Microbial metabolomic responses to changes in temperature and salinity along the western Antarctic Peninsula.

Seasonal cycles within the marginal ice zones in polar regions include large shifts in temperature and salinity that strongly influence microbial abundance and physiology. However, the combined effects of concurrent temperature and salinity change on microbial community structure and biochemical composition during transitions between seawater and sea ice are not well understood. Coastal marine communities along the western Antarctic Peninsula were sampled and surface seawater was incubated at combinations of temperature and salinity mimicking the formation (cold, salty) and melting (warm, fresh) of sea ice to evaluate how these factors may shape community composition and particulate metabolite pools during seasonal transitions. Bacterial and algal community structures were tightly coupled to each other and distinct across sea-ice, seawater, and sea-ice-meltwater field samples, with unique metabolite profiles in each habitat. During short-term (approximately 10-day) incubations of seawater microbial communities under different temperature and salinity conditions, community compositions changed minimally while metabolite pools shifted greatly, strongly accumulating compatible solutes like proline and glycine betaine under cold and salty conditions. Lower salinities reduced total metabolite concentrations in particulate matter, which may indicate a release of metabolites into the labile dissolved organic matter pool. Low salinity also increased acylcarnitine concentrations in particulate matter, suggesting a potential for fatty acid degradation and reduced nutritional value at the base of the food web during freshening. Our findings have consequences for food web dynamics, microbial interactions, and carbon cycling as polar regions undergo rapid climate change.

Selective occurrence of Rhizobiales in frost flowers on the surface of young sea ice near Barrow, Alaska and distribution in the polar marine rare biosphere.

Frost flowers are highly saline ice structures that grow on the surface of young sea ice, a spatially extensive environment of increasing importance in the Arctic Ocean. In a previous study, we reported organic components of frost flowers in the form of elevated levels of bacteria and exopolymers relative to underlying ice. Here, DNA was extracted from frost flowers and young sea ice, collected in springtime from a frozen lead offshore of Barrow, Alaska, to identify bacteria in these understudied environments. Evaluation of the distribution of 16S rRNA genes via four methods (microarray analysis, T-RFLP, clone library and shotgun metagenomic sequencing) indicated distinctive bacterial assemblages between the two environments, with frost flowers appearing to select for Rhizobiales. A phylogenetic placement approach, used to evaluate the distribution of similar Rhizobiales sequences in other polar marine studies, indicated that some of the observed strains represent widely distributed members of the marine rare biosphere in both the Arctic and Antarctic.

Did life originate from a global chemical reactor?

Many decades of experimental and theoretical research on the origin of life have yielded important discoveries regarding the chemical and physical conditions under which organic compounds can be synthesized and polymerized. However, such conditions often seem mutually exclusive, because they are rarely encountered in a single environmental setting. As such, no convincing models explain how living cells formed from abiotic constituents. Here, we propose a new approach that considers the origin of life within the global context of the Hadean Earth. We review previous ideas and synthesize them in four central hypotheses: (i) Multiple microenvironments contributed to the building blocks of life, and these niches were not necessarily inhabitable by the first organisms; (ii) Mineral catalysts were the backbone of prebiotic reaction networks that led to modern metabolism; (iii) Multiple local and global transport processes were essential for linking reactions occurring in separate locations; (iv) Global diversity and local selection of reactants and products provided mechanisms for the generation of most of the diverse building blocks necessary for life. We conclude that no single environmental setting can offer enough chemical and physical diversity for life to originate. Instead, any plausible model for the origin of life must acknowledge the geological complexity and diversity of the Hadean Earth. Future research may therefore benefit from identifying further linkages between organic precursors, minerals, and fluids in various environmental contexts.

A comparison of triple-therapy with double-therapy immunosuppression in cadaveric renal transplantation.

Triple-therapy (low-dose cyclosporine-azathioprine-prednisone) immunosuppression regimen was compared with double-therapy (cyclosporine-prednisone) in 91 consecutive nonrandomized adult cadaveric renal transplant recipients. Both groups were comparable with respect to ethnic diversity, prior transplants, and diabetes. The majority of patients with delayed function (ATN) were maintained on triple therapy, and the use of antilymphocyte agents was more common in the triple-therapy group (52% vs. 7%; P = 0.0001). Triple-therapy patients experienced increased acute rejection episodes (1.4 vs. 0.8 per patient, P = 0.03), required more courses of additional steroid pulse therapy (4.3 vs. 1.6 per patient; P = 0.001), and developed serious infections more frequently (37% vs. 15%; P = 0.05), especially CMV infections (17% vs. 0; P = 0.03), compared with double-therapy patients. However, the increased overall infection rate and CMV infection rate were observed only in those patients who received antilymphocyte agents compared with those who did not (46% vs. 21%; P = 0.02 for all infections, 26% vs. 4%; P = 0.006 for CMV). Additional steroid pulse therapy was associated with increased CMV infections (24% vs. 0; P = 0.03) but not with overall infections. One-year allograft and patient survival were equivalent in both groups. Exclusion of ATN patients from analysis did not alter the findings. This experience confirms the overall efficacy of triple-therapy immunosuppression in renal transplant recipients but suggests that triple therapy may be associated with more acute rejection episodes, greater immunosuppression requirements, and a resultant increase in infections, especially CMV.

Early cannulation of plasma TFE and Gore-Tex grafts for hemodialysis: a prospective randomized study.

Fifty-one consecutive vascular access procedures were randomized to either the Medtronic plasma TFE or Gore-Tex polytetrafluoroethylene (PTFE) conduits in patients requiring immediate dialysis from December 1989 to April 1990. There were 49 forearm loop fistulas and 2 upper arm grafts. Fifty of these fistulas were cannulated within 48 h of placement to avoid use of subclavian venous catheters for hemodialysis. Complications related to the early cannulation of these fistulas included 2 hematomas in the plasma TFE group, and 3 hematomas in the Gore-Tex group (p = 1.00). Two patients with Gore-Tex grafts were systemically heparinized prior to hematoma formation after thrombectomy of their accesses. There were no adverse sequelae in these 5 patients, and none of the hematomas interfered with further dialytic therapy. One patient in the plasma TFE group and 3 patients in the Gore-Tex group developed cellulitis within the first month of placement (p = 0.65). All were treated with intravenous vancomycin with resolution of the erythema. None of the plasma TFE and 3 of the Gore-Tex fistulas thrombosed within 30 days of placement (p = 0.22). All were salvaged by thrombectomy. Both the plasma TFE and Gore-Tex vascular conduits may be used after surgical placement for early dialytic therapy and are associated with minimal early complications. The early use of these fistulas may eliminate the need for subclavian venous cannulation in most patients with renal failure, thus diminishing the incidence of subclavian venous stenosis and thrombosis. Further observation of these grafts will be necessary to determine the effect of immediate cannulation on their long-term performance for hemodialysis.

Submarine atmospheres.

Nuclear submariners live and work in an atmosphere composed of approximately 80% naturally occurring nitrogen, 19% oxygen (manufactured aboard ship), and a complex mixture of inorganic and organic contaminants. The concentrations of contaminants exist as a balance between the rates of production from human and operational activities and the rate of removal by engineering systems. The biological effects of inorganic gases, particularly carbon dioxide, have been extensively studied. Investigators are now attempting to define the composition and concentration of volatile organic compounds that accumulate during 90-day submergences. Medical studies have not conclusively shown that crewmembers incur adverse health effects from continuous exposures to the sealed atmospheres of nuclear submarines.

Physiologic and performance measurements in simulated airborne combined stress environments.

The Naval Air Development Center's Human Centrifuge was used to assess the effects of repeated exposures to a simulated Air Combat Maneuvering (ACM) environment on various measures of physiological function and psychomotor performance. The environment consisted of a realistic ACM profile that included associated noise, high speed/stall buffet conditions, and increased intra-cockpit temperatures. The effects of varying the subject's seatback angle, as a function of the environment, was also measured. Analysis of the various physiological and performance data revealed the following: 1) heart rate was negatively correlated with tracking accuracy under the combined stress conditions of this study, 2) test conditions that included acceleration and buffet resulted in a significant decrement in tracking accuracy, 3) the addition of increased intra-cocpit temperatures, when combined with acceleration and/or buffet, produced a significant decrease in tracking accuracy, 4) increasing the seatback angle from the vertical partially ameliorated the effects of the other stressors. Details of these findings, as well as results of various biochemical analyses, are discussed.