Structure and function of natural sulphide-oxidizing microbial mats under dynamic input of light and chemical energy

We studied the interaction between phototrophic and chemolithoautotrophic sulphide-oxidizing microorganisms in natural microbial mats forming in sulphidic streams. The structure of these mats varied between two end-members: one characterized by a layer dominated by large sulphur-oxidizing bacteria (SOB; mostly Beggiatoa-like) on top of a cyanobacterial layer (B/C mats) and the other with an inverted structure (C/B mats). C/B mats formed where the availability of oxygen from the water column was limited (<5 mu M). Aerobic chemolithotrophic activity of the SOB depended entirely on oxygen produced locally by cyanobacteria during high light conditions. In contrast, B/C mats formed at locations where oxygen in the water column was comparatively abundant (445 mu M) and continuously present. Here SOB were independent of the photosynthetic activity of cyanobacteria and outcompeted the cyanobacteria in the uppermost layer of the mat where energy sources for both functional groups were concentrated. Outcompetition of photosynthetic microbes in the presence of light was facilitated by the decoupling of aerobic chemolithotrophy and oxygenic phototrophy. Remarkably, the B/C mats conserved much less energy than the C/B mats, although similar amounts of light and chemical energy were available. Thus ecosystems do not necessarily develop towards optimal energy usage. Our data suggest that, when two independent sources of energy are available, the structure and activity of microbial communities is primarily determined by the continuous rather than the intermittent energy source, even if the time-integrated energy flux of the intermittent energy source is greater

Oscillatory porewater bioadvection in marine sediments induced by hydraulic activities of Arenicola marina

We employed real‐time pressure recording and high temporal resolution two‐dimensional oxygen imaging to characterize the porewater bioadvection related to hydraulic activities of Arenicola marina, a widespread representative of benthic macrofauna. Behavior‐specific positive and negative pressure oscillations and hydraulic pulses resulted in bidirectional porewater flow and highly dynamic redox oscillations on the scale of minutes. Pumping of water by the worm into its blind‐ending burrow pressurized the sediment and caused sediment oxygenation at depth and the exit of anoxic porewater into the overlying water. The sediment volume that was affected by bioadvective transport of oxygen and the porewater flow patterns varied strongly among sediment types. In low‐permeability sediments, localized plumes of anoxic porewater ascended from the sediment, presumably through sedimentary cracks, while porewater flowed evenly through highly permeable sediments. Hydraulic behaviors that moved water out through the open tail shaft caused a reduction of porewater pressures below the hydrostatic baseline which resulted in the collapse of plumes and enhanced oxygen penetration into the surficial sediments. Porewater bioadvection and the related perfusing and oscillatory phenomena will affect a variety of biogeochemical and ecological processes, including organic matter mineralization, benthic recruitment, and prey localization. We suggest that bidirectional porewater bioadvection and the associated transient geochemical conditions are prevalent features of biogenically active sediments

High spatial resolution measurement of oxygen consumption rates in permeable sediments

A method is presented for the measurement of depth profiles of volumetric oxygen consumption rates in permeable sediments with high spatial resolution. When combined with in situ oxygen microprofiles measured by microsensors, areal rates of aerobic respiration in sediments can be calculated. The method is useful for characterizing sediments exposed to highly dynamic advective water exchange, such as intertidal sandy sediments. The method is based on percolating the sediment in a sampling core with aerated water and monitoring oxygen in the sediment using either an oxygen microelectrode or a planar oxygen optode. The oxygen consumption rates are determined using three approaches: (1) as the initial rate of oxygen decrease measured at discrete points after the percolation is stopped, (2) from oxygen microprofiles measured sequentially after the percolation is stopped, and (3) as a derivative of steady-state oxygen microprofiles measured during a constant percolation of the sediment. The spatial resolution of a typical 3 to 4 cm profile within a measurement time of 1 to 2 h is better with planar optodes (˜0.3 mm) then with microelectrodes (2 to 5 mm), whereas the precision of oxygen consumption rate measurements at individual points is similar (0.1 to 0.5 µmol L–1 min–1) for both sensing methods. The method is consistent with the established methods (interfacial gradients combined with Fick’s law of diffusion, benthic-chambers), when tested on the same sediment sample under identical, diffusion-controlled conditions

The influence of pore-water advection, benthic photosynthesis, and respiration on calcium carbonate dynamics in reef sands

To investigate diel calcium carbonate (CaCO₃) dynamics in permeable coral reef sands, we measured pore-water profiles and fluxes of oxygen (O₂), nutrients, pH, calcium (Ca²⁺), and alkalinity (TA) across the sediment-water interface in sands of different permeability at Heron Reef, Australia. Background flushing rates were high, most likely as a result of infaunal burrow irrigation, but flux chamber stirring enhanced pore-water exchange. Light and pore-water advection fueled high rates of benthic primary production and calcification in sunlit surface sediments. In the light, benthic photosynthesis and calcification induced surface minima in Ca²⁺ and TA and peaks in pH and O₂. Oxygen penetration depth in coarse sands decreased from ~ 1.2 cm during the day to ~ 0.6 cm at night. Total oxygen uptake (TOU) in dark chambers was three to fourteen times greater than diffusive uptake and showed a direct effect of pore-water advection. Greater sediment oxygen consumption rates were observed in higher permeability sands. In the dark, TA release was not stimulated by increasing TOU because of a damping effect of pore-water advection on metabolic CaCO₃ dissolution efficiency. On a daily basis, CaCO₃ undergoes net dissolution in Heron Reef sands. However, pore-water advection can reverse the CaCO₃ budget and promote CaCO₃ preservation under the most energetic conditions

Sulfur Respiration in a Marine Chemolithoautotrophic Beggiatoa Strain

The chemolithoautotrophic strain Beggiatoa sp. 35Flor shows an unusual migration behavior when cultivated in a gradient medium under high sulfide fluxes. As common for Beggiatoa spp., the filaments form a mat at the oxygen–sulfide interface. However, upon prolonged incubation, a subpopulation migrates actively downward into the anoxic and sulfidic section of the medium, where the filaments become gradually depleted in their sulfur and polyhydroxyalkanoates (PHA) inclusions. This depletion is correlated with the production of hydrogen sulfide. The sulfur- and PHA-depleted filaments return to the oxygen–sulfide interface, where they switch back to depositing sulfur and PHA by aerobic sulfide oxidation. Based on these observations we conclude that internally stored elemental sulfur is respired at the expense of stored PHA under anoxic conditions. Until now, nitrate has always been assumed to be the alternative electron acceptor in chemolithoautotrophic Beggiatoa spp. under anoxic conditions. As the medium and the filaments were free of oxidized nitrogen compounds we can exclude this metabolism. Furthermore, sulfur respiration with PHA under anoxic conditions has so far only been described for heterotrophic Beggiatoa spp., but our medium did not contain accessible organic carbon. Hence the PHA inclusions must originate from atmospheric CO2 fixed by the filaments while at the oxygen–sulfide interface. We propose that the directed migration of filaments into the anoxic section of an oxygen–sulfide gradient system is used as a last resort to preserve cell integrity, which would otherwise be compromised by excessive sulfur deposition occurring in the presence of oxygen and high sulfide fluxes. The regulating mechanism of this migration is still unknown

Mechanisms of transient nitric oxide and nitrous oxide production in a complex biofilm

Nitric oxide (NO) and nitrous oxide (N2O) are formed during N-cycling in complex microbial communities in response to fluctuating molecular oxygen (O2) and nitrite (NO2−) concentrations. Until now, the formation of NO and N2O in microbial communities has been measured with low spatial and temporal resolution, which hampered elucidation of the turnover pathways and their regulation. In this study, we combined microsensor measurements with metabolic modeling to investigate the functional response of a complex biofilm with nitrifying and denitrifying activity to variations in O2 and NO2−. In steady state, NO and N2O formation was detected if ammonium (NH4+) was present under oxic conditions and if NO2− was present under anoxic conditions. Thus, NO and N2O are produced by ammonia-oxidizing bacteria (AOB) under oxic conditions and by heterotrophic denitrifiers under anoxic conditions. NO and N2O formation by AOB occurred at fully oxic conditions if NO2− concentrations were high. Modeling showed that steady-state NO concentrations are controlled by the affinity of NO-consuming processes to NO. Transient accumulation of NO and N2O occurred upon O2 removal from, or NO2− addition to, the medium only if NH4+ was present under oxic conditions or if NO2− was already present under anoxic conditions. This showed that AOB and heterotrophic denitrifiers need to be metabolically active to respond with instantaneous NO and N2O production upon perturbations. Transiently accumulated NO and N2O decreased rapidly after their formation, indicating a direct effect of NO on the metabolism. By fitting model results to measurements, the kinetic relationships in the model were extended with dynamic parameters to predict transient NO release from perturbed ecosystems

Platform for enhanced detection efficiency in luminescence-based sensors

Luminescence-based biochip measurement platforms are employed in a wide range of biological applications, such as biomedical diagnostics. Based on an understanding of the anisotropic emission properties of luminescence emitters close to a dielectric interface, a simple strategy for producing a better than 25-fold enhancement of the detected luminescence is presented. This strategy is demonstrated for low cost polymer platforms compatible with mass-production

The in situ light microenvironment of corals

We used a novel diver-operated microsensor system to collect in situ spectrally resolved light fields on corals with a micrometer spatial resolution. The light microenvironment differed between polyp and coenosarc tissues with scalar irradiance (400-700 nm) over polyp tissue, attenuating between 5.1- and 7.8-fold from top to base of small hemispherical coral colonies, whereas attenuation was at most 1.5-fold for coenosarc tissue. Fluctuations in ambient solar irradiance induced changes in light and oxygen microenvironments, which were more pronounced and faster in coenosarc compared with polyp tissue. Backscattered light from the surrounding benthos contributed > 20% of total scalar irradiance at the coral tissue surface and enhanced symbiont photosynthesis and the local O2 concentration, indicating an important role of benthos optics for coral ecophysiology. Light fields on corals are species and tissue specific and exhibit pronounced variation on scales from micrometers to decimeters. Consequently, the distribution, genetic diversity, and physiology of coral symbionts must be coupled with the measurements of their actual light microenvironment to achieve a more comprehensive understanding of coral ecophysiology. © 2014, by the Association for the Sciences of Limnology and Oceanography, Inc

Spatial patterns and links between microbial community composition and function in cyanobacterial mats

We imaged reflectance and variable fluorescence in 25 cyanobacterial mats from four distant sites around the globe to assess, at different scales of resolution, spatial variabilities in the physiological parameters characterizing their photosynthetic capacity, including the absorptivity by chlorophyll a (Achl), maximum quantum yield of photosynthesis (Ymax), and light acclimation irradiance (Ik). Generally, these parameters significantly varied within individual mats on a sub-millimeter scale, with about 2-fold higher variability in the vertical than in the horizontal direction. The average vertical profiles of Ymax and Ik decreased with depth in the mat, while Achl exhibited a sub-surface maximum. The within-mat variability was comparable to, but often larger than, the between-sites variability, whereas the within-site variabilities (i.e., between samples from the same site) were generally lowest. When compared based on averaged values of their photosynthetic parameters, mats clustered according to their site of origin. Similar clustering was found when the community composition of the mats' cyanobacterial layers were compared by automated ribosomal intergenic spacer analysis (ARISA), indicating a significant link between the microbial community composition and function. Although this link is likely the result of community adaptation to the prevailing site-specific environmental conditions, our present data is insufficient to identify the main factors determining these patterns. Nevertheless, this study demonstrates that the spatial variability in the photosynthetic capacity and light acclimation of benthic phototrophic microbial communities is at least as large on a sub-millimeter scale as it is on a global scale, and suggests that this pattern of variability scaling is similar for the microbial community composition. © 2014 Al-Najjar, Ramette, Kühl, Hamza, Klatt and Polerecky

Забезпечення якості медичної допомоги в умовах запровадження в Україні обов'язкового медичного страхування (адміністративно-правові принципи та складові елементи)

Аналізуються адміністративно правові принципи та складові елементи забезпечення якості медичної допомоги в умовах запровадження в Україні обов’язкового медичного страхування. Особлива увага приділена питанням контролю якості медичної допомоги. Ключові слова: якість надання медичної допомоги, обов’язкове медичне страхування.Анализируются административно правовые принципы и составляющие части обеспечения качества медицинской помощи в условиях утверждения в Украине обязательного медицинского страхования. Особое внимание уделено вопросам контроля качества оказания медицинской помощи. Ключевые слова: качество медицинской помощи, обязательное медицинское страхование.Administrative and legal principles and component parts of providing medical care quality in conditions of introducing compulsory medical insurance in Ukraine are analyzed in the article. Special attention is paid to the control provision of medical care quality. Key words: medical care quality, compulsory medical insurance