Kevorkian Richard T, Sipes Katie, Winstead Rachel, Paul Raegan, Lloyd Karen G
Department of Microbiology, University of Tennessee, Knoxville, TN, United States.
Front Microbiol. 2022 Mar 17;13:847563. doi: 10.3389/fmicb.2022.847563. eCollection 2022.
As marine sediments are buried, microbial communities transition from sulfate-reduction to methane-production after sulfate is depleted. When this biogenic methane diffuses into the overlying sulfate-rich sediments, it forms a sulfate-methane transition zone (SMTZ) because sulfate reducers deplete hydrogen concentrations and make hydrogenotrophic methanogenesis exergonic in the reverse direction, a process called the anaerobic oxidation of methane (AOM). Microbial participation in these processes is often inferred from geochemistry, genes, and gene expression changes with sediment depth, using sedimentation rates to convert depth to time. Less is known about how natural sediments transition through these geochemical states transition in real-time. We examined 16S rRNA gene amplicon libraries and metatranscriptomes in microcosms of anoxic sediment from the White Oak River estuary, NC, with three destructively sampled replicates with methane added (586-day incubations) and three re-sampled un-amended replicates (895-day incubations). Sulfate dropped to a low value (∼0.3 mM) on similar days for both experiments (312 and 320 days, respectively), followed by a peak in hydrogen, intermittent increases in methane-cycling archaea starting on days 375 and 362 (mostly spp. and spp., and sp. ANME-3), and a methane peak 1 month later. However, methane δC values only show net methanogenesis 6 months after methane-cycling archaea increase and 4 months after the methane peak, when sulfate is consistently below 0.1 mM and hydrogen increases to a stable 0.61 ± 0.13 nM (days 553-586, = 9). Sulfate-reducing bacteria (mostly spp. and sp. SEEP-SRB1) increase in relative abundance only during this period of net methane production, suggesting syntrophy with methanogens in the absence of sulfate. The transition from sulfate reduction to methane production in marine sediments occurs through a prolonged period of methane-cycling by methanogens at low sulfate concentrations, and steady growth of sulfate reducers along with methanogens after sulfate is depleted.
随着海洋沉积物的埋藏，在硫酸盐耗尽后，微生物群落从硫酸盐还原转变为甲烷生成。当这种生物成因甲烷扩散到上覆的富含硫酸盐的沉积物中时，就会形成一个硫酸盐 - 甲烷过渡带（SMTZ），因为硫酸盐还原菌会耗尽氢气浓度，并使氢营养型甲烷生成在相反方向上成为放能反应，这个过程称为甲烷厌氧氧化（AOM）。微生物对这些过程的参与通常是通过地球化学、基因以及基因表达随沉积物深度的变化来推断的，利用沉积速率将深度转换为时间。关于天然沉积物如何实时经历这些地球化学状态转变的了解较少。我们研究了北卡罗来纳州白橡树河口缺氧沉积物微观模型中的16S rRNA基因扩增文库和宏转录组，有三个添加甲烷的破坏性采样重复样本（586天培养）和三个重新采样的未添加样本重复样本（895天培养）。在两个实验中，硫酸盐在相似的天数（分别为312天和320天）下降到低值（约0.3 mM），随后氢气出现峰值，甲烷循环古菌在第375天和362天开始间歇性增加（主要是 属、 属和ANME - 3属），1个月后出现甲烷峰值。然而，甲烷δC值仅在甲烷循环古菌增加6个月后以及甲烷峰值4个月后才显示净甲烷生成，此时硫酸盐持续低于0.1 mM，氢气增加到稳定的0.61±0.13 nM（第553 - 586天，n = 9）。硫酸盐还原细菌（主要是 属和SEEP - SRB1属）仅在净甲烷生成期间相对丰度增加，这表明在没有硫酸盐的情况下与产甲烷菌存在共生关系。海洋沉积物中从硫酸盐还原到甲烷生成的转变是通过产甲烷菌在低硫酸盐浓度下长时间的甲烷循环以及硫酸盐耗尽后硫酸盐还原菌与产甲烷菌的稳定生长而发生的。
