Biocentre, Institute for Molecular Biosciences, Goethe-University, Frankfurt, Germany.
PLoS One. 2011 Jan 31;6(1):e16392. doi: 10.1371/journal.pone.0016392.
Bacteria are generally assumed to be monoploid (haploid). This assumption is mainly based on generalization of the results obtained with the most intensely studied model bacterium, Escherichia coli (a gamma-proteobacterium), which is monoploid during very slow growth. However, several species of proteobacteria are oligo- or polyploid, respectively. To get a better overview of the distribution of ploidy levels, genome copy numbers were quantified in four species of three different groups of proteobacteria. A recently developed Real Time PCR approach, which had been used to determine the ploidy levels of halophilic archaea, was optimized for the quantification of genome copy numbers of bacteria. Slow-growing (doubling time 103 minutes) and fast-growing (doubling time 25 minutes) E. coli cultures were used as a positive control. The copy numbers of the origin and terminus region of the chromosome were determined and the results were in excellent agreement with published data. The approach was also used to determine the ploidy levels of Caulobacter crescentus (an alpha-proteobacterium) and Wolinella succinogenes (an epsilon-proteobacterium), both of which are monoploid. In contrast, Pseudomonas putida (a gamma-proteobacterium) contains 20 genome copies and is thus polyploid. A survey of the proteobacteria with experimentally-determined genome copy numbers revealed that only three to four of 11 species are monoploid and thus monoploidy is not typical for proteobacteria. The ploidy level is not conserved within the groups of proteobacteria, and there are no obvious correlations between the ploidy levels with other parameters like genome size, optimal growth temperature or mode of life.
细菌通常被认为是单倍体（单倍体）。这种假设主要是基于对研究最深入的模式细菌大肠杆菌（γ-变形菌）的结果的概括，在非常缓慢的生长过程中，大肠杆菌是单倍体。然而，几种变形菌分别是寡倍体或多倍体。为了更好地了解倍性水平的分布，我们在三种不同的变形菌组的四个种中定量了基因组拷贝数。一种最近开发的实时 PCR 方法已被用于确定嗜盐古菌的倍性水平，我们对其进行了优化，以用于定量细菌的基因组拷贝数。我们使用缓慢生长（倍增时间 103 分钟）和快速生长（倍增时间 25 分钟）的大肠杆菌培养物作为阳性对照。确定了染色体的起点和终点区域的拷贝数，结果与已发表的数据非常吻合。该方法还用于确定新月形柄杆菌（α-变形菌）和脱硫弧菌（ε-变形菌）的倍性水平，它们都是单倍体。相比之下，假单胞菌（γ-变形菌）含有 20 个基因组拷贝，因此是多倍体。对具有实验确定的基因组拷贝数的变形菌的调查显示，在 11 个种中只有三到四个是单倍体，因此单倍体不是变形菌的典型特征。在变形菌组内，倍性水平并不保守，与其他参数（如基因组大小、最佳生长温度或生活方式）之间也没有明显的相关性。
