The Bartonella quintana Extracytoplasmic Function Sigma Factor RpoE Has a Role in Bacterial Adaptation to the Arthropod Vector Environment

Bartonella quintana is a vector-borne bacterial pathogen that causes fatal disease in humans. During the infectious cycle, B. quintana transitions from the hemin-restricted human bloodstream to the hemin-rich body louse vector. Because extracytoplasmic function (ECF) sigma factors often regulate adaptation to environmental changes, we hypothesized that a previously unstudied B. quintana ECF sigma factor, RpoE, is involved in the transition from the human host to the body louse vector. The genomic context of B. quintana rpoE identified it as a member of the ECF15 family of sigma factors found only in alphaproteobacteria. ECF15 sigma factors are believed to be the master regulators of the general stress response in alphaproteobacteria. In this study, we examined the B. quintana RpoE response to two stressors that are encountered in the body louse vector environment, a decreased temperature and an increased hemin concentration. We determined that the expression of rpoE is significantly upregulated at the body louse (28°C) versus the human host (37°C) temperature. rpoE expression also was upregulated when B. quintana was exposed to high hemin concentrations. In vitro and in vivo analyses demonstrated that RpoE function is regulated by a mechanism involving the anti-sigma factor NepR and the response regulator PhyR. The ΔrpoE ΔnepR mutant strain of B. quintana established that RpoE-mediated transcription is important in mediating the tolerance of B. quintana to high hemin concentrations. We present the first analysis of an ECF15 sigma factor in a vector-borne human pathogen and conclude that RpoE has a role in the adaptation of B. quintana to the hemin-rich arthropod vector environment

Comparative materials differences revealed in engineered bone as a function of cell-specific differentiation

An important aim of regenerative medicine is to restore tissue function with implantable, laboratory-grown constructs that contain tissue-specific cells that replicate the function of their counterparts in the healthy native tissue. It remains unclear, however, whether cells used in bone regeneration applications produce a material that mimics the structural and compositional complexity of native bone. By applying multivariate analysis techniques to micro-Raman spectra of mineralized nodules formed in vitro, we reveal cell-source-dependent differences in interactions between multiple bone-like mineral environments. Although osteoblasts and adult stem cells exhibited bone-specific biological activities and created a material with many of the hallmarks of native bone, the 'bone nodules' formed from embryonic stem cells were an order of magnitude less stiff, and lacked the distinctive nanolevel architecture and complex biomolecular and mineral composition noted in the native tissue. Understanding the biological mechanisms of bone formation in vitro that contribute to cell-source-specific materials differences may facilitate the development of clinically successful engineered bone