Borrelia burgdorferi, the causative agent of Lyme disease, traverses through vastly distinct environments between the tick vector and the multiple phases of the mammalian infection that requires genetic adaptation for the progression of pathogenesis. Borrelial gene expression is highly responsive to changes in specific environmental signals that initiate the RpoS regulon for mammalian adaptation, but the mechanism(s) for direct detection of environmental cues has yet to be identified. Secondary messenger cyclic adenosine monophosphate (cAMP) produced by adenylate cyclase is responsive to environmental signals, such as carbon source and pH, in many bacterial pathogens to promote virulence by altering gene regulation. B. burgdorferi encodes a single non-toxin class IV adenylate cyclase (bb0723, cyaB). This study investigates cyaB expression along with its influence on borrelial virulence regulation and mammalian infectivity. Expression of cyaB was specifically induced with co-incubation of mammalian host cells that was not observed with cultivated tick cells suggesting that cyaB expression is influenced by cellular factor(s) unique to mammalian cell lines. The 3' end of cyaB also encodes a small RNA, SR0623, in the same orientation that overlaps with bb0722. The differential processing of cyaB and SR0623 transcripts may alter the ability to influence function in the form of virulence determinant regulation and infectivity. Two independent cyaB deletion B31 strains were generated in 5A4-NP1 and ML23 backgrounds and complemented with the cyaB ORF alone that truncates SR0623, cyaB with intact SR0623, or cyaB with a mutagenized full length SR0623 to evaluate the influence on transcriptional and post-transcriptional regulation of borrelial virulence factors and infectivity. In the absence of cyaB, expression and production of ospC was significantly reduced, while the protein levels for BosR and DbpA were substantially lower than parental strains. Infectivity studies with both independent cyaB mutants demonstrated an attenuated phenotype with reduced colonization of tissues during early disseminated infection. This work suggests that B. burgdorferi utilizes cyaB and potentially cAMP as a regulatory pathway to modulate borrelial gene expression and protein production to promote borrelial virulence and dissemination in the mammalian host.

中文翻译：

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伯氏疏螺旋体伯德弗里腺苷酸环化酶CyaB对毒力因子的产生和哺乳动物的感染很重要

莱姆病的病原体伯氏疏螺旋体遍历壁虱媒介和哺乳动物感染的多个阶段之间的截然不同的环境，这需要遗传适应病程的发展。Borrelial基因表达对特定环境信号的变化具有高度响应性，这些变化启动了RpoS regulon用于哺乳动物的适应，但是直接检测环境线索的机制尚未确定。腺苷酸环化酶产生的次级信使环状单磷酸腺苷（cAMP）对许多细菌病原体中的环境信号（如碳源和pH）有反应，以通过改变基因调控来提高毒力。B. burgdorferi编码单个IV类非毒素腺苷酸环化酶（bb0723，cyaB）。这项研究调查cyaB表达以及其对Borelial毒力调节和哺乳动物感染性的影响。通过用培养的壁虱细胞未观察到的哺乳动物宿主细胞共孵育来特异性诱导cyaB的表达，这表明cyaB的表达受哺乳动物细胞系特有的细胞因子的影响。cyaB的3'末端还以与bb0722重叠的相同方向编码小RNA SR0623。cyaB和SR0623转录本的差异处理可能以毒力决定因素调节和感染性的形式改变影响功能的能力。在5A4-NP1和ML23背景中产生了两个独立的cyaB缺失B31菌株，并与单独的cyaB ORF互补，后者将SR0623，具有完整SR0623的cyaB截短，或诱变的全长SR0623的cyaB，以评估对硼毒力因子和感染性的转录和转录后调控的影响。在不存在cyaB的情况下，ospC的表达和产量显着降低，而BosR和DbpA的蛋白质水平则明显低于亲本菌株。对两个独立的cyaB突变体的感染性研究表明，在早期传播的感染过程中，表型减弱，组织定植减少。这项工作表明，B。burgdorferi利用cyaB和潜在的cAMP作为调节途径来调节borrelial基因的表达和蛋白质的产生，从而促进borrelial毒力和在哺乳动物宿主中的传播。