Microbial communities from weathered outcrops of a sulfide-rich ultramafic intrusion, and implications for mine waste management.

The Duluth Complex (DC) contains sulfide-rich magmatic intrusions that represent one of the largest known economic deposits of copper, nickel, and platinum group elements. Previous work showed that microbial communities associated with experimentally-weathered DC waste rock and tailings were dominated by uncultivated taxa and organisms not typically associated with mine waste. However, those experiments were designed for kinetic testing and do not necessarily represent the conditions expected for long-term environmental weathering. We used 16S rRNA gene methods to characterize the microbial communities present on the surfaces of naturally-weathered and historically disturbed outcrops of DC material. Rock surfaces were dominated by diverse uncultured Ktedonobacteria, Acetobacteria, and Actinobacteria, with abundant algae and other phototrophs. These communities were distinct from microbial assemblages from experimentally-weathered DC rocks, suggesting different energy and nutrient resources in environmental samples. Sulfide mineral incubations performed with and without algae showed that photosynthetic microorganisms could have an inhibitory effect on autotrophic populations, resulting in slightly lower sulfate release and differences in dominant microorganisms. The microbial assemblages from these weathered outcrops show how communities develop during weathering of sulfide-rich DC rocks and represent baseline data that could evaluate the effectiveness of future reclamation of waste produced by large-scale mining operations.

Convergent Community Assembly among Globally Separated Acidic Cave Biofilms.

Acidophilic bacteria and archaea inhabit extreme geochemical "islands" that can tell us when and how geographic barriers affect the biogeography of microorganisms. Here, we describe microbial communities from extremely acidic (pH 0 to 1) biofilms, known as snottites, from hydrogen sulfide-rich caves. Given the extreme acidity and subsurface location of these biofilms, and in light of earlier work showing strong geographic patterns among snottite Acidithiobacillus populations, we investigated their structure and diversity in order to understand how geography might impact community assembly. We used 16S rRNA gene cloning and fluorescence in situ hybridization (FISH) to investigate 26 snottite samples from four sulfidic caves in Italy and Mexico. All samples had very low biodiversity and were dominated by sulfur-oxidizing bacteria in the genus Acidithiobacillus. Ferroplasma and other archaea in the Thermoplasmatales ranged from 0 to 50% of total cells, and relatives of the bacterial genera Acidimicrobium and Ferrimicrobium were up to 15% of total cells. Rare phylotypes included Sulfobacillus spp. and members of the phyla "Candidatus Dependentiae" and "Candidatus Saccharibacteria" (formerly TM6 and TM7). Although the same genera of acidophiles occurred in snottites on separate continents, most members of those genera represent substantially divergent populations, with 16S rRNA genes that are only 95 to 98% similar. Our findings are consistent with a model of community assembly where sulfidic caves are stochastically colonized by microorganisms from local sources, which are strongly filtered through environmental selection for extreme acid tolerance, and these different colonization histories are maintained by dispersal restrictions within and among caves. IMPORTANCE Microorganisms that are adapted to extremely acidic conditions, known as extreme acidophiles, are catalysts for rock weathering, metal cycling, and mineral formation in naturally acidic environments. They are also important drivers of large-scale industrial processes such as biomining and contaminant remediation. Understanding the factors that govern their ecology and distribution can help us better predict and utilize their activities in natural and engineered systems. However, extremely acidic habitats are unusual in that they are almost always isolated within circumneutral landscapes. So where did their acid-adapted inhabitants come from, and how do new colonists arrive and become established? In this study, we took advantage of a unique natural experiment in Earth's subsurface to show how isolation may have played a role in the colonization history, community assembly, and diversity of highly acidic microbial biofilms.

Lighting Effects on the Development and Diversity of Photosynthetic Biofilm Communities in Carlsbad Cavern, New Mexico.

Photosynthetic cave communities ("lampenflora") proliferate in Carlsbad Cavern and other show caves worldwide due to artificial lighting. These biofilms mar the esthetics and can degrade underlying cave surfaces. The National Park Service recently modernized the lighting in Carlsbad Cavern to a light-emitting diode (LED) system that allows adjustment of the color temperature and intensity. We hypothesized that lowering the color temperature would reduce photopigment development. We therefore assessed lampenflora responses to changes in lighting by monitoring photosynthetic communities over the course of a year. We measured photopigments using reflected-light spectrophotometric observations and analyzed microbial community composition with 16S and 18S rRNA gene amplicon sequencing. Reflected-light spectrophotometry revealed that photosynthetic biofilm development is affected by lighting intensity, color temperature, substrate type, and cleaning of the substrate. Gene sequencing showed that the most abundant phototrophs were Cyanobacteria and members of the algal phyla Chlorophyta and Ochrophyta At the end of the study, visible growth of lampenflora was seen at all sites. At sites that had no established biofilm at the start of the study period, Cyanobacteria became abundant and outpaced an increase in eukaryotic algae. Microbial diversity also increased over time at these sites, suggesting a possible pattern of early colonization and succession. Bacterial community structure showed significant effects of all variables: color temperature, light intensity, substrate type, site, and previous cleaning of the substrate. These findings provide fundamental information that can inform management practices; they suggest that altering lighting conditions alone may be insufficient to prevent lampenflora growth.IMPORTANCE Artificial lighting in caves visited by tourists ("show caves") can stimulate photosynthetic algae and cyanobacteria, called "lampenflora," which are unsightly and damage speleothems and other cave surfaces. The most common mitigation strategy employs bleach, but altering intensities and wavelengths of light might be effective and less harsh. Carlsbad Cavern in New Mexico, a U.S. National Park and UNESCO World Heritage Site, has visible lampenflora despite adjustment of LED lamps to decrease the energetic blue light. This study characterized the lampenflora communities and tested the effects of color temperature, light intensity, rock or sediment texture, and time on lampenflora development. DNA amplicon sequence data show a variety of algae and cyanobacteria and also heterotrophic bacteria. This study reveals microbial dynamics during colonization of artificially lit surfaces and indicates that while lowering the color temperature may have an effect, management of lampenflora will likely require additional chemical or UV treatment.

Stepwise Assembly of an Electroactive Framework from a Co6 S8 Superatomic Metalloligand and Cuprous Iodide Building Units.

Invited for the cover of this issue is Christopher Bejger and co-workers at UNC Charlotte, Columbia University, and Donghua University. The image depicts a pair of star clusters in the constellation Perseus as the structure of two metal clusters in the reported framework. Read the full text of the article at 10.1002/chem.20201215.

Stepwise Assembly of an Electroactive Framework from a Co6 S8 Superatomic Metalloligand and Cuprous Iodide Building Units.

The design of metal-organic frameworks (MOFs) that incorporate more than one metal cluster constituent is a challenging task. Conventional one-pot reaction protocols require judicious selection of ligand and metal ion precursors, yet remain unpredictable. Stable, preformed nanoclusters, with ligand shells that can undergo additional coordination-driven reactions, provide a platform for assembling multi-cluster solids with precision. Herein, a discrete Co6 S8 (PTA)6 (PTA=1,3,5-triaza-7-phosphaadamantane) superatomic-metalloligand is assembled into a three-dimensional (3D) coordination polymer comprising Cu4 I4 secondary building units (SBUs). The resulting heterobimetallic framework (1) contains two distinct cluster constituents and bifunctional PTA linkers. Solid-state diffuse reflectance studies reveal that 1 is an optical semiconductor with a band-gap of 1.59 eV. Framework-modified electrodes exhibit reversible redox behavior in the solid state arising from the Co6 S8 superatoms, which remain intact during framework synthesis.

Diverse Communities of hgcAB+ Microorganisms Methylate Mercury in Freshwater Sediments Subjected to Experimental Sulfate Loading.

Methylmercury (MeHg) is a bioaccumulative neurotoxin produced by certain sulfate-reducing bacteria and other anaerobic microorganisms. Because microorganisms differ in their capacity to methylate mercury, the abundance and distribution of methylating populations may determine MeHg production in the environment. We compared rates of MeHg production and the distribution of hgcAB genes in epilimnetic sediments from a freshwater lake that were experimentally amended with sulfate levels from 7 to 300 mg L-1. The most abundant hgcAB sequences were associated with clades of Methanomicrobia, sulfate-reducing Deltaproteobacteria, Spirochaetes, and unknown environmental sequences. The hgcAB+ communities from higher sulfate amendments were less diverse and had relatively more Deltaproteobacteria, whereas the communities from lower amendments were more diverse with a larger proportion of hgcAB sequences affiliated with other clades. Potential methylation rate constants varied 52-fold across the experiment. Both potential methylation rate constants and % MeHg were the highest in sediments from the lowest sulfate amendments, which had the most diverse hgcAB+ communities and relatively fewer hgcAB genes from clades associated with sulfate reduction. Although pore water sulfide concentration covaried with hgcAB diversity across our experimental sulfate gradient, major changes in the community of hgcAB+ organisms occurred prior to a significant buildup of sulfide in pore waters. Our results indicate that methylating communities dominated by diverse anaerobic microorganisms that do not reduce sulfate can produce MeHg as effectively as communities dominated by sulfate-reducing populations.

Cellular distribution of secretory pathway markers in the haploid synergid cells of Arabidopsis thaliana.

In flowering plants, cell-cell communication plays a key role in reproductive success, as both pollination and fertilization require pathways that regulate interactions between many different cell types. Some of the most critical of these interactions are those between the pollen tube (PT) and the embryo sac, which ensure the delivery of sperm cells required for double fertilization. Synergid cells function to attract the PT through secretion of small peptides and in PT reception via membrane-bound proteins associated with the endomembrane system and the cell surface. While many synergid-expressed components regulating PT attraction and reception have been identified, few tools exist to study the localization of membrane-bound proteins and the components of the endomembrane system in this cell type. In this study, we describe the localization and distribution of seven fluorescent markers that labelled components of the secretory pathway in synergid cells of Arabidopsis thaliana. These markers were used in co-localization experiments to investigate the subcellular distribution of the two PT reception components LORELEI, a GPI-anchored surface protein, and NORTIA, a MILDEW RESISTANCE LOCUS O protein, both found within the endomembrane system of the synergid cell. These secretory markers are useful tools for both reproductive and cell biologists, enabling the analysis of membrane-associated trafficking within a haploid cell actively involved in polar transport.

NUCLEAR FACTOR Y, Subunit A (NF-YA) Proteins Positively Regulate Flowering and Act Through FLOWERING LOCUS T.

Photoperiod dependent flowering is one of several mechanisms used by plants to initiate the developmental transition from vegetative growth to reproductive growth. The NUCLEAR FACTOR Y (NF-Y) transcription factors are heterotrimeric complexes composed of NF-YA and histone-fold domain (HFD) containing NF-YB/NF-YC, that initiate photoperiod-dependent flowering by cooperatively interacting with CONSTANS (CO) to drive the expression of FLOWERING LOCUS T (FT). This involves NF-Y and CO binding at distal CCAAT and proximal "CORE" elements, respectively, in the FT promoter. While this is well established for the HFD subunits, there remains some question over the potential role of NF-YA as either positive or negative regulators of this process. Here we provide strong support, in the form of genetic and biochemical analyses, that NF-YA, in complex with NF-YB/NF-YC proteins, can directly bind the distal CCAAT box in the FT promoter and are positive regulators of flowering in an FT-dependent manner.

Water-Soluble Isatoic Anhydrides: A Platform for RNA-SHAPE Analysis and Protein Bioconjugation.

N-(3-Iodopropyl)isatoic anhydride (IPIA) has been demonstrated to serve as an efficient substrate for the development of an extended bioconjugation platform. Derivatives of IPIA are water-soluble and adaptable and share a common chromophore, rendering them easily quantifiable. We demonstrate the preparation of the readily diversified bioconjugation platform technology and application of the reagents in RNA-SHAPE analysis.

MILDEW RESISTANCE LOCUS O Function in Pollen Tube Reception Is Linked to Its Oligomerization and Subcellular Distribution.

Sexual reproduction in flowering plants requires communication between synergid cells and a tip-elongating pollen tube (PT) for the successful delivery of sperm cells to the embryo sac. The reception of the PT relies on signaling within the synergid cell that ultimately leads to the degeneration of the receptive synergid and PT rupture, releasing the sperm cells for double fertilization. In Arabidopsis (Arabidopsis thaliana), NORTIA, a member of the MILDEW RESISTANCE LOCUS O (MLO) family of proteins, plays a critical role in the communication processes regulating PT reception. In this study, we determined that MLO function in PT reception is dependent on MLO protein localization into a Golgi-associated compartment before PT arrival, indicating that PT-triggered regulation of the synergid secretory system is important for synergid function during pollination. Additionally, a structure-function analysis revealed that MLO homooligomerization, mediated by the amino-terminal region of the protein, and carboxyl-terminal tail identity both contribute to MLO activity during PT reception.

Thiazolothiazole Fluorophores Exhibiting Strong Fluorescence and Viologen-Like Reversible Electrochromism.

The synthesis, electrochemical, and photophysical characterization of N,N'-dialkylated and N,N'-dibenzylated dipyridinium thiazolo[5,4-d]thiazole derivatives are reported. The thiazolothiazole viologens exhibit strong blue fluorescence with high quantum yields between 0.8-0.96. The dioctyl, dimethyl, and dibenzyl derivatives also show distinctive and reversible yellow to dark blue electrochromism at low reduction potentials. The fused bicyclic thiazolo[5,4-d]thiazole heterocycle allows the alkylated pyridinium groups to remain planar, strongly affecting their electrochemical properties. The singlet quantum yield is greatly enhanced with quaternarization of the peripheral 4-pyridyl groups (ΦF increases from 0.22 to 0.96) while long-lived fluorescence lifetimes were observed between 1.8-2.4 ns. The thiazolothiazole viologens have been characterized using cyclic voltammetry, UV-visible absorbance and fluorescence spectroscopy, spectroelectrochemistry, and time-resolved photoluminescence. The electrochromic properties observed in solution, in addition to their strong fluorescent emission properties, which can be suppressed upon 2 e- reduction, make these materials attractive for multifunctional optoelectronic, electron transfer sensing, and other photochemical applications.

Efficient Low-pH Iron Removal by a Microbial Iron Oxide Mound Ecosystem at Scalp Level Run.

Acid mine drainage (AMD) is a major environmental problem affecting tens of thousands of kilometers of waterways worldwide. Passive bioremediation of AMD relies on microbial communities to oxidize and remove iron from the system; however, iron oxidation rates in AMD environments are highly variable among sites. At Scalp Level Run (Cambria County, PA), first-order iron oxidation rates are 10 times greater than at other coal-associated iron mounds in the Appalachians. We examined the bacterial community at Scalp Level Run to determine whether a unique community is responsible for the rapid iron oxidation rate. Despite strong geochemical gradients, including a >10-fold change in the concentration of ferrous iron from 57.3 mg/liter at the emergence to 2.5 mg/liter at the base of the coal tailings pile, the bacterial community composition was nearly constant with distance from the spring outflow. Scalp Level Run contains many of the same taxa present in other AMD sites, but the community is dominated by two strains of Ferrovum myxofaciens, a species that is associated with high rates of Fe(II) oxidation in laboratory studies.IMPORTANCE Acid mine drainage pollutes more than 19,300 km of rivers and streams and 72,000 ha of lakes worldwide. Remediation is frequently ineffective and costly, upwards of $100 billion globally and nearly $5 billion in Pennsylvania alone. Microbial Fe(II) oxidation is more efficient than abiotic Fe(II) oxidation at low pH (P. C. Singer and W. Stumm, Science 167:1121-1123, 1970, https://doi.org/10.1126/science.167.3921.1121). Therefore, AMD bioremediation could harness microbial Fe(II) oxidation to fuel more-cost-effective treatments. Advances will require a deeper understanding of the ecology of Fe(II)-oxidizing microbial communities and the factors that control their distribution and rates of Fe(II) oxidation. We investigated bacterial communities that inhabit an AMD site with rapid Fe(II) oxidation and found that they were dominated by two operational taxonomic units (OTUs) of Ferrovum myxofaciens, a taxon associated with high laboratory rates of iron oxidation. This research represents a step forward in identifying taxa that can be used to enhance cost-effective AMD bioremediation.

Novel Microbial Assemblages Dominate Weathered Sulfide-Bearing Rock from Copper-Nickel Deposits in the Duluth Complex, Minnesota, USA.

The Duluth Complex in northeastern Minnesota hosts economically significant deposits of copper, nickel, and platinum group elements (PGEs). The primary sulfide mineralogy of these deposits includes the minerals pyrrhotite, chalcopyrite, pentlandite, and cubanite, and weathering experiments show that most sulfide-bearing rock from the Duluth Complex generates moderately acidic leachate (pH 4 to 6). Microorganisms are important catalysts for metal sulfide oxidation and could influence the quality of water from mines in the Duluth Complex. Nevertheless, compared with that of extremely acidic environments, much less is known about the microbial ecology of moderately acidic sulfide-bearing mine waste, and so existing information may have little relevance to those microorganisms catalyzing oxidation reactions in the Duluth Complex. Here, we characterized the microbial communities in decade-long weathering experiments (kinetic tests) conducted on crushed rock and tailings from the Duluth Complex. Analyses of 16S rRNA genes and transcripts showed that differences among microbial communities correspond to pH, rock type, and experimental treatment. Moreover, microbial communities from the weathered Duluth Complex rock were dominated by taxa that are not typically associated with acidic mine waste. The most abundant operational taxonomic units (OTUs) were from the genera Meiothermus and Sulfuriferula, as well as from diverse clades of uncultivated Chloroflexi, Acidobacteria, and Betaproteobacteria Specific taxa, including putative sulfur-oxidizing Sulfuriferula spp., appeared to be primarily associated with Duluth Complex rock, but not pyrite-bearing rocks subjected to the same experimental treatment. We discuss the implications of these results for the microbial ecology of moderately acidic mine waste with low sulfide content, as well as for kinetic testing of mine waste.IMPORTANCE Economic sulfide mineral deposits in the Duluth Complex may represent the largest undeveloped source of copper and nickel on Earth. Microorganisms are important catalysts for sulfide mineral oxidation, and research on extreme acidophiles has improved our ability to manage and remediate mine wastes. We found that the microbial assemblages associated with weathered rock from the Duluth Complex are dominated by organisms not widely associated with mine waste or mining-impacted environments, and we describe geochemical and experimental influences on community composition. This report will be a useful foundation for understanding the microbial biogeochemistry of moderately acidic mine waste from these and similar deposits.

Functional analysis of related CrRLK1L receptor-like kinases in pollen tube reception.

The Catharanthus roseus Receptor-Like Kinase 1-like (CrRLK1L) family of 17 receptor-like kinases (RLKs) has been implicated in a variety of signaling pathways in Arabidopsis, ranging from pollen tube (PT) reception and tip growth to hormonal responses. The extracellular domains of these RLKs have malectin-like domains predicted to bind carbohydrate moieties. Domain swap analysis showed that the extracellular domains of the three members analyzed (FER, ANX1, HERK1) are not interchangeable, suggesting distinct upstream components, such as ligands and/or co-factors. In contrast, their intercellular domains are functionally equivalent for PT reception, indicating that they have common downstream targets in their signaling pathways. The kinase domain is necessary for FER function, but kinase activity itself is not, indicating that other kinases may be involved in signal transduction during PT reception.

Ball and Socket Assembly of Binary Superatomic Solids Containing Trinuclear Nickel Cluster Cations and Fulleride Anions.

The superlattice structures of hierarchical cluster solids are dictated by short-range interactions between constituent building blocks. Here we show that shape complementary sites, as well as halogen and chalcogen bonding between exposed capping ligands and fullerides, govern the packing arrangement of the resulting binary solids. Four new superatomic solids, [Ni3(µ3-I)2(µ2-dppm)3+](C60•-) (1·C60), [Ni3(µ3-I)2(µ2-dppm)3+](C70-)2 (1·C70), [Ni3(µ3-Te)2(µ2-dppm)3+](C60•-) (2·C60), and [Ni3(µ3-Te)2(µ2-dppm)3](C70-)2 (2·C70), (dppm = Ph2PCH2PPh2) were prepared and crystallized from solution. All four compounds were characterized by single crystal X-ray diffraction, IR spectroscopy, and SQUID magnetometry. Charge transfer between the molecular clusters is confirmed via optical spectroscopy and structural data. Compounds 1·C60 and 2·C60 are paramagnetic and 100 times more conductive than the constituent cluster precursors. The obtained solids exhibit close contacts, indicative of halogen/chalcogen bonds, between the fulleride anions and the nickel cluster capping ligands (I/Te) in the solid-state.

Comparison of qSOFA and SIRS for predicting adverse outcomes of patients with suspicion of sepsis outside the intensive care unit.

BACKGROUND: The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3) Task Force recently introduced a new clinical score termed quick Sequential (Sepsis-related) Organ Failure Assessment (qSOFA) for identification of patients at risk of sepsis outside the intensive care unit (ICU). We attempted to compare the discriminatory capacity of the qSOFA versus the Systemic Inflammatory Response Syndrome (SIRS) score for predicting mortality, ICU-free days, and organ dysfunction-free days in patients with suspicion of infection outside the ICU. METHODS: The Weill Cornell Medicine Registry and Biobank of Critically Ill Patients is an ongoing cohort of critically ill patients, for whom biological samples and clinical information (including vital signs before and during ICU hospitalization) are prospectively collected. Using such information, qSOFA and SIRS scores outside the ICU (specifically, within 8 hours before ICU admission) were calculated. This study population was therefore comprised of patients in the emergency department or the hospital wards who had suspected infection, were subsequently admitted to the medical ICU and were included in the Registry and Biobank. RESULTS: One hundred fifty-two patients (67% from the emergency department) were included in this study. Sixty-seven percent had positive cultures and 19% died in the hospital. Discrimination of in-hospital mortality using qSOFA [area under the receiver operating characteristic curve (AUC), 0.74; 95% confidence intervals (CI), 0.66-0.81] was significantly greater compared with SIRS criteria (AUC, 0.59; 95% CI, 0.51-0.67; p = 0.03). The qSOFA performed better than SIRS regarding discrimination for ICU-free days (p = 0.04), but not for ventilator-free days (p = 0.19), any organ dysfunction-free days (p = 0.13), or renal dysfunction-free days (p = 0.17). CONCLUSIONS: In patients with suspected infection who eventually required admission to the ICU, qSOFA calculated before their ICU admission had greater accuracy than SIRS for predicting mortality and ICU-free days. However, it may be less clear whether qSOFA is also better than SIRS criteria for predicting ventilator free-days and organ dysfunction-free days. These findings may help clinicians gain further insight into the usefulness of qSOFA.

Metatranscriptomic analysis of diminutive Thiomargarita-like bacteria ("Candidatus Thiopilula" spp.) from abyssal cold seeps of the Barbados Accretionary Prism.

Large sulfur-oxidizing bacteria in the family Beggiatoaceae are important players in the global sulfur cycle. This group contains members of the well-known genera Beggiatoa, Thioploca, and Thiomargarita but also recently identified and relatively unknown candidate taxa, including "Candidatus Thiopilula" spp. and "Ca. Thiophysa" spp. We discovered a population of "Ca. Thiopilula" spp. colonizing cold seeps near Barbados at a ∼4.7-km water depth. The Barbados population consists of spherical cells that are morphologically similar to Thiomargarita spp., with elemental sulfur inclusions and a central vacuole, but have much smaller cell diameters (5 to 40 µm). Metatranscriptomic analysis revealed that when exposed to anoxic sulfidic conditions, Barbados "Ca. Thiopilula" organisms expressed genes for the oxidation of elemental sulfur and the reduction of nitrogenous compounds, consistent with their vacuolated morphology and intracellular sulfur storage capability. Metatranscriptomic analysis further revealed that anaerobic methane-oxidizing and sulfate-reducing organisms were active in the sediment, which likely provided reduced sulfur substrates for "Ca. Thiopilula" and other sulfur-oxidizing microorganisms in the community. The novel observations of "Ca. Thiopilula" and associated organisms reported here expand our knowledge of the globally distributed and ecologically successful Beggiatoaceae group and thus offer insight into the composition and ecology of deep cold seep microbial communities.

Geochemical niches of iron-oxidizing acidophiles in acidic coal mine drainage.

A legacy of coal mining in the Appalachians has provided a unique opportunity to study the ecological niches of iron-oxidizing microorganisms. Mine-impacted, anoxic groundwater with high dissolved-metal concentrations emerges at springs and seeps associated with iron oxide mounds and deposits. These deposits are colonized by iron-oxidizing microorganisms that in some cases efficiently remove most of the dissolved iron at low pH, making subsequent treatment of the polluted stream water less expensive. We used full-cycle rRNA methods to describe the composition of sediment communities at two geochemically similar acidic discharges, Upper and Lower Red Eyes in Somerset County, PA, USA. The dominant microorganisms at both discharges were acidophilic Gallionella-like organisms, "Ferrovum" spp., and Acidithiobacillus spp. Archaea and Leptospirillum spp. accounted for less than 2% of cells. The distribution of microorganisms at the two sites could be best explained by a combination of iron(II) concentration and pH. Populations of the Gallionella-like organisms were restricted to locations with pH>3 and iron(II) concentration of >4 mM, while Acidithiobacillus spp. were restricted to pH<3 and iron(II) concentration of <4 mM. Ferrovum spp. were present at low levels in most samples but dominated sediment communities at pH<3 and iron(II) concentration of >4 mM. Our findings offer a predictive framework that could prove useful for describing the distribution of microorganisms in acid mine drainage, based on readily accessible geochemical parameters.

Sedimenticola thiotaurini sp. nov., a sulfur-oxidizing bacterium isolated from salt marsh sediments, and emended descriptions of the genus Sedimenticola and Sedimenticola selenatireducens.

A marine facultative anaerobe, strain SIP-G1T, was isolated from salt marsh sediments, Falmouth, MA, USA. Phylogenetic analysis of its 16S rRNA gene sequence indicated that it belongs to an unclassified clade of Gammaproteobacteria that includes numerous sulfur-oxidizing bacteria that are endosymbionts of marine invertebrates endemic to sulfidic habitats. Strain SIP-G1T is a member of the genus Sedimenticola, of which there is one previously described isolate, Sedimenticola selenatireducens AK4OH1T. S. selenatireducens AK4OH1T was obtained for further characterization and comparison with strain SIP-G1T. The two strains were capable of coupling the oxidation of thiosulfate, tetrathionate, elemental sulfur and sulfide to autotrophic growth and they produced sulfur inclusions as metabolic intermediates. They showed varying degrees of O2 sensitivity, but when provided amino acids or peptides as a source of energy, they appeared more tolerant of O2 and exhibited concomitant production of elemental sulfur inclusions. The organic substrate preferences and limitations of these two organisms suggest that they possess an oxygen-sensitive carbon fixation pathway(s). Organic acids may be used to produce NADPH through the TCA cycle and are used in the formation of polyhydroxyalkanoates. Cell-wall-deficient morphotypes appeared when organic compounds (especially acetate) were present in excess and reduced sulfur was absent. Levels of DNA-DNA hybridization (∼47%) and phenotypic characterization indicate that strain SIP-G1T represents a separate species within the genus Sedimenticola, for which the name Sedimenticola thiotaurini sp. nov. is proposed. The type strain is SIP-G1T ( = ATCC BAA-2640T = DSM 28581T). The results also justify emended descriptions of the genus Sedimenticola and of S. selenatireducens.