Max Planck Institute for Marine Microbiology, Celsiusstraße 1, 28359, Bremen, Germany.
Alfred Wegener Institute for Polar and Marine Research, Biologische Anstalt Helgoland, P.O. Box 180, 27483, Helgoland, Germany.
Microbiome. 2023 Apr 17;11(1):77. doi: 10.1186/s40168-023-01517-x.
Blooms of marine microalgae play a pivotal role in global carbon cycling. Such blooms entail successive blooms of specialized clades of planktonic bacteria that collectively remineralize gigatons of algal biomass on a global scale. This biomass is largely composed of distinct polysaccharides, and the microbial decomposition of these polysaccharides is therefore a process of prime importance.
In 2020, we sampled a complete biphasic spring bloom in the German Bight over a 90-day period. Bacterioplankton metagenomes from 30 time points allowed reconstruction of 251 metagenome-assembled genomes (MAGs). Corresponding metatranscriptomes highlighted 50 particularly active MAGs of the most abundant clades, including many polysaccharide degraders. Saccharide measurements together with bacterial polysaccharide utilization loci (PUL) expression data identified β-glucans (diatom laminarin) and α-glucans as the most prominent and actively metabolized dissolved polysaccharide substrates. Both substrates were consumed throughout the bloom, with α-glucan PUL expression peaking at the beginning of the second bloom phase shortly after a peak in flagellate and the nadir in bacterial total cell counts.
We show that the amounts and composition of dissolved polysaccharides, in particular abundant storage polysaccharides, have a pronounced influence on the composition of abundant bacterioplankton members during phytoplankton blooms, some of which compete for similar polysaccharide niches. We hypothesize that besides the release of algal glycans, also recycling of bacterial glycans as a result of increased bacterial cell mortality can have a significant influence on bacterioplankton composition during phytoplankton blooms. Video Abstract.
海洋微藻的爆发在全球碳循环中起着关键作用。这种爆发伴随着浮游细菌专门类群的连续爆发，这些细菌集体将全球范围内的数十亿吨藻类生物量再矿化。这些生物量主要由不同的多糖组成，因此这些多糖的微生物分解是一个非常重要的过程。
2020 年，我们在 90 天的时间里对德国北海的一个完整的两阶段春季爆发进行了采样。来自 30 个时间点的细菌浮游生物宏基因组允许重建 251 个宏基因组组装基因组（MAG）。相应的宏转录组突出了 50 个特别活跃的 MAG，它们属于最丰富的类群，包括许多多糖降解菌。糖的测量值加上细菌多糖利用基因座（PUL）表达数据确定了β-葡聚糖（硅藻褐藻淀粉）和α-葡聚糖是最突出和被积极代谢的溶解多糖底物。这两种底物在整个爆发期间都被消耗，α-葡聚糖 PUL 表达在第二爆发阶段开始时达到峰值，此时鞭毛虫数量达到峰值，细菌总数达到最低点。
我们表明，溶解多糖的数量和组成，特别是丰富的储存多糖，对浮游植物爆发期间丰富的细菌浮游生物成员的组成有显著影响，其中一些成员竞争类似的多糖生态位。我们假设，除了藻类糖的释放外，由于细菌细胞死亡率的增加而导致的细菌糖的再循环也可能对浮游植物爆发期间的细菌浮游生物组成产生重大影响。视频摘要。
