Climate change is projected to cause brownification of some coastal seas due to increased runoff of terrestrially derived organic matter. We carried out a mesocosm experiment (15 d) to test the ...effect of this on the planktonic ecosystem expecting reduced primary production and shifts in the phytoplankton community composition. The experiment was set up in 2.2 m3 mesocosm bags using four treatments, each with three replicates: control (Contr) without any manipulation, organic carbon additive HuminFeed (Hum; 2 mg L−1), inorganic nutrients (Nutr; 5.7 μM NH4 and 0.65 μM PO4), and combined Nutr and Hum (Nutr + Hum) additions. Measured variables included organic and inorganic nutrient pools, chlorophyll a (Chla), primary and bacterial production and particle counts by flow cytometry. The bags with added inorganic nutrients developed a phytoplankton bloom that depleted inorganic N at day 6, followed by a rapid decline in Chla. Brownification did not reduce primary production at the tested concentration. Bacterial production was lowest in the Contr, but similar in the three treatments receiving additions likely due to increased carbon available for heterotrophic bacteria. Picoeukaryotes clearly benefited by brownification after inorganic N depletion, which could be due to more effective nutrient recycling, nutrient affinity, light absorption, or alternatively lower grazing pressure. In conclusion, brownification shifted the phytoplankton community composition towards smaller species with potential effects on carbon fluxes, such as sinking rates and export to the sea floor.
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•Modest brownification did not affect primary production, but increased bacterial production.•Concentration of inorganic nitrogen was the primary driver for the phytoplankton development.•Brownification benefitted picophytoplankton.
Fluvial networks are globally relevant for the processing of dissolved organic matter (DOM). To investigate the change in molecular DOM diversity along the river course, high-field FTICR mass ...spectrometry and NMR spectroscopy of riverine DOM as well as bacterial abundance and activity were measured in a third order stream along a land-use gradient from pristine, agricultural to urban landscapes. DOM composition showed a clear evolution along the river course with an initial decrease of average oxidation and unsaturation followed by an increased relative abundance of CHNO and CHOS compounds introduced by agriculture and waste water, respectively. DOM composition was dominated by rather unsaturated CHO compounds (H/C ≤ 1) in headwaters and by more aliphatic molecules at downstream sites. Oxygenated functional groups shifted from aromatic ethers and hydroxyl groups to aliphatic carboxylic acids and aliphatic hydroxyl groups. This massive dislocation of oxygen significantly increased the diversity of atomic environments in branched aliphatic groups from headwater to downstream DOM. Mass spectra of DOM enabled the detection of compositional relationships to bacterial abundance and activity which was positively related to more aliphatic components (H/C > 1) and negatively related to unsaturated components. FTICR mass and NMR spectra corroborated the initial decline in DOM molecular diversity predicted by the River Continuum Concept (RCC) but demonstrated an anthropogenic increase in the molecular diversity of DOM further downstream. While the high DOM molecular diversity in first order headwater streams was the result of small scale ecosystem plurality, agriculture and waste water treatment introduced many components in the lower reaches. These anthropogenic influences together with massive bacterial oxidation of DOM contributed to a growth of molecular diversity of downstream DOM whose composition and structure differed entirely from those found in pristine headwaters.
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•DOM composition evolved from unsaturated to more aliphatic components.•Proportions of CHNO and CHOS compounds increased downstream.•Bacterial activity was positively related to more aliphatic components.•DOM diversity decreased in the upper part (river continuum concept).•DOM diversity increased in the lower part with agriculture and urban areas.
Bacterial abundance (BA), bacterial production (BP), chlorophyll a (Chl a) and primary production (PP) were estimated during Dec 2016–Jan 2017 at three discrete locations viz. the coastal waters, ...oceanic waters and near coral islands in the eastern Arabian Sea (EAS). During the study period, total bacterial counts were 0.2–1.2 × 109 cells L−1 and Chl a concentration was <0.1–1.2 mg m−3 in the EAS. Bacterial carbon (BC) was 50% of the Chl a-carbon representing phytoplankton biomass in all three locations. The BP (0.2–7.2 mg C m−3 d−1) was also high relative to the concomitantly measured PP (0.01–17 mg C m−3 d−1). Higher ratios of BC:Chl a-C and BP:PP compared to typical ratios in marine environments suggest dominance of allochthonous organic matter. Our analysis indicate that the dissolved organic carbon (DOC) pool which could result from the slow decomposition of the phytoplankton bloom of the preceding southwest monsoon (SWM) season, from the organic matter transported via estuaries and from anthropogenic activities comprises of labile as well as semi-labile components. It possibly fuels much of the bacterial carbon demand that greatly exceeds primary production in all three locations causing net heterotrophic condition which could contribute to increased flux of CO2 to the atmosphere, deoxygenation of coastal waters and threaten fisheries in the EAS during winter.
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•BC biomass comprised 50% of the phytoplankton biomass.•BP:PP ratios were 0.5->1.•Higher BC:Chl a-C and BP:PP in coastal, coral reef lagoons as well as in open ocean.•BC was higher than PP so EAS is net heterotrophic due to allochthonous inputs.
Information on microbial metabolic activity is essential for quantifying carbon and energy flows through marine food webs. We quantified community (Rcom) and prokaryotic (Rpro) respiration rates, ...bacterial production (BP), bacterial abundance (BA), and bacterial growth efficiencies (BGE) in the Perdido and Coatzacoalcos basins of the Gulf of Mexico (GOM) during summer and winter conditions in 2016. Our results showed seasonal, regional, and mesoscale eddy influences on those metabolic variables. Rpro accounted for >60% of total respiration in both regions, being three times higher in stations influenced by a cyclonic eddy (CE) in September (24.1 μM O2 d−1) than in stations affected by an anticyclonic eddy in March (7.2 μM O2 d−1) within the Coatzacoalcos basin where the eddy-trapping mechanism advected biomass-enriched waters from the Bay of Campeche. The eddy-stirring mechanism produced horizontal and vertical dipole patterns of metabolic variables increasing up to one order of magnitude Rcom and Rpro while decreasing BGE to 25-fold from the southeastern to the northwestern edges in CEs. This finding indicates that dissolved organic matter is more actively taken up to build bacterial biomass on the eastern edge of CEs in the GOM, while Rpro and Rcom increase on the western edges. Satellite integrated primary production was coupled with surface Rpro and Rcom at CEs and no eddies. BP was mainly regulated by CEs and was about 50% higher in the Coatzacoalcos basin (~0.03–0.14 μmol C L−1 d−1). BP increased in zones with high Rpro and Rcom, suggesting that Rcom is associated with heterotrophic prokaryote activity in both basins. BGE was lower than 25% within the upper 500 m during both cruises, but the highest values were quantified in the euphotic zone and during the September cruise. Metabolic variables integrated over the water column showed that 40–80% of the microbial activity occurred between the base of the euphotic zone and 150 m depth. Our findings contribute to a better understanding of the metabolic activity of the microbial communities in two regions of the GOM influenced by mesoscale eddies.
•Prokaryotic respiration represented 60% of total respiration in the Gulf of Mexico.•Integrated metabolic variables in 100–150 m accounted for 40–80% of total activity.•Respiration rates enhanced below the euphotic zone and with cyclonic eddies.•Eddy stirring/trapping mechanisms modulated metabolic variables in cyclonic eddies.•Bacterial growth efficiency was up to 25% within the upper 500 m in the Gulf of Mexico.
Climate-induced changes in the composition of organic matter sources in Chukchi Sea sediments could have major implications on carbon cycling, carbon sequestration, and food sources for lower benthic ...trophic levels. The aim of this study was two-fold: (1) to identify the proportional contributions of organic matter from various primary producers (phytoplankton, terrestrial, and bacterial) to depth-stratified sediments (0–5 cm) across the Arctic Chukchi Sea shelf using essential amino acid (EAA) specific stable carbon isotope biomarkers; and (2) to experimentally evaluate sediment bacterial production under different temperature scenarios. Proportional contributions of EAA sources to surface sediments had little relationship with environmental variables across the Chukchi Shelf and only showed noticeably higher terrestrial proportions in surface sediments in a high-deposition region in the southern study area. Across all sediment depth strata, the majority of EAA in sediments (∼76%) originated from terrestrial sources and may be indicative of accumulation over time due to slow degradation processes of this source within sediments. The different EAA sources showed no significant differences in proportional contributions with sediment depth except for phytoplankton-derived EAA, which decreased with increasing sediment depth. These patterns indicate a well-mixed upper sediment horizon, possibly from bioturbation activities by the abundant benthos. One EAA source assumed to respond quickly to changing environmental conditions are bacteria. To evaluate if and how bacterial production would respond to elevated temperatures, sediment bacterial production was measured experimentally using phospholipid fatty acid (PLFA) analysis. Bacterial production was initially (first 24 h) higher at 5 °C than at 0 °C; however, a drawdown of substrate or potential increase in predation activity and viral lysis resulted in bacterial production to subsequently be similar at both temperature settings. Overall results of this study suggest that terrestrial and bacterial carbon sources may become more prominent in a future, warmer Arctic. Identifying current patterns and potential shifts in organic matter sources with changes in temperature can aid in the understanding of the consequences of climate change in terms of organic matter presence and flow through benthic consumers that use these shelf sediments as feeding grounds.
Cadaverine. a natural polyamine with multiple bioactivities that is widely distributed in prokaryotes and eukaryotes, is becoming an important industrial chemical. Cadaverine exhibits broad prospects ...for various applications, especially as an important monomer for bio-based polyamides. Cadaverine-based polyamide PA 5X has broad application prospects owing to its environmentally friendly characteristics and exceptional performance in water absorption and dimensional stability. In this review, we summarize recent findings on the biosynthesis, metabolism, and physiological function of cadaverine in bacteria, with a focus on the regu- latory mechanism of cadaverine synthesis in Escherichia coil （E. coli）. We also describe recent developments in bacterial production of cadaverine by direct fermentation and whole-cell bioconversion, and recent approaches for the separation and purification of cadaverine. In addition, we present an overview of the ap- plication of cadaverine in the synthesis of completely bio-based polyamides. Finally. we provide an outlook and suggest future developments to advance the production of cadaverine from renewable resources.
Coral releases mucus into the surrounding seawater, providing an important organic and nutrient source for bacteria in coral reef systems. Despite thorough investigation in previous studies, bacteria ...respiration and grazing mortality by nanoplankton in coral reef systems remain poorly understood. To understand organic matter cycle in reef systems, it is necessary to reveal how coral mucus influences the energy and material transfer efficiency of the microbial loop. Here, we examined the production and grazing mortality of bacteria using a dilution method and the respiration of bacteria by directly measuring oxygen consumption in Acropora mucus-supplemented seawater (MuSW) multiple times over several years. The mucus significantly enhanced the bacterial production in MuSW compared with that in seawater. Bacterial respiration in MuSW was also significantly higher than that in seawater (SW). Bacterial carbon demand in MuSW was also higher than that in SW; however, bacterial growth efficiency did not change significantly. These results suggest that coral mucus benefits both bacterial growth and respiration. On the other hand, bacterial grazing mortality was not significantly different between MuSW and SW, suggesting that coral mucus did not directly enhance the activity and/or growth of bacterial grazers. According to previous reports, nanoflagellate number increases in response to an increase in bacteria. This suggests that coral mucus would have an indirect and delayed impact on bacterial grazers, whereas it would have a direct and immediate impact on bacteria. This study highlights that coral mucus raises the level of bacterial activity and could drive matter cycles through the microbial loop in reef systems.
•This study highlights the importance of coral mucus on microbial activity.•Coral mucus enhanced both bacterial production and respiration in seawater.•Coral mucus did not affect bacterial growth efficiency.•Coral mucus did not directly enhance activity of bacterial grazer in seawater.•Coral mucus would drive microbial loop by altering microbial activity in reef system.
Streams are important sites of transformation of dissolved organic matter (DOM). The molecular characterization of DOM-quality changes requires sophisticated analytical evaluation techniques. The ...goal of our study was to link molecular DOM transformation with bacterial activity. We measured the degradation of leaf leachate over a gradient of bacterial production obtained by different rates of percolation of sediments in seven experimental flumes on five sampling dates. We developed a new strategy for evaluating molecular formula data sets obtained by ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS), in which the time-dependent change of component abundance was fitted by a linear regression model after normalization of mass peak intensities. All components were categorized by calculating the slope (change of percent intensity per day) in each of the seven flumes. These slopes were then related to cumulative bacterial production. The concentration of DOM decreased quickly in all flumes. Bacterial activity was higher in flumes with percolated sediment than in those without percolation, whereas plankton bacterial activity was higher in flumes without percolation or without sediment. There were no differences in molecular-DOM characteristics between flumes, but there were distinct changes over time. Positive slopes, i.e. increasing intensities over time, were found for small molecules (MW < 450 Da) and high O/C ratios, whereas decreasing intensities were observed less often and only for large molecules and low O/C ratios. The positive slopes of produced components showed a positive relationship to bacterial production for small and for oxygen-rich components. The negative slopes of degraded components were negatively related to bacterial production for large and for oxygen-deficient molecules. Overall, the approach provided new insights into the transformation of specific molecular DOM components.
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•We developed a new approach to evaluate DOM quality transformation.•There were distinct changes in molecular-DOM characteristics over time.•Small molecules were produced and large molecules were degraded.•The transformation of few components was related to bacterial activity.
Large amounts of anthropogenic East Asian (EA) particulate matters (PM), containing inorganic nutrients and organic matter, are deposited in the oligotrophic Northwest Pacific Ocean. However, the ...effects of such deposition on marine microbes remain unclear. In this study, the effect of EA PM deposition on marine bacteria was assessed by five on-board microcosm experiments, conducted in oligotrophic basins of the South China Sea. The addition of EA PM to the sampling water induced a clear shift in bacterial community composition from prevailing oligotrophs (i.e., SAR 11 clade, Prochlorococcus, AEGEAN-169 marine group) to less common copiotrophs (i.e., Alteromonas, Ruegeria, Flavobacteriaceae) and thus a slight increase in bacterial diversity. The shift to more active community composition, as well as stimulation of PM nutrients, resulted in a large increase in cell-specific and bulk bacterial production. In contrast, there were only minor changes in bacterial abundance, possibly due to increased top-down mortality. The EA PM also exhibited a stronge toxic effect on pico-cyanobacteria, leading to a significant decrease in their proportion. Moreover, the responses of bacterial metabolism and community composition exhibited significant relationships with the hydrographic condition of the locations. Stronger promotion effects of the EA PM on bacterial production and community shift from oligotrophs to copiotrophs was demonstrated at the more oligotrophic sites with lower chlorophyll a concentrations. These results suggest that PM deposition from polluted areas has the potential to alter the typical oligotrophic microbiomes and change the net metabolic balance of the bacterial community. These will then influence the dynamics of carbon flow in microbial food webs and biogeochemical cycles, especially with the trend of global warming and expansion of low-chlorophyll regions.
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•Bacterial production was strongly stimulated by East Asian aerosols.•Aerosol input shifted the typical oligotrophic microbiomes towards copiotrophs.•Diversity of bacterial community showed slight increases in oligotrophic stations.•Aerosol input stimulated instantaneous growth rates and top-down mortality.•Response of bacteria tend to increase with increasing degree of oligotrophy.
Aquifers are important reservoirs for organic carbon. A fundamental understanding of the role of groundwater ecosystems in carbon cycling, however, is still missing. Using sediment flow-through ...microcosms, long-term (171d) experiments were conducted to test two scenarios. First, aquifer sediment microbial communities received dissolved organic matter (DOM) at low concentration and typical to groundwater in terms of composition (DOM-1x). Second, sediments received an elevated concentration of DOM originating from soil (DOM-5x). Changes in DOM composition were analyzed
via
NMR and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Carbon production, physiological adaptations and biodiversity of groundwater, and sediment prokaryotic communities were monitored by total cell counts, substrate use arrays, and deep amplicon sequencing. The experiments showed that groundwater microbial communities do not react very fast to the sudden availability of labile organic carbon from soil in terms of carbon degradation and biomass production. It took days to weeks for incoming DOM being efficiently degraded and pronounced cell production occurred. Once conditioned, the DOM-1x supplied sediments mineralized 294(±230) μgC L
−1
sed
d
−1
, 10-times less than the DOM-5x fed sediment communities 2.9(±1.1) mgC L
−1
sed
d
−1
. However, the overall biomass carbon production was hardly different in the two treatments with 13.7(±4.8) μgC L
−1
sed
d
−1
and 14.3(±3.5) μgC L
−1
sed
d
−1
, respectively, hinting at a significantly lower carbon use efficiency with higher DOM availability. However, the molecularly more diverse DOM from soil fostered a higher bacterial diversity. Taking the irregular inputs of labile DOM into account, shallow aquifers are assumed to have a low resilience. Lacking a highly active and responsive microbial community, oligotrophic aquifers are at high risk of contamination with organic chemicals.
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