The osmolyte dimethylsulfoniopropionate (DMSP) is produced in petagram amounts by marine microorganisms. Estuaries provide natural gradients in salinity and nutrients, factors known to regulate DMSP production; yet there have been no molecular studies of DMSP production and cycling across these gradients. Here, we study the abundance, distribution and transcription of key DMSP synthesis (e.g. dsyB and mmtN) and catabolic (e.g. dddP and dmdA) genes along the salinity gradient of the Changjiang Estuary. DMSP levels did not correlate with Chl a across the salinity gradient. In contrast, DMSP concentration, abundance of bacterial DMSP producers and their dsyB and mmtN transcripts were lowest in the freshwater samples and increased abruptly with salinity in the transitional and seawater samples. Metagenomics analysis suggests bacterial DMSP-producers were more abundant than their algal equivalents and were more prominent in summer than winter samples. Bacterial DMSP catabolic genes and their transcripts followed the same trend of being greatly enhanced in transitional and seawater samples with higher DMSP levels than freshwater samples. DMSP cleavage was likely the dominant catabolic pathway, with DMSP lyase genes being ~4.3-fold more abundant than the demethylase gene dmdA. This is an exemplar study for future research on microbial DMSP cycling in estuary environments.

中文翻译：

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长江口细菌二甲基磺丙酸产生和分解基因时空分布

海洋微生物以拍克量生产渗透质二甲基磺基丙酸酯 (DMSP)。河口提供盐度和养分的自然梯度，这是调节 DMSP 生产的已知因素；然而，还没有关于 DMSP 产生和跨这些梯度循环的分子研究。在这里，我们研究了沿长江口盐度梯度的关键DMSP合成（例如dsyB和mmtN）和分解代谢（例如dddP和dmdA ）基因的丰度、分布和转录。DMSP 水平与盐度梯度中的叶绿素a无关。相比之下，DMSP 浓度、细菌 DMSP 生产者的丰度及其dsyB和mmtN转录物在淡水样品中最低，而在过渡和海水样品中随着盐度的增加而突然增加。宏基因组学分析表明，细菌 DMSP 生产者比它们的藻类等价物更丰富，并且在夏季比冬季样本更突出。细菌 DMSP 分解代谢基因及其转录物遵循相同的趋势，即在 DMSP 水平高于淡水样品的过渡和海水样品中显着增强。DMSP 裂解可能是主要的分解代谢途径，DMSP 裂解酶基因比去甲基化酶基因dmdA丰富约 4.3 倍。这是未来河口环境中微生物 DMSP 循环研究的示范性研究。