Microbial metabolisms and calcification in freshwater biofilms

In dieser Arbeit wurden Biofilme zweier CO2-entgasender Karstwasserbäche in Deutschland, welche in ihrem Verlauf flußabwärts hohe Kalziumkarbonat-Übersättigungen erreichen, bezüglich der mikrobiellen Effekte auf die CaCO3-Fällung, Wasserchemie des Mikro- und Makromilieus, Stabile Isotopenverhältnisse und Kalktuff-Gefügebildung untersucht. In situ und ex situ Mikroelektroden-Messungen an kalzifizierenden Biofilmen, welche hauptsächlich von filamentösen Cyanobakterien aufgebaut werden, zeigen, daß unter Belichtung eine CaCO3-Fällung durch Photosynthese induziert, unter Dunkelheit dagegen eine Fällung verhindert wird. Eine Photosynthese-induzierte CaCO3-Fällung wurde ebenso bestätigt durch 45Ca-Tracer-Experimente und Massenbilanzrechnungen. Die in den Kalktuff-Stromatolithen aufgezeichneten stabilen Sauerstoff- und Kohlenstoff-Isotopenwerte ließen keinen Photosynthese-Effekt erkennen, trotz der offensichtlichen Photosynthese-induzierten Fällung. Entsprechend kann das Fehlen einer 13C-Anreichungen in Karbonatmineralen nicht als Indikator für ein Fehlen eines Photosynthese-Effektes auf eine Karbonatfällung gewertet werden Ebenso kann das Verkalkungsmuster von Cyanobakterien nicht zur Unterscheidung von Photosynthese-induzierter und physikochemisch induzierter CaCO3-Fällung herangezogen werden. Insbesondere tritt in den photosynthetisch verkalkten Kalktuff-Biofilmen anstatt Polysaccharidscheiden-Imprägnation eine -Inkrustation auf, sprich ein Verkalkungsmuster, welches vormals als Indikator für physikochemisch-erzwungene Fällung angesehen wurde. Auch wenn Kalktuff-Stromatolithen durch Photosynthese-induzierte Kalzitfällung gebildet werden, so zeigen doch Massenbilanzrechnungen, daß die Biofilmverkalkung für nur etwa 10-20% des Ca2+-Entzuges im Bachwasser verantwortlich ist, während der verbliebene Ca2+-Entzug mit physikochemischer Fällung auf Ästen und Blättern sowie in Form feinkörnige Kalzitpartikel erklärt werden muß. Entsprechend sind die Effekte einer Photosynthese-induzierten Fällung verdünnt, und damit mit herkömmlichen Wasseranalysen kaum nachweisbar, außer bei Gewässern mit geringen Fließgeschwindigkeiten. Auf der anderen Seite können endolithische Cyanobakterien-Biofilme wie auch Moose aufgrund ihrer geringeren Photosynthese-Leistung keine Kalkfällung induzieren, wie ex situ Mikroelektroden-Messungen belegen. Biofilm-freie Kalksubstrate führen trotz hoher Übersättigungen des Umgebungsmilieus zu keiner spontanen Kalkfällung, wohingegen Kalktuffbiofilme unter denselben Bedingungen eine Fällung induzieren. Dies zeigt, daß Photosynthese ein entscheidender Mechanismus zur Überwindung kinetischer Barrieren der CaCO3-Fällung ist, sogar in hochgradig übersättigten Milieus. Modellrechnungen des Photosynthese-Effekts unter verschiedenen pH, DIC und Ca2+-Konzentrationen zeigen, daß die Voraussetzungen einer Photosynthese-induzierten Karbonatfällung (1) optimale pH-DIC-Bedingungen mit niedrigem DIC-Puffereffekt, (2) ausreichende initiale Mineralsättigungen, und (3) nicht extrem niedrige Ca2+-Konzentrationen sind. Außerdem können hohe Ionenstärken eine Photosynthese-induzierte Fällung beeinträchtigen oder verhindern. Sicherlich muß auch die Photosynthese-Aktivität der Biofilme für eine Verschiebung des Karbonatgleichgewichtes auf oder in den Biofilmen hoch genug sein. Die meisten dieser Voraussetzungen lassen sich auch auf Karbonatfällungen übertragen, welche durch andere Arten mikrobieller Stoffwechselaktivität wie Sulphatreduktion induziert werden. Die Schlußfolgerung ist daher, daß die oben genannten Voraussetzungen wichtige Schlüssel für das Verständnis der Bildung und generelle Verteilung karbonatischer Mikrobialithe durch die Erdgeschichte hindurch sind

Endolithic microbial habitats hosted in carbonate nodules currently forming within sediment at a high methane flux site in the sea of Japan

Concretionary carbonates in deep-sea methane seep fields are formed as a result of microbial methane degradation, called anaerobic oxidation of methane (AOM). Recently, active microorganisms, including anaerobic methanotrophic archaea, were discovered from methane seep-associated carbonate outcroppings on the seafloor. However sedimentary buried carbonate nodules are a hitherto unknown microbial habitat. In this study, we investigated the microbial community structures in two carbonate nodules collected from a high methane flux site in a gas hydrate field off the Oki islands in the Sea of Japan. The nodules were formed around sulfate-methane interfaces (SMI) corresponding to 0.7 and 2.2 m below the seafloor. Based on a geochemical analysis, light carbon isotopic values ranging from −54.91‰ to −37.32‰ were found from the nodules collected at the shallow SMI depth, which were attributed to the high contributions of AOM-induced carbonate precipitation. Signatures of methanotrophic archaeal populations within the sedimentary buried nodule were detected based on microbial community composition analyses and quantitative real-time PCR targeted 16S rRNA, and functional genes for AOM. These results suggest that the buried carbonate nodule currently develops AOM-related microbial communities, and grows depending on the continued AOM under high methane flux conditions

Significant contribution of subseafloor microparticles to the global manganese budget

Ferromanganese minerals are widely distributed in subseafloor sediments and on the seafloor in oceanic abyssal plains. Assessing their input, formation and preservation is important for understanding the global marine manganese cycle and associated trace elements. However, the extent of ferromanganese minerals buried in subseafloor sediments remains unclear. Here we show that abundant (108–109 particles cm−3) micrometer-scale ferromanganese mineral particles (Mn-microparticles) are found in the oxic pelagic clays of the South Pacific Gyre (SPG) from the seafloor to the ~100 million-year-old sediments above the basement. Three-dimensional micro-texture, and major and trace element compositional analyses revealed that these Mn-microparticles consist of poorly crystalline ferromanganese oxides precipitating from bottom water. Based on our findings, we extrapolate that 1.5–8.8 × 1028 Mn-microparticles, accounting for 1.28–7.62 Tt of manganese, are globally present in oxic subseafloor sediments. This estimate is at least two orders of magnitude larger than the manganese budget for nodules and crusts on the seafloor. Subseafloor Mn-microparticles thus contribute significantly to the global manganese budget.This study was supported in part by the Japan Society for the Promotion of Science (JSPS) Strategic Fund for Strengthening Leading-Edge Research and Development (to JAMSTEC and F.I.), the JSPS Funding Program for Next Generation World-Leading Researchers (GR102 to F.I.), JSPS Grant-in-Aid for Scientific Research (24687004 and 15H05608 to Y.M., 25871219 to G.-I.U., 15H02810 to R.W., 18H04134, 17H06458 and 17H04582 to Y.T., and 26251041 to F.I.), JSPS Grant-in-Aid for JSPS Fellows (14J00199 to G.-I.U.), and Ministry of Education, Culture, Sports, Science, and Technology (MEXT) Fund Leading Initiative for Excellent Young Researchers (to Kochi University and G.-I.U.)

Microbial effects on biofilm calcification, ambient water chemistry and stable isotope records in a highly supersaturated setting (Westerhöfer Bach, Germany)

Cyanobacteria-dominated biofilms in a CO2-degassing karst-water creek (Westerhöfer Bach, Germany) were investigated with regard to the effects of microbial activity on CaCO3 precipitation, water chemistry of micro- and macroenvironments, stable isotopic records, and tufa fabric formation. Ex situ microelectrode measurements of pH, O2, Ca2+ and CO32− revealed that annually laminated calcified biofilms composed mainly of filamentous cyanobacteria (tufa stromatolites) strongly induced CaCO3 precipitation by photosynthesis under illumination, but inhibited precipitation by respiration in the dark. In contrast, endolithic cyanobacterial biofilms and mosses did not cause photosynthesis-induced precipitation under experimental conditions. No spontaneous precipitation occurred on bare limestone substrates, despite high calcite supersaturation of the ambient water. Mass balance calculations suggest that biofilm photosynthesis was responsible for 10–20% of Ca2+ loss in the creek, while the remaining Ca2+ loss derived from physicochemical precipitation on branches, leaves and as fine-grained calcite particles. Neither analysis of bulk water chemistry nor oxygen nor carbon stable isotopic records of the tufa stromatolites confirmed photosynthetic effects, despite the evident photosynthesis-induced calcite precipitation. Oxygen stable isotopic values reflected seasonal changes in water temperature, and carbon stable isotope values probably recorded carbon isotopic composition of dissolved inorganic carbon in the creek water. Annual lamination and fabric formation of the tufa stromatolites is suggested to vary with photosynthesis-induced calcite precipitation rates that are affected by temperature dependency of diffusion coefficients. Photosynthesis-induced precipitation resulted in encrusted cyanobacterial sheaths, reflecting syntaxial overgrowth of microcrystalline cyanobacterial tubes by microspar, instead of microcrystalline sheath impregnation, which was previously suggested as an indicator of photosynthesis-induced precipitation. Therefore, sheath impregnation or encrustation by CaCO3 cannot be used to distinguish photosynthesis-induced from physicochemically-induced CaCO3 precipitation

Metabolic Microenvironmental Control by Photosynthetic Biofilms under Changing Macroenvironmental Temperature and pH Conditions▿ †

Ex situ microelectrode experiments, using cyanobacterial biofilms from karst water creeks, were conducted under various pH, temperature, and constant-alkalinity conditions to investigate the effects of changing environmental parameters on cyanobacterial photosynthesis-induced calcification. Microenvironmental chemical conditions around calcifying sites were controlled by metabolic activity over a wide range of photosynthesis and respiration rates, with little influence from overlying water conditions. Regardless of overlying water pH levels (from 7.8 to 8.9), pH at the biofilm surface was approximately 9.4 in the light and 7.8 in the dark. The same trend was observed at various temperatures (4°C and 17°C). Biological processes control the calcium carbonate saturation state (Ω) in these and similar systems and are able to maintain Ω at approximately constant levels over relatively wide environmental fluctuations. Temperature did, however, have an effect on calcification rate. Calcium flux in this system is limited by its diffusion coefficient, resulting in a higher calcium flux (calcification and dissolution) at higher temperatures, despite the constant, biologically mediated pH. The ability of biological systems to mitigate the effects of environmental perturbation is an important factor that must be considered when attempting to predict the effects of increased atmospheric partial CO2 pressure on processes such as calcification and in interpreting microfossils in the fossil record

Strontium isotopic age of the Torinosu Limestone in Niyodo Village, Kochi Prefecture, SW Japan.

高知県仁淀村に分布する鳥巣層群谷地層中の石灰岩のSr同位体比は，続成作用の効果を考慮した結果，解像度のよい年代値として利用できることが明らかになった．カソードルミネッセンス法による観察結果と微量元素濃度の分析結果は，石灰岩中の構成物のうち，腕足類化石が最もよく堆積時の初生的な海水Sr同位体比を保持することを示す．また，層孔虫や石灰海綿 Chatetopsis sp.は腕足類よりやや高いSr同位体比を示し，それによる年代のずれは後期ジュラ紀から前期白亜紀においては2.8 m.y.に達するため，これらの化石は詳細な年代の議論に使うことはできない．腕足類から得られたSr同位体比を最新のSr同位体比曲線に合わせると，谷地層下部の石灰岩体の堆積年代は，146.1～148.4 Ma（中期Tithonian）と計算される．Sr同位体比から得られた石灰岩の堆積年代は微化石年代と整合的であり，より解像度が高い．Strontium isotopic ratio provides high-resolution ages of the limestone of Yatsuji Formation (Torinosu Group) in Niyodo Village (Kochi Prefecture), on the basis of considering diagenetic effects. Results of cathodoluminescence and trace elements analysis revealed that brachiopod shell is retaining the original marine strontium isotopic value. Stromatoporoids and a calcified sponge Chatetopsis sp. tend to record higher values than the brachiopod shells collected from the same horizon. Their differences are attain to +0.00005, and which corresponds to 2.8 m.y. during late Jurassic to early Cretaceous periods. Therefore, we concluded that stromatoporoids and Chatetopsis sp. are not suitable for the precise age determination. Obtained strontium isotope data of brachiopod shells are converted to depositional age by fitting to recently proposed strontium isotopic curve (LOWESS Look-up Table Version 4). The depositional age of the limestone body of the lower Yatsuji Formation is 146.1-148.4 Ma (middle Tithonian). This age is consistent with microfossil ages, and has higher time resolution.本論は高知大学海洋コア総合研究センター共同利用研究（課題番号 04B011; 代表者，狩野彰宏）の成果である