Spectral and thermodynamic properties of methanobactin from γ-proteobacterial methane oxidizing bacteria: A case for copper competition on a molecular level

Methanobactin (mb) is a low molecular mass copper-binding molecule analogous to iron-binding siderophores. The molecule is produced by many methanotrophic or methane oxidizing bacteria (MOB), but has only been characterized to date in one MOB, Methylosinus trichosporium OB3b. To explore the potential molecular diversity in this novel class of metal binding compound, the spectral (UV-visible, fluorescent, and electron paramagnetic resonance) and thermodynamic properties of mb from two gamma-proteobacterial MOB. Methylococcus capsulatus Bath and Methylomicrobium album BG8, were determined and compared to the mb from the alpha-proteobacterial MOB, M. trichosporium OB3b. The mb from both gamma-proteobacterial MOB differed from the mb from M. trichosporium O83b in molecular mass and spectral properties. Compared to mb from M. trichosporium OB3b, the extracellular concentrations were low, as were copper-binding constants of mb from both gamma-proteobacterial MOB. In addition, the mb from M. trichosporium OB3b removed Cu(I) from the mb of both gamma-proteobacterial MOB. Taken together the results suggest mb may be a factor in regulating methanotrophic community structure in copper-limited environments. (C) 2010 Elsevier Inc. All rights reserved.