Manganese is a Deinococcus radiodurans growth limiting factor in rich culture medium

To understand the effects triggered by Mn2+ on Deinococcus radiodurans, the proteome patterns associated with different growth phases were investigated. In particular, under physiological conditions we tested the growth rate and the biomass yield of D. radiodurans cultured in rich medium supplemented or not with MnCl₂. The addition of 2.5–5.0 µM MnCl₂ to the medium neither altered the growth rate nor the lag phase, but significantly increased the biomass yield. When higher MnCl₂ concentrations were used (10–250 µM), biomass was again found to be positively affected, although we did observe a concentration-dependent lag phase increase. The in vivo concentration of Mn2+ was determined in cells grown in rich medium supplemented or not with 5 µM MnCl₂. By atomic absorption spectroscopy, we estimated 0.2 and 0.75 mM Mn2+ concentrations in cells grown in control and enriched medium, respectively. We qualitatively confirmed this observation using a fluorescent turn-on sensor designed to selectively detect Mn2+ in vivo. Finally, we investigated the proteome composition of cells grown for 15 or 19 h in medium to which 5 µM MnCl₂ was added, and we compared these proteomes with those of cells grown in the control medium. The presence of 5 µM MnCl₂ in the culture medium was found to alter the pI of some proteins, suggesting that manganese affects post-translational modifications. Further, we observed that Mn2+ represses enzymes linked to nucleotide recycling, and triggers overexpression of proteases and enzymes linked to the metabolism of amino acids.