Isolation, cultivation, and genome analysis of proteorhodopsin-containing SAR116-clade strain Candidatus Puniceispirillum marinum IMCC1322.

Strain IMCC1322 was isolated from a surface water sample from the East Sea of Korea. Based on 16S rRNA analysis, IMCC1322 was found to belong to the OCS28 sub-clade of SAR116. The cells appeared as short vibrioids in logarithmic-phase culture, and elongated spirals during incubation with mitomycin or in aged culture. Growth characteristics of strain IMCC1322 were further evaluated based on genomic information; proteorhodopsin (PR), carbon monoxide dehydrogenase, and dimethylsulfoniopropionate (DMSP)-utilizing enzymes. IMCC1322 PR was characterized as a functional retinylidene protein that acts as a light-driven proton pump in the cytoplasmic membrane. However, the PR-dependent phototrophic potential of strain IMCC1322 was only observed under CO-inhibited and nutrient-limited culture conditions. A DMSP-enhanced growth response was observed in addition to cultures grown on C1 compounds like methanol, formate, and methane sulfonate. Strain IMCC1322 cultivation analysis revealed biogeochemical processes characteristic of the SAR116 group, a dominant member of the microbial community in euphotic regions of the ocean. The polyphasic taxonomy of strain IMCC1322 is given as Candidatus Puniceispirillum marinum, and was confirmed by chemotaxonomic tests, in addition to 16S rRNA phylogeny and cultivation analyses.

Cyanobacterial light-driven proton pump, gloeobacter rhodopsin: complementarity between rhodopsin-based energy production and photosynthesis.

A homologue of type I rhodopsin was found in the unicellular Gloeobacter violaceus PCC7421, which is believed to be primitive because of the lack of thylakoids and peculiar morphology of phycobilisomes. The Gloeobacter rhodopsin (GR) gene encodes a polypeptide of 298 amino acids. This gene is localized alone in the genome unlike cyanobacterium Anabaena opsin, which is clustered together with 14 kDa transducer gene. Amino acid sequence comparison of GR with other type I rhodopsin shows several conserved residues important for retinal binding and H+ pumping. In this study, the gene was expressed in Escherichia coli and bound all-trans retinal to form a pigment (λmax  = 544 nm at pH 7). The pKa of proton acceptor (Asp121) for the Schiff base, is approximately 5.9, so GR can translocate H+ under physiological conditions (pH 7.4). In order to prove the functional activity in the cell, pumping activity was measured in the sphaeroplast membranes of E. coli and one of Gloeobacter whole cell. The efficient proton pumping and rapid photocycle of GR strongly suggests that Gloeobacter rhodopsin functions as a proton pumping in its natural environment, probably compensating the shortage of energy generated by chlorophyll-based photosynthesis without thylakoids.

Relationship between olfactory function and olfactory neuronal population in C57BL6 mice injected intraperitoneally with 3-methylindole.

OBJECTIVE: It is not known how many olfactory receptor neurons should be intact to maintain olfaction in mouse models treated with 3-methylindole. The aim of this study is to investigate the relationship between a simple olfactory test outcome and the olfactory neuronal population. STUDY DESIGN: Mouse model. SETTING: Animal laboratory of the Seoul National University Bundang Hospital. SUBJECTS AND METHODS: Olfactory dysfunction was induced by intraperitoneal injection of 3-methylindole in 38 six-week-old female C57BL6 mice. Olfactory function was evaluated by a food-finding test following 72-hour starvation. The olfactory neuronal population was quantified by olfactory marker protein (OMP) expression. RESULTS: The average time for finding food was 8.1 seconds in control mice. It was 13.4, 84.4, 90.1, and 111.4 seconds for mice injected with 100, 200, 300, and 400 µg/g of 3-methylindole, respectively. Harvesting the whole olfactory neuroepithelium, densitometric analysis showed significant decrease of OMP in the 300- and 400-µg/g groups as compared with controls (18.8% and 17.5% of relative density, respectively). In the olfactory bulb, there was a significant decrease of OMP in the 200-, 300-, and 400-µg/g groups (44.5%, 37.0%, and 9.0% of relative density, respectively). The food-finding time had a significant reverse correlation with the relative density of OMP both in the olfactory bulb and in the olfactory neuroepithelium. CONCLUSION: Our study showed that olfactory impairment was correlated with olfactory neuronal population in mice treated with 3-methylindole. The food-finding test would be a useful tool that could be easily performed without special training in the 3-methylindole-treated C57BL6 anosmic mouse model.