Movile Cave is an unusual groundwater ecosystem that is supported by in situ chemoautotrophic production. The cave atmosphere contains 1-2% methane (CH4), although much higher concentrations are found in gas bubbles that keep microbial mats afloat on the water surface. As previous analyses of stable carbon isotope ratios have suggested that methane oxidation occurs in this environment, we hypothesized that aerobic methane-oxidizing bacteria (methanotrophs) are active in Movile Cave. To identify the active methanotrophs in the water and mat material from Movile Cave, a microcosm was incubated with a 10%13CH4 headspace in a DNA-based stable isotope probing (DNA-SIP) experiment. Using improved centrifugation conditions, a 13C-labelled DNA fraction was collected and used as a template for polymerase chain reaction amplification. Analysis of genes encoding the small-subunit rRNA and key enzymes in the methane oxidation pathway of methanotrophs identified that strains of Methylomonas, Methylococcus and Methylocystis/Methylosinus had assimilated the 13CH4, and that these methanotrophs contain genes encoding both known types of methane monooxygenase (MMO). Sequences of non-methanotrophic bacteria and an alga provided evidence for turnover of CH4 due to possible cross-feeding on 13C-labelled metabolites or biomass. Our results suggest that aerobic methanotrophs actively convert CH4 into complex organic compounds in Movile Cave and thus help to sustain a diverse community of microorganisms in this closed ecosystem.
This paper presents the results of a laboratory study on the influence of heterotrophic bacteria on dissolution of a silicate mineral (K-feldspar) under a variety of growth conditions. Twenty seven strains of heterotrophic bacteria were isolated from a feldspar-rich soil (Shap, NW England). Liquid and solid minimal aerobic media (C/N-sufficient, K-limited, Fe-limited, N-limited and glucose/NH4Cl only) at 26ºC were used for isolation of the bacteria. The media selected bacterial isolates that were fastgrowing aerobic heterotrophs able to use glucose as the sole source of carbon and energy. The extent of mineral dissolution (in the presence of the isolates) was assessed after 48 h of incubation by measuring the release of Al from the K-feldspar by ICP-AES. More detailed dissolution experiments were carried out with one of the strains, Serratia marcescens, an isolate that was very effective in enhancing feldspar dissolution. The main conclusions of this study are: (1) the degree of enhancement of K-feldspar dissolution varied with bacterial isolate and growth conditions; (2) enhancement of dissolution began during stationary phase growth; (3) the production of chelating compounds (exopolymers, siderophores, pigments) during the stationary phase might be a possible mechanism for bacterially enhanced K-feldspar dissolution; (4) the frequent sub-culturing of isolates can have a significant effect on their physiological characteristics and may possibly influence their capacity to enhance mineral dissolution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.