Rv3737 is required for Mycobacterium tuberculosis growth in vitro and in vivo and correlates with bacterial load and disease severity in human tuberculosis

Background: Rv3737 is the sole homologue of multifunctional transporter ThrE in Mycobacterium tuberculosis (Mtb). In this study, we aimed to investigate whether this transporter participates in vitro and in vivo survival of Mtb.

Methods: To characterize the role of Rv3737, we constructed and characterized a Mtb H37RvΔRv3737. This strain was evaluated for altered growth rate and macrophage survival using a cell model of infection. In addition, the comparative analysis was conducted to determine the association between Rv3737 mRNA expression and disease severity in active pulmonary TB patients.

Results: The H37RvΔRv3737 strain exhibited significantly slow growth rate compared to H37Rv-WT strain in standard culture medium. Additionally, the survival rate of H37Rv-WT strain in macrophages was 2 folds higher than that of H37RvΔRv3737 at 72 h. A significantly higher level of TNF-α and IL-6 mRNA expression was observed in macrophages infected with H37RvΔRv3737 as compared to H37Rv-WT. Of note, Rv3737 expression was significantly increased in clinical Mtb isolates than H37Rv-WT. The relative expression level of Rv3737 was positively correlated with lung cavity number of TB patients. Similarly, the higher Rv3737 mRNA level resulted in lower C(t) value by Xpert MTB/RIF assay, demonstrating that a positive correlation between Rv3737 expression and bacterial load in TB patients.

Conclusions: Our data takes the lead in demonstrate that the threonine transporter Rv3737 is required for in vitro growth and survival of bacteria inside macrophages. In addition, the expression level of Rv3737 may be associated with bacterial load and disease severity in pulmonary tuberculosis patients.