Core metabolism plasticity in phytoplankton: Response of Dunaliella tertiolecta to oil exposure

Human alterations to the marine environment such as an oil spill can induce oxidative stress in phytoplankton. Exposure to oil has been shown to be lethal to most phytoplankton species, but some are able to survive and grow at unaffected or reduced growth rates, which appears to be independent of the class and phylum of the phytoplankton and their ability to consume components of oil heterotrophically. The goal of this article is to test the role of core metabolism plasticity in the oil-resisting ability of phytoplankton. Experiments were performed on the oil- resistant chlorophyte, Dunaliella tertiolecta, in control and water accommodated fractions of oil, with and without metabolic inhibitors targeting the core metabolic pathways. We observed that inhibiting pathways such as photosynthetic electron transport (PET) and pentose-phosphate pathway were lethal; however, inhibition of pathways such as mitochondrial electron transport and cyclic electron transport caused growth to be arrested. Pathways such as photorespiration and Kreb's cycle appear to play a critical role in the oil-tolerating ability of D. tertiolecta. Analysis of photo-physiology revealed reduced PET under inhibition of photorespiration but not Kreb's cycle. Further studies showed enhanced flux through Kreb's cycle suggesting increased energy production and photorespiration counteract oxidative stress. Lastly, reduced extracellular carbohydrate secretion under oil exposure indicated carbon and energy conservation, which together with enhanced flux through Kreb's cycle played a major role in the survival of D. tertiolecta under oil exposure by meeting the additional energy demands. Overall, we present data that suggest the role of phenotypic plasticity of multiple core metabolic pathways in accounting for the oxidative stress tolerating ability of certain phytoplankton species.

Influence of nutrient status on the response of the diatom Phaeodactylum tricornutum to oil and dispersant

Phytoplankton play a central role in our ecosystems, they are responsible for nearly 50 percent of the global primary productivity and major drivers of macro-elemental cycles in the ocean. Phytoplankton are constantly subjected to stressors, some natural such as nutrient limitation and some manmade such as oil spills. With increasing oil exploration activities in coastal zones in the Gulf of Mexico and elsewhere, an oil spill during nutrient-limited conditions for phytoplankton growth is highly likely. We performed a multifactorial study exposing the diatom Phaeodactylum tricornutum (UTEX 646) to oil and/or dispersants under nitrogen and silica limitation as well as co-limitation of both nutrients. Our study found that treatments with nitrogen limitation (-N and–N-Si) showed overall lower growth and chlorophyll a, lower photosynthetic antennae size, lower maximum photosynthetic efficiency, lower protein in exopolymeric substance (EPS), but higher connectivity between photosystems compared to non-nitrogen limited treatments (-Si and +N+Si) in almost all the conditions with oil and/or dispersants. However, certain combinations of nutrient limitation and oil and/or dispersant differed from this trend indicating strong interactive effects. When analyzed for significant interactive effects, the–N treatment impact on cellular growth in oil and oil plus dispersant conditions; and oil and oil plus dispersant conditions on cellular growth in–N-Si and–N treatments were found to be significant. Overall, we demonstrate that nitrogen limitation can affect the oil resistant trait of P. tricornutum, and oil with and without dispersants can have interactive effects with nutrient limitation on this diatom.

Molecular mechanism of oil induced growth inhibition in diatoms using Thalassiosira pseudonana as the model species

The 2010 Deepwater Horizon oil-spill exposed the microbes of Gulf of Mexico to unprecedented amount of oil. Conclusive evidence of the underlying molecular mechanism(s) on the negative effects of oil exposure on certain phytoplankton species such as Thalassiosira pseudonana is still lacking, curtailing our understanding of how oil spills alter community composition. We performed experiments on model diatom T. pseudonana to understand the mechanisms underpinning observed reduced growth and photosynthesis rates during oil exposure. Results show severe impairment to processes upstream of photosynthesis, such as light absorption, with proteins associated with the light harvesting complex damaged while the pigments were unaffected. Proteins associated with photosynthetic electron transport were also damaged, severely affecting photosynthetic apparatus and depriving cells of energy and carbon for growth. Negative growth effects were alleviated when an organic carbon source was provided. Further investigation through proteomics combined with pathway enrichment analysis confirmed the above findings, while highlighting other negatively affected processes such as those associated with ferroxidase complex, high-affinity iron-permease complex, and multiple transmembrane transport. We also show that oxidative stress is not the primary route of negative effects, rather secondary. Overall, this study provides a mechanistic understanding of the cellular damage that occurs during oil exposure to T. pseudonana.

An integrated in vivo and in silico analysis of the metabolism disrupting effects of CPI-613 on embryo-larval zebrafish (Danio rerio)

CPI-613 is a mitochondrial metabolism disrupter that inhibits tricarboxylic acid (TCA) cycle activity. The consequences of TCA cycle disruption on various metabolic pathways and overall organismal physiology are not fully known. The present study integrates in vivo experimental data with an in silico stoichiometric metabolism model of zebrafish to study the metabolic pathways perturbed under CPI-613 exposure. Embryo-larval life stages of zebrafish (Danio rerio) were exposed to 1 μM CPI-613 for 20 days. Whole-organism respirometry measurements showed an initial suppression of O₂ consumption at Day 5 of exposure, followed by recovery comparable to the solvent control (0.01% DMSO) by Day 20. Comparison of whole-transcriptome RNA-sequencing at Day 5 vs. 20 of exposure showed functional categories related to O₂ binding and transport, antioxidant activity, FAD binding, and hemoglobin complexes, to be commonly represented. Metabolic enzyme gene expression changes and O₂ consumption rate was used to parametrize two in silico stoichiometric metabolic models representative of Day 5 or 20 of exposure. Computational simulations predicted impaired ATP synthesis, α-ketoglutarate dehydrogenase (KGDH) activity, and fatty acid β-oxidation at Day 5 vs. 20 of exposure. These results show that the targeted disruption of KGDH may also impact oxidative phosphorylation (ATP synthesis) and fatty acid metabolism (β-oxidation), in turn influencing cellular bioenergetics and the observed reduction in whole-organism O₂ consumption rate. The results of this study provide an integrated in vivo and in silico framework to study the impacts of metabolic disruption on organismal physiology.

The Interplay of Phototrophic and Heterotrophic Microbes Under Oil Exposure: A Microcosm Study

Microbial interactions influence nearly one-half of the global biogeochemical flux of major elements of the marine ecosystem. Despite their ecological importance, microbial interactions remain poorly understood and even less is known regarding the effects of anthropogenic perturbations on these microbial interactions. The Deepwater Horizon oil spill exposed the Gulf of Mexico to ∼4.9 million barrels of crude oil over 87 days. We determined the effects of oil exposure on microbial interactions using short- and long-term microcosm experiments with and without Macondo surrogate oil. Microbial activity determined using radiotracers revealed that oil exposure negatively affected substrate uptake by prokaryotes within 8 h and by eukaryotes over 72 h. Eukaryotic uptake of heterotrophic exopolymeric substances (EPS) was more severely affected than prokaryotic uptake of phototrophic EPS. In addition, our long-term exposure study showed severe effects on photosynthetic activity. Lastly, changes in microbial relative abundances and fewer co-occurrences among microbial species were mostly driven by photosynthetic activity, treatment (control vs. oil), and prokaryotic heterotrophic metabolism. Overall, oil exposure affected microbial co-occurrence and/or interactions possibly by direct reduction in abundance of one of the interacting community members and/or indirect by reduction in metabolism (substrate uptake or photosynthesis) of interacting members.

Marine phytoplankton responses to oil and dispersant exposures: Knowledge gained since the Deepwater Horizon oil spill

The Deepwater Horizon oil spill of 2010 brought the ecology and health of the Gulf of Mexico to the forefront of the public's and scientific community's attention. Not only did we need a better understanding of how this oil spill impacted the Gulf of Mexico ecosystem, but we also needed to apply this knowledge to help assess impacts from perturbations in the region and guide future response actions. Phytoplankton represent the base of the food web in oceanic systems. As such, alterations of the phytoplankton community propagate to upper trophic levels. This review brings together new insights into the influence of oil and dispersant on phytoplankton. We bring together laboratory, mesocosm and field experiments, including insights into novel observations of harmful algal bloom (HAB) forming species and zooplankton as well as bacteria-phytoplankton interactions. We finish by addressing knowledge gaps and highlighting key topics for research in novel areas.

Polycyclic aromatic hydrocarbons (PAHs) and putative PAH-degrading bacteria in Galveston Bay, TX (USA), following Hurricane Harvey (2017)

Hurricane Harvey was the wettest hurricane in US history bringing record rainfall and widespread flooding in Houston, TX. The resulting storm- and floodwaters largely emptied into the Galveston Bay. Surface water was collected from 10 stations during five cruises to investigate the concentrations and sources of 16 priority polycyclic aromatic hydrocarbons (PAHs), and relative abundances of PAH-degrading bacteria. Highest PAH levels (102-167 ng/L) were detected during the first sampling event, decreasing to 36-69 ng/L within a week. Four sites had elevated concentrations of carcinogenic benzo[a]pyrene that exceeded the Texas Standard for Surface Water threshold. The highest relative abundances of known PAH-degrading bacteria Burkholderiaceae, Comamonadaceae, and Sphingomonadales were detected during the first and second sampling events. PAH origins were about 60% pyrogenic, 2% petrogenic, and the remainder of mixed sources. This study improves our understanding on the fate, source, and distributions of PAHs in Galveston Bay after an extreme flooding event.

Diatom aggregation when exposed to crude oil and chemical dispersant: Potential impacts of ocean acidification

Diatoms play a key role in the marine carbon cycle with their high primary productivity and release of exudates such as extracellular polymeric substances (EPS) and transparent exopolymeric particles (TEP). These exudates contribute to aggregates (marine snow) that rapidly transport organic material to the seafloor, potentially capturing contaminants like petroleum components. Ocean acidification (OA) impacts marine organisms, especially those that utilize inorganic carbon for photosynthesis and EPS production. Here we investigated the response of the diatom Thalassiosira pseudonana grown to present day and future ocean conditions in the presence of a water accommodated fraction (WAF and OAWAF) of oil and a diluted chemically enhanced WAF (DCEWAF and OADCEWAF). T. pseudonana responded to WAF/DCEWAF but not OA and no multiplicative effect of the two factors (i.e., OA and oil/dispersant) was observed. T. pseudonana released more colloidal EPS (< 0.7 μm to > 3 kDa) in the presence of WAF/DCEWAF/OAWAF/OADCEWAF than in the corresponding Controls. Colloidal EPS and particulate EPS in the oil/dispersant treatments have higher protein-to-carbohydrate ratios than those in the control treatments, and thus are likely stickier and have a greater potential to form aggregates of marine oil snow. More TEP was produced in response to WAF than in Controls; OA did not influence its production. Polyaromatic hydrocarbon (PAH) concentrations and distributions were significantly impacted by the presence of dispersants but not OA. PAHs especially Phenanthrenes, Anthracenes, Chrysenes, Fluorenes, Fluoranthenes, Pyrenes, Dibenzothiophenes and 1-Methylphenanthrene show major variations in the aggregate and surrounding seawater fraction of oil and oil plus dispersant treatments. Studies like this add to the current knowledge of the combined effects of aggregation, marine snow formation, and the potential impacts of oil spills under ocean acidification scenarios.

Exoenzymes as a Signature of Microbial Response to Marine Environmental Conditions

Microbial heterotopic metabolism in the ocean is fueled by a supply of essential nutrients acquired via exoenzymes catalyzing depolymerization of high-molecular-weight compounds. Although the rates of activity for a variety of exoenzymes across various marine environments are well established, the factors regulating the production of these exoenzymes, and to some extent their correlation with microbial community composition, are less known. This study focuses on addressing these challenges using a mesocosm experiment that compared a natural seawater microbial community (control) and exposed (to oil) treatment. Exoenzyme activities for β-glucosidase, leucine aminopeptidase (LAP), and lipase were significantly correlated with dissolved nutrient concentrations. We measured correlations between carbon- and nitrogen-acquiring enzymes (β-glucosidase/lipase versus LAP) and found that the correlation of carbon-acquiring enzymes varies with the chemical nature of the available primary carbon source. Notably, a strong correlation between particulate organic carbon and β-glucosidase activity demonstrates their polysaccharide depolymerization in providing the carbon for microbial growth. Last, we show that exoenzyme activity patterns are not necessarily correlated with prokaryotic community composition, suggesting a redundancy of exoenzyme functions among the marine microbial community and substrate availability. This study provides foundational work for linking exoenzyme function with dissolved organic substrate and downstream processes in marine systems.IMPORTANCE Microbes release exoenzymes into the environment to break down complex organic matter and nutrients into simpler forms that can be assimilated and utilized, thereby addressing their cellular carbon, nitrogen, and phosphorus requirements. Despite its importance, the factors associated with the synthesis of exoenzymes are not clearly defined, especially for the marine environment. Here, we found that exoenzymes associated with nitrogen and phosphorus acquisition were strongly correlated with inorganic nutrient levels, while those associated with carbon acquisition depended on the type of organic carbon available. We also show a linear relationship between carbon- and nitrogen-acquiring exoenzymes and a strong correlation between microbial biomass and exoenzymes, highlighting their significance to microbial productivity. Last, we show that changes in microbial community composition are not strongly associated with changes in exoenzyme activity profiles, a finding which reveals a redundancy of exoenzyme activity functions among microbial community. These findings advance our understanding of previously unknown factors associated with exoenzyme production in the marine environment.

Trait-dependent variability of the response of marine phytoplankton to oil and dispersant exposure

The Deepwater Horizon oil spill released millions of barrels of crude oil into the Gulf of Mexico, and saw widespread use of the chemical dispersant Corexit. We assessed the role of traits, such as cell size, cell wall, motility, and mixotrophy on the growth and photosynthetic response of 15 phytoplankton taxa to oil and Corexit. We collected growth and photosynthetic data on five algal cultures. These responses could be separated into resistant (Tetraselmis astigmatica, Ochromonas sp., Heterocapsa pygmaea) and sensitive (Micromonas pusilla, Prorocentrum minimum). We combined this data with 10 species previously studied and found that cell size is most important in determining the biomass response to oil, whereas motility/mixotrophy is more important in the dispersed oil. Our analysis accounted for a third of the variance observed, so further work is needed to identify other factors that contribute to oil resistance.

Biological response to dissolved versus dispersed oil

The water-soluble compounds of oil (e.g. low molecular weight PAHs) dissolve as a function of their physicochemical properties and environmental conditions, while the non-soluble compounds exist as dispersed droplets. Both the chemical and physical form of oil will affect the biological response. We present data from a mesocosm study comparing the microbial response to the water-soluble fraction (WSF), versus a water-accommodated fraction of oil (WAF), which contains both dispersed and dissolved oil components. WAF and WSF contained similar concentrations of low molecular weight PAHs, but concentrations of 4- and 5-ring PAHs were higher in WAF compared to WSF. Microbial communities were significantly different between WSF and WAF treatments, primary productivity was reduced more in WSF than in WAF, and concentrations of transparent exopolymeric particles were highest in WSF and lowest in the controls. These differences highlight the importance of dosing strategy for mesocosm and toxicity tests.

Role of Polysaccharides in Diatom Thalassiosira pseudonana and its Associated Bacteria in Hydrocarbon Presence

Diatoms secrete a significant amount of polysaccharides, which can serve as a critical organic carbon source for bacteria. The 2010 Deepwater Horizon oil spill exposed the Gulf of Mexico to substantial amounts of oil that also impacted the phytoplankton community. Increased production of exopolymeric substances was observed after this oil spill. Polysaccharides make up a major fraction of exopolymeric substances; however, their physiological role during an oil spill remains poorly understood. Here, we analyzed the role of polysaccharides in the growth and physiology of the oil-sensitive diatom Thalassiosira pseudonana and how they shape the surrounding bacterial community and its activity in the presence of oil. We found that inhibition of chrysolaminarin synthesis had a negative effect on the growth of T pseudonana and intracellular monosaccharide accumulation, which in turn suppressed photosynthesis by feedback inhibition. In addition, by acting as a carbon reserve, chrysolaminarin helped in the recovery of T pseudonana in the presence of oil. Inhibition of chrysolaminarin synthesis also influenced the bacterial community in the free-living fraction but not in the phycosphere. Exposure to oil alone led to increased abundance of oil-degrading bacterial genera and the activity of exoenzyme lipase. Our data show that chrysolaminarin synthesis plays an important role in the growth and survival of T pseudonana in the presence of oil, and its inhibition can influence the composition and activity of the surrounding bacterial community.

Growth dynamics and domoic acid production of Pseudo-nitzschia sp. in response to oil and dispersant exposure

The diatom genus Pseudo-nitzschia is a common component of phytoplankton communities in the Gulf of Mexico and is potentially toxic as some species produce the potent neurotoxin domoic acid. The impact of oil and chemical dispersants on Pseudo-nitzschia spp. and domoic acid production have not yet been studied; preliminary findings from a mesocosm experiment suggest this genus may be particularly resilient. A toxicological study was conducted using a colony of Pseudo-nitzschia sp. isolated from a station off the coast of Louisiana in the Gulf of Mexico. The cultures were exposed to a water accommodated fraction (WAF) of oil and a diluted chemically enhanced WAF (DCEWAF) which was a mix of oil and dispersant (20:1). Exposure to WAF induced a lag phase but did not inhibit growth rates once in exponential growth. Cultures grown in DCEWAF did not experience a lag phase but had significantly lower growth rates than the Control and WAF cultures. The cellular quota of domoic acid was higher in cultures treated with DCEWAF and WAF relative to their control values, and half of the domoic acid had leaked out of the cells into the surrounding seawater in the DCEWAF cultures while all the domoic acid remained inside the cells in WAF-treated cultures. These results suggest that the presence of oil could lead to toxic blooms, but that the application of dispersant could decrease bioaccumulation of domoic acid through the food web.

Response of natural phytoplankton communities exposed to crude oil and chemical dispersants during a mesocosm experiment

During the 2010 Deepwater Horizon oil spill, the chemical dispersant Corexit was applied over vast areas of the Gulf of Mexico. Marine phytoplankton play a key role in aggregate formation through the production of extracellular polymeric materials (EPS), an important step in the biological carbon pump. This study examined the impacts of oil and dispersants on the composition and physiology of natural marine phytoplankton communities from the Gulf of Mexico during a 72-hour mesocosm experiment and consequences to carbon export. The communities were treated using the water accommodated fraction (WAF) of oil, which was produced by adding Macondo surrogate oil to natural seawater and mixed for 24 h in the dark. A chemically enhanced WAF (CEWAF) was made in a similar manner, but using a mixture of oil and the dispersant Corexit in a 20:1 ratio as well as a diluted CEWAF (DCEWAF). Phytoplankton communities exposed to WAF showed no significant changes in PSII quantum yield (F_v/F_m) or electron transfer rates (ETR_max) compared to Control communities. In contrast, both F_v/F_m and ETR_max declined rapidly in communities treated with either CEWAF or DCEWAF. Analysis of other photophysiological parameters showed that photosystem II (PSII) antenna size and PSII connectivity factor were not altered by exposure to DCEWAF, suggesting that processes downstream of PSII were affected. The eukaryote community composition in each experimental tank was characterized at the end of the 72 h exposure time using 18S rRNA sequencing. Diatoms dominated the communities in both the control and WAF treatments (52 and 56% relative abundance respectively), while in CEWAF and DCEWAF treatments were dominated by heterotrophic Euglenozoa (51 and 84% respectively). Diatoms made up the largest relative contribution to the autotrophic eukaryote community in all treatments. EPS concentration was four times higher in CEWAF tanks compared to other treatments. Changes in particle size distributions (a proxy for aggregates) over time indicated that a higher degree of particle aggregation occurred in both the CEWAF and DCEWAF treatments than the WAF or Controls. Our results demonstrate that chemically dispersed oil has more negative impacts on photophysiology, phytoplankton community structure and aggregation dynamics than oil alone, with potential implications for export processes that affect the distribution and turnover of carbon and oil in the water column.

Extracellular polymeric substances (EPS) producing and oil degrading bacteria isolated from the northern Gulf of Mexico

Sinking marine oil snow was found to be a major mechanism in the transport of spilled oil from the surface to the deep sea following the Deepwater Horizon (DwH) oil spill. Marine snow formation is primarily facilitated by extracellular polymeric substances (EPS), which are mainly composed of proteins and carbohydrates secreted by microorganisms. While numerous bacteria have been identified to degrade oil, there is a paucity of knowledge on bacteria that produce EPS in response to oil and Corexit exposure in the northern Gulf of Mexico (nGoM). In this study, we isolated bacteria from surface water of the nGoM that grow on oil or Corexit dispersant. Among the 100 strains isolated, nine were identified to produce remarkable amounts of EPS. 16S rRNA gene analysis revealed that six isolates (strains C1, C5, W10, W11, W14, W20) belong to the genus Alteromonas; the others were related to Thalassospira (C8), Aestuariibacter (C12), and Escherichia (W13a). The isolates preferably degraded alkanes (17–77%), over polycyclic aromatic hydrocarbons (0.90–23%). The EPS production was determined in the presence of a water accommodated fraction (WAF) of oil, a chemical enhanced WAF (CEWAF), Corexit, and control. The highest production of visible aggregates was found in Corexit followed by CEWAF, WAF, and control; indicating that Corexit generally enhanced EPS production. The addition of WAF and Corexit did not affect the carbohydrate content, but significantly increased the protein content of the EPS. On the average, WAF and CEWAF treatments had nine to ten times more proteins, and Corexit had five times higher than the control. Our results reveal that Alteromonas and Thalassospira, among the commonly reported bacteria following the DwH spill, produce protein rich EPS that could have crucial roles in oil degradation and marine snow formation. This study highlights the link between EPS production and bacterial oil-degrading capacity that should not be overlooked during spilled oil clearance.

Physiological response of 10 phytoplankton species exposed to macondo oil and the dispersant, Corexit

Culture experiments were conducted on ten phytoplankton species to examine their biological and physiological responses during exposure to oil and a combination of oil and dispersant. The species tested included a range of taxa typically found in the Gulf of Mexico such as cyanobacteria, chlorophytes, and diatoms. Cultures were exposed to Macondo surrogate oil using the water accommodated fraction (WAF), and dispersed oil using a chemically enhanced WAF (CEWAF) and diluted CEWAF, to replicate conditions following the Deepwater Horizon spill in the Gulf of Mexico. A range of responses were observed, that could broadly class the algae as either "robust" or "sensitive" to oil and/or dispersant exposure. Robust algae were identified as Synechococcus elongatus, Dunaliella tertiolecta, two pennate diatoms Phaeodactylum tricornutum and Navicula sp., and Skeletonema grethae CCMP775, and were largely unaffected by any of the treatments (no changes to growth rate or time spent in lag phase relative to controls). The rest of the phytoplankton, all centric diatoms, exhibited at least some combination of reduced growth rates or increased lag time in response to oil and/or dispersant exposure. Photophysiology did not have a strong treatment effect, with significant inhibition of photosynthetic efficiency (F_v /F_m ) only observed in the CEWAF, if at all. We found that the effects of oil and dispersants on phytoplankton physiology were species-dependent, and not always detrimental. This has significant implications on how oil spills might impact phytoplankton community structure and bloom dynamics in the Gulf of Mexico, which in turn impacts higher trophic levels.

Diagnostic tool to ascertain marine phytoplankton exposure to chemically enhanced water accommodated fraction of oil using Fourier Transform Infrared spectroscopy

Phytoplankton alter their macromolecule composition in response to changing environmental conditions. Often these changes are consistent and can be used as indicators to predict their exposure to a given condition. FTIR-spectroscopy is a powerful tool that provides rapid snapshot of microbial samples. We used FTIR to develop signature macromolecular composition profiles of three cultures: Skeletonema costatum, Emiliania huxleyi, and Navicula sp., exposed to chemically enhanced water accommodated oil fraction (CEWAF) in artificial seawater and control. Using a multivariate model created with a Partial Least Square Discriminant Analysis of the FTIR-spectra, classification of CEWAF exposed versus control samples was possible. This model was validated using aggregate samples from a mesocosm study. Analysis of spectra and PCA-loadings plot showed changes to carbohydrates and proteins in response to CEWAF. Overall we developed a robust multivariate model that can be used to identify if a phytoplankton sample has been exposed to oil with dispersant.

Extracellular Enzyme Activity Profile in a Chemically Enhanced Water Accommodated Fraction of Surrogate Oil: Toward Understanding Microbial Activities After the Deepwater Horizon Oil Spill

Extracellular enzymes and extracellular polymeric substances (EPS) play a key role in overall microbial activity, growth and survival in the ocean. EPS, being amphiphilic in nature, can act as biological surfactant in an oil spill situation. Extracellular enzymes help microbes to digest and utilize fractions of organic matter, including EPS, which can stimulate growth and enhance microbial activity. These natural processes might have been altered during the 2010 Deepwater Horizon oil spill due to the presence of hydrocarbon and dispersant. This study aims to investigate the role of bacterial extracellular enzymes during exposure to hydrocarbons and dispersant. Mesocosm studies were conducted using a water accommodated fraction of oil mixed with the chemical dispersant, Corexit (CEWAF) in seawater collected from two different locations in the Gulf of Mexico and corresponding controls (no additions). Activities of five extracellular enzymes typically found in the EPS secreted by the microbial community - α- and β-glucosidase, lipase, alkaline phosphatase, leucine amino-peptidase - were measured using fluorogenic substrates in three different layers of the mesocosm tanks (surface, water column and bottom). Enhanced EPS production and extracellular enzyme activities were observed in the CEWAF treatment compared to the Control. Higher bacterial and micro-aggregate counts were also observed in the CEWAF treatment compared to Controls. Bacterial genera in the order Alteromonadaceae were the most abundant bacterial 16S rRNA amplicons recovered. Genomes of Alteromonadaceae commonly have alkaline phosphatase and leucine aminopeptidase, therefore they may contribute significantly to the measured enzyme activities. Only Alteromonadaceae and Pseudomonadaceae among bacteria detected here have higher percentage of genes for lipase. Piscirickettsiaceae was abundant; genomes from this order commonly have genes for leucine aminopeptidase. Overall, this study provides insights into the alteration to the microbial processes such as EPS and extracellular enzyme production, and to the microbial community, when exposed to the mixture of oil and dispersant.

Metabolism in anoxic permeable sediments is dominated by eukaryotic dark fermentation

Permeable sediments are common across continental shelves and are critical contributors to marine biogeochemical cycling. Organic matter in permeable sediments is dominated by microalgae, which as eukaryotes have different anaerobic metabolic pathways to prokaryotes such as bacteria and archaea. Here we present analyses of flow-through reactor experiments showing that dissolved inorganic carbon is produced predominantly as a result of anaerobic eukaryotic metabolic activity. In our experiments, anaerobic production of dissolved inorganic carbon was consistently accompanied by large dissolved H2 production rates, suggesting the presence of fermentation. The production of both dissolved inorganic carbon and H2 persisted following administration of broad spectrum bactericidal antibiotics, but ceased following treatment with metronidazole. Metronidazole inhibits the ferredoxin/hydrogenase pathway of fermentative eukaryotic H2 production, suggesting that pathway as the source of H2 and dissolved inorganic carbon production. Metabolomic analysis showed large increases in lipid production at the onset of anoxia, consistent with documented pathways of anoxic dark fermentation in microalgae. Cell counts revealed a predominance of microalgae in the sediments. H2 production was observed in dark anoxic cultures of diatoms (Fragilariopsis sp.) and a chlorophyte (Pyramimonas) isolated from the study site, substantiating the hypothesis that microalgae undertake fermentation. We conclude that microalgal dark fermentation could be an important energy-conserving pathway in permeable sediments.

A cohort study to identify simple clinical tests for chronic respiratory failure in obese patients with sleep-disordered breathing

BACKGROUND

Chronic respiratory failure complicating sleep-disordered breathing in obese patients has important adverse clinical implications in terms of morbidity, mortality and healthcare utilisation. Screening strategies are essential to identify obese patients with chronic respiratory failure.

METHOD

Prospective data were collected from patients with obesity-related sleep-disordered breathing admitted for respiratory assessment at a UK national sleep and ventilation centre. Hypercapnia was defined as an arterial partial pressure of carbon dioxide of >6kPa.

RESULTS

245 obese patients (56±13 years) with a body mass index of 48±12 kg/m(2), forced vital capacity (FVC) of 2.1±1.1 L, daytime oximetry (SpO2) of 91±6% and abnormal overnight oximetry were included in the analysis. Receiver operator curve analysis for the whole group showed that an FVC ≤3 L had a sensitivity of 90% and a specificity of 41% in predicting hypercapnia, and an SpO2 ≤95% had a sensitivity of 83% and a specificity of 63% in predicting hypercapnia. Gender differences were observed and receiver operator curve analysis demonstrated 'cut-offs' for (1) SpO2 of ≤95% for men and ≤93% for women and (2) FVC of ≤3.5 L for men and ≤2.3 L for women, in predicting hypercapnia.

CONCLUSIONS

The measurement of FVC and clinic SpO2 in obese patients with abnormal overnight limited respiratory studies predicted hypercapnia. This may have clinical utility in stratifying patients attending sleep clinics.

Antibody prevalence of Orientia tsutsugamushi, Rickettsia typhi and TT118 spotted fever group rickettsiae among Malaysian blood donors and febrile patients in the urban areas

The seroprevalence of Orientia tsutsugamushi (OT), Rickettsia typhi (RT) and TT118 spotted fever group rickettsiae (SFGR) among blood donors and febrile Malaysian patients in the urban areas was determined. Of the 240 blood donors, 5.4%, 9.2% and 1.7% had either present or previous exposure to OT, RT and SFG rickettsiae, respectively. Patients admitted to an urban hospital had high seroprevalences of OT (43.5%) and RT (22.9%), as compared to SFGR (11.6%). Antibody levels suggestive of recent infections of scrub typhus, murine typhus and tick typhus were detected in 16.8%, 12.7% and 8.2% of patients respectively. No significant difference was noted in the distribution of rickettsial antibodies among urban patients from 2 geographical locations. However, the serologic patterns of rickettsial infection in the urban areas were different form those of rural areas.

Borrelia burgdorferi (strain B. afzelii) antibodies among Malaysian blood donors and patients

In this study, the presence of IgG and IgM antibodies against Borrelia burgdorferi (strain B. afzelii) among Malaysian blood donors and patients admitted to hospital with various infectious diseases was determined. Sera were screened using enzyme-linked immunosorbent assay (ELISA); positive sera were then subjected to Western blot testing. All but one of the blood donors were negative for borrelial antibodies. Of 121 patients' sera, IgM antibodies were detected in 24 (19.8%) and IgG antibodies were detected in 5 (4.1%) sera. Only one of two patients with skin manifestations suggestive of Lyme disease had IgM antibody against B. afzelii. Of 30 patients with exposure to tick typhus, 4 (13.3%) were IgM positive and 1 (3.3%) was IgG positive. Based on the detection of antigenic bands by Western blot, 6 patients' sera showed positive reactions. Antigenic bands of p39, p41 and p59/62 kDa were the commonest findings of Western blotting. This study provides serological evidence of B. afzelii infections in Malaysia; further investigation is needed to correlate serological and clinical findings.

Seroepidemiologic survey of Orientia tsutsugamushi, Rickettsia typhi, and TT118 spotted fever group rickettsiae in rubber estate workers in Malaysia

The seroprevalence of Orientia tsutsugamushi, Rickettsia typhi, and TT118 spotted fever group (SFG) rickettsiae in 300 rubber estate workers in Slim River, Malaysia was determined in December 1996 and March 1997. In December, which was the wet season, 23.3%, 3.0%, and 57.3% of the population had antibodies detected against the three rickettsiae, respectively. The highest seropositive rate of 40% was detected for single infection with SFG rickettsiae, followed by a rate of 15.3% for both O. tsutsugamushi and SFG rickettsiae among the rubber estate workers. Subjects less than 21 years old had a lower seroprevalence of SFG rickettsiae compared with the other age groups. Indians had a higher seroprevalence of O. tsutsugamushi compared with other ethnic groups. Rubber tappers had a higher seroprevalence of SFG rickettsiae compared with other occupational groups. During the dry season in March 1997, there was a significant increase in the seroprevalence of R. typhi. The seroconversion rates for IgM against O. tsutsugamushi, R. typhi, and SFG rickettsiae were 5.7%, 12.3%, and 15.1%, respectively, during the four-month period. Significant variations of antibody titers towards the three rickettsiae was noted among subjects who were bled twice. This suggests a significant and continual exposure of rubber estate workers to the three rickettsiae.