Bioreactivity of estuarine dissolved organic matter: A combined geochemical and microbiological approach

An integrated multidisciplinary study utilizing geochemical and microbial ecological approaches was conducted to characterize the origins, chemical nature, and quantities of dissolved and particulate organic matter (OM) utilized by heterotrophic bacteria in a temperate estuary. C: N, stable isotope (delta C-13), and lipid biomarker analyses revealed differences in the inferred reactivity of autochthonous versus allochthonous OM sources. Isotopic comparison of OM size fractions and bacterial nucleic acids suggests that high-molecular-weight dissolved OM (DOM) is consistently linked to bacterial biomass synthesis along the estuarine salinity gradient. Polyunsaturated fatty acids (as percent of total fatty acids, FA) were a reliable predictor of DOM decomposition in bioassays, thus providing an indicator directly linking DOM reactivity to its composition. Significant positive correlations between FA diagnostic of bacterial sources and lipid biomarker compounds diagnostic of planktonic origin indicate a systematic bacterial response to autochthonous DOM sources along the estuarine continuum. These findings further suggest that, although the geochemical signature of algal-derived OM in the dissolved phase may appear quantitatively insignificant, this fraction may nevertheless represent a principal source of bioreactive OM to heterotrophic bacteria in estuarine waters

MSH3 polymorphisms and protein levels affect CAG repeat instability in huntington's disease mice

Expansions of trinucleotide CAG/CTG repeats in somatic tissues are thought to contribute to ongoing disease progression through an affected individual's life with Huntington's disease or myotonic dystrophy. Broad ranges of repeat instability arise between individuals with expanded repeats, suggesting the existence of modifiers of repeat instability. Mice with expanded CAG/CTG repeats show variable levels of instability depending upon mouse strain. However, to date the genetic modifiers underlying these differences have not been identified. We show that in liver and striatum the R6/1 Huntington's disease (HD) (CAG)~100 transgene, when present in a congenic C57BL/6J (B6) background, incurred expansion-biased repeat mutations, whereas the repeat was stable in a congenic BALB/cByJ (CBy) background. Reciprocal congenic mice revealed the Msh3 gene as the determinant for the differences in repeat instability. Expansion bias was observed in congenic mice homozygous for the B6 Msh3 gene on a CBy background, while the CAG tract was stabilized in congenics homozygous for the CBy Msh3 gene on a B6 background. The CAG stabilization was as dramatic as genetic deficiency of Msh2. The B6 and CBy Msh3 genes had identical promoters but differed in coding regions and showed strikingly different protein levels. B6 MSH3 variant protein is highly expressed and associated with CAG expansions, while the CBy MSH3 variant protein is expressed at barely detectable levels, associating with CAG stability. The DHFR protein, which is divergently transcribed from a promoter shared by the Msh3 gene, did not show varied levels between mouse strains. Thus, naturally occurring MSH3 protein polymorphisms are modifiers of CAG repeat instability, likely through variable MSH3 protein stability. Since evidence supports that somatic CAG instability is a modifier and predictor of disease, our data are consistent with the hypothesis that variable levels of CAG instability associated with polymorphisms of DNA repair genes may have prognostic implications for various repeat-associated diseases

A global database of dissolved organic matter (DOM) concentration measurements in coastal waters (CoastDOM v1)

Measurements of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) con-centrations are used to characterize the dissolved organic matter (DOM) pool and are important components ofbiogeochemical cycling in the coastal ocean. Here, we present the first edition of a global database (CoastDOMv1; available at https://doi.org/10.1594/PANGAEA.964012, L\uf8nborg et al., 2023) compiling previously pub-lished and unpublished measurements of DOC, DON, and DOP in coastal waters. These data are complementedby hydrographic data such as temperature and salinity and, to the extent possible, other biogeochemical variables(e.g. chlorophyll a, inorganic nutrients) and the inorganic carbon system (e.g. dissolved inorganic carbon andtotal alkalinity). Overall, CoastDOM v1 includes observations of concentrations from all continents. However,most data were collected in the Northern Hemisphere, with a clear gap in DOM measurements from the SouthernHemisphere. The data included were collected from 1978 to 2022 and consist of 62 338 data points for DOC,20 356 for DON, and 13 533 for DOP. The number of measurements decreases progressively in the sequenceDOC > DON > DOP, reflecting both differences in the maturity of the analytical methods and the greater focuson carbon cycling by the aquatic science community. The global database shows that the average DOC concen-tration in coastal waters (average \ub1 standard deviation (SD): 182 \ub1 314 μmol C L−1; median: 103 μmol C L−1) is13-fold higher than the average coastal DON concentration (13.6 \ub1 30.4 μmol N L−1; median: 8.0 μmol N L−1),which is itself 39-fold higher than the average coastal DOP concentration (0.34 \ub1 1.11 μmol P L−1; median:0.18 μmol P L−1). This dataset will be useful for identifying global spatial and temporal patterns in DOM and willhelp facilitate the reuse of DOC, DON, and DOP data in studies aimed at better characterizing local biogeochem-ical processes; closing nutrient budgets; estimating carbon, nitrogen, and phosphorous pools; and establishing abaseline for modelling future changes in coastal waters

Effects of sunlight on decomposition of estuarine dissolved organic C, N and P and bacterial metabolism

The effects of natural sunlight and microbial decomposition on DOC, DON, and DOP were investigated along the salinity gradient of a temperate coastal plain estuary. The impact of sunlight-irradiated DOM on bacterial properties (bacterial abundance, production, bacterial growth efficiency [BGE]) was also followed. Surface-water light levels resulted in no detectable abiotic production of NH4+ or PO43- or loss of DOC. Bacterial decomposition of DOC was enhanced by 27 to 200 % in irradiated relative to dark treatments. There was, however, no corresponding enhancement in DON and DOP remineralization. Significant differences in bacterial decomposition of light-exposed DOC were frequently observed following prolonged incubation (\u3e7 d), suggesting that enhanced reactivity may result from photochemical modification of higher molecular weight organic matter. BGE in light relative to dark treatments was positively correlated (r(2) = 0.38, p \u3c 0.01) with in situ NH4+ concentrations. In light treatments, significantly lower N and P remineralization in August 1999 corresponded with low in situ inorganic nutrient concentrations and bacterial growth efficiency (BGE) and with elevated bacterial DOC utilization. In contrast, enhanced DOC reactivity in April 2000 during nutrient-replete conditions corresponded with net immobilization of inorganic N and P by bacterial biomass production, but without a concomitant impact on BGE. These findings suggest that the combination of photochemical and microbial alteration of DOM may increase bacterial demand for inorganic nutrients, alter BGE, and influence the partitioning of C between bacterial biomass and respiration