Bohórquez Julio, McGenity Terry J, Papaspyrou Sokratis, García-Robledo Emilio, Corzo Alfonso, Underwood Graham J C
Department of Biology, Faculty of Marine and Environmental Science, University of CádizPuerto Real, Spain; School of Biological Sciences, University of EssexColchester, UK.
School of Biological Sciences, University of Essex Colchester, UK.
Front Microbiol. 2017 Feb 27;8:245. doi: 10.3389/fmicb.2017.00245. eCollection 2017.
Intertidal areas support extensive diatom-rich biofilms. Such microphytobenthic (MPB) diatoms exude large quantities of extracellular polymeric substances (EPS) comprising polysaccharides, glycoproteins and other biopolymers, which represent a substantial carbon pool. However, degradation rates of different EPS components, and how they shape heterotrophic communities in sediments, are not well understood. An aerobic mudflat-sediment slurry experiment was performed in the dark with two different EPS carbon sources from a diatom-dominated biofilm: colloidal EPS (cEPS) and the more complex hot-bicarbonate-extracted EPS. Degradation rate constants determined over 9 days for three sediment fractions [dissolved organic carbon (DOC), total carbohydrates (TCHO), and (cEPS)] were generally higher in the colloidal-EPS slurries (0.105-0.123 d) compared with the hot-bicarbonate-extracted-EPS slurries (0.060-0.096 d). Addition of hot-bicarbonate-EPS resulted in large increases in dissolved nitrogen and phosphorous by the end of the experiment, indicating that the more complex EPS is an important source of regenerated inorganic nutrients. Microbial biomass increased ~4-6-fold over 9 days, and pyrosequencing of bacterial 16S rRNA genes revealed that the addition of both types of EPS greatly altered the bacterial community composition (from 0 to 9 days) compared to a control with no added EPS. Bacteroidetes (especially ) and Verrucomicrobia increased significantly in relative abundance in both the hot-bicarbonate-EPS and colloidal-EPS treatments. These differential effects of EPS fractions on carbon-loss rates, nutrient regeneration and microbial community assembly improve our understanding of coastal-sediment carbon cycling and demonstrate the importance of diverse microbiota in processing this abundant pool of organic carbon.
潮间带区域存在大量富含硅藻的生物膜。这类微型底栖藻类（MPB）硅藻会分泌大量细胞外聚合物（EPS），其由多糖、糖蛋白和其他生物聚合物组成，是一个可观的碳库。然而，不同EPS组分的降解速率以及它们如何塑造沉积物中的异养群落，目前还不太清楚。在黑暗条件下进行了一项需氧泥滩沉积物泥浆实验，使用了来自硅藻主导生物膜的两种不同EPS碳源：胶体EPS（cEPS）和更复杂的热碳酸氢盐提取EPS。在9天内测定的三种沉积物组分[溶解有机碳（DOC）、总碳水化合物（TCHO）和（cEPS）]的降解速率常数，胶体EPS泥浆（0.105 - 0.123 d⁻¹）通常高于热碳酸氢盐提取EPS泥浆（0.060 - 0.096 d⁻¹）。到实验结束时，添加热碳酸氢盐EPS导致溶解氮和磷大幅增加，这表明更复杂的EPS是再生无机养分的重要来源。微生物生物量在9天内增加了约4 - 6倍，对细菌16S rRNA基因进行焦磷酸测序显示，与未添加EPS的对照相比，添加两种类型的EPS都极大地改变了细菌群落组成（从0天到9天）。在热碳酸氢盐EPS和胶体EPS处理中，拟杆菌门（特别是 ）和疣微菌门的相对丰度均显著增加。EPS组分对碳损失率、养分再生和微生物群落组装的这些不同影响，增进了我们对海岸沉积物碳循环的理解，并证明了多样的微生物群落在处理这一丰富有机碳库中的重要性。
