THE EFFECT OF Mn(II) ON THE AUTOINDUCING GROWTH INHIBITION FACTOR INDeinococcus radiodurans

Purification from Deinococcus radiodurans of a 66 kDa ABC transporter acting on peptides containing at least 3 amino acids

Deinococcus radiodurans is a Gram positive bacterium the capability of which to withstand high doses of ionizing radiations is well known. Physiologically speaking, D. radiodurans is a proteolytic prokaryote able to express and secrete quite a number of proteases, and to use amino acids as an energy source. When considering this, it is surprising that little information is available on the biochemical components responsible for the uptake of peptides in D. radiodurans. Here we report on the purification and characterization of an ABC peptide transporter, isolated from D. radiodurans cells grown in tryptone-glucose-yeast extract (TGY) medium. In particular, we show here that the action of this transporter (denoted DR1571, SwissProt data bank accession number Q9RU24 UF71_DEIRA) is exerted on peptides containing at least 3 amino acids. Further, using tetra-peptides as model systems, we were able to observe that the DR1571 protein does not bind to peptides containing phenylalanine or valine, but associates with high efficiency to tetra-glycine, and with moderate affinity to tetra-peptides containing arginine or aspartate.

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.

Mechanisms of Stress Resistance and Gene Regulation in the Radioresistant Bacterium Deinococcus radiodurans

The bacterium Deinococcus radiodurans reveals extraordinary resistance to ionizing radiation, oxidative stress, desiccation, and other damaging conditions. In this review, we consider the main molecular mechanisms underlying such resistance, including the action of specific DNA repair and antioxidation systems, and transcription regulation during the anti-stress response.