Functional characterization of flavobacteria rhodopsins reveals a unique class of light-driven chloride pump in bacteria.

Light-activated, ion-pumping rhodopsins are broadly distributed among many different bacteria and archaea inhabiting the photic zone of aquatic environments. Bacterial proton- or sodium-translocating rhodopsins can convert light energy into a chemiosmotic force that can be converted into cellular biochemical energy, and thus represent a widespread alternative form of photoheterotrophy. Here we report that the genome of the marine flavobacterium Nonlabens marinus S1-08(T) encodes three different types of rhodopsins: Nonlabens marinus rhodopsin 1 (NM-R1), Nonlabens marinus rhodopsin 2 (NM-R2), and Nonlabens marinus rhodopsin 3 (NM-R3). Our functional analysis demonstrated that NM-R1 and NM-R2 are light-driven outward-translocating H(+) and Na(+) pumps, respectively. Functional analyses further revealed that the light-activated NM-R3 rhodopsin pumps Cl(-) ions into the cell, representing the first chloride-pumping rhodopsin uncovered in a marine bacterium. Phylogenetic analysis revealed that NM-R3 belongs to a distinct phylogenetic lineage quite distant from archaeal inward Cl(-)-pumping rhodopsins like halorhodopsin, suggesting that different types of chloride-pumping rhodopsins have evolved independently within marine bacterial lineages. Taken together, our data suggest that similar to haloarchaea, a considerable variety of rhodopsin types with different ion specificities have evolved in marine bacteria, with individual marine strains containing as many as three functionally different rhodopsins.

Solute carriers (SLC) in inflammatory bowel disease: a potential target of probiotics?

Transporter proteins of the solute carriers (SLCs) family play a role in epithelial permeability and barrier function in the intestine, and polymorphisms in SLC genes are associated with inflammatory bowel disease. Many SLCs also mediate the bioavailability of pharmaceutical compounds, and the modulation of such transport systems to increase drug efficacy is, therefore, of great interest. We have undertaken a large-scale project to evaluate whether bacteria can modulate the expression of SLCs in the intestine. Here we report the effect of VSL[sharp]3 (a high-potency probiotic preparation) on the expression of 3 large solute carrier families, SLC4, SLC21, and SLC22, which are involved in the transport of bicarbonates, organic anions and cations, and affect the bioavailability of several pharmaceutical compounds. Two groups of animals (VSL[sharp]3 and phosphate-buffered saline controls) were studied for SLC expression in the intestine by Real-Time PCR at the beginning (day 1) and at the end (day 20) of the treatment, and 7 days after the interruption of the treatment. An effect of VSL[sharp]3 administration was detected on the expression of 10% of the studied genes. This reached statistical significance (P=0.01) for the poorly characterized sodium-borate cotransporter SLC4A11, which showed a 5-times lower expression in VSL[sharp]3 than in control mice on day 1 of probiotic treatment. VSL[sharp]3-driven changes in the expression levels of SLC transporters might contribute to its reported effects on intestinal permeability. The elucidation of SLC4A11 function in the intestine will be the key to fully evaluate the relevance of specific findings.

Expression profiles of branchial FXYD proteins in the brackish medaka Oryzias dancena: a potential saltwater fish model for studies of osmoregulation.

FXYD proteins are novel regulators of Na(+)-K(+)-ATPase (NKA). In fish subjected to salinity challenges, NKA activity in osmoregulatory organs (e.g., gills) is a primary driving force for the many ion transport systems that act in concert to maintain a stable internal environment. Although teleostean FXYD proteins have been identified and investigated, previous studies focused on only a limited group of species. The purposes of the present study were to establish the brackish medaka (Oryzias dancena) as a potential saltwater fish model for osmoregulatory studies and to investigate the diversity of teleostean FXYD expression profiles by comparing two closely related euryhaline model teleosts, brackish medaka and Japanese medaka (O. latipes), upon exposure to salinity changes. Seven members of the FXYD protein family were identified in each medaka species, and the expression of most branchial fxyd genes was salinity-dependent. Among the cloned genes, fxyd11 was expressed specifically in the gills and at a significantly higher level than the other fxyd genes. In the brackish medaka, branchial fxyd11 expression was localized to the NKA-immunoreactive cells in gill epithelia. Furthermore, the FXYD11 protein interacted with the NKA α-subunit and was expressed at a higher level in freshwater-acclimated individuals relative to fish in other salinity groups. The protein sequences and tissue distributions of the FXYD proteins were very similar between the two medaka species, but different expression profiles were observed upon salinity challenge for most branchial fxyd genes. Salinity changes produced different effects on the FXYD11 and NKA α-subunit expression patterns in the gills of the brackish medaka. To our knowledge, this report is the first to focus on FXYD expression in the gills of closely related euryhaline teleosts. Given the advantages conferred by the well-developed Japanese medaka system, we propose the brackish medaka as a saltwater fish model for osmoregulatory studies.