Bacterial Microbiota of Ostreobium, the Coral-Isolated Chlorophyte Ectosymbiont, at Contrasted Salinities.

Microscopic filaments of the siphonous green algae Ostreobium (Ulvophyceae, Bryopsidales) colonize and dissolve the calcium carbonate skeletons of coral colonies in reefs of contrasted salinities. Here, we analyzed their bacterial community's composition and plasticity in response to salinity. Multiple cultures of Pocillopora coral-isolated Ostreobium strains from two distinct rbcL lineages representative of IndoPacific environmental phylotypes were pre-acclimatized (>9 months) to three ecologically relevant reef salinities: 32.9, 35.1, and 40.2 psu. Bacterial phylotypes were visualized for the first time at filament scale by CARD-FISH in algal tissue sections, within siphons, at their surface or in their mucilage. Ostreobium-associated microbiota, characterized by bacterial 16S rDNA metabarcoding of cultured thalli and their corresponding supernatants, were structured by host genotype (Ostreobium strain lineage), with dominant Kiloniellaceae or Rhodospirillaceae (Alphaproteobacteria, Rhodospirillales) depending on Ostreobium lineage, and shifted Rhizobiales' abundances in response to the salinity increase. A small core microbiota composed of seven ASVs (~1.5% of thalli ASVs, 19-36% cumulated proportions) was persistent across three salinities in both genotypes, with putative intracellular Amoebophilaceae and Rickettsiales_AB1, as well as Hyphomonadaceae and Rhodospirillaceae also detected within environmental (Ostreobium-colonized) Pocillopora coral skeletons. This novel knowledge on the taxonomic diversity of Ostreobium bacteria paves the way to functional interaction studies within the coral holobiont.

Functional diversity of microboring Ostreobium algae isolated from corals.

The filamentous chlorophyte Ostreobium sp. dominates shallow marine carbonate microboring communities, and is one of the major agents of reef bioerosion. While its large genetic diversity has emerged, its physiology remains little known, with unexplored relationship between genotypes and phenotypes (endolithic versus free-living growth forms). Here, we isolated nine strains affiliated to two lineages of Ostreobium (>8% sequence divergence of the plastid gene rbcL), one of which was assigned to the family Odoaceae, from the fast-growing coral host Pocillopora acuta Lamarck 1816. Free-living isolates maintained their bioerosive potential, colonizing pre-bleached coral carbonate skeletons. We compared phenotypes, highlighting shifts in pigment and fatty acid compositions, carbon to nitrogen ratios and stable isotope compositions (δ13 C and δ15 N). Our data show a pattern of higher chlorophyll b and lower arachidonic acid (20:4ω6) content in endolithic versus free-living Ostreobium. Photosynthetic carbon fixation and nitrate uptake, quantified via 8 h pulse-labeling with 13 C-bicarbonate and 15 N-nitrate, showed lower isotopic enrichment in endolithic compared to free-living filaments. Our results highlight the functional plasticity of Ostreobium phenotypes. The isotope tracer approach opens the way to further study the biogeochemical cycling and trophic ecology of these cryptic algae at coral holobiont and reef scales.

Driving Habits and Reaction Times on a Driving Simulation in Older Drivers With Chronic Heart Failure.

BACKGROUND: Judgement and reaction times during complex tasks like driving may be impaired in older adults with chronic heart failure (HF). This study sought to report the driving habits and reaction times of older patients with HF in a specially designed urban driving simulation. METHODS AND RESULTS: We conducted a prospective observational study in HF patients and controls. Patients in both groups underwent cognitive testing and screening for depression. Current drivers undertook a questionnaire regarding driving habits followed by an urban road driving simulation consisting of 3 laps. Five separate hazards appeared in the third lap without warning. Reaction times and stopping distances to the hazards were calculated. Of 247 patients with HF approached for the study, 124 had already voluntarily stopped driving owing to HF (n = 92) or other medical conditions (n = 32), 60 had never had a license, and 32 declined to participate. Of the 74 controls approached, 1 was not currently driving owing to a medical condition and 46 declined to participate. Patients in both groups had similar levels of cognitive function, mood and driving habits. 30 patients with HF (mean age, 74 ± 5 years; median NT-proBNP 1510 pg/mL [interquartile range (IQR), 546-3084 pg/L]) and 26 controls (mean age, 73 ± 5 years; median NT-proBNP 135 pg/mL [IQR, 73-182 pg/L]) completed the simulation. During lap 3, there was no difference in the driving speed between patients (mean 22.0 ± 4.5 mph) and controls (mean 21.7 ± 3.3 mph; P = .80). Patients had longer reaction times (median, 1.10 seconds; IQR, 0.98-1.30 seconds) than controls (median, 0.96 seconds; IQR, 0.83-1.10 seconds; P = .02), but there was no difference in stopping distances (patients: median, 43.9 m [IQR, 32.2-49.5 m]; controls: median, 38.1 m [IQR, 32.3-48.8 m]; P = .31). CONCLUSIONS: Many older adults with HF no longer drive. Those who continue to drive seem to be safe to drive on simulated urban roads.