Bacterial extracellular enzymatic activity in globally changing aquatic ecosystems (original) (raw)
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Deep Sea Research Part II: Topical Studies in Oceanography, 2002
Despite the importance of hydrolytic activities by bacterial extracellular enzymes (EE) in the temperate ocean, little is known about the role of extracellular enzymatic activity (EEA) in determining the fate of particulate organic matter (POM) in polar seas. To explore the issue further, we measured various chemical and bacterial parameters in the near-01C waters of the North Water during the months of May and July of 1998. Seawater (SW) samples were collected by Niskin bottle at the depth of the chlorophyll fluorescence maximum (8-90 m), while samples of sinking particles and aggregates were collected in short-term (0.5-1.2 d), unpoisoned, floating sediment traps deployed at depths typically below the mixed layer (50-136 m). Samples were analyzed for POC, PON, and abundance of total and actively respiring bacteria. They were also incubated with fluorescently tagged substrate analogs to measure potential maximal rates of three classes of EE (leucine-aminopeptidase, chitobiase, and b-glucosidase) at -11C. The percentage of actively respiring bacteria was always higher in sediment trap samples than in SW (medians of 38% and 24% versus 10% and 12% in May and July, respectively). Cell-specific rates of EEA were also higher in the trap samples and, for both sample types, similar to published rates from temperate waters. Rates of EEA when scaled to the abundance of actively respiring bacteria, however, did not differ between sample types, suggesting that the elevated EEA associated with sinking material is due to the greater abundance of metabolically active cells supported by such material and not due to enhanced enzyme expression in general, as suggested by previous studies. In this study, leucine-aminopeptidase activity was always much higher than the other classes of EEA, becoming even more dominant later in the season; it always correlated positively with the abundance of both total and actively respiring bacteria. Enzyme ratios indicating protease dominance corresponded with the seasonal increases in C/N ratios of both suspended and sinking POM. Overall the results suggest bacterial responses to seasonal changes in POM quality through differential expression of EE and an important role for proteases in influencing the nitrogen content of organic matter even at near-01 temperatures in this polynya. r
Analysis of Atlantic and Northern Gulf Coast Wetland Bacterial Extracellular Enzyme Activity
2019
Sea-level rise is projected to cause saltwater marshes to migrate landward replacing brackish and freshwater marshes. Coastal wetlands are important sinks of carbon, phosphorous, and nitrogen, so it is important to understand the function of their microbial communities. This study aims to categorize the difference in function between different spatially distinct wetland marsh types in advance of the expected alteration of the wetland ecosystems. Extracellular microbial enzymatic activity was measured to understand organic matter decomposition and nutrient mineralization in different marsh types. We measured the activities of the extracellular enzymes β-glucosidase, NAGase, peroxidase, phenol oxidase, and phosphatase across sites along the Northern Gulf of Mexico and Atlantic coast. Both tidal salt and tidal fresh marsh sediment were sampled at each location. Higher salinity depressed the activity of NAGase. Salinity did not have a significant effect on phosphatase activity. High salinity slightly repressed carbondegrading enzyme β-glucosidase activity but increased peroxidase and phenol oxidase activities. Sediments with high organic matter content had lower enzyme activities. Warmer water temperature sites tended to exhibit higher overall enzyme activity. This study finds that increasingly saline wetlands will cause a change in nutrient cycling functionality. Saltwater intrusion into fresh marsh will reduce the capacity for nitrate removal leading to potential coastal eutrophication, and saltwater intrusion will increase carbon metabolism leading to less accretion than in freshwater marshes further amplifying the effect of sea-level rise.
SCIENCE CHINA Earth Sciences, 2023
Interactions between chemodiverse dissolved organic matter (DOM) and biodiverse microbes are governed by a myriad of intrinsic and extrinsic factors which are not well understood. Here, we update and bridge the gap of this interdisciplinary theme comprehensively. At an ecosystem level, aquatic ecosystems dominated by algae-sourced DOM (e.g., eutrophic lake or coastal upwelling areas) harbor more biolabile DOM, such as directly assimilable monomers and readily hydrolysable biopolymers. However, other ecosystems prevailed by DOM supply from soil and vascular plants (e.g., river or wetland) have more biorefractory DOM, such as low molecular weight (LMW) residue of aliphatic C skeletons and geopolymers. A variety of heterotrophic bacteria, archaea, fungi, phagotrophic protists, and even photoautotrophic phytoplankton shows genomic and/or culturing experimental evidence of being able to process a diverse type of organics. The various biodegradable organics have different chemical structures and chemical bonds such as carbohydrates, amino acids, proteins, lignins, lipids, carboxylic acids, humic acids, hydrocarbons, and nanoplastics. Meanwhile, bio-production of metabolism intermediates and/or biorefractory organics (e.g., carboxyl-rich alicyclic molecules, CRAM) is observed despite general decay of bulk dissolved organic carbon (DOC) during bioassay experiments. In particular, emerging evidence shows that archaea contribute significantly to biomass in the marine mesopelagic zone and subsurface environments and their abundance often increases with depth in sediments. Furthermore, not only intrinsic factors (e.g., DOM composition and structure), but also extrinsic ones (e.g., sunlight and dissolved oxygen) play important roles in interplays between DOM and microbes.
Aquatic Microbial Ecology, 2011
We monitored the dynamics of extracellular organic matter in 3 mesocosms: one dominated by a heterotrophic (microbial) community with negligible autotrophic activity (net heterotrophic system), a second where a small Phaeocystis bloom developed (production and loss almost balanced), and a third harboring a large diatom bloom (net autotrophic system). In all mesocosms, meso-and macroscopic heterotrophic organisms were excluded to primarily study extracellular organic matter production and turnover by specific algae and microbial loop organisms, respectively. Concentration and composition of dissolved organic matter (DOM), i.e. dissolved organic carbon (DOC), monosaccharides and total carbohydrates (MCHO and TCHO), free and combined neutral carbohydrates (DFCHO and DCCHO), as well as free and combined amino acids (DFAA and DCAA) were measured. In addition, net and gross community production rates were determined to calculate C-budgets. Whereas concentrations and composition of MCHO differed very little among the 3 mesocosms, dynamics of TCHO, DFCHO, and DCCHO differed significantly. Concentrations of DFAA were higher in both algal mesocosms compared to the heterotrophic system, and composition of DFAA was significantly different in the Phaeocystis and Diatom tanks. The composition and concentration of DCAA, however, were similar in all 3 mesocosms. Total dissolved carbohydrates and amino acids comprised a substantial fraction of the DOC pool. Dynamics of these DOC fractions, however, could only partly explain those of DOC, implying either that other dissolved compounds were important for overall C-cycling, or that microbial degradation of DOM affects the detection of carbohydrates and protein components.
The impact of microbial metabolism on marine dissolved organic matter
Microbes mediate global biogeochemical cycles through their metabolism, and all metabolic processes begin with the interaction between the microbial cell wall or membrane and the external environment. For all heterotrophs and many autotrophs, critical growth substrates and factors are present within the dilute and heterogeneous mixture of compounds that constitutes dissolved organic matter (DOM). In short, the microbe-molecule interaction is one of the fundamental reactions within the global carbon cycle. Here, I summarize recent findings from studies that examine DOM-microbe interactions from either the DOM perspective (organic geochemistry) or the microbe perspective (microbial ecology). Gaps in our knowledge are highlighted and future integrative research directions are proposed.
Environmental Microbiology, 2018
Bacteria are major drivers of biogeochemical nutrient cycles and energy fluxes in marine environments, yet how bacterial communities respond to environmental change is not well known. Metagenomes allow examination of genetic responses of the entire microbial community to environmental change. However, it is challenging to link metagenomes directly to biogeochemical process rates. Here, we investigate metagenomic responses in natural bacterioplankton communities to selected environmental stressors in the Baltic Sea, including increased river input, increased nutrient concentration, and reduced oxygen level. This allowed us to identify informative prokaryotic gene markers, responding to environmental perturbation. Our results demonstrate that metagenomic and metabolic changes in bacterial communities in response to environmental stressors is influenced both by the initial community composition and by the biogeochemical factors shaping the functional response. Furthermore, the different sources of dissolved organic matter (DOM) had the largest impact on metagenomic blueprint. Most prominently, changes in DOM loads 2 influenced specific transporter types reflecting the substrate availability and DOC assimilation and consumption pathways. The results provide new knowledge for developing models of ecosystem structure and biogeochemical cycling in future climate change scenarios and advance our exploration of the potential use of marine microorganisms as markers for environmental conditions. Introduction Prokaryotic microbial communities respond rapidly to environmental changes e.g. substrate composition, oxygen concentration, nutrient supply and salinity by changes in their community composition and gene expression (
Marine Ecology Progress Series, 1993
Organic material entering the oceanic mesopelagic zone may either reenter the euphotic zone or settle into deeper waters. Therefore it is important to know about mechanisms and efficiency of substrate conversion in this water layer. Bactenal biomass, bactena secondary production (BSP), extracellular peptidase activity (EPA) and particulate organic nitrogen (PON) were measured in vertical profiles of the North Atlantic (46O N 18" W; 57" N 23" W) dunng the Joint Global Ocean F l u Study (JGOFS) cruise in May 1989. The magnitude of these parameters decreased differently with depth. The strongest decreases were observed for bacterial production (3H-thymidine incorporation) and peptide turnover (using the substrate analog leucine-methylcoumarinylamide). Bacterial biomass and peptidase potential activity were not reduced as much in the mesopelagic zone. Peptidase potential per unit cell biomass of mesopelagic bactena was 2 to 3 times higher than that of bacteria in surface water. Nevertheless bacterial growth at depth was slow, due to slow actual hydrolysis. Values of theoretical PON hydrolysis were calculated from PON measurements and protein hydrolysis rates. These corresponded well to bacterial production rates, and the degree of correspondence increased from a factor of 0.63 (PON hydrolysis/BSP) in the mixed surface layer to 0.87 in the mesopelagic zone. Thus we hypothesized a n effective coupling between particle hydrolysis and uptake of hydrolysate by bacteria, which depletes the deeper water of e a s~l y degradable substrates as hydrolysates usually are. The low enzymatic PON turnover rate of 0.04 d -' in the subeuphotic zone suggests that residence time of particles within a depth stratum may be important for its contribution to export, storage and recycling of organlc matter.