Publications

4467

“ Candidatus Liberibacter asiaticus” (CLas) is an uncultivable α -proteobacterium causing the most destructive and currently incurable citrus disease, Huanglongbing (HLB). The transcription factors (TFs) of CLas are involved in various biological processes. However, the functions of most TFs remain unverified. BolA is reported to be an important transcriptional regulator related to bacterial growth and virulence. Here, the role of BolA in CLas was investigated using gene deletion and complementation assays in the heterologous host Sinorhizobium meliloti ( Sme ). The results showed that BolA CLas and BolA Sme are similar in sequence and transcriptional regulation. BolA positively regulates biofilm formation—evidenced by the significant downregulation of a key gene ( cyaA ) in the mutant (Δ BolA Sme ), without affecting bacterial growth. The upregulation of 16 differentially expressed genes (DEGs) related to flagellar assembly indicated that BolA negatively regulates CLas motility. BolA deletion also led to the downregulation of ABC transporters (15 DEGs) and lipid metabolism genes (13 DEGs), correlating with reduced stress tolerance. Furthermore, BolA CLas is involved in modulating heme metabolism, as well as protein export, folding, sorting, and degradation. Finally, in vivo screening identified two compounds as BolA inhibitors, which significantly reduced CLas titer in infected periwinkle leaves. Taken together, this study constitutes a relevant step toward the understanding of CLas virulence by demonstrating that BolA is a key TF involved in biofilm formation, stress response, motility, and bacterial physiology, thereby presenting a potential target for disease control.

Candidatus Rickettsia colombiensis is a new candidate species of Rickettsiae spotted fever group that have been isolated only from ticks. The pathogenicity of Ca. R. colombiensis to human and animals is unknown. This study evaluated the pathogenic potential of Ca. R. colombiensis in Syrian hamsters and assessed the cross-reactivity between Ca. R. colombiensis and other Rickettsia in human and hamster sera. Shell vial technique was employed to isolate Ca. R. colombiensis. Subsequently, five male Syrian hamsters were inoculated intraperitoneally (IP) and five intradermally (ID) with 1 × 106 Vero cells infected with Ca. R. colombiensis. One control hamster was used in each group. The health status was assessed daily, and necropsies were performed. Serum samples were tested by indirect immunofluorescence and tissues were processed by qPCR and histological stains. All Syrian hamsters remained healthy during the trial. No histopathological damages associated with rickettsial infection were observed. No Rickettsial DNA was detected in tissues. Syrian hamsters showed IgG antibody titers ranging from 1:64 to 1:1024. Control hamsters were negative. Regarding human sera, 56% (84/150) had IgG cross-reactivity antibodies against Ca. R. colombiensis. Subsequently, in a selected subset of 30 sera with moderate to high titers, all samples reacted with Ca. R. colombiensis antigen. Under specific conditions of this study, Ca. R. colombiensis did not behave as a highly virulent pathogen in the hamster model, although all infected Syrian hamsters developed IgG antibodies responses. Regarding cross-reactivity, it is possible to serologically diagnose rickettsial infection using Ca. R. colombiensis as an antigen.