在细菌种群中,细微的表达差异可能会通过形成不同的生态型来促进生态专业化。在无障碍的栖息地,这个过程很可能先于种群分化,并可能预测物种形成事件。为了检查这一点,我们使用了四种测序的细菌Shewanellabaltica,OS155,OS185,OS195和OS223,作为评估原核生物种群中转录变异和生态型形成的模型。所有菌株都是从整个波罗的海水柱的不同深度分离的,占据以各种非生物参数为特征的不同生态位。虽然基因组序列几乎100%保守,当在标准化条件下在实验室中生长时,所有菌株表现出不同的生长速率,提示显著的表达变异。使用生态类型模拟算法,与从同一水柱中分离出的32个其他Baltica菌株相比,所有菌株都被认为是离散的生态型,表明生态分歧。接下来,我们使用包含代表OS155,OS185,OS195和OS223核心基因组的寡核苷酸探针的定制微阵列载玻片来检测在相同条件下生长的菌株之间的自然转录变异。在所有四个菌株中都注意到显着的转录变异。差异表达的基因谱似乎与原始分离深度下环境的代谢特征一致。转录模式变异,例如此处强调的变异,可以用作细菌生态型形成中短期进化的指标。重要性真核研究表明,同一人群中的个体之间存在相当大的转录差异。有人认为,真核基因表达的自然变异可能会产生重大的进化后果,并可能解释密切相关物种的大规模表型差异。如人类和黑猩猩(M.-C.King和A.C.Wilson,Science188:107-116,1975,http://dx.doi.org/10.1126/science.1090005;M.F.Oleksiak,G.A.丘吉尔,D.L.Crawford,NatGenet32:261-266,2002,http://dx.doi.org/10.1038/ng983)。然而,基因表达的自然变异在原核生物中的理解要少得多。在这项研究中,我们使用了四个测序的海洋细菌Shewanellabaltica菌株,以更好地了解分层原核种群的自然转录差异。我们发现在相同的实验室条件下培养的四种S.baltica菌株之间存在大量低幅度的表达变化。总的来说,我们的结果表明,转录变异是生态物种形成的重要因素。
In bacterial populations, subtle expressional differences may promote ecological specialization through the formation of distinct ecotypes. In a barrier-free habitat, this process most likely precedes population divergence and may predict speciation events. To examine this, we used four sequenced strains of the bacterium Shewanella baltica, OS155, OS185, OS195, and OS223, as models to assess transcriptional variation and ecotype formation within a prokaryotic population. All strains were isolated from different depths throughout a water column of the Baltic Sea, occupying different ecological niches characterized by various abiotic parameters. Although the genome sequences are nearly 100% conserved, when grown in the laboratory under standardized conditions, all strains exhibited different growth rates, suggesting significant expressional variation. Using the Ecotype Simulation algorithm, all strains were considered to be discrete ecotypes when compared to 32 other S. baltica strains isolated from the same water column, suggesting ecological divergence. Next, we employed custom microarray slides containing oligonucleotide probes representing the core genome of OS155, OS185, OS195, and OS223 to detect natural transcriptional variation among strains grown under identical conditions. Significant transcriptional variation was noticed among all four strains. Differentially expressed gene profiles seemed to coincide with the metabolic signatures of the environment at the original isolation depth. Transcriptional pattern variations such as the ones highlighted here may be used as indicators of short-term evolution emerging from the formation of bacterial ecotypes. IMPORTANCE Eukaryotic studies have shown considerable transcriptional variation among individuals from the same population. It has been suggested that natural variation in eukaryotic gene expression may have significant evolutionary consequences and may explain large-scale phenotypic divergence of closely related species, such as humans and chimpanzees (M.-C. King and A. C. Wilson, Science 188:107-116, 1975, http://dx.doi.org/10.1126/science.1090005; M. F. Oleksiak, G. A. Churchill, and D. L. Crawford, Nat Genet 32:261-266, 2002, http://dx.doi.org/10.1038/ng983). However, natural variation in gene expression is much less well understood in prokaryotic organisms. In this study, we used four sequenced strains of the marine bacterium Shewanella baltica to better understand the natural transcriptional divergence of a stratified prokaryotic population. We found substantial low-magnitude expressional variation among the four S. baltica strains cultivated under identical laboratory conditions. Collectively, our results indicate that transcriptional variation is an important factor for ecological speciation.