3. Results and discussion
3.1. Microbial enzyme activities
Extensive HO-3867 of microbial exopolymeric substances (EPS) were observed in the field, as microbial aggregates developed ubiquitously in the oil-contaminated surface waters in early May 2010 (Passow et al., 2012), and in the laboratory in roller table bottle incubations using fresh oil slick samples and Gulf of Mexico surface water (Ziervogel et al., 2012). This aggregation of organisms and organic material changed with time, as demonstrated by measurements of cellular activity, cell numbers, and dissolved organic matter concentrations and characteristics (Ziervogel et al., 2012). The current experiments using these laboratory-generated oil aggregates demonstrate that they showed distinctive patterns as well as rates of microbial enzyme activities that differed substantially from those of the oil-amended water (the roller table water from which the aggregates were isolated), and the ambient sea surface water without any oil contamination that had been incubated in parallel roller table experiments.
At the initial timepoint of our hydrolysis time series experiment (day 1), aggregate-associated activities were dominated by a different spectrum of enzymes than for oil-water or ambient-water, and were also considerably more rapid overall (Fig. 1). In the aggregate sample, laminarin and pullulan hydrolysis rates were very high; xylan and chondroitin hydrolysis rates were an order of magnitude lower, and arabinogalactan hydrolysis was barely detectable. In the oil water from which the aggregates had been removed, in contrast, hydrolysis of all six polysaccharides was detected, but at much lower rates than in aggregates. Laminarin and xylan hydrolysis rates were highest, fucoidan and pullulan were hydrolyzed half to two-thirds as rapidly, and chondroitin and arabinogalactan hydrolysis rates were a factor of 10 lower than for laminarin and xylan. Hydrolysis rates in the ambient water were lower than in the oil water; xylan and fucoidan were hydrolyzed most rapidly, followed by chondroitin, and only arabinogalactan hydrolysis was not detectable at the first timepoint in ambient water.
Fig. 1. Hydrolysis rates of six polysaccharides in (a) oil aggregates; (b) oil water (the water![image]()
from which the aggregates had been removed; see text for details); (c) ambient water (water incubated on the roller table for the same time period as for the oil-water bottles; see text for details). Error bars show the range of duplicate incubations. Substrates: pull=pullulan, lam=laminarin, xyl=xylan, fu=fucoidan, ara=arabinogalactan, chon=chondroitin sulfate. Note scale difference between oil aggregates, and oil water and ambient water.Figure optionsDownload full-size imageDownload as PowerPoint slide
The differences in initial patterns of enzyme activities among the oil-aggregates, oil-water, and ambient water can be visualized by normalizing each hydrolysis rate to the highest rate measured in a specific incubation after 1 day of incubation (Fig. 2). Among the enzyme activities tested, the oil aggregates showed a pattern with extreme ranges (two substrates with comparatively high rates, three with comparatively low rates), the ambient water showed a pattern of more even rates (five substrates hydrolyzed, rates differed by ca. a factor of 4), and oil water showed an intermediate pattern (two substrates with comparatively high rates, two with intermediate rates, two with comparatively low rates).
Fig. 2. Normalied hydrolysis rates of six polysaccharides after 1 day incubation in oil aggregates, oil water, and ambient water. For each incubation type, rates were normalized to the highest rate measured in that incubation (e.g., normalized to laminarin hydrolysis in oil aggregates and in oil water, and to xylan hydrolysis in ambient water; see Fig. 1). Substrate abbreviations as in Fig. 1.Figure optionsDownload full-size imageDownload as PowerPoint slide
Patterns of enzymatic activities, evolution of these patterns (see below), and hydrolysis rates differed between the oil aggregates, oil water, and ambient water (Fig. 1 and Fig. 2). Differences in cell numbers are not likely sufficient to account for dif
3.1. Microbial enzyme activities
Extensive HO-3867 of microbial exopolymeric substances (EPS) were observed in the field, as microbial aggregates developed ubiquitously in the oil-contaminated surface waters in early May 2010 (Passow et al., 2012), and in the laboratory in roller table bottle incubations using fresh oil slick samples and Gulf of Mexico surface water (Ziervogel et al., 2012). This aggregation of organisms and organic material changed with time, as demonstrated by measurements of cellular activity, cell numbers, and dissolved organic matter concentrations and characteristics (Ziervogel et al., 2012). The current experiments using these laboratory-generated oil aggregates demonstrate that they showed distinctive patterns as well as rates of microbial enzyme activities that differed substantially from those of the oil-amended water (the roller table water from which the aggregates were isolated), and the ambient sea surface water without any oil contamination that had been incubated in parallel roller table experiments.
At the initial timepoint of our hydrolysis time series experiment (day 1), aggregate-associated activities were dominated by a different spectrum of enzymes than for oil-water or ambient-water, and were also considerably more rapid overall (Fig. 1). In the aggregate sample, laminarin and pullulan hydrolysis rates were very high; xylan and chondroitin hydrolysis rates were an order of magnitude lower, and arabinogalactan hydrolysis was barely detectable. In the oil water from which the aggregates had been removed, in contrast, hydrolysis of all six polysaccharides was detected, but at much lower rates than in aggregates. Laminarin and xylan hydrolysis rates were highest, fucoidan and pullulan were hydrolyzed half to two-thirds as rapidly, and chondroitin and arabinogalactan hydrolysis rates were a factor of 10 lower than for laminarin and xylan. Hydrolysis rates in the ambient water were lower than in the oil water; xylan and fucoidan were hydrolyzed most rapidly, followed by chondroitin, and only arabinogalactan hydrolysis was not detectable at the first timepoint in ambient water.
Fig. 1. Hydrolysis rates of six polysaccharides in (a) oil aggregates; (b) oil water (the water
from which the aggregates had been removed; see text for details); (c) ambient water (water incubated on the roller table for the same time period as for the oil-water bottles; see text for details). Error bars show the range of duplicate incubations. Substrates: pull=pullulan, lam=laminarin, xyl=xylan, fu=fucoidan, ara=arabinogalactan, chon=chondroitin sulfate. Note scale difference between oil aggregates, and oil water and ambient water.Figure optionsDownload full-size imageDownload as PowerPoint slideThe differences in initial patterns of enzyme activities among the oil-aggregates, oil-water, and ambient water can be visualized by normalizing each hydrolysis rate to the highest rate measured in a specific incubation after 1 day of incubation (Fig. 2). Among the enzyme activities tested, the oil aggregates showed a pattern with extreme ranges (two substrates with comparatively high rates, three with comparatively low rates), the ambient water showed a pattern of more even rates (five substrates hydrolyzed, rates differed by ca. a factor of 4), and oil water showed an intermediate pattern (two substrates with comparatively high rates, two with intermediate rates, two with comparatively low rates).
Fig. 2. Normalied hydrolysis rates of six polysaccharides after 1 day incubation in oil aggregates, oil water, and ambient water. For each incubation type, rates were normalized to the highest rate measured in that incubation (e.g., normalized to laminarin hydrolysis in oil aggregates and in oil water, and to xylan hydrolysis in ambient water; see Fig. 1). Substrate abbreviations as in Fig. 1.Figure optionsDownload full-size imageDownload as PowerPoint slide
Patterns of enzymatic activities, evolution of these patterns (see below), and hydrolysis rates differed between the oil aggregates, oil water, and ambient water (Fig. 1 and Fig. 2). Differences in cell numbers are not likely sufficient to account for dif