Substantial Carbohydrate Hydrolase Activities in the Water Column of the Guaymas Basin (Gulf of California)

The Guaymas Basin spreading center situated in the Gulf of California is characterized by a thick layer of organic-rich sediments that are thermally altered by hydrothermal fluids, thereby providing a bottom water source of dissolved organic carbon (DOC) to the water column. The potential for heterotrophic microbial communities in the water column to metabolize this organic matter source has not yet been investigated, however. In order to assess heterotrophic potential in the water column of the Guaymas Basin, we measured the activities of carbohydrate-hydrolyzing extracellular enzymes at the chlorophyll maximum, the oxygen minimum, the deep-water turbidity plume, and bottom waters. These measurements were carried out using water obtained from repeat CTD casts over the course of a week, and from bottom water collected by HOV Alvin at hydrothermally active areas with extensive chemosynthetic microbial mats. Repeat measurements at subsurface depths were very comparable across sampling dates and CTD casts. Exo-acting (terminal-unit-cleaving) monosaccharide hydrolase activities were typically higher in deeper waters than in surface waters, despite colder temperatures. In bottom water, the spectrum of endo-acting (mid-chain-cleaving) polysaccharide hydrolase activities was broader than at shallower depths. The high enzyme activities in Guaymas Basin bottom waters indicate an unusually active heterotrophic community that is responding to influx of DOC and nutrients into bottom waters from the hydrothermally affected sediments, or to the availability of chemosynthetically produced biomass

Enhanced protein and carbohydrate hydrolyses in plume-associated deepwaters initially sampled during the early stages of the Deepwater Horizon oil spill

Oil spilled in the ocean can be biodegraded through a cascade of microbial processes, including direct degradation of petroleum-derived hydrocarbons, as well as subsequent degradation of transformation byproducts and exopolymeric substances (EPS) that are produced by microbes to emulsify hydrocarbons and facilitate access to oil. In the aftermath of the Deepwater Horizon oil spill, we measured enzymatic hydrolysis of carbohydrates and peptides in waters initially collected from within and outside of the deep hydrocarbon plume. The rationale is that the presence of EPS and other transformation byproducts in the deepwater plume may have enhanced heterotrophic bacterial metabolism in the cold deepwater environment. Our investigation targets carbohydrate and peptide hydrolase activities as indicators of the degradation of high molecular weight organic matter, including EPS substrates. Deepwater associated with the hydrocarbon plume revealed higher peptidase activity compared to non-plume deepwater samples. Enzymatic hydrolysis of carbohydrates, measured by the means of exo-acting enzyme activity (β-glucosidase), was also more rapid inside compared to outside the deepwater plume. Hydrolysis rates and patterns of endo-acting polysaccharide hydrolases, measured by means of distinct polysaccharide substrates in longer-term incubations, demonstrated more rapid plume-associated hydrolysis of two (laminarin and xylan) of the three substrates hydrolyzed in deepwaters. Our results indicate that microbial communities associated with the deepwater plume exhibited 'primed' responses to addition of specific substrates, which may structurally resemble components found in bacterial EPS and oil degradation byproducts. Bacterial transformation of oil-degradation byproducts thus likely contributed to microbial growth and respiration measured inside the deepwater plume

Enhanced formation of transparent exopolymer particles (TEP) under turbulence during phytoplankton growth

Small-scale turbulence in the surface ocean is ubiquitous, influencing phytoplankton dynamics with consequences for energy flow. The underlying mechanisms that drive changes in phytoplankton dynamics under turbulence are not well constrained. We investigated growth of four phytoplankton species at different turbulence levels in oscillating grid tanks. We also measured transparent exopolymer particles (TEP) from phytoplankton exudates, which play a major role in biogeochemical fluxes in the ocean. Turbulence levels in the tanks reflected in situ conditions in surface waters from the open ocean to higher turbulent environments such as estuaries. Growth rates were unaffected by turbulence while TEP concentrations as xanthan gum (XG) equivalents normalized to algal cells showed generally higher levels in the high turbulence compared to the low turbulence treatments particularly during initial algal growth. Results from a mixing experiment without algal cells and XG also revealed enhanced formation of TEP-like particles under high mixing conditions, indicating that TEP formation in the phytoplankton turbulence treatments was mainly driven by physical processes, such as enhanced encounter rates of TEP-precursors under high mixing. Our results underline the importance of small-scale turbulence on TEP formation with possible consequences for particle aggregation and vertical carbon fluxes in the ocean

Microbial enzymatic activity and secondary production in sediments affected by the sedimentation pulse following the Deepwater Horizon oil spill

A large fraction of the spilled oil from the Deepwater Horizon (DwH) blowout in April 2010 reached the seafloor via sinking oil aggregates (oil snow) in a massive sedimentation that continued until late summer 2010 ("Dirty blizzard"). We measured heterotrophic microbial metabolic rates as well as porewater and sedimentary geochemical parameters at sites proximate to and distant from the wellhead to investigate microbial responses to the "Dirty Blizzard". Lipase activity and rates of bacterial protein production were highest and leucine-aminopeptidase activity was lowest in 0-2 cm sediment layers at the sites proximate to the wellhead. These results suggest that the presence of the oil snow stimulated benthic microbial enzymatic hydrolysis of oil-derived organic matter that was depleted in peptide substrates at the time of our sampling. The strong gradients in porewater DOC, NH4+, and HPO43- concentrations in the upper 6 cm of the sediments near the wellhead likewise indicate elevated heterotrophic responses to recently-sedimented organic matter. In addition to enhanced microbial activities in the 0-2 cm sediment layers, we found peaks of total organic carbon and elevated microbial metabolic rates down to 10 cm at the sites closest to the wellhead. Our results indicate distinct benthic metabolic responses of heterotrophic microbial communities, even three months after the ending of the "Dirty Blizzard". Compared to other deep-sea environments, however, metabolic rates associated with the recently deposited particulate matter around the wellhead were only moderately enhanced. Oil contaminants at the seafloor may therefore have prolonged residence times, enhancing the potential for longer-term ecological consequences in deep-sea environments

Changes in the spectrum and rates of extracellular enzyme activities in seawater following aggregate formation

Marine snow aggregates are heavily colonized by heterotrophic microorganisms that express high levels of hydrolytic activities, making aggregates hotspots for carbon remineralization in the ocean. To assess how aggregate formation influences the ability of seawater microbial communities to access organic carbon, we compared hydrolysis rates of six polysaccharides in coastal seawater after aggregates had been formed (via incubation on a roller table) with hydrolysis rates in seawater from the same site that had not incubated on a roller table (referred to as whole seawater). Hydrolysis rates in the aggregates themselves were up to three orders of magnitude higher on a volume basis than in whole seawater. The enhancement of enzyme activity in aggregates relative to whole seawater differed by substrate, suggesting that the enhancement was under cellular control, rather than due to factors such as lysis or grazing. A comparison of hydrolysis rates in whole seawater with those in aggregate-free seawater, i.e. the fraction of water from the roller bottles that did not contain aggregates, demonstrated a nuanced microbial response to aggregate formation. Activities of laminarinase and xylanase enzymes in aggregate-free seawater were higher than in whole seawater, while activities of chondroitin, fucoidan, and arabinogalactan hydrolyzing enzymes were lower than in whole seawater. These data suggest that aggregate formation enhanced production of laminarinase and xylanase enzymes, and the enhancement also affected the surrounding seawater. Decreased activities of chondroitin, fucoidan, and arabinoglactan-hydrolyzing enzymes in aggregate-free seawaters relative to whole seawater are likely due to shifts in enzyme production by the aggregate-associated community, coupled with the effects of enzyme degradation. Enhanced activities of laminarin- and xylan-hydrolyzing enzymes in aggregate-free seawater were due at least in part to cell-free enzymes. Measurements of enzyme lifetime using commercial enzymes suggest that hydrolytic cell-free enzymes may be active over timescales of days to weeks. Considering water residence times of up to 10 days in the investigation area (Apalachicola Bay), enzymes released from aggregates may be active over timescales long enough to affect carbon cycling in the Bay as well as in the adjacent Gulf of Mexico. Aggregate formation may thus be an important mechanism shaping the spectrum of enzymes active in the ocean, stimulating production of cell-free enzymes and leading to spatial and temporal decoupling of enzyme activity from the microorganisms that produced them

Comparison of multivariate microbial datasets with the Shannon index: An example using enzyme activity from diverse marine environments

a b s t r a c t Heterotrophic microbial communities contain substantial functional diversity, so studies of community function often generate multivariate data sets. Techniques for data reduction and analysis can help elucidate qualitative differences among sites from multivariate data sets that may be difficult to grasp intuitively from raw data. The Shannon index is one such technique, used commonly in ecological studies to quantify species evenness. Here, the Shannon index is used to compare quantitatively the extent to which complex microbial communities vary in their capability to access polysaccharides. It is maximized when hydrolysis rates for all polysaccharides are equal and minimized when the range among individual hydrolysis rates at a given site is large. Application of the technique to depth profiles of polysaccharide hydrolysis rates from four distinct pelagic marine environments indicates that, in three of four cases, surface water communities accessed substrates at a more even rate than in deeper waters. The technique could usefully be applied to other types of data obtained in studies of microbial activity and the geochemical effects

Marine snow formation in the aftermath of the Deepwater Horizon oil spill in the Gulf of Mexico

The large marine snow formation event observed in oil-contaminated surface waters of the Gulf of Mexico (GoM) after the Deepwater Horizon accident possibly played a key role in the fate of the surface oil. We characterized the unusually large and mucus-rich marine snow that formed and conducted roller table experiments to investigate their formation mechanisms. Once marine snow lost its buoyancy, its sinking velocity, porosity and excess density were then similar to those of diatom or miscellaneous aggregates. The hydrated density of the component particles of the marine snow from the GoM was remarkably variable, suggesting a wide variety of component types. Our experiments suggest that the marine snow appearing at the surface after the oil spill was formed through the interaction of three mechanisms: (1) production of mucous webs through the activities of bacterial oil-degraders associated with the floating oil layer; (2) production of oily particulate matter through interactions of oil components with suspended matter and their coagulation; and (3) coagulation of phytoplankton with oil droplets incorporated into aggregates. Marine snow formed in some, but not all, experiments with water from the subsurface plume of dissolved hydrocarbons, emphasizing the complexity of the conditions leading to the formation of marine snow in oil-contaminated seawater at depth

Oil-derived marine aggregates - hot spots of polysaccharide degradation by specialized bacterial communities

Aggregates generated in the laboratory from incubations of seawater and surface-water oil collected in the initial phase of the Deepwater Horizon oil spill resemble the oil-aggregates observed in situ. Here, we investigated the enzyme activities and microbial community composition of laboratory generated oil-aggregates, focusing on the abilities of these communities to degrade polysaccharides, which are major components of marine organic matter and are abundant constituents of exopolymeric substances (EPS) generated by oil-associated bacteria in response to the presence of oil. The patterns of polysaccharide-hydrolyzing enzyme activities in oil aggregates were very different from those in the water surrounding the aggregates after formation, and in the surface water that did not contain the oil. Specific oil aggregate-associated hydrolysis rates were also considerably higher than in the water surrounding the aggregates. The differences in initial hydrolysis profiles, and in evolution of these profiles with time, points to specialized metabolic abilities among the oil-aggregate communities compared to oil-water and ambient water communities. The composition of the oil-aggregate community indicates a multifunctional microbial assemblage containing primary oil-degrading and exopolysaccharide-producing members of the Gammaproteobacteria, and diverse members of the Alphaproteobacteria, Bacteroidetes and Planktomycetales that most likely participate in the breakdown of oil-derived bacterial biopolymers. Formation and aging of oil-aggregates encourages the growth and transformation of microbial communities that are specialized in degradation of petroleum, as well as their secondary degradation products

Editorial: Microbial exopolymers: Sources, chemico-physiological properties, and ecosystem effects in the marine environment

A large proportion of the total carbon in theWorld Ocean is in the formof dissolved organic matter (DOM), which is comparable in mass to the carbon in atmospheric CO2 (Hansell and Carlson, 1998). A major source of this material derives from the synthesis and release of exopolymers, or extracellular polymeric substances (EPS), mainly by bacteria and eukaryotic phytoplankton (Verdugo, 1994; Aluwihare et al., 1997). An initial understanding on the secretion of EPS by microorganisms, and their potential stabilizing effects for microbial cells, emerged during the last century with the first report by ZoBell and Allen (1935). We now know that most bacteria, and other microorganisms, occur associated with biofilms, either attached to surfaces or as suspended-aggregates in the water column. Exopolymer secretions thus serve important functions in marine environments, where they may be involved in microbial adhesion to solid surfaces and biofilm formation (Thavasi and Banat, 2014). They have also been shown to be involved in emulsification of hydrocarbon oils to enhance biodegradation (Gutierrez et al., 2013), mediating the fate and mobility of heavymetals and tracemetal nutrients (Bhaskar and Bhosle, 2005; Gutierrez et al., 2008, 2012), or interacting with dissolved and/or particulate organic matter (Long and Azam, 2001). This wide spectrum of functional activity is reflected not merely in the complex chemistry of these biopolymers, but also in the diversity of bacterial and phytoplankton genera found producing them