Keto acids prevent the toxic effects of light by inhibiting superoxide production and inhibit the rate of cysteine oxidation, an amino acid present in excess in the medium because of the cysteine auxotrophy of L. pneumophila species [46]. The presence of glutamate as well as pyruvate may Talazoparib datasheet lead to the formation of antioxidant compounds that directly or indirectly help a subpopulation

of injured cells to recover during the plating procedure [26–35]. However, when other antioxidant compounds, including ascorbic acid, propyl gallate or α-ketoglutarate, were added to the standard medium, they failed to significantly restore the culturability of non-culturable L. pneumophila cells (Table 1). Therefore, the action of pyruvate and glutamate may not be associated with their antioxidant properties. Pyruvate and glutamate may be involved in the complex life cycle of L. pneumophila. Although signal molecules that trigger L. pneumophila differentiation from

the replicative to the non-replicative and transmissive form have been thoroughly studied [7, 9–11], the signal triggering the reciprocal transition from the transmissive to the replicative form remains unknown. Several observations imply that amino acids are the primary signals driving differentiation from the transmissive find more to the replicative form of L. pneumophila, and it is therefore plausible that glutamate, one of the most abundant amino acids, might Smad signaling stimulate this differentiation [7]. Also, pyruvate can be converted into carbohydrates via gluconeogenesis, to the amino acid alanine, to fatty acids or to energy through acetyl-CoA. Thus, a combination of the actions of glutamate, alanine and perturbations in fatty acid metabolism [9] may act as an integrated signal to trigger the transition from the virulent to the replicative form of

L. pneumophila. Conclusion Our results suggest that the restoration of non-culturable L. pneumophila observed in presence of pyruvate and glutamate may be a consequence of their ability to help the injured cells to recover after a stress. However, we cannot exclude the possibility that pyruvate very and glutamate also drive differentiation from the transmissive to the replicative form of L. pneumophila. Moreover, we report evidence that this extracellular signal leads to the transition from a not-culturable form to a culturable form of L. pneumophila, providing a means for recovering virulent and previously uncultivated forms of L. pneumophila. These new media may be valuable for reducing the risks associated with underestimation of virulent cell counts of L. pneumophila in environmental samples. Methods Strain and growth conditions CIP 103854 T, L. pneumophila Philadelphia was used. Bacteria were frozen at −80°C until use.