovación | Ref. PID2019-110011RB-C3

Predicting plankton net community production in the Atlantic Ocean

We present, test and implement two contrasting models to predict euphotic zone net community production (NCP), which are based on 14C primary production (PO14CP) to NCP relationships over two latitudinal (ca. 30°S–45°N) transects traversing highly productive and oligotrophic provinces of the Atlantic Ocean (NADR, CNRY, BENG, NAST-E, ETRA and SATL, Longhurst et al., 1995 [An estimation of global primary production in the ocean from satellite radiometer data. Journal of Plankton Research 17, 1245–1271]). The two models include similar ranges of PO14CP and community structure, but differ in the relative influence of allochthonous organic matter in the oligotrophic provinces. Both models were used to predict NCP from PO14CP measurements obtained during 11 local and three seasonal studies in the Atlantic, Pacific and Indian Oceans, and from satellite-derived estimates of PO14CP. Comparison of these NCP predictions with concurrent in situ measurements and geochemical estimates of NCP showed that geographic and annual patterns of NCP can only be predicted when the relative trophic importance of local vs. distant processes is similar in both modeled and predicted ecosystems. The system-dependent ability of our models to predict NCP seasonality suggests that trophic-level dynamics are stronger than differences in hydrodynamic regime, taxonomic composition and phytoplankton growth. The regional differences in the predictive power of both models confirm the existence of biogeographic differences in the scale of trophic dynamics, which impede the use of a single generalized equation to estimate global marine plankton NCP. This paper shows the potential of a systematic empirical approach to predict plankton NCP from local and satellite-derived P estimates

Co-occurrence and diversity patterns of benthonic and planktonic communities in a shallow marine ecosystem

Marine microorganisms are involved in a variety of biogeochemical cycles and live in diverse ecological communities where they interact with each other and with other organisms to guarantee ecosystem functions. The present study focused on a shallow marine environment located in Ría de Vigo (NW, Spain), where sediment and size-fractionated plankton samples were collected from 2016 to 2018. DNA metabarcoding was used to describe the eukaryote and prokaryote composition and diversity in sediments and plankton and to depict possible associations among the most frequent and abundant organisms by co-occurrence network analysis. High eukaryote and prokaryote diversity indices were obtained in all compartments. Significant differences among eukaryote and prokaryote communities were found between sediment and plankton samples, with a high percentage of exclusive operational taxonomic units (OTUs) associated with each compartment, especially from sediment. Despite these differences, shared taxa between water and sediment were also obtained, suggesting a relatively meaningful exchange of organisms between both environmental compartments. Significant co-occurrences were mainly obtained between prokaryotes (41%), followed by eukaryotes–prokaryotes (32%) and between eukaryotes (27%). The abundant and strong positive correlations between organisms, including representatives from the sediment and the water column, suggested an essential role of biotic interactions as community-structuring factors in shallow waters where beneficial associations likely prevail. This study provides a novel approach for the detailed description of the eukaryote and prokaryote diversity and co-occurrence patterns in a shallow marine area, including both the sediment and different water-size fractions. The high diversity obtained and the detection of predominantly coexisting interactions among organisms from sediment and the overlying water column suggest a movement of species between both habitats and therefore confirm the importance of integratively studying shallow marine ecosystems.Xunta de Galicia | Ref. IN606A-2018/020Xunta de Galicia | Ref. IN607B 2019/01Agencia Estatal de Investigación | Ref. CTM2017-83362-RInterreg España-Portugal | Ref. 20200474_BLUEBIOLA

Linking the impact of bacteria on phytoplankton growth with microbial community composition and co-occurrence patterns

The interactions between microalgae and bacteria have recently emerged as key control factors which might contribute to a better understanding on how phytoplankton communities assemble and respond to environmental disturbances. We analyzed partial 16S rRNA and 18S rRNA genes from a total of 42 antibiotic bioassays, where phytoplankton growth was assessed in the presence or absence of an active bacterial community. A significant negative impact of bacteria was observed in 18 bioassays, a significant positive impact was detected in 5 of the cases, and a non-detectable effect occurred in 19 bioassays. Thalasiossira spp., Chlorophytes, Vibrionaceae and Alteromonadales were relatively more abundant in the samples where a positive effect of bacteria was observed compared to those where a negative impact was observed. Phytoplankton diversity was lower when bacteria negatively affect their growth than when the effect was beneficial. The phytoplankton-bacteria co-occurrence subnetwork included many significant Chlorophyta-Alteromonadales and Bacillariophyceae-Alteromonadales positive associations. Phytoplankton-bacteria co-exclusions were not detected in the network, which contrasts with the negative effect of bacteria on phytoplankton growth frequently detected in the bioassays, suggesting strong competitive interactions. Overall, this study adds strong evidence supporting the key role of phytoplanktonbacteria interactions in the microbial communities.Agencia Estatal de Investigación | Ref. CTM2017-83362-RAgencia Estatal de Investigación | Ref. PID2019-110011RB-C33Xunta de Galicia | Ref. ED481A-2019/290Xunta de Galicia | Ref. ED481A-2018/288Universidade de Vigo/CISU

Impact of atmospheric deposition on the metabolism of coastal microbial communities

11 páginas, 3 tablas, 5 figurasThe impact of rain water collected at marine, urban and rural sites on coastal phytoplankton biomass, primary production and community composition as well as the effect on microbial plankton metabolism was studied in 3 microcosm experiments conducted under contrasting spring, autumn and winter conditions. The measured responses were highly variable. Rainwater additions increased chlorophyll a (Chl a) concentration (5–68% difference between rainwater treatments relative to the control) in all experiments and reduced or stimulated primary production (PP) depending on the treatment and the experiment (from −10 to +169% relative to the control). Autotrophic stimulation was highest in spring, probably related to the low initial natural nutrient concentrations. Under winter nutrient replete conditions, rainwater inputs changed the phytoplankton community although this change did not promote increases in primary production. Enhancement of net autotrophy (increase of net oxygen production up to 227%) after rainwater inputs were only found during the period of low nutrient availability. Inputs of dissolved organic nitrogen (DON) explained a large fraction of the variability in the response of PP, Chl a, community respiration (CR) and net community production (NCP). Our results suggest that differences in the initial environmental conditions (i.e. nutrient availability), rainwater composition and the ability of the present autotrophic communities to utilize the new nutrients result in substantial changes in the microbial responses and associated biologically-mediated carbon fluxes. As atmospheric nutrient inputs into coastal oceans are increasing rapidly, our results help to understand the effects of different inputs on the metabolism of distinct microbial communitiesThis research was supported by the Galician Government (Xunta de Galicia) through the grants 07MMA002402PR (IMAN) and PGIDIT06PXIB312222PR (AddEx). S.M-G. and E.E.G-M. were funded by F.P.U. fellowships and E.T. by a Ramón y Cajal contract of the Spanish Ministry of Science and InnovationPeer reviewe

Bacterial community composition and optical signature of DOM shape empirical leucine-to-carbon conversion factors in north-eastern Atlantic waters (0-4000 m)

Oral communicationMicrobial heterotrophic activity is a major process regulating the flux of dissolved organic matter (DOM) in the ocean. DOM quantity and quality strongly influence its microbial utilization and fate in the ocean. In order to broaden the vertical resolution of leucine-to-carbon conversion factors (CFs), needed for converting substrate incorporation into biomass production by heterotrophic bacteria, nine dilution experiments were performed in the north Atlantic. We found a very consistent depth-stratification in empirical CFs values from epipelagic to bathypelagic waters (3.95 &#177; 0.05 to 0.90 &#177; 0.51 kg C mol Leu-1). Our results demonstrated that the customarily used CF of 1.55 kg C mol Leu-1 in oceanic waters leads to an underestimation of prokaryotic heterotrophic production in epi- and mesopelagic waters, while it causes a severe overestimation in bathypelagic waters. Pearson correlations showed that CFs were related not only to hydrographic variables but also to specific phylogenetic groups and DOM quality and quantity indicators. Furthermore, a multiple linear regression model predicting CFs from relatively simple hydrographic and optical spectroscopic measurements is provided. Taken together, our results suggest that differences in CFs throughout the water column might be mostly associated to the quality of DOM affecting the response of particular phylogenetic groups.ASL

Deep ocean prokaryotes and fluorescent dissolved organic matter reflect the history of the water masses across the Atlantic Ocean

Organic matter is known to influence community composition and metabolism of marine prokaryotes. However, few studies have addressed this linkage in the deep ocean. We studied the relationship between fluorescent dissolved organic matter and prokaryotic community composition in meso- and bathypelagic water masses along a surface productivity gradient crossing the subtropical and tropical Atlantic Ocean. Four fluorescence components were identified, three humic-like and one protein-like. The distributions of the humic-like components were significantly explained by water mass mixing, apparent oxygen utilisation (AOU) and epipelagic productivity proxies in varying degrees, while the protein-like component was explained only by water mass mixing and epipelagic productivity. The diversity and taxonomic composition of the prokaryotic community differed between water masses: the Nitrosopumilales order dominated in water masses with high AOU and humic-like fluorescence (notably, the SubPolar Mode Water), and tended to co-occur with Marine Group II archaea, the SAR324 clade and Thiomicrospirales, while bathypelagic water masses displayed greater abundances of members of Marinimicrobia, SAR202 and SAR324. Water mass mixing regression models suggested that the distribution of some taxa (e.g., Marinimicrobia, SAR202) was dominated by mixing and selection within the water masses during ageing, while others (chiefly, Alteromonadales) were mostly influenced by local processes. Our results suggest a link between the composition of the prokaryotic community, oxygen utilisation and the signal of fluorescent dissolved organic matter, and has implications for our understanding of the processes that shape carbon cycling and prokaryotic communities in the deep ocean.3,26