Crump Byron C, Peranteau Cherie, Beckingham Barbara, Cornwell Jeffrey C
University of Maryland Center for Environmental Science, Horn Point Laboratory, 2020 Horns Point Rd., Cambridge, MD 21613, USA.
Appl Environ Microbiol. 2007 Nov;73(21):6802-10. doi: 10.1128/AEM.00648-07. Epub 2007 Aug 31.
Anoxia occurs in bottom waters of stratified estuaries when respiratory consumption of oxygen, primarily by bacteria, outpaces atmospheric and photosynthetic reoxygenation. Once water becomes anoxic, bacterioplankton must change their metabolism to some form of anaerobic respiration. Analysis of redox chemistry in water samples spanning the oxycline of Chesapeake Bay during the summer of 2004 suggested that there was a succession of respiratory metabolism following the loss of oxygen. Bacterial community doubling time, calculated from bacterial abundance (direct counts) and production (anaerobic leucine incorporation), ranged from 0.36 to 0.75 day and was always much shorter than estimates of the time that the bottom water was anoxic (18 to 44 days), indicating that there was adequate time for bacterial community composition to shift in response to changing redox conditions. However, community composition (as determined by PCR-denaturing gradient gel electrophoresis analysis of 16S rRNA genes) in anoxic waters was very similar to that in surface waters in June when nitrate respiration was apparent in the water column and only partially shifted away from the composition of the surface community after nitrate was depleted. Anoxic water communities did not change dramatically until August, when sulfate respiration appeared to dominate. Surface water populations that remained dominant in anoxic waters were Synechococcus sp., Gammaproteobacteria in the SAR86 clade, and Alphaproteobacteria relatives of Pelagibacter ubique, including a putative estuarine-specific Pelagibacter cluster. Populations that developed in anoxic water were most similar (<92% similarity) to uncultivated Firmicutes, uncultivated Bacteroidetes, Gammaproteobacteria in the genus Thioalcalovibrio, and the uncultivated SAR406 cluster. These results indicate that typical estuarine bacterioplankton switch to anaerobic metabolism under anoxic conditions but are ultimately replaced by different organisms under sulfidic conditions.
当主要由细菌进行的氧气呼吸消耗超过大气和光合作用的再充氧时，分层河口的底层水域就会出现缺氧现象。一旦水体变为缺氧状态，浮游细菌必须将其新陈代谢转变为某种形式的无氧呼吸。对2004年夏季切萨皮克湾氧跃层水样的氧化还原化学分析表明，在氧气消失后存在一系列呼吸代谢过程。根据细菌丰度（直接计数）和产量（厌氧亮氨酸掺入）计算得出的细菌群落倍增时间为0.36至0.75天，且始终远短于底层水缺氧时间的估计值（18至44天），这表明细菌群落组成有足够的时间响应不断变化的氧化还原条件而发生转变。然而，缺氧水域中的群落组成（通过对16S rRNA基因进行PCR-变性梯度凝胶电泳分析确定）与6月表层水域的非常相似，当时水柱中明显存在硝酸盐呼吸，而在硝酸盐耗尽后才部分偏离表层群落的组成。直到8月硫酸盐呼吸似乎占主导地位时，缺氧水域群落才发生显著变化。在缺氧水域中仍占主导地位的表层水种群包括聚球藻属、SAR86分支中的γ-变形菌以及与嗜盐栖热袍菌亲缘关系较近的α-变形菌，其中包括一个假定的河口特异性嗜盐栖热袍菌簇。在缺氧水域中发展起来的种群与未培养的厚壁菌门、未培养的拟杆菌门、硫代碱弧菌属中的γ-变形菌以及未培养的SAR406簇最为相似（相似度<92%）。这些结果表明，典型的河口浮游细菌在缺氧条件下会转变为无氧代谢，但在硫化条件下最终会被不同的生物体所取代。
