Gut microbiota utilize immunoglobulin A for mucosal colonization.

The immune system responds vigorously to microbial infection while permitting lifelong colonization by the microbiome. Mechanisms that facilitate the establishment and stability of the gut microbiota remain poorly described. We found that a regulatory system in the prominent human commensal Bacteroides fragilis modulates its surface architecture to invite binding of immunoglobulin A (IgA) in mice. Specific immune recognition facilitated bacterial adherence to cultured intestinal epithelial cells and intimate association with the gut mucosal surface in vivo. The IgA response was required for B. fragilis (and other commensal species) to occupy a defined mucosal niche that mediates stable colonization of the gut through exclusion of exogenous competitors. Therefore, in addition to its role in pathogen clearance, we propose that IgA responses can be co-opted by the microbiome to engender robust host-microbial symbiosis.

The uptake and excretion of partially oxidized sulfur expands the repertoire of energy resources metabolized by hydrothermal vent symbioses.

Symbiotic associations between animals and chemoautotrophic bacteria crowd around hydrothermal vents. In these associations, symbiotic bacteria use chemical reductants from venting fluid for the energy to support autotrophy, providing primary nutrition for the host. At vents along the Eastern Lau Spreading Center, the partially oxidized sulfur compounds (POSCs) thiosulfate and polysulfide have been detected in and around animal communities but away from venting fluid. The use of POSCs for autotrophy, as an alternative to the chemical substrates in venting fluid, could mitigate competition in these communities. To determine whether ESLC symbioses could use thiosulfate to support carbon fixation or produce POSCs during sulfide oxidation, we used high-pressure, flow-through incubations to assess the productivity of three symbiotic mollusc genera-the snails Alviniconcha spp. and Ifremeria nautilei, and the mussel Bathymodiolus brevior-when oxidizing sulfide and thiosulfate. Via the incorporation of isotopically labelled inorganic carbon, we found that the symbionts of all three genera supported autotrophy while oxidizing both sulfide and thiosulfate, though at different rates. Additionally, by concurrently measuring their effect on sulfur compounds in the aquaria with voltammetric microelectrodes, we showed that these symbioses excreted POSCs under highly sulfidic conditions, illustrating that these symbioses could represent a source for POSCs in their habitat. Furthermore, we revealed spatial disparity in the rates of carbon fixation among the animals in our incubations, which might have implications for the variability of productivity in situ. Together, these results re-shape our thinking about sulfur cycling and productivity by vent symbioses, demonstrating that thiosulfate may be an ecologically important energy source for vent symbioses and that they also likely impact the local geochemical regime through the excretion of POSCs.

Metatranscriptomics reveal differences in in situ energy and nitrogen metabolism among hydrothermal vent snail symbionts.

Despite the ubiquity of chemoautotrophic symbioses at hydrothermal vents, our understanding of the influence of environmental chemistry on symbiont metabolism is limited. Transcriptomic analyses are useful for linking physiological poise to environmental conditions, but recovering samples from the deep sea is challenging, as the long recovery times can change expression profiles before preservation. Here, we present a novel, in situ RNA sampling and preservation device, which we used to compare the symbiont metatranscriptomes associated with Alviniconcha, a genus of vent snail, in which specific host-symbiont combinations are predictably distributed across a regional geochemical gradient. Metatranscriptomes of these symbionts reveal key differences in energy and nitrogen metabolism relating to both environmental chemistry (that is, the relative expression of genes) and symbiont phylogeny (that is, the specific pathways employed). Unexpectedly, dramatic differences in expression of transposases and flagellar genes suggest that different symbiont types may also have distinct life histories. These data further our understanding of these symbionts' metabolic capabilities and their expression in situ, and suggest an important role for symbionts in mediating their hosts' interaction with regional-scale differences in geochemistry.

Persistent neck disease after chemoradiation for head and neck squamous cell carcinoma.

OBJECTIVE: This study aimed to identify the incidence of residual viable neck disease in patients with mucosal squamous cell carcinoma of the upper aero-digestive tract, following primary chemoradiation at a tertiary centre. STUDY DESIGN: Retrospective review. METHODS: Retrospective chart review of patients treated with primary chemoradiation for squamous cell carcinoma of the aero-digestive tract between August 2001 and August 2008. Neck status pre- and post-treatment was the primary focus. RESULTS: Forty-two patients with node-positive disease prior to chemoradiation were included. Thirty-seven (88.1 per cent) achieved complete response to treatment: no patient in this group underwent neck dissection, five died due to recurrence at the primary site or distant metastasis, and none suffered neck recurrence. Five (11.9 per cent) patients achieved partial response to chemoradiation and underwent neck dissection; viable tumour was found in one patient. CONCLUSION: Our data support conservative management of the neck in patients with complete response to chemoradiation, and consolidation neck dissection in patients with partial response.

Factors that influence the accumulation of copper and cadmium by transplanted eastern oysters (Crassostrea virginica) in the Patuxent River, Maryland.

To investigate the continued accumulation of copper and cadmium by oysters in the Patuxent River, MD, which have been at high levels since at least the mid 1960s, hatchery-raised Eastern oysters were transplanted into trays at four sites in the upper estuary. At each site two groups of oysters were used to determine growth and mortality, and another group was sampled for meat condition, metal concentration and body burden. Copper in oysters in the discharge of a coal-fired power plant was significantly greater than at all other sites, but maximum concentration of 310 micrograms g-1 was well below the maximum of 1880 micrograms g-1 detected in 1982. Cadmium levels were also significantly greater in the discharge than at the other sites, but probably because of higher discharge temperatures. Trace metal loadings, the local salinity gradient and the higher temperatures caused by power plant operation all appear to contribute to metal accumulation by oysters in the upper Patuxent estuary.

Silver uptake and subsequent effects on growth and species composition in an estuarine community.

Silver within Chesapeake Bay is rapidly taken up by phytoplankton, in accordance with geochemical controls over silver speciation. Phytoplankton accumulate large cellular burdens at non-lethal concentrations, setting up the potential for transfer of silver to herbivores that graze upon the phytoplankton community. However, the American oyster, Crassostrea virginica, does not assimilate silver from phytoplankton, but rather from that dissolved in water. Oysters can accumulate high burdens of silver via this uptake pathway, without apparent effect. There is another, perhaps more significant, mechanism by which silver can impact higher trophic levels. Continuous inputs of low concentrations of silver can cause large changes in species composition and species succession in Chesapeake Bay phytoplankton communities maintained in experimental ecosystems. In addition, oyster growth was reduced significantly relative to growth of oysters of unaltered communities. Such indirect effects of low levels of toxic substances, although difficult to detect, must be considered when assessments of pollutant impacts are made.