Microbial diversity in an early earth analogue: From ancient novelty to modern commonality

Life emerged and diversified in the absence of molecular oxygen 1. The prevailing anoxia and unique sulfur chemistry in the Paleo-, Meso- and Neoarchean, and early Proterozoic eons may have supported microbial communities that are drastically different than those currently thriving on the earth’s surface 2–4. Zodletone spring in southwestern Oklahoma represents a unique habitat where spatial sampling could substitute for geological eons: from the anoxic, surficial light-exposed sediments simulating a preoxygenated earth, to overlaid water column where air exposure simulates the relentless oxygen intrusion during the Neo-Proterozoic 5. We discovered a remarkably diverse microbial community in the spring sediments, with two thirds (340/516) of the metagenomic assembled genomes belonging to 200 bacterial and archaeal families that were either previously undescribed or are extremely rare elsewhere on earth. Such diversity is underpinned by the widespread occurrence of sulfite-, thiosulfate-, tetrathionate-, and sulfur-reduction, in contrast with a paucity of sulfate-reduction metabolism in those taxa. This greatly expands the diversity of lineages mediating reductive sulfur cycling processes in the tree of life. In the overlaying water community oxygen intrusion leads to the establishment of a significantly less diverse community dominated by well-characterized lineages and the prevalence of oxidative sulfur cycling processes. Such transition from ancient novelty to modern commonality underscores the profound impact of the great oxygenation event on the earth’s surficial anoxic community.. It also suggests that novel and rare lineages encountered in current anaerobic habitats could represent taxa once thriving on the anoxic earth that have failed to adapt to the progressive oxygenation.

Microbial diversity and sulfur cycling in an early earth analogue: From ancient novelty to modern commonality

Life emerged and diversified in the absence of molecular oxygen. The prevailing anoxia and unique sulfur chemistry in the Paleo-, Meso- and Neoarchean, and early Proterozoic eons may have supported microbial communities that are drastically different than those currently thriving on the earth surface. Zodletone spring in southwestern Oklahoma represents a unique habitat where spatial sampling could substitute for geological eons: from the anoxic, surficial light exposed sediments simulating a preoxygenated earth, to overlaid water column where air exposure simulates the relentless oxygen intrusion during the Neo Proterozoic. We document a remarkably diverse microbial community in the anoxic spring sediments, with 340/516 (65.89%) of genomes recovered in a metagenomic survey belonging to 200 bacterial and archaeal families that were either previously undescribed or that exhibit an extremely rare distribution on the current earth. Such diversity is underpinned by the widespread occurrence of sulfite-, thiosulfate, tetrathionate-, and sulfur-reduction, and paucity of sulfate-reduction machineries in these taxa, hence greatly expanding lineages mediating reductive sulfur cycling processes in the tree of life. Analysis of the overlaying water community demonstrated that oxygen intrusion lead to the development of a significantly less diverse community dominated by well-characterized lineages and a prevalence of oxidative sulfur cycling processes. Such transition from ancient novelty to modern commonality underscores the profound impact of the great oxygenation event on the earth surficial anoxic community. It also suggests that novel and rare lineages encountered in current anaerobic habitats could represent taxa once thriving in an anoxic earth, but have failed to adapt to earth progressive oxygenation.

Which management option has the highest greenhouse gas reduction potential for drained peatlands?

<p>Almost all peatlands in the Netherlands are drained for agricultural purposes or in the past for peat extraction. What remains is a peatland area of about 300.000 ha of which 85 % is used for agriculture. As a result of peat oxidation, these areas are still subsiding by about 1 cm per year. Another effect is the enormous emission of CO<sub>2</sub>, which contributes to about 4% of total Dutch greenhouse gas emissions. With the awareness of a changing climate and the need for protection against flooding of coastal areas, solutions are being searched to reduce or stop peat oxidation and coinciding land subsidence and CO<sub>2</sub> emission.</p><p>In this presentation we will show different management options (subsoil irrigation, pressurized subsoil irrigation, paludiculture) which are currently being tested in the Netherlands. They will be put into perspective of data from other European studies. These options all focus on increasing the groundwater table to lower oxygen intrusion and consequently lower aerobic decomposition. Depending on crop choices, water levels may need to stay 40 cm below the surface to maximize fodder plant yields, or go to surface level to increase peat ecosystem functions like C-sequestration. The management options range from maintaining the current land-use by elevating summer water levels, with submerged drainage, to the development of peat-forming plant species by complete rewetting. Data of the effects of these management options on CO<sub>2</sub> emission show that Sphagnum farming is the most promising mitigation option to reduce greenhouse gas emission from drained peatlands. It turned the land from a carbon and greenhouse gas source into a sink.</p>

How to make intensively used peat meadows sustainable for the future? Four management options to potentially reduce peat oxidation

<p>Almost all peatlands in the Netherlands are drained for agricultural purposes or in the past for peat extraction. What remains is a peatland area of about 300.000 ha of which 85 % is used for agriculture. As a result of peat oxidation, these areas are still subsiding by about 1 cm per year. Another effect is the enormous emission of CO<sub>2</sub>, which contributes to about 4% of total Dutch greenhouse gas emissions. With the awareness of a changing climate and the need for protection against flooding of coastal areas, solutions are being searched to reduce or stop peat oxidation and coinciding land subsidence and CO<sub>2</sub> emission.</p><p>In this presentation we will show four different management options which are currently being tested in the Netherlands. These options all focus on increasing the groundwater table to lower oxygen intrusion and consequently lower aerobic decomposition. Depending on crop choices water levels may need to stay 40 cm below the surface to maximize fodder plant yields. We expect a trade-off between land-use intensity (yields) and CO<sub>2</sub> emission reduction. The management options range from maintaining the current land-use by elevating summer water levels with submerged drainage pipes to the development of peat-forming plant species by complete rewetting. Data of the effects of these management options on CO<sub>2</sub> emission will be shown and with that the effectiveness of reducing peat oxidation.</p>

Controls on mobility of heavy metals of mine tailings in a karst area as shown by multi-stable isotopes tracing: δ18O/δ2H in soil water and δ34S of soil soluble SO42-

<p>The collapse of a tailings dam of a Pb-Zn mine, caused by a storm in 1978, resulted in severe heavy metals contamination in the valley downstream the mine, located in the Guangxi Province, southwest of China. The metals still pose a risk to the adjacent fragile karst environment. Especially, the potential for leaching of the heavy metals to the adjacent environment is of concern due to the high average annual precipitation of >1500 mm in the subtropical climate. Previous studies have classified areas of the valley as slightly (SP), moderately (MP) or heavily polluted (HP) based on heavy metals content (Pb, Cd, As, Cu, Zn) of the upper 20 cm of the soils. We analysed soil and sediment profiles up to 2 m deep, obtained in areas of the three pollutions levels, for basic chemical and physical parameters including pH, total organic carbon (TOC), soil moisture, particle size, total metals concentrations (Pb, Zn, Cd, and Cu), and δ<sup>18</sup>O and δ<sup>2</sup>H of soil moisture. Further, we measured the δ<sup>34</sup>S of soil extractable sulphate, and the content of chromium-reducible sulphur (CRS) and soluble sulphates (SS), to investigate the link between sulphur cycling and heavy metals mobilization. Today, four decades after the dam collapse, heavy metal concentrations are still highly elevated in the valley. In the HP profile concentrations of Pb, Cd, Cu and Zn range between 800–8120, 8–132, 156–616, and 2647–12250 mg/kg, respectively, between surface and 2 m depth. Concentrations of CRS in the HP profile of 287–5530 mg/kg were observed, while no CRS could be extracted from the SP and MP soil profiles. The δ<sup>34</sup>S-SO<sub>4</sub><sup>2-</sup> of the HP profile (0.4‰–16.0‰) matches values previously measured in the original tailing. The matching δ<sup>34</sup>S-SO<sub>4</sub><sup>2-</sup> and elevated CRS values of the HP profile indicate that the valley contains thick deposits (up to at least a 2 meters) of resettled tailings sediments of the original upstream tailings dam. However, these sediments are clayey, with >50%wt being <0.002 mm in particle size, allowing only a slow advective water and solute movement to or from (leaching) the sediment. A currently low, yet possibly significant(!), heavy metals leaching is further indicated by the only slightly acidic pH (6-6.5) which indicate a lack of oxygen intrusion into the sediments and reaction with the CRS content. Also, the HP profile had soluble sulphate concentrations of 532–1156 mg S/kg which were reasonably comparable to the values measured in the less polluted areas, implying a history without large amounts of CRS oxidation. Further, Pb and Cu concentration in the HP profile shows a continuous (high) distribution vs. depth which also suggests a history without extremely low pH. Finally, deuterium-excess values can be interpreted as showing diffusive, rather than advective, water and solute movement. While, accordingly, the heavy metals currently appear relatively well stabilized towards leaching, any management that increases oxygen intrusion or water exchange will impose a high risk of immediate and severe environmental pollution to the adjacent aqueous environment.</p>

Simultaneous phosphorus uptake and denitrification by EBPR-r biofilm under aerobic conditions: effect of dissolved oxygen

A biofilm process, termed enhanced biological phosphorus removal and recovery (EBPR-r), was recently developed as a post-denitrification approach to facilitate phosphorus (P) recovery from wastewater. Although simultaneous P uptake and denitrification was achieved despite substantial intrusion of dissolved oxygen (DO >6 mg/L), to what extent DO affects the process was unclear. Hence, in this study a series of batch experiments was conducted to assess the activity of the biofilm under various DO concentrations. The biofilm was first allowed to store acetate (as internal storage) under anaerobic conditions, and was then subjected to various conditions for P uptake (DO: 0–8 mg/L; nitrate: 10 mg-N/L; phosphate: 8 mg-P/L). The results suggest that even at a saturating DO concentration (8 mg/L), the biofilm could take up P and denitrify efficiently (0.70 mmol e−/g total solids*h). However, such aerobic denitrification activity was reduced when the biofilm structure was physically disturbed, suggesting that this phenomenon was a consequence of the presence of oxygen gradient across the biofilm. We conclude that when a biofilm system is used, EBPR-r can be effectively operated as a post-denitrification process, even when oxygen intrusion occurs.

Unique Ecophysiology among U(VI)-Reducing Bacteria as Revealed by Evaluation of Oxygen Metabolism in Anaeromyxobacter dehalogenans Strain 2CP-C

ABSTRACT Anaeromyxobacter spp. respire soluble hexavalent uranium, U(VI), leading to the formation of insoluble U(IV), and are present at the uranium-contaminated Oak Ridge Integrated Field Research Challenge (IFC) site. Pilot-scale in situ bioreduction of U(VI) has been accomplished in area 3 of the Oak Ridge IFC site following biostimulation, but the susceptibility of the reduced material to oxidants (i.e., oxygen) compromises long-term U immobilization. Following oxygen intrusion, attached Anaeromyxobacter dehalogenans cells increased approximately 5-fold from 2.2 × 107 ± 8.6 × 106 to 1.0 × 108 ± 2.2 × 107 cells per g of sediment collected from well FW101-2. In the same samples, the numbers of cells of Geobacter lovleyi, a population native to area 3 and also capable of U(VI) reduction, decreased or did not change. A. dehalogenans cells captured via groundwater sampling (i.e., not attached to sediment) were present in much lower numbers (<1.3 × 104 ± 1.1 × 104 cells per liter) than sediment-associated cells, suggesting that A. dehalogenans cells occur predominantly in association with soil particles. Laboratory studies confirmed aerobic growth of A. dehalogenans strain 2CP-C at initial oxygen partial pressures (pO2) at and below 0.18 atm. A negative linear correlation [μ = (−0.09 × pO2) + 0.051; R 2 = 0.923] was observed between the instantaneous specific growth rate μ and pO2, indicating that this organism should be classified as a microaerophile. Quantification of cells during aerobic growth revealed that the fraction of electrons released in electron donor oxidation and used for biomass production (fs ) decreased from 0.52 at a pO2 of 0.02 atm to 0.19 at a pO2 of 0.18 atm. Hence, the apparent fraction of electrons utilized for energy generation (i.e., oxygen reduction) (fe ) increased from 0.48 to 0.81 with increasing pO2, suggesting that oxygen is consumed in a nonrespiratory process at a high pO2. The ability to tolerate high oxygen concentrations, perform microaerophilic oxygen respiration, and preferentially associate with soil particles represents an ecophysiology that distinguishes A. dehalogenans from other known U(VI)-reducing bacteria in area 3, and these features may play roles for stabilizing immobilized radionuclides in situ.

Effects of applied voltages and dissolved oxygen on sustained power generation by microbial fuel cells

Oxygen intrusion into the anode chamber through proton exchange membrane can result in positive redox conditions in fed-batch, two chamber MFCs at the end of a cycle when the substrate is depleted. A slight increase in dissolved oxygen to 0.3 mg/L during MFC operation was not found to adversely affect power generation over subsequent cycles if sufficient substrate (acetate) was provided. Purging the anode chamber with air or pure oxygen for up to 10 days and 10 hrs also did not affect power generation, as power rapidly returned to previous levels when the chamber was sparged with nitrogen gas. When MFCs are connected in series, voltage reversal can occur resulting in a positive voltage applied to the anode biofilm. To investigate if this adversely affected the bacteria, voltages of 1, 2, 3, 4, and 9 V, were applied for 1 hr to the MFC before reconnecting it back to a fixed external load (1,000 Ω). A voltage of &lt;2 V did not affect power generation. However, applying 3 V resulted in a 15 h lag phase before recovery, and 9 V produced a 60 h lag phase suggesting substantial damage to the bacteria that required re-growth of bacteria in the biofilm. These results indicate that charge reversal will be a more serious problem than oxygen intrusion into the anode chamber for sustained performance of MFCs.