Department of Molecular Biology, Princeton University, Princeton, NJ, United States of America.
PLoS One. 2020 Mar 12;15(3):e0230006. doi: 10.1371/journal.pone.0230006. eCollection 2020.
The Caulobacter genus, including the widely-studied model organism Caulobacter crescentus, has been thought to be non-pathogenic and thus proposed as a bioengineering vector for various environmental remediation and medical purposes. However, Caulobacter species have been implicated as the causative agents of several hospital-acquired infections, raising the question of whether these clinical isolates represent an emerging pathogenic species or whether Caulobacters on whole possess previously-unappreciated virulence capability. Given the proposed environmental and medical applications for C. crescentus, understanding the potential pathogenicity of this bacterium is crucial. Consequently, we sequenced a clinical Caulobacter isolate to determine if it has acquired novel virulence determinants. We found that the clinical isolate represents a new species, Caulobacter mirare that, unlike C. crescentus, grows well in standard clinical culture conditions. C. mirare phylogenetically resembles both C. crescentus and the related C. segnis, which was also thought to be non-pathogenic. The similarity to other Caulobacters and lack of obvious pathogenesis markers suggested that C. mirare is not unique amongst Caulobacters and that consequently other Caulobacters may also have the potential to be virulent. We tested this hypothesis by characterizing the ability of Caulobacters to infect the model animal host Galleria mellonella. In this context, two different lab strains of C. crescentus proved to be as pathogenic as C. mirare, while lab strains of E. coli were non-pathogenic. Further characterization showed that Caulobacter pathogenesis in the Galleria model is mediated by lipopolysaccharide (LPS), and that differences in LPS chemical composition across species could explain their differential toxicity. Taken together, our findings suggest that many Caulobacter species can be virulent in specific contexts and highlight the importance of broadening our methods for identifying and characterizing potential pathogens.
弯曲杆菌属，包括广泛研究的模式生物新月弯孢菌，一直被认为是非致病性的，因此被提议作为各种环境修复和医学目的的生物工程载体。然而，弯曲杆菌种已被认为是几种医院获得性感染的病原体，这就提出了一个问题，即这些临床分离株是否代表一种新兴的致病种，或者整个弯曲杆菌属是否具有以前未被认识到的毒力能力。鉴于新月弯孢菌被提议用于环境和医学应用，了解这种细菌的潜在致病性至关重要。因此，我们对临床分离的弯曲杆菌进行了测序，以确定它是否获得了新的毒力决定因素。我们发现，临床分离株代表了一个新物种，即 mirare 弯孢菌，它与 crescentus 不同，在标准的临床培养条件下生长良好。mirare 弯孢菌在系统发育上与 crescentus 和相关的 segnis 相似，后者也被认为是非致病性的。与其他弯曲杆菌的相似性和缺乏明显的发病机制标记表明，mirare 弯孢菌在弯曲杆菌属中并非独一无二，因此其他弯曲杆菌属也可能具有毒力潜力。我们通过表征弯曲杆菌属感染模型动物宿主大蜡螟的能力来验证这一假设。在这种情况下，两种不同的 crescentus 实验室菌株被证明与 mirare 弯孢菌一样具有致病性，而大肠杆菌的实验室菌株则没有致病性。进一步的特征表明，弯曲杆菌属在大蜡螟模型中的发病机制是由脂多糖（LPS）介导的，并且物种之间 LPS 化学组成的差异可以解释它们的毒性差异。总的来说，我们的发现表明，许多弯曲杆菌属在特定情况下可能具有致病性，并强调了拓宽我们识别和表征潜在病原体的方法的重要性。
