Consequences of Thymidine Catabolism for Estimates of Bacterial Production: An Example from a Coastal Marine Sediment

Radioactively labeled thymidine (TdR) has been used extensively to measure bacterial production in aquatic environments, but critical assumptions of the TdR technique often have gone untested. In this study of a coastal marine sediment, the metabolic fate of methyl [3H]TdR and methyl [14C]TdR was at variance with the assumptions necessary for determining bacterial production. Only 2% of incorporated radioactivity was recovered in the DNA fraction of TCA-insoluble material following time-course incubations of l-300 min. At least the methyl group of TdR was extensively catabolized, as shown by copious production of 14C02. The temporal patterns of 3H : 14C ratios in macromolecular fractions indicated that products of catabolism were recycled into the DNA fraction. The accuracy of the TdR technique depends in large part on the degree to which such catabolism occurs

Response of sedimentary bacteria in a Louisiana salt marsh to contamination by diesel fuel

In a 28 d microcosm study, we examined the effects of diesel-contaminated sediment on the sedimentary bacterial community of a Louisiana (USA) salt marsh that has been chronically exposed to petroleum hydrocarbons for decades. Diesel contaminants in microcosms as determined from polycyclic aromatic hydrocarbon (PAH) concentration ranged from 0.55 to 55 ppm (dry weight). Bacterial metabolism (incorporation of 14C-acetate and 3H-leucine) and bacterial abundance were not affected by diesel-contaminated sediment at any concentration. Bacterial degradation of 14C-phenanthrene, however, increased in direct proportion to the amount of diesel- contaminated sediment added. Ambient sediment also exhibited significant capacity to degrade PAH. The half life of phenanthrene (based on 14C-phenanthrene-degradation experiments) ranged from 137 d in ambient sediments to 4.5 d in sediment chronically exposed to high levels of diesel-contaminated sediments for 28 d. Two- and three-ring PAH, including naphthalenes, phenanthrenes, and dibenzothiophenes, constituted the bulk of PAH composition of diesel and were rapidly metabolized. Alkylated PAH were also readily metabolized. The rapid removal of PAH suggests that even if the marsh were exposed to chronically high levels of petroleum hydrocarbons, chemical evidence of the contaminants would not be detected in sediments. Collectively, these results are consistent with the hypothesis that the bacterial community in this salt marsh has adapted to chronic exposure to petroleum hydrocarbons

Response of a benthic food web to hydrocarbon contamination

Direct and indirect effects of diesel-contaminated sediment on microalgae, meiofauna, and meiofauna-microalgae trophic interactions were examined in a microcosm study of the sediment community from a Spartina alterniflora salt marsh. Microcosms of natural sediment were given small dally doses of contaminated sediment over a 28-d period, creating low-, medium-, and high-diesel treatment concentrations of ~ 0.5, 5.5, and 55 ppm PAH, respectively. Diesel caused initial (within 7 h) reductions in microalgal grazing by meiobenthic harpacticoid copepods. Over longer periods of exposure (7-28 d), grazing on microalgae by copepods as a group was reduced in high-diesel treatments, primarily because of high copepod mortality. In contrast, grazing by and abundance of Cletocamptus deitersi (a copepod) was significantly enhanced in high-diesel treatments. Concurrent with reduced grazing by copepods, nematode grazing rates increased significantly in high-diesel treatments, indicating possible competition for microalgae between copepods and nematodes. In spite of transiently enhanced grazing by nematodes and C. deitersi, total meiofaunal grazing on microalgae was reduced in high-diesel treatments. Increased Chl a : pheopigment ratios in contaminated sediments were also indicative of reduced grazing pressure. A large (10x) increase in microalgal biomass was observed in high-diesel treatments and was likely a consequence of reduced meiofaunal grazing. The general responses observed in microcosms were also observed in a field study of polycyclic aromatic hydrocarbon contamination. Collectively, our data indicate that benthic microalgal biomass is controlled by meiofaunal grazing and that meiofauna may compete for limited algal resources. Furthermore, consideration of multiple trophic levels and their interactions allows a more complete and ecologically meaningful understanding of the mechanisms by which contaminants induce changes in natural communities

Variability in the Bulk Composition and Abundance of Dissolved Organic Matter In the Lower Mississippi and Pearl Rivers

[1] In this study, we examined the temporal and spatial variability of dissolved organic matter (DOM) abundance and composition in the lower Mississippi and Pearl rivers and effects of human and natural influences. In particular, we looked at bulk C/N ratio, stable isotopes (delta N-15 and delta C-13) and C-13 nuclear magnetic resonance (NMR) spectrometry of high molecular weight (HMW; 0.2 mu m to 1 kDa) DOM. Monthly water samples were collected at one station in each river from August 2001 to 2003. Surveys of spatial variability of total dissolved organic carbon (DOC) and nitrogen ( DON) were also conducted in June 2003, from 390 km downstream in the Mississippi River and from Jackson to Stennis Space Center in the Pearl River. Higher DOC ( 336 - 1170 mu M), C/N ratio,% aromaticity, and more depleted delta N-15 (0.76 - 2.1 parts per thousand) were observed in the Pearl than in the lower Mississippi River (223 - 380 mu M, 4.7 - 11.5 parts per thousand, respectively). DOC, C/N ratio, delta C-13, delta N-15, and % aromaticity of Pearl River HMW DOM were correlated with water discharge, which indicated a coupling between local soil inputs and regional precipitation events. Conversely, seasonal variability in the lower Mississippi River was more controlled by spatial variability of a larger integrative signal from the watershed as well as in situ DOM processing. Spatially, very little change occurred in total DOC in the downstream survey of the lower Mississippi River, compared to a decrease of 24% in the Pearl River. Differences in DOM between these two rivers were reflective of the Mississippi River having more extensive river processing of terrestrial DOM, more phytoplankton inputs, and greater anthropogenic perturbation than the Pearl River

Diagnostic Delay Is Associated with Complicated Disease and Growth Impairment in Paediatric Crohn\u27s Disease

Background: Paediatric data on the association between diagnostic delay and inflammatory bowel disease [IBD] complications are lacking. We aimed to determine the effect of diagnostic delay on stricturing/fistulising complications, surgery, and growth impairment in a large paediatric cohort, and to identify predictors of diagnostic delay. Methods: We conducted a national, prospective, multicentre IBD inception cohort study including 1399 children. Diagnostic delay was defined as time from symptom onset to diagnosis \u3e75th percentile. Multivariable proportional hazards [PH] regression was used to examine the association between diagnostic delay and stricturing/fistulising complications and surgery, and multivariable linear regression to examine the association between diagnostic delay and growth. Predictors of diagnostic delay were identified using Cox PH regression. Results: Overall (64% Crohn\u27s disease [CD]; 36% ulcerative colitis/IBD unclassified [UC/IBD-U]; 57% male]), median time to diagnosis was 4.2 (interquartile range [IQR] 2.0-9.2) months. For the overall cohort, diagnostic delay was \u3e9.2 months; in CD, \u3e10.8 months and in UC/IBD-U, \u3e6.6 months. In CD, diagnostic delay was associated with a 2.5-fold higher rate of strictures/internal fistulae (hazard ratio [HR] 2.53, 95% confidence interval [CI] 1.41-4.56). Every additional month of diagnostic delay was associated with a decrease in height-for-age z-score of 0.013 standard deviations [95% CI 0.005-0.021]. Associations persisted after adjusting for disease location and therapy. No independent association was observed between diagnostic delay and surgery in CD or UC/IBD-U. Diagnostic delay was more common in CD, particularly small bowel CD. Abdominal pain, including isolated abdominal pain in CD, was associated with diagnostic delay. Conclusions: Diagnostic delay represents a risk factor for stricturing/internal fistulising complications and growth impairment in paediatric CD

Reduction of Natural Killer but Not Effector CD8 T Lymphoyctes in Three Consecutive Cases of Severe/Lethal H1N1/09 Influenza A Virus Infection

Background: The cause of severe disease in some patients infected with pandemic influenza A virus is unclear. Methodology/Principal Findings: We present the cellular immunology profile in the blood, and detailed clinical (and postmortem) findings of three patients with rapidly progressive infection, including a pregnant patient who died. The striking finding is of reduction in natural killer (NK) cells but preservation of activated effector CD8 T lymphocytes; with viraemia in the patient who had no NK cells. Comparison with control groups suggests that the reduction of NK cells is unique to these severely ill patients. Conclusion/Significance: Our report shows markedly reduced NK cells in the three patients that we sampled and raises the hypothesis that NK may have a more significant role than T lymphocytes in controlling viral burden when the host is confronted with a new influenza A virus subtype

Is the meiofauna a good indicator for climate change and anthropogenic impacts?

Our planet is changing, and one of the most pressing challenges facing the scientific community revolves around understanding how ecological communities respond to global changes. From coastal to deep-sea ecosystems, ecologists are exploring new areas of research to find model organisms that help predict the future of life on our planet. Among the different categories of organisms, meiofauna offer several advantages for the study of marine benthic ecosystems. This paper reviews the advances in the study of meiofauna with regard to climate change and anthropogenic impacts. Four taxonomic groups are valuable for predicting global changes: foraminifers (especially calcareous forms), nematodes, copepods and ostracods. Environmental variables are fundamental in the interpretation of meiofaunal patterns and multistressor experiments are more informative than single stressor ones, revealing complex ecological and biological interactions. Global change has a general negative effect on meiofauna, with important consequences on benthic food webs. However, some meiofaunal species can be favoured by the extreme conditions induced by global change, as they can exhibit remarkable physiological adaptations. This review highlights the need to incorporate studies on taxonomy, genetics and function of meiofaunal taxa into global change impact research

The Influence of deep-sea bed CO2 sequestration on small metazoan (meiofaunal) community structure and function

We conducted a series of experiments in Monterey Submarine Canyon to examine potential ecological impacts of deep-ocean CO2 sequestration. Our focus was on responses of meiofaunal invertebrates (< 1 mm body length) living within the sediment at depths ranging between 3000-3600 m. Our particular emphasis was on harpacticoid copepods and nematodes. In the first phase of our DOE funding, we reported findings that suggest substantial (~80%) mortality to harpacticoid copepods. In the second phase of our funding we published additional findings from phase one and conducted follow-up experiments in the Monterey Canyon and in the laboratory. In one experiment we looked for evidence that meiofauna seek to escape areas where CO2 concentrations are elevated. âÂÂEmergence trapsâ near the source of the CO2-rich seawater caught significantly more harpacticoids than those far from it. The harpacticoids apparently attempted to escape from the advancing front of carbon dioxide-rich seawater and therefore presumably found exposure to it to be stressful. Although most were adversely affected, species differed significantly in the degree of their susceptibility. Unexpectedly, six species showed no effect and may be resistant. The hypothesis that harpacticoids could escape the effects of carbon dioxide-rich seawater by moving deeper into the seabed was not supported. Exposure to carbon dioxide-rich seawater created partially defaunated areas, but we found no evidence that disturbance-exploiting harpacticoid species invaded during the recovery of the affected area. Based on a detailed analysis of nematode biovolumes, we postulated that the nematode community in Monterey Canyon throughout the upper 3 cm suffered a high rate of mortality after exposure to CO2, and that nematodes were larger because postmortem expansions in body length and width occurred. Decomposition rates were probably low and corpses did not disintegrate in 30 days. The observable effects of a reduction in pH to about 7.0 after 30 days were as great as an extreme pH reduction (5.4), suggesting that âÂÂmoderateâ CO2 exposure, compared to the range of exposures possible following CO2 release, causes high mortality rates in the two most abundant sediment-dwelling metazoans (nematodes and copepods). While we found evidence for negative impacts on deep-sea benthos, we also observed that small-scale experiments with CO2 releases were difficult to replicate in the deep sea. Specifically, in one CO2-release experiment in the Monterey Canyon we did not detect an adverse impacts on benthic meiofauan. In laboratory experiments, we manipulated seawater acidity by addition of HCl and by increasing CO2 concentration and observed that two coastal harpacticoid copepod species were both more sensitive to increased acidity when generated by CO2. Copepods living in environments more prone to hypercapnia, such as mudflats, may be less sensitive to future acidification. Ocean acidification is also expected to alter the toxicity of waterborne metals by influencing their speciation in seawater. CO2 enrichment did not affect the free-ion concentration of Cd but did increase the free-ion concentration of Cu. Antagonistic toxicities were observed between CO2 with Cd, Cu and Cu free-ion. This interaction could be due to a competition for H+ and metals for binding sites

Density-dependent influences on feeding and metabolism in a freshwater snail

We used laboratory experiments to assess the degree of, and the underlying mechanism for, density dependence in the grazing rate of the pulmonate gastropod Physella virgata. Both fecal pellet production and uptake and incorporation of 14C radioisotopes from labeled periphyton were used as indices of grazing rates. Pronounced density-dependent reductions in grazing rate were observed, especially at densities above 4 snails/-25 cm2 periphyton grazing area. Radioisotope experiments also indicated that proportions of ingested 14C periphyton retained in snail tissue and respired as carbon dioxide increased at higher densities, suggesting that both assimilation efficiency and respiratory costs increase at higher densities. Constant replacement of water in aquaria did not remove density-dependent effects on grazing, suggesting that a dissolved metabolite is not responsible. Experiments where tiles were pre-conditioned with snails grazing at several densities actually stimulated grazing in subsequently added snails, suggesting that substrate-borne cues are also not responsible for density-dependent reductions in grazing rate. Behavioral inferference (in the form of shell-shaking after contacts with other snails) did, however, increase at higher densities, and may be partially reponsible for depressed grazing rates. © 1994 Springer Verlag

The Influence of deep-sea bed CO₂ sequestration on small metazoan (meiofaunal) community structure and function

We conducted a series of experiments in Monterey Submarine Canyon to examine potential ecological impacts of deep-ocean CO2 sequestration. Our focus was on responses of meiofaunal invertebrates (< 1 mm body length) living within the sediment at depths ranging between 3000-3600 m. Our particular emphasis was on harpacticoid copepods and nematodes. In the first phase of our DOE funding, we reported findings that suggest substantial (~80%) mortality to harpacticoid copepods. In the second phase of our funding we published additional findings from phase one and conducted follow-up experiments in the Monterey Canyon and in the laboratory. In one experiment we looked for evidence that meiofauna seek to escape areas where CO2 concentrations are elevated. âÂÂEmergence trapsâ near the source of the CO2-rich seawater caught significantly more harpacticoids than those far from it. The harpacticoids apparently attempted to escape from the advancing front of carbon dioxide-rich seawater and therefore presumably found exposure to it to be stressful. Although most were adversely affected, species differed significantly in the degree of their susceptibility. Unexpectedly, six species showed no effect and may be resistant. The hypothesis that harpacticoids could escape the effects of carbon dioxide-rich seawater by moving deeper into the seabed was not supported. Exposure to carbon dioxide-rich seawater created partially defaunated areas, but we found no evidence that disturbance-exploiting harpacticoid species invaded during the recovery of the affected area. Based on a detailed analysis of nematode biovolumes, we postulated that the nematode community in Monterey Canyon throughout the upper 3 cm suffered a high rate of mortality after exposure to CO2, and that nematodes were larger because postmortem expansions in body length and width occurred. Decomposition rates were probably low and corpses did not disintegrate in 30 days. The observable effects of a reduction in pH to about 7.0 after 30 days were as great as an extreme pH reduction (5.4), suggesting that âÂÂmoderateâ CO2 exposure, compared to the range of exposures possible following CO2 release, causes high mortality rates in the two most abundant sediment-dwelling metazoans (nematodes and copepods). While we found evidence for negative impacts on deep-sea benthos, we also observed that small-scale experiments with CO2 releases were difficult to replicate in the deep sea. Specifically, in one CO2-release experiment in the Monterey Canyon we did not detect an adverse impacts on benthic meiofauan. In laboratory experiments, we manipulated seawater acidity by addition of HCl and by increasing CO2 concentration and observed that two coastal harpacticoid copepod species were both more sensitive to increased acidity when generated by CO2. Copepods living in environments more prone to hypercapnia, such as mudflats, may be less sensitive to future acidification. Ocean acidification is also expected to alter the toxicity of waterborne metals by influencing their speciation in seawater. CO2 enrichment did not affect the free-ion concentration of Cd but did increase the free-ion concentration of Cu. Antagonistic toxicities were observed between CO2 with Cd, Cu and Cu free-ion. This interaction could be due to a competition for H+ and metals for binding sites