Department of Microbiology and Immunology, University at Buffalo, State University of New York, Buffalo, New York, USA.
mBio. 2012 Sep 25;3(5). doi: 10.1128/mBio.00200-12. Print 2012.
Transformation of genetic material between bacteria was first observed in the 1920s using Streptococcus pneumoniae as a model organism. Since then, the mechanism of competence induction and transformation has been well characterized, mainly using planktonic bacteria or septic infection models. However, epidemiological evidence suggests that genetic exchange occurs primarily during pneumococcal nasopharyngeal carriage, which we have recently shown is associated with biofilm growth, and is associated with cocolonization with multiple strains. However, no studies to date have comprehensively investigated genetic exchange during cocolonization in vitro and in vivo or the role of the nasopharyngeal environment in these processes. In this study, we show that genetic exchange during dual-strain carriage in vivo is extremely efficient (10(-2)) and approximately 10,000,000-fold higher than that measured during septic infection (10(-9)). This high transformation efficiency was associated with environmental conditions exclusive to the nasopharynx, including the lower temperature of the nasopharynx (32 to 34°C), limited nutrient availability, and interactions with epithelial cells, which were modeled in a novel biofilm model in vitro that showed similarly high transformation efficiencies. The nasopharyngeal environmental factors, combined, were critical for biofilm formation and induced constitutive upregulation of competence genes and downregulation of capsule that promoted transformation. In addition, we show that dual-strain carriage in vivo and biofilms formed in vitro can be transformed during colonization to increase their pneumococcal fitness and also, importantly, that bacteria with lower colonization ability can be protected by strains with higher colonization efficiency, a process unrelated to genetic exchange.
Although genetic exchange between pneumococcal strains is known to occur primarily during colonization of the nasopharynx and colonization is associated with biofilm growth, this is the first study to comprehensively investigate transformation in this environment and to analyze the role of environmental and bacterial factors in this process. We show that transformation efficiency during cocolonization by multiple strains is very high (around 10(-2)). Furthermore, we provide novel evidence that specific aspects of the nasopharyngeal environment, including lower temperature, limited nutrient availability, and epithelial cell interaction, are critical for optimal biofilm formation and transformation efficiency and result in bacterial protein expression changes that promote transformation and fitness of colonization-deficient strains. The results suggest that cocolonization in biofilm communities may have important clinical consequences by facilitating the spread of antibiotic resistance and enabling serotype switching and vaccine escape as well as protecting and retaining poorly colonizing strains in the pneumococcal strain pool.
20 世纪 20 年代，人们首次使用肺炎链球菌作为模型生物观察到细菌间遗传物质的转化。从那时起，人们已经很好地描述了感受态诱导和转化的机制，主要使用浮游细菌或脓毒感染模型。然而，流行病学证据表明，遗传交换主要发生在肺炎球菌鼻咽定植期间，我们最近的研究表明，这与生物膜生长有关，并与多种菌株的共定植有关。然而，迄今为止，尚无研究全面调查体外和体内共定植期间的遗传交换，也未研究鼻咽环境在这些过程中的作用。在这项研究中，我们表明体内两株菌同时定植时的遗传交换效率极高（10(-2)），大约是脓毒感染时测量的 10(-9)的 10000000 倍。这种高转化效率与鼻咽特有的环境条件有关，包括鼻咽温度较低（32 至 34°C）、营养物质有限以及与上皮细胞的相互作用，这些条件在体外新型生物膜模型中得到了模拟，该模型也显示出类似的高转化效率。鼻咽环境因素的综合作用对于生物膜的形成以及组成型上调感受态基因和下调荚膜的表达至关重要，这促进了转化。此外，我们还表明，体内两株菌同时定植和体外形成的生物膜在定植过程中可以被转化，以提高其肺炎链球菌的适应性，重要的是，具有较低定植能力的细菌可以被具有更高定植效率的菌株保护，这个过程与遗传交换无关。
虽然已知肺炎链球菌株之间的遗传交换主要发生在鼻咽定植期间，并且定植与生物膜生长有关，但这是第一项全面研究该环境中转化并分析环境和细菌因素在该过程中作用的研究。我们表明，多株菌共定植时的转化效率非常高（约 10(-2)）。此外，我们提供了新的证据表明，鼻咽环境的特定方面，包括较低的温度、有限的营养供应和上皮细胞相互作用，对于最佳生物膜形成和转化效率至关重要，并导致细菌蛋白表达的变化，从而促进转化和定植缺陷株的适应性。结果表明，生物膜群落中的共定植可能会通过促进抗生素耐药性的传播以及实现血清型转换和疫苗逃逸，并保护和保留在肺炎链球菌菌株库中定植能力较差的菌株，从而对临床产生重要影响。
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