嗜热蓝藻Synechococcus在光营养极限下的同源基因组进化

C Logan Pierpont, Jacob J Baroch, Matthew J Church, Scott R Miller
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引用次数: 0

摘要

与中嗜热微生物相比,嗜热微生物的细胞和基因组较小,水平获得的基因比例较高,核苷酸和氨基酸组成特征独特。在这里,我们采用了一种综合方法来研究 Synechococcus A/B 蓝藻(包括地球上最耐热的光养菌)嗜热性的这些明显相关因素。系统发生组学证实了不同耐热生态型的独特起源,生态上不同但相互重叠的种群之间持续的低水平基因流动塑造了这些地热梯度的表型特征分布。耐热性更强的菌株基因组确实更小,但基因组的缩小与群落丰富度和代谢多样性的降低有关,而与细胞大小无关。在Synechococcus进化过程中,横向基因转移只发挥了有限的作用,但耐热性最强的菌株获得了一种Thermus tRNA修饰酶,这种酶可能会稳定高温下的翻译。虽然核苷酸碱基组成与耐热性无关,但我们发现在最高温度下,天冬氨酸普遍被谷氨酸取代,氨基酸组成也发生了巨大变化,这与之前的预测大相径庭。我们的结论是,Synechococcus A/B基因组的多样化在很大程度上不符合温度适应的标准观点。此外,与耐热性较差的品系相比,耐热性最强的品系的碳固定比光合氧进化更耐热。这表明,在这些细菌的温度适应过程中,光反应过程中产生的还原力更多地流向二氧化碳以外的电子汇。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Idiosyncratic genome evolution of the thermophilic cyanobacterium Synechococcus at the limits of phototrophy
Thermophilic microorganisms are expected to have smaller cells and genomes compared with mesophiles, a higher proportion of horizontally acquired genes, and distinct nucleotide and amino acid composition signatures. Here, we took an integrative approach to investigate these apparent correlates of thermophily for Synechococcus A/B cyanobacteria, which include the most heat-tolerant phototrophs on the planet. Phylogenomics confirmed a unique origin of different thermotolerance ecotypes, with low levels of continued gene flow between ecologically divergent but overlapping populations, which has shaped the distribution of phenotypic traits along these geothermal gradients. More thermotolerant strains do have smaller genomes, but genome reduction is associated with a decrease in community richness and metabolic diversity, rather than with cell size. Horizontal gene transfer played only a limited role during Synechococcus evolution, but, the most thermotolerant strains have acquired a Thermus tRNA modification enzyme that may stabilize translation at high temperatures. Although nucleotide base composition was not associated with thermotolerance, we found a general replacement of aspartate with glutamate, as well as a dramatic remodeling of amino acid composition at the highest temperatures that substantially differed from previous predictions. We conclude that Synechococcus A/B genome diversification largely does not conform to the standard view of temperature adaptation. In addition, carbon fixation was more thermolabile than photosynthetic oxygen evolution for the most thermotolerant strains compared with less tolerant lineages. This suggests that increased flow of reducing power generated during the light reactions to an electron sink(s) beyond carbon dioxide has emerged during temperature adaptation of these bacteria.
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