Bacteriorhodopsin-like proteins provide archaea and eubacteria with a unique bioenergetic pathway comprising light-driven transmembrane proton translocation by a single retinal-binding protein. Recently, homologous proteins were found to perform photosensory functions in lower eukaryotes, but no active ion transport by eukaryotic rhodopsins was detected. By demonstrating light-driven proton pumping in a fungal rhodopsin from Leptosphaeria maculans , we present a case of a retinal-based proton transporter from a eukaryote. This result implies that in addition to oxidative phosphorylation and chlorophyll photosynthesis, some lower eukaryotes may have retained the archaeal route of building an electrochemical transmembrane gradient of protons.

Objective and background: The aim of this in vitro study was to compare the efficiency of a photodynamic therapy (PDT) technique employing rose bengal (RB) and methylene blue (MB) as photosensitizers (PSs) to reduce the viability of Enterococcus faecalis , a well-known pathogen found in root canal systems. Currently, in several clinical applications, including in the field of endodontics, MB is employed in association with a red laser source for the photoinactivation of pathogenic bacteria. Methods: In this study, MB was used at 0.01% (31.2 mol/L) in association with a red (660 nm) laser as the excitation source in the MB group (MBG). Alternatively, the same test was performed with RB (25 mol/L) that was associated with a green (532 nm) light laser source in the RB group (RBG). A saline solution (0.9%) was used in the control group. The colony-forming units per milliliter (CFU/mL) were calculated after 24 h of incubation at 37°C, and the statistical analysis was performed using ANOVA. Results: The results showed a significant reduction in the CFU/mL in the RBG group (0.12 × 10 ⁸ ) compared with the control (2.82 × 10 ⁸ ) and MBG groups (2.66 × 10 ⁸ ). For the concentration and laser intensity employed in the experiments, the MBG group repeatedly showed no significant reduction in bacterial counts compared with the control. Therefore, the best result regarding the reduction of E. faecalis viable cells was obtained with RB as the PS. Conclusions: PDT may be improved if RB is used in association with a green light laser source for the inactivation of E. faecalis .