Effect of levels of acetate on the mevalonate pathway of Borrelia burgdorferi.

Abstract

Borrelia burgdorferi, the agent of Lyme disease, is a spirochetal pathogen with limited metabolic capabilities that survives under highly disparate host-specific conditions. However, the borrelial genome encodes several proteins of the mevalonate pathway (MP) that utilizes acetyl-CoA as a substrate leading to intermediate metabolites critical for biogenesis of peptidoglycan and post-translational modifications of proteins. In this study, we analyzed the MP and contributions of acetate in modulation of adaptive responses in B. burgdorferi. Reverse-transcription PCR revealed that components of the MP are transcribed as individual open reading frames. Immunoblot analysis using monospecific sera confirmed synthesis of members of the MP in B. burgdorferi. The rate-limiting step of the MP is mediated by HMG-CoA reductase (HMGR) via conversion of HMG-CoA to mevalonate. Recombinant borrelial HMGR exhibited a K(m) value of 132 µM with a V(max) of 1.94 µmol NADPH oxidized minute(-1) (mg protein)(-1) and was inhibited by statins. Total protein lysates from two different infectious, clonal isolates of B. burgdorferi grown under conditions that mimicked fed-ticks (pH 6.8/37°C) exhibited increased levels of HMGR while other members of the MP were elevated under unfed-tick (pH 7.6/23°C) conditions. Increased extra-cellular acetate gave rise to elevated levels of MP proteins along with RpoS, CsrA(Bb) and their respective regulons responsible for mediating vertebrate host-specific adaptation. Both lactone and acid forms of two different statins inhibited growth of B. burgdorferi strain B31, while overexpression of HMGR was able to partially overcome that inhibition. In summary, these studies on MP and contributions of acetate to host-specific adaptation have helped identify potential metabolic targets that can be manipulated to reduce the incidence of Lyme disease.