Brian T. Glazer

Soluble Mn(III) in Suboxic Zones

Soluble manganese(III) [Mn(III)] has been thought to disproportionate to soluble Mn(II) and particulate MnIVO2 in natural waters, although it persists as complexes in laboratory solutions. We report that, in the Black Sea, soluble Mn(III) concentrations were as high as 5 micromolar and constituted up to 100% of the total dissolved Mn pool. Depth profiles indicated that soluble Mn(III) was produced at the top of the suboxic zone by Mn(II) oxidation and at the bottom of the suboxic zone by MnIVO2 reduction, then stabilized in each case by unknown natural ligands. We also found micromolar concentrations of dissolved Mn(III) in the Chesapeake Bay. Dissolved Mn(III) can maintain the existence of suboxic zones because it can act as either an electron acceptor or donor. Our data indicate that Mn(III) should be ubiquitous at all water column and sediment oxic/anoxic interfaces in the environment.

Sulfur speciation monitored in situ with solid state gold amalgam voltammetric microelectrodes: polysulfides as a special case in sediments, microbial mats and hydrothermal vent waters{{

Sulfur speciation was determined in real time in salt marsh microbial mats, subtidal sediments and hydrothermal vent diffuse flow waters using solid state gold-amalgam voltammetric microelectrodes. Chemical species were measured in situ without any sample manipulation or processing. The partially oxidized sulfur species detected were polysulfides, thiosulfate, elemental sulfur and tetrathionate. Fe(III) oxidation of hydrogen sulfide does not occur within the mats where microbially mediated processes are responsible for oxidation of H2S. In sediments and diffuse flow vent waters, Fe(III) phases are the direct oxidant of H2S. Sulfur speciation determined in this work is due to in situ biogeochemical processes and is not due to artefacts of sample manipulation. The voltammetric data show that polysulfides are the first detectable intermediate during sulfide oxidation which is consistent with previous laboratory studies.

Potential for Microscale Bacterial Fe Redox Cycling at the Aerobic-Anaerobic Interface

Recent studies of bacterial Fe(II) oxidation at circumneutral pH by a newly-isolated lithotrophic β-Proteobacterium (strain TW2) are reviewed in relation to a conceptual model that accounts for the influence of biogenic Fe(III)-binding ligands on patterns of Fe(II) oxidation and Fe(III) oxide deposition in opposing gradients of Fe(II) and O2. The conceptual model envisions complexation of Fe(III) by biogenic ligands as mechanism which alters the locus of Fe(III) oxide deposition relative to Fe(II) oxidation so as to delay/retard cell encrustation with Fe(III) oxides. Experiments examining the potential for bacterial Fe redox cycling in microcosms containing ferrihydrite-coated sand and a coculture of a lithotrophic Fe(II)-oxidizing bacterium (strain TW2) and a dissimilatory Fe(III)-reducing bacterium (Shewanella algae strain BrY) are described and interpreted in relation to an extended version of the conceptual model in which Fe(III)-binding ligands promote rapid microscale Fe redox cycling. The coculture systems showed minimal Fe(III) oxide accumulation at the sand-water interface, despite intensive O2 input from the atmosphere and measurable dissolved O2 to a depth of 2 mm below the sand-water interface. In contrast, a distinct layer of oxide precipitates formed in systems containing Fe(III)-reducing bacteria alone. Voltammetric microelectrode measurements revealed much lower concentrations of dissolved Fe(II) in the coculture systems. Examination of materials from the cocultures by fluorescence in situ hybridization indicated close physical juxtapositioning of Fe(II)-oxidizing and Fe(III)reducing bacteria in the upper few mm of sand. Together these results indicate that Fe(II)-oxidizing bacteria have the potential to enhance the coupling of Fe(II) oxidation and Fe(III) reduction at redox interfaces, thereby promoting rapid microscale cycling of Fe.

Iron and Sulfur Chemistry in a Stratified Lake: Evidence for Iron-Rich Sulfide Complexes

A four month study of a man-made lake used for hydroelectric power generation in northeastern Pennsylvania USA was conducted to investigate seasonal anoxia and the effects of sulfide species being transported downstream of the power generation equipment. Water column analyses show that the system is iron-rich compared to sulfide. Total Fe(II) concentrations in the hypolimnion are typically at least twice the total sulfide levels. In situ voltammetric analyses show that free Fe(II) as [Fe(H2O)6]2+ or free H2S as H2S/HS- are either not present or at trace levels and that iron-rich sulfide complexes are present. From the in situ data and total Fe(II) and H2S measurements, we infer that these iron-rich sulfide complexes may have stoichiometries such as Fe2SH3+ (or polymeric forms of this and other stoichiometries). These iron-rich sulfide complexes appear related to dissolution of the iron-rich FeS mineral, mackinawite, because IAP calculations on data from discrete bottle samples obtained from bottom waters are similar to the pKsp of mackinawite. Soluble iron-sulfide species are stable in the absence of O2 (both in lake waters and the pipeline) and transported several miles during power generation. However, iron-sulfide complexes can react with O2 to oxidize sulfide and can also dissociate releasing volatile H2S when the waters containing them are exposed to the atmosphere downstream of the powerplant. Sediment analyses show that the lake is rich in oxidized iron solids (both crystalline and amorphous). Fe concentrations in FeS solids are low (<5 μmole/grdry wt) and the pyrite concentration ranges from about equal to the solid FeS to 30 times the solid FeS concentration. The degree of pyritization is below 0.12 indicating that pyrite formation is limited by free sulfide, which can react with the iron-rich sulfide complexes.

Redox Speciation and Distribution within Diverse Iron-dominated Microbial Habitats at Loihi Seamount

Deep-sea hydrothermal systems such as the Loihi Seamount hydrothermal field are important examples of environments where both chemical and biological oxidation of Fe can occur simultaneously, and provide an ideal system to study the speciation and distribution of redox-sensitive bio-reactive elements such as Fe, Mn and S. A total of 13 discrete ROV dives were conducted within the Loihi Summit area over three cruises in 2006, 2007, and 2008. Here, we present and compare data from 17 distinct sites of historical and current interest, from focused and diffuse hydrothermal flow localities, over the three-year sampling period. We coupled an in situ electrochemical analyzer (ISEA) to a sensor wand and a high-resolution in situ micromanipulator deployed from ROV Jason-II to measure dissolved redox species within hydrothermal fluids and microbial mats at Loihi Seamount in complement to analyses on discrete samples collected using Titanium samplers. We compare in situ electrochemical data with traditional geochemical sampling and analysis techniques, and provide a geochemical context for past, on-going, and planned microbial ecology studies.

An oligarchic microbial assemblage in the anoxic bottom waters of a volcanic subglacial lake

In 2006, we sampled the anoxic bottom waters of a volcanic lake beneath the Vatnajökull ice cap (Iceland). The sample contained 5 × 105 cells per ml, and whole-cell fluorescent in situ hybridization (FISH) and PCR with domain-specific probes showed these to be essentially all bacteria, with no detectable archaea. Pyrosequencing of the V6 hypervariable region of the 16S ribosomal RNA gene, Sanger sequencing of a clone library and FISH-based enumeration of four major phylotypes revealed that the assemblage was dominated by a few groups of putative chemotrophic bacteria whose closest cultivated relatives use sulfide, sulfur or hydrogen as electron donors, and oxygen, sulfate or CO2 as electron acceptors. Hundreds of other phylotypes are present at lower abundance in our V6 tag libraries and a rarefaction analysis indicates that sampling did not reach saturation, but FISH data limit the remaining biome to <10–20% of all cells. The composition of this oligarchy can be understood in the context of the chemical disequilibrium created by the mixing of sulfidic lake water and oxygenated glacial meltwater.

The roles of anoxia, H2S, and storm events in fish kills of dead-end canals of Delaware inland bays

In 2001, the development of seasonal anoxia was studied in two waterways located at the head of Delaware’s northern inland bay, Rehoboth Bay. Bald Eagle Creek is a northern tributary of the bay, which has tidal exchange with Torquay Canal (a dead-end canal) via a short channel with a 1.4 m sill. Mean low water depth in Torquay Canal is about 2 m, but dredging produced over a dozen depressions with a total water depth of 5.5 m. During the summer of 2000, four major fish kills were reported in Torquay Canal and Bald Eagle Creek with more than 2.5 million juvenile menhaden (Brevoortia tyrannus) killed. Low O2 concentration was assumed to be the problem but production of toxic H2S is more likely. From late spring 2001, we conducted in situ determination of temperature, salinity, pH, dissolved O2, and H2S in Torquay Canal and Bald Eagle Creek. During spring, water column stratification began in the depressions with warmer and less salty water observed in the upper layer, and cooler, saltier water below 2 m. O2 was at saturation levels in the surface waters but was not detectable below 2 m by the end of May. The depressions were anoxic with H2S accumulating to mM concentrations in June. A storm event prior to July 12 mixed these two layers with a subsequent loss of H2S. The H2S levels again increased in the deep water due to stratification and reached another maximum in late August. Another storm event occurred at this time resulting in no detectable O2 and up to 400 μM H2S in surface waters. H2S appears to be the primary reason for fish kills in these tributaries. Aerators installed in Torquay Canal on June 21 had no significant effect on abating stratification and anoxic conditions beyond their immediate area.

Microbial activity in the marine deep biosphere: progress and prospects

The vast marine deep biosphere consists of microbial habitats within sediment, pore waters, upper basaltic crust and the fluids that circulate throughout it. A wide range of temperature, pressure, pH, and electron donor and acceptor conditions exists—all of which can combine to affect carbon and nutrient cycling and result in gradients on spatial scales ranging from millimeters to kilometers. Diverse and mostly uncharacterized microorganisms live in these habitats, and potentially play a role in mediating global scale biogeochemical processes. Quantifying the rates at which microbial activity in the subsurface occurs is a challenging endeavor, yet developing an understanding of these rates is essential to determine the impact of subsurface life on Earths global biogeochemical cycles, and for understanding how microorganisms in these “extreme” environments survive (or even thrive). Here, we synthesize recent advances and discoveries pertaining to microbial activity in the marine deep subsurface, and we highlight topics about which there is still little understanding and suggest potential paths forward to address them. This publication is the result of a workshop held in August 2012 by the NSF-funded Center for Dark Energy Biosphere Investigations (C-DEBI) “theme team” on microbial activity (www.darkenergybiosphere.org).

The Architecture of Iron Microbial Mats Reflects the Adaptation of Chemolithotrophic Iron Oxidation in Freshwater and Marine Environments

Microbes form mats with architectures that promote efficient metabolism within a particular physicochemical environment, thus studying mat structure helps us understand ecophysiology. Despite much research on chemolithotrophic Fe-oxidizing bacteria, Fe mat architecture has not been visualized because these delicate structures are easily disrupted. There are striking similarities between the biominerals that comprise freshwater and marine Fe mats, made by Beta- and Zetaproteobacteria, respectively. If these biominerals are assembled into mat structures with similar functional morphology, this would suggest that mat architecture is adapted to serve roles specific to Fe oxidation. To evaluate this, we combined light, confocal, and scanning electron microscopy of intact Fe microbial mats with experiments on sheath formation in culture, in order to understand mat developmental history and subsequently evaluate the connection between Fe oxidation and mat morphology. We sampled a freshwater sheath mat from Maine and marine stalk and sheath mats from Loihi Seamount hydrothermal vents, Hawaii. Mat morphology correlated to niche: stalks formed in steeper O2 gradients while sheaths were associated with low to undetectable O2 gradients. Fe-biomineralized filaments, twisted stalks or hollow sheaths, formed the highly porous framework of each mat. The mat-formers are keystone species, with nascent marine stalk-rich mats comprised of novel and uncommon Zetaproteobacteria. For all mats, filaments were locally highly parallel with similar morphologies, indicating that cells were synchronously tracking a chemical or physical cue. In the freshwater mat, cells inhabited sheath ends at the growing edge of the mat. Correspondingly, time lapse culture imaging showed that sheaths are made like stalks, with cells rapidly leaving behind an Fe oxide filament. The distinctive architecture common to all observed Fe mats appears to serve specific functions related to chemolithotrophic Fe oxidation, including (1) removing Fe oxyhydroxide waste without entombing cells or clogging flow paths through the mat and (2) colonizing niches where Fe(II) and O2 overlap. This work improves our understanding of Fe mat developmental history and how mat morphology links to metabolism. We can use these results to interpret biogenicity, metabolism, and paleoenvironmental conditions of Fe microfossil mats, which would give us insight into Earths Fe and O2 history.

A distinct and active bacterial community in cold oxygenated fluids circulating beneath the western flank of the Mid-Atlantic ridge.

The rock-hosted, oceanic crustal aquifer is one of the largest ecosystems on Earth, yet little is known about its indigenous microorganisms. Here we provide the first phylogenetic and functional description of an active microbial community residing in the cold oxic crustal aquifer. Using subseafloor observatories, we recovered crustal fluids and found that the geochemical composition is similar to bottom seawater, as are cell abundances. However, based on relative abundances and functional potential of key bacterial groups, the crustal fluid microbial community is heterogeneous and markedly distinct from seawater. Potential rates of autotrophy and heterotrophy in the crust exceeded those of seawater, especially at elevated temperatures (25 °C) and deeper in the crust. Together, these results reveal an active, distinct, and diverse bacterial community engaged in both heterotrophy and autotrophy in the oxygenated crustal aquifer, providing key insight into the role of microbial communities in the ubiquitous cold dark subseafloor biosphere.