The passive yet successful way of planktonic life: genomic and experimental analysis of the ecology of a free-living polynucleobacter population.
The passive yet successful way of planktonic life: genomic and experimental analysis of the ecology of a free-living polynucleobacter population.
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DOI：
10.1371/journal.pone.0032772
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发表时间：
2012
期刊：
影响因子：
3.7
通讯作者：
Wu QL
中科院分区：
文献类型：
--
作者：
Hahn MW;Scheuerl T;Jezberová J;Koll U;Jezbera J;Šimek K;Vannini C;Petroni G;Wu QL
细菌分类群Polynuclearnecessarius subspecies asybioticus代表了一组在淡水栖息地广泛分布的淡水细菌。在不同的淡水生境中，这些细菌占浮游细菌总细胞的不到1%至70%（平均约20%）。这个分类群的普遍性最近被解释为分类群内生态多样化，即谱系对特定环境条件的专业化;然而，具体适应的细节尚不清楚。在这里，我们调查了通过基因组和实验分析的生态适应的一个持久的人口居住在一个小的酸性池塘。调查种群（F10谱系）的平均贡献率为11%，总浮游细菌在池塘的植被期（无冰期，通常是5月至11月）。只有一个低程度的遗传多样性的人口可以揭示。这些细菌的特征在于小的基因组大小（2.1 Mb），参与环境信号转导的基因数量相对较少，并且缺乏运动性和群体感应。实验表明，这些细菌生活作为化学有机营养生物主要利用低分子量的底物来自腐殖物质的光氧化。进化的基因组精简导致了一种高度被动的生活方式，到目前为止，只有生活在环境稳定、营养贫乏的近海系统中的浮游海洋生物群中的自由生活的细菌才知道。令人惊讶的是，这样的生活方式也是成功的，在一个高度动态和营养丰富的环境，如水柱的调查池塘，这是经历完全mixis和明显的分层在昼夜周期。显然，代谢和生态多样性不是在高度动态的环境条件下长期建立丰富的细菌种群的先决条件。当将所获得的关于生态学和所研究的谱系的适应性的见解推广到其他多核生物谱系时，应谨慎行事。
The bacterial taxon Polynucleobacter necessarius subspecies asymbioticus represents a group of planktonic freshwater bacteria with cosmopolitan and ubiquitous distribution in standing freshwater habitats. These bacteria comprise <1% to 70% (on average about 20%) of total bacterioplankton cells in various freshwater habitats. The ubiquity of this taxon was recently explained by intra-taxon ecological diversification, i.e. specialization of lineages to specific environmental conditions; however, details on specific adaptations are not known. Here we investigated by means of genomic and experimental analyses the ecological adaptation of a persistent population dwelling in a small acidic pond. The investigated population (F10 lineage) contributed on average 11% to total bacterioplankton in the pond during the vegetation periods (ice-free period, usually May to November). Only a low degree of genetic diversification of the population could be revealed. These bacteria are characterized by a small genome size (2.1 Mb), a relatively small number of genes involved in transduction of environmental signals, and the lack of motility and quorum sensing. Experiments indicated that these bacteria live as chemoorganotrophs by mainly utilizing low-molecular-weight substrates derived from photooxidation of humic substances. Evolutionary genome streamlining resulted in a highly passive lifestyle so far only known among free-living bacteria from pelagic marine taxa dwelling in environmentally stable nutrient-poor off-shore systems. Surprisingly, such a lifestyle is also successful in a highly dynamic and nutrient-richer environment such as the water column of the investigated pond, which was undergoing complete mixis and pronounced stratification in diurnal cycles. Obviously, metabolic and ecological versatility is not a prerequisite for long-lasting establishment of abundant bacterial populations under highly dynamic environmental conditions. Caution should be exercised when generalizing the obtained insights into the ecology and adaptation of the investigated lineage to other Polynucleobacter lineages.
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