Miranda, M.L., Osterholz, H., Giebel, H.A., Bruhnke, P., Dittmar, T., Zielinski, O., 2020. Impact of UV radiation on DOM transformation on molecular level using FT-ICR-MS and PARAFAC. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 230, 118027.

http://www.sciencedirect.com/science/article/pii/S1386142520300032 Dissolved organic matter (DOM) is an omnipresent constituent of natural water bodies. Reuse and transformation of DOM compounds in the water column is driven by physicochemical and biological processes leading to the production of refractory DOM. Typically, breakdown of DOM chemical compounds into smaller or more condensed fragments is triggered by ultraviolet (UV) radiation. Here, we present a study on the photodegradation of DOM produced during an incubation experiment with a natural microbial community. At the end of the first incubation without UV irradiation, the samples from 3 mesocosms were filtered to remove microbes and particles and continuously exposed to UV radiation (280 -365 nm). We investigated DOM in depth via monitoring of dissolved organic carbon (DOC) concentrations, DOM molecular characterization by Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) and excitation emission matrix spectroscopy (EEMS). Analysis of variance indicated no significant differences in the DOCconcentration between treatments. Main peaks in the fluorescent DOM (FDOM) were photo-bleached by UV radiation, and an increase in the fluorescent intensity of selected peaks was observed on irradiated samples toward the end of the experiment. Parallel factor analysis (PARAFAC) indicated the presence of three main components in all treatments: C1 (Marine humic M), C2 (Bacterial produced humic C), C3 (Tyrosine), and an additional component in the dark incubation of mesocosm 3, C4 (Tryptophan). Despite an intensive filtration protocol through 0.7, 0.2 and 0.1 μm filters, low bacterial abundances were determined (<2.5 × 10-3 cells mL-1). We observed a direct correlation between structural indices and the intensity of PARAFAC components. Average double bond equivalent and aromaticity were strongly positively correlated with PARAFAC components C1 and C2 for one or more mesocosm. Moreover, FT-ICR-MS showed that under the tested conditions, the recalcitrance of the DOM assessed as the similarity to a deep ocean DOM reference did not increase on molecular level. Thus, mechanisms other than photochemical transformations of relatively recent DOM are likely necessary to facilitate long-term stability of DOM in the oceans.

Miyajima, Y., Watanabe, Y., Goto, A.S., Jenkins, R.G., Sakai, S., Matsumoto, R., Hasegawa, T., 2020. Archaeal lipid biomarker as a tool to constrain the origin of methane at ancient methane seeps: Insight into subsurface fluid flow in the geological past. Journal of Asian Earth Sciences 189, 104134.

http://www.sciencedirect.com/science/article/pii/S1367912019304869 The origin of methane discharged at ancient methane seeps is a key to understand subsurface fluid-flow processes in sedimentary basins. The carbon isotopic composition of methane-seep carbonates can be used to estimate the origin of methane, but mixing of multiple carbon sources results in ambiguous interpretation. We here constrained the origin of methane at ancient seeps by using the carbon isotopic composition and the isotope fractionation of lipid biomarkers of anaerobic methane-oxidizing archaea. We estimated the carbon-isotope 13 fractionation between methane and biomarkers as the offset between their δ C values at modern seep sites in the Japan Sea and other regions of the world. The biomarker pentamethylicosane (PMI) extracted from a modern seep carbonate of the Japan Sea shows a 44‰ offset from the seep methane. On the basis of literature data, we calculated the carbon-isotope offset as mostly ~20 -60‰ for PMI at modern seeps across the world. We 13 also assessed the relationship of the δ C values between methane and biomarkers by regression analysis on the 13 data taken at the modern seeps, obtaining regression formulas to estimate the δ C values of methane from those of biomarkers. For ancient seeps, we examined Miocene to Pleistocene methane-seep carbonate rocks collected 13 from Japan Sea sediments. PMI extracted from these ancient carbonates have δ C values ranging from -137‰ 13 to -93‰. Using the δ C values of PMI and the carbon-isotope offset and regression formulas, we estimated that the methane at the ancient seeps was mainly of biogenic origin and migrated from the shallow subsurface.

Miyazawa, D., Thanh, L.T.H., Tani, A., Shintani, M., Loc, N.H., Hatta, T., Kimbara, K., 2019. Isolation and characterization of genes responsible for naphthalene degradation from thermophilic naphthalene degrader, Geobacillus sp. JF8. Microorganisms 8, 44.