Photoferrotrophs thrive in an Archean Ocean analogue.

Considerable discussion surrounds the potential role of anoxygenic phototrophic Fe(II)-oxidizing bacteria in both the genesis of Banded Iron Formations (BIFs) and early marine productivity. However, anoxygenic phototrophs have yet to be identified in modern environments with comparable chemistry and physical structure to the ancient Fe(II)-rich (ferruginous) oceans from which BIFs deposited. Lake Matano, Indonesia, the eighth deepest lake in the world, is such an environment. Here, sulfate is scarce (<20 micromol x liter(-1)), and it is completely removed by sulfate reduction within the deep, Fe(II)-rich chemocline. The sulfide produced is efficiently scavenged by the formation and precipitation of FeS, thereby maintaining very low sulfide concentrations within the chemocline and the deep ferruginous bottom waters. Low productivity in the surface water allows sunlight to penetrate to the >100-m-deep chemocline. Within this sulfide-poor, Fe(II)-rich, illuminated chemocline, we find a populous assemblage of anoxygenic phototrophic green sulfur bacteria (GSB). These GSB represent a large component of the Lake Matano phototrophic community, and bacteriochlorophyll e, a pigment produced by low-light-adapted GSB, is nearly as abundant as chlorophyll a in the lake's euphotic surface waters. The dearth of sulfide in the chemocline requires that the GSB are sustained by phototrophic oxidation of Fe(II), which is in abundant supply. By analogy, we propose that similar microbial communities, including populations of sulfate reducers and photoferrotrophic GSB, likely populated the chemoclines of ancient ferruginous oceans, driving the genesis of BIFs and fueling early marine productivity.

Rates and pathways of CH4 oxidation in ferruginous Lake Matano, Indonesia.

This study evaluates rates and pathways of methane (CH4 ) oxidation and uptake using 14 C-based tracer experiments throughout the oxic and anoxic waters of ferruginous Lake Matano. Methane oxidation rates in Lake Matano are moderate (0.36 nmol L-1  day-1 to 117 µmol L-1  day-1 ) compared to other lakes, but are sufficiently high to preclude strong CH4 fluxes to the atmosphere. In addition to aerobic CH4 oxidation, which takes place in Lake Matano's oxic mixolimnion, we also detected CH4 oxidation in Lake Matano's anoxic ferruginous waters. Here, CH4 oxidation proceeds in the apparent absence of oxygen (O2 ) and instead appears to be coupled to some as yet uncertain combination of nitrate ( NO 3 - ), nitrite ( NO 2 - ), iron (Fe) or manganese (Mn), or sulfate ( SO 4 2 - ) reduction. Throughout the lake, the fraction of CH4 carbon that is assimilated vs. oxidized to carbon dioxide (CO2 ) is high (up to 93%), indicating extensive CH4 conversion to biomass and underscoring the importance of CH4 as a carbon and energy source in Lake Matano and potentially other ferruginous or low productivity environments.

Recovering cellular biomass from fluids using chemical flocculation.

We developed an efficient, scalable and inexpensive method for recovering cellular biomass from complex fluid matrices that cannot be processed using conventional filtration methods. The method uses chemical flocculation with iron oxyhydroxides, is capable of recovering greater than 90% of cellular biomass from fluids with more than 103 cells ml-1 , and was validated using both mock communities and field samples. High quality DNA can be readily extracted from iron flocs using standard soil extraction kits. We applied chemical flocculation to fracing fluids from British Columbia, Canada and recovered a diversity of microbial taxa including abundant members of the Epsilon- and Deltaproteobacteria previously recovered from shale gas operations in the United States. Application of chemical flocculation presents new opportunities for scalable time-series monitoring and experimentation on complex fluid matrices including microbial community profiling and shotgun metagenomics over gas production well completion cycles.