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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >In situ analysis of nitrogen fixation and metabolic switching in unicellular thermophilic cyanobacteria inhabiting hot spring microbial mats
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In situ analysis of nitrogen fixation and metabolic switching in unicellular thermophilic cyanobacteria inhabiting hot spring microbial mats

机译：居住在温泉微生物垫中的单细胞嗜热蓝细菌中固氮和代谢转换的原位分析

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摘要

Genome sequences of two Synechococcus ecotypes inhabiting the Octopus Spring microbial mat in Yellowstone National Park revealed the presence of all genes required for nitrogenase biosynthesis. We demonstrate that nif genes of the Synechococcus ecotypes are expressed in situ in a region of the mat that varies in temperature from 53.5℃ to 63.4℃ (average 60℃); transcripts are only detected at the end of the day when the mat becomes anoxic. Nitrogenase activity in mat samples was also detected in the evening. Hitherto, N_2 fixation in hot spring mats was attributed either to filamentous cyanobacteria (not present at > 50℃ in these mats) or to heterotrophic bacteria. To explore how energy-generating processes of the Synechococcus ecotypes track natural light and O_2 conditions, we evaluated accumulation of transcripts encoding proteins involved in photosynthesis, respiration, and fermentation. Transcripts from photosynthesis (cpcF, cpcE, psaB, and psbB) and respiration (coxA and cydA) genes declined in the evening. In contrast, transcripts encoding enzymes that may participate in fermentation fell into two categories; some (ldh, pdhB, ald, and ackA) decreased in the evening, whereas others (pflB. pflA, adhE, and acs) increased at the end of the day and remained high into the night. Energy required for N_2 fixation during the night may be derived from fermentation pathways that become prominent as the mat becomes anoxic. In a broader context, our data suggest that there are critical regulatory switches in situ that are linked to the diel cycle and that these switches alter many metabolic processes within the microbial mat.
机译：居住在黄石国家公园八达通春季微生物垫中的两种聚球菌生态型的基因组序列揭示了固氮酶生物合成所需的所有基因的存在。我们证明了Syechococcus生态型的nif基因在温度从53.5℃到63.4℃（平均60℃）变化的垫子区域中原位表达。仅在垫子缺氧的一天结束时才检测到成绩单。晚上还检测到垫子样品中的固氮酶活性。迄今为止，温泉垫中的N_2固定归因于丝状蓝细菌（在这些垫中温度不高于50℃）或异养细菌。为了探索生态球菌的能量生成过程如何跟踪自然光和O_2条件，我们评估了编码与光合作用，呼吸作用和发酵有关的蛋白质的转录物的积累。在晚上，来自光合作用（cpcF，cpcE，psaB和psbB）和呼吸（coxA和cydA）基因的转录物下降。相比之下，编码可能参与发酵的酶的转录本分为两类。一些（ldh，pdhB，ald和ackA）在晚上减少，而其他（pflB。pflA，adhE和acs）在一天结束时增加并一直保持到深夜。夜间固定N_2所需的能量可能来自发酵途径，随着垫子变得缺氧，发酵途径变得更加突出。在更广泛的范围内，我们的数据表明存在与diel循环相关的关键性调节开关，并且这些开关改变了微生物垫内的许多代谢过程。

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