PDF(Pubmed)
Abstract：
BACKGROUND: Marine microalgae (phytoplankton) mediate almost half of the worldwide photosynthetic carbon dioxide fixation and therefore play a pivotal role in global carbon cycling, most prominently during massive phytoplankton blooms. Phytoplankton biomass consists of considerable proportions of polysaccharides, substantial parts of which are rapidly remineralized by heterotrophic bacteria. We analyzed the diversity, activity, and functional potential of such polysaccharide-degrading bacteria in different size fractions during a diverse spring phytoplankton bloom at Helgoland Roads (southern North Sea) at high temporal resolution using microscopic, physicochemical, biodiversity, metagenome, and metaproteome analyses.
RESULTS: Prominent active 0.2-3 µm free-living clades comprised Aurantivirga, \"Formosa\", Cd. Prosiliicoccus, NS4, NS5, Amylibacter, Planktomarina, SAR11 Ia, SAR92, and SAR86, whereas BD1-7, Stappiaceae, Nitrincolaceae, Methylophagaceae, Sulfitobacter, NS9, Polaribacter, Lentimonas, CL500-3, Algibacter, and Glaciecola dominated 3-10 µm and > 10 µm particles. Particle-attached bacteria were more diverse and exhibited more dynamic adaptive shifts over time in terms of taxonomic composition and repertoires of encoded polysaccharide-targeting enzymes. In total, 305 species-level metagenome-assembled genomes were obtained, including 152 particle-attached bacteria, 100 of which were novel for the sampling site with 76 representing new species. Compared to free-living bacteria, they featured on average larger metagenome-assembled genomes with higher proportions of polysaccharide utilization loci. The latter were predicted to target a broader spectrum of polysaccharide substrates, ranging from readily soluble, simple structured storage polysaccharides (e.g., laminarin, α-glucans) to less soluble, complex structural, or secreted polysaccharides (e.g., xylans, cellulose, pectins). In particular, the potential to target poorly soluble or complex polysaccharides was more widespread among abundant and active particle-attached bacteria.
CONCLUSIONS: Particle-attached bacteria represented only 1% of all bloom-associated bacteria, yet our data suggest that many abundant active clades played a pivotal gatekeeping role in the solubilization and subsequent degradation of numerous important classes of algal glycans. The high diversity of polysaccharide niches among the most active particle-attached clades therefore is a determining factor for the proportion of algal polysaccharides that can be rapidly remineralized during generally short-lived phytoplankton bloom events. Video Abstract.
RESULTS: Prominent active 0.2-3 µm free-living clades comprised Aurantivirga, \"Formosa\", Cd. Prosiliicoccus, NS4, NS5, Amylibacter, Planktomarina, SAR11 Ia, SAR92, and SAR86, whereas BD1-7, Stappiaceae, Nitrincolaceae, Methylophagaceae, Sulfitobacter, NS9, Polaribacter, Lentimonas, CL500-3, Algibacter, and Glaciecola dominated 3-10 µm and > 10 µm particles. Particle-attached bacteria were more diverse and exhibited more dynamic adaptive shifts over time in terms of taxonomic composition and repertoires of encoded polysaccharide-targeting enzymes. In total, 305 species-level metagenome-assembled genomes were obtained, including 152 particle-attached bacteria, 100 of which were novel for the sampling site with 76 representing new species. Compared to free-living bacteria, they featured on average larger metagenome-assembled genomes with higher proportions of polysaccharide utilization loci. The latter were predicted to target a broader spectrum of polysaccharide substrates, ranging from readily soluble, simple structured storage polysaccharides (e.g., laminarin, α-glucans) to less soluble, complex structural, or secreted polysaccharides (e.g., xylans, cellulose, pectins). In particular, the potential to target poorly soluble or complex polysaccharides was more widespread among abundant and active particle-attached bacteria.
CONCLUSIONS: Particle-attached bacteria represented only 1% of all bloom-associated bacteria, yet our data suggest that many abundant active clades played a pivotal gatekeeping role in the solubilization and subsequent degradation of numerous important classes of algal glycans. The high diversity of polysaccharide niches among the most active particle-attached clades therefore is a determining factor for the proportion of algal polysaccharides that can be rapidly remineralized during generally short-lived phytoplankton bloom events. Video Abstract.
摘要：
背景：海洋微藻（浮游植物）介导了全球近一半的光合二氧化碳固定，因此在全球碳循环中起着关键作用，在大量浮游植物开花期间最突出。浮游植物生物量由相当比例的多糖组成，其中大部分被异养细菌迅速再矿化。我们分析了多样性，活动,在HelgolandRoads（北海南部）以高分辨率的时间分辨率在不同大小的春季浮游植物盛开期间，这种多糖降解细菌的功能潜力，物理化学,生物多样性,宏基因组，和元蛋白质组分析。
结果：突出的活性0.2-3µm自由生活进化枝包括Aurantivirga，\"Formosa\",CD。Prosiliicoccus,NS4NS5Amylibacter,Planktomarina,SAR11Ia,SAR92和SAR86，而BD1-7，葡萄科，Nitrincoleaceae，菊科，硫杆菌属,NS9，杆菌属，Lentimonas,CL500-3,Algibacter,和Glaciecola主导3-10µm和>10µm颗粒。在编码的多糖靶向酶的分类组成和库方面，颗粒附着的细菌更加多样化，并且随着时间的推移表现出更动态的适应性变化。总的来说,获得了305个物种水平的宏基因组组装基因组，包括152个颗粒附着的细菌，其中100个在采样地点是新颖的，其中76个代表新物种。与自由生活的细菌相比，它们具有平均更大的宏基因组组装基因组和更高比例的多糖利用基因座。后者被预测为目标更广泛的多糖底物，范围从易溶，简单的结构化储存多糖(例如，laminarin,α-葡聚糖)溶解性较低，复杂的结构，或分泌的多糖(例如，木聚糖,纤维素,果胶）。特别是,在丰富且活性颗粒附着的细菌中，靶向难溶性或复杂多糖的潜力更为普遍。
结论：颗粒附着细菌仅占所有水华相关细菌的1％，然而，我们的数据表明，许多丰富的活性进化枝在许多重要类别的藻类聚糖的溶解和随后的降解中起着关键的把关作用。因此，在最活跃的颗粒附着进化枝中，多糖生态位的高度多样性是藻类多糖比例的决定因素，藻类多糖在通常短暂的浮游植物水华事件中可以迅速再矿化。视频摘要。
结果：突出的活性0.2-3µm自由生活进化枝包括Aurantivirga，\"Formosa\",CD。Prosiliicoccus,NS4NS5Amylibacter,Planktomarina,SAR11Ia,SAR92和SAR86，而BD1-7，葡萄科，Nitrincoleaceae，菊科，硫杆菌属,NS9，杆菌属，Lentimonas,CL500-3,Algibacter,和Glaciecola主导3-10µm和>10µm颗粒。在编码的多糖靶向酶的分类组成和库方面，颗粒附着的细菌更加多样化，并且随着时间的推移表现出更动态的适应性变化。总的来说,获得了305个物种水平的宏基因组组装基因组，包括152个颗粒附着的细菌，其中100个在采样地点是新颖的，其中76个代表新物种。与自由生活的细菌相比，它们具有平均更大的宏基因组组装基因组和更高比例的多糖利用基因座。后者被预测为目标更广泛的多糖底物，范围从易溶，简单的结构化储存多糖(例如，laminarin,α-葡聚糖)溶解性较低，复杂的结构，或分泌的多糖(例如，木聚糖,纤维素,果胶）。特别是,在丰富且活性颗粒附着的细菌中，靶向难溶性或复杂多糖的潜力更为普遍。
结论：颗粒附着细菌仅占所有水华相关细菌的1％，然而，我们的数据表明，许多丰富的活性进化枝在许多重要类别的藻类聚糖的溶解和随后的降解中起着关键的把关作用。因此，在最活跃的颗粒附着进化枝中，多糖生态位的高度多样性是藻类多糖比例的决定因素，藻类多糖在通常短暂的浮游植物水华事件中可以迅速再矿化。视频摘要。
