Lemon myrtle extract inhibits lactate production by Streptococcus mutans.

Backhousia citriodora (lemon myrtle) extract has been found to inhibit glucansucrase activity, which plays an important role in biofilm formation by Streptococcus mutans. In addition to glucansucrase, various virulence factors in S. mutans are involved in the initiation of caries. Lactate produced by S. mutans demineralizes the tooth enamel. This study investigated whether lemon myrtle extract can inhibit S. mutans lactate production. Lemon myrtle extract reduced the glycolytic pH drop in S. mutans culture and inhibited lactate production by at least 46%. Ellagic acid, quercetin, hesperetin, and myricetin, major polyphenols in lemon myrtle, reduced the glycolytic pH drop and lactate production, but not lactate dehydrogenase activity. Furthermore, these polyphenols reduced the viable S. mutans cell count. Thus, lemon myrtle extracts may inhibit S. mutans-mediated acidification of the oral cavity, thereby preventing dental caries and tooth decay.

Effects of cane use on walking parameters and lower limb muscle activity in adults with spastic cerebral palsy: a cross-sectional study.

[Purpose] Adults with cerebral palsy often use a cane as a walking aid because of their decreased gait ability. However, it is unclear whether this affects lower limb muscle activity during walking. The purpose of this study was to clarify the influence of using a cane during walking on the spatio-temporal parameters of walking, lower limb muscle activity, and lower limb muscle coactivation in adults with spastic cerebral palsy. [Participants and Methods] Eleven participants with cerebral palsy were included. The spatio-temporal parameters of walking, lower limb muscle activity, and coactivation of lower limb muscle were measured during a 10 m trial with no cane, one cane, and two canes. [Results] Walking speed was lower and the stride time longer when using two canes than when using no cane. All muscle activities significantly reduced when using two canes. No significant difference was observed between using no cane and one cane, except for walking speed. In addition, there was no significant difference in coactivation between the conditions. [Conclusion] This study revealed that when two canes were used, the walking speed was reduced, and lower limb muscle activity was reduced, reducing the burden. In contrast, the movement pattern was not suggested to have changed.

Culture in 10% O2 enhances the production of active hormones in neuro-endocrine cells by up-regulating the expression of processing enzymes.

To closely mimic physiological conditions, low oxygen cultures have been employed in stem cell and cancer research. Although in vivo oxygen concentrations in tissues are often much lower than ambient 21% O2 (ranging from 3.6 to 12.8% O2), most cell cultures are maintained at 21% O2 To clarify the effects of the O2 culture concentration on the regulated secretion of peptide hormones in neuro-endocrine cells, we examined the changes in the storage and release of peptide hormones in neuro-endocrine cell lines and endocrine tissues cultured in a relatively lower O2 concentration. In both AtT-20 cells derived from the mouse anterior pituitary and freshly prepared mouse pituitaries cultured in 10% O2 for 24 h, the storage and regulated secretion of the mature peptide hormone adrenocorticotropic hormone were significantly increased compared with those in cells and pituitaries cultured in ambient 21% O2, whereas its precursor proopiomelanocortin was not increased in the cells and tissues after being cultured in 10% O2 Simultaneously, the prohormone-processing enzymes PC1/3 and carboxypeptidase E were up-regulated in cells cultured in 10% O2, thus facilitating the conversion of prohormones to their active form. Similarly, culturing the mouse ß-cell line MIN6 and islet tissue in 10% O2 also significantly increased the conversion of proinsulin into mature insulin, which was secreted in a regulated manner. These results suggest that culture under 10% O2 is more optimal for endocrine tissues/cells to efficiently generate and secrete active peptide hormones than ambient 21% O2.

An XAFS study of Cs adsorption by the precipitation bands of Mn-Fe-based Prussian blue analogues spontaneously formed in agarose gel.

The adsorption of Cs+ ions by the precipitation bands of a Mn-Fe based Prussian blue analogue (Mn-Fe PBA) that form spontaneously in agarose gel was investigated by X-ray absorption fine structure spectroscopy coupled with scanning electron microscopy (SEM) and X-ray fluorescence (XRF) distribution analysis. Two gel samples were prepared by contacting a gel containing 0.05 M [Fe(CN)6]3- and 2.3 mass% agarose with a 0.50 M MnSO4 solution, into one of which a 0.10 M CsCl solution was introduced. The SEM images and the XRF intensity distributions reveal that Mn-Fe PBA forms cubic crystallites (approx. 3 × 3 × 3 µm in size) in the gels that trap Cs+ ions with considerably high affinity. Cs L3-edge and Mn K-edge X-ray absorption near-edge structure (XANES) spectra, which were analyzed with the aid of FEFF simulations, strongly suggest that Cs adsorption occurs at relatively large defect sites close to the sub-cube faces in the PBA. This suggestion is supported by Cs L3-edge extended X-ray absorption fine structure spectroscopy, which suggested that the first and second coordination shells around the Cs+ ions are at a Cs-O distance of 0.35 ± 0.02 nm and a Cs-N distance of 0.43 ± 0.01 nm, respectively, with coordination numbers of 1.5 ± 0.5 and 3.0 ± 0.5. The Mn K-edge XANES data also suggest that H2O molecules, which initially occupy many cubic centers in the Mn-Fe PBAs, are mostly displaced during Cs adsorption. These findings provide valuable insight toward fully understanding Cs adsorption by Mn-Fe PBA.

Integrated approach to understanding the onset and pathogenesis of black band disease in corals.

Emerging infectious diseases are contributing to global declines in coral reef ecosystems, highlighting a growing need for aetiological knowledge to develop effective management strategies. In this review, we focus on black band disease (BBD), one of the most virulent diseases and the only polymicrobial disease so far known to affect corals. A multipartite microbial consortium dominated by Cyanobacteria, but also including sulfur-cycling bacteria, other bacterial groups and members of the Archaea and Eukarya, forms a sulfide-rich anaerobic mat that migrates across the surface of coral colonies, killing the underlying tissues. The polymicrobial nature of the disease challenges classic aetiological approaches to unravelling disease causation. Here, we synthesize current knowledge on the range of pathogens forming the microbial consortium with recent studies on the transmission, biogeochemistry and environmental drivers of BBD to develop a conceptual model of BBD pathogenesis. The model illustrates how the development of BBD virulence factors is linked to a cascade of microbial community shifts and associated functional roles that progressively develop the microbial consortium from comparatively benign cyanobacterial patches to virulent BBD lesions. This review showcases how an approach that integrates multiple key aspects of the disease provides insights essential to elucidating the aetiology of BBD.

Inhibitory effects of hydroxylated cinnamoyl esters on lipid absorption and accumulation.

Obesity is a risk factor associated with several lifestyle-related diseases, for example, diabetes, high blood pressure, hyperlipidemia and cancer. Caffeic acid 2-phenylethyl ester (CAPE, 1), a naturally-occurring compound found in various plants and propolis, which exhibits anti-inflammatory, immunomodulatory and cytotoxic activities and inhibits 3T3-L1 differentiation to adipocytes. As part of our efforts to moderate lifestyle-related diseases, we synthesized analogs of 1 and studied their effects on pancreatic lipase activities, lipid absorption, and 3T3-L1 differentiation. We found that catechols 1-4 show inhibitory activities against pancreatic lipase in a dose-dependent manner in vitro. Compounds 1-3 proved to be more potent inhibitors of pancreatic lipase than 5, 6, 8, and 9, which have one hydroxyl group, respectively. Compound 7 has three aromatic hydroxyl groups and restrains greater lipase inhibitory activity than the other compounds. In addition, 7 and 3 significantly suppress a rise in blood triglyceride (TG) levels in mice given corn oil orally. Furthermore, 2 and 3 are more potent at preventing 3T3-L1 differentiation (lipid accumulation) than 1, while 7 is more potent than 3, 8, and 9 in these assays. Compounds 2, 3, and 7 inhibit lipid absorption and accumulation, with new compound 7 being the most potent. These results indicate that 7 may have potential benefits as a health agent with anti-obesity properties.

Microbes guide corals looking to find a home.

Coral reefs are facing unprecedented anthropogenic pressures impacting critical processes such as recruitment of juvenile corals. Through larval choice assays and co-occurrence network analyses, a recent study by Turnlund et al. identified microbial taxa within reef biofilms that positively correlate and therefore have potential key roles in inducing coral settlement.

Pyrosequencing-based profiling of archaeal and bacterial 16S rRNA genes identifies a novel archaeon associated with black band disease in corals.

Black band disease (BBD) is a microbial consortium that creates anoxic, sulfide-rich microenvironments and kills underlying coral tissues as it rapidly migrates across colonies. Although bacterial communities associated with BBD have been studied extensively, the presence and roles of archaea are unexplored. Using amplicon-pyrosequencing of 16S ribosomal RNA genes, we investigated the community structure of both archaea and bacteria within microbial lesions of BBD and the less-virulent precursor stage, 'cyanobacterial patches' (CP), affecting the coral Montipora hispida. We detected characteristic shifts in microbial communities during the development of BBD from CP, reflecting microenvironmental changes within lesions. Archaeal profiles in CP suggested a diverse assemblage affiliated with the Thaumarchaeota and Euryarchaeota, similar to communities described for oxic marine environments. In contrast, a novel ribotype, distantly affiliated to the Euryarchaeota, dominated up to 94% of archaeal sequences retrieved from BBD. The physiological characteristics of this dominant archaeal ribotype are unknown because of the novelty of its 16S ribosomal RNA gene sequences; however, their prominent associations with BBD lesions suggest the ability to thrive in the organic- and sulfide-rich anoxic microenvironment characteristic of BBD lesions. Discovery of this novel archaeal ribotype provides new insights into the microbial ecology and aetiology of BBD.

[Minute granular lesions of the retinal pigment epithelium related to choroidal hyperpermeability in patients with central serous chorioretinopathy].

PURPOSE: To investigate the relationship between increased permeability of choroidal vessels revealed by indocyanine green angiography (ICGA) and lesions of retinal pigment epithelium (RPE) revealed by Retro-mode (RM) in the eyes of patients with central serous chorioretinopathy (CSC). DESIGN: A retrospective cross-sectional study. PATIENTS AND METHODS: We examined the minute granular lesions (MGLs) of the RPE using RM imaging (scanning laser ophthalmoscopy), in relation to the choroidal hyperpermeability visualized by indocyanine green angiography (ICGA) in 40 eyes of 20 Japanese patients with CSC. We classified them into two groups: eyes (25 eyes) with various retinal lesions and eyes without retinal lesions (15 eyes). RESULTS: MGLs of the RPE in RM imaging were seen in 38 of 40 eyes (95%). The MGLs were detected in all 25 eyes in the group of various retinal lesions, and in 13 of 15 eyes (87%)in the group without retinal lesions. The area of MGLs exceeded the choroidal hyperpermeability in 18 eyes (45%), was the same as choroidal hyperpermeability in 15 eyes (38%), while 7 eyes (17%) had no hyperpermeability. CONCLUSIONS: Choroidal hyperpermeability may be a possible cause of MGLs in the eyes of patients with CSC.

[Clinical findings and macular lesions in basal laminar drusen].

PURPOSE: To investigate the clinical characteristics and accompanying macular lesions in Japanese patients with basal laminar drusen (BLD). DESIGN: Retrospective cross-sectional study. PATIENTS AND METHODS: Fifty four eyes of 27 Japanese patients with BLD were examined for the clinical characteristics of BLD and accompanying macular lesions using retro-mode imaging (Scanning Laser Ophthalmoscope F-10, Nidek) in addition to current methods such as fluorescein angiography (FA), indocyanine green angiography (IA), fundus autofluorescence (FAF) and spectral domain optical coherence tomography (SD-OCT). RESULTS: 1)BLD was more clearly identified using retro-mode imaging than any of the other current imaging methods, and was divided into two types: a crater type (relatively sparsely distributed BLD with many soft drusens) and a mesh type (uniformly distributed BLD). 2) BLD in both eyes was more common in female patients, and had the same type, distribution and similar macular lesions in both eyes. 3) Among the macular lesions, we observed macular atrophy, retinal angiomatous proliferation and vitelliform detachment in many patients, in contrast to few cases of choroidal neovascularization and no polypoidal choroidal vasculopathy. CONCLUSIONS: BLD may be regarded as a disease that is different from age-related macular degeneration (AMD).

Effects of Fear of Falling on the Single-Step Threshold for Lateral Balance Recovery in Older Women.

BACKGROUND AND PURPOSE: Fear of falling is associated with poor physical health and influences postural stability during whole-body movement. The ability to recover from lateral balance loss is required to prevent falls; however, the relationship between lateral balance recovery and fear of falling has not been established. This study aimed to investigate whether fear of falling is associated with the stepping threshold for lateral balance recovery. METHODS: This study included 56 ambulatory, community-dwelling women aged 65 years or older. We determined the single-step threshold as the maximum lean magnitude normalized with body weight from which participants could be suddenly released and still recover balance using a single side step. The short-form Falls Efficacy Scale International was used as a measure of fear of falling. RESULTS AND DISCUSSION: The single-step threshold significantly correlated with age ( rs =-0.603) and the short-form Falls Efficacy Scale International score ( rs =-0.439). Ordinal regression analysis revealed that age (odds ratio, 0.826; 95% confidence interval, 0.742-0.920) and the short-form Falls Efficacy Scale International score (odds ratio, 0.811; 95% confidence interval, 0.680-0.966) were significantly associated with the single-step threshold, such that older age and greater fear of falling each independently predicted that failure to recover balance with a single step would occur at a lower percentage of body weight. CONCLUSIONS: Greater fear of falling was associated with reduced ability to recover from lateral balance loss in addition to aging. Future studies should explore whether evidence-based interventions to reduce fear of falling combined with perturbation training might lead to improved ability to recover from balance loss.

Developmental changes in straight gait in childhood.

BACKGROUND: Understanding typical gait development is critical in developing suitable physical therapy methods for gait disorders. This study investigated the developmental changes and controlling mechanisms of straight gait. METHODS: We conducted an experimental procedure among 90 participants, including 76 typically developing children and 14 healthy adults. The children were divided according to age into 3-4, 5-6, 7-8, and 9-10-year age groups. We created two indices to quantify straight gait using the extrapolated center of mass (XCOM; goal index, XCOMG and actual progress index, XCOMP), which were calculated and compared between the groups. Stepwise multiple regression was used to examine the effects of each gait variable on XCOMG and XCOMP. To eliminate the effects of multicollinearity, correlation coefficients were calculated for all gait variables. RESULTS: Both XCOMG and XCOMP decreased gradually with age and were significantly larger in the 3-4 and 5-6 year groups than in the adult group. Multiple regression analysis showed that step velocity, step width, and the coefficiente of variation (CV) of the step width had independent coefficients of variation for the XCOMG, and the symmetry index of step time, step width, and the CV of the step width had independent CV for the XCOMP. These variables were selected as significant variables. The results showed that meandering gait was more pronounced at younger ages. Furthermore, straight gait observed in adulthood was achieved by the age of 7. CONCLUSION: Pace (step velocity) and stability (step width and CV of step width) may contribute to XCOMG, which assesses the ability to proceed in the direction of the target. Stability and symmetry may contribute to XCOMP, which assesses the ability to walk straight in one's own direction of progress. Physical therapists could apply these indices in children to assess their ability to walk straight.

Physical activity is associated with walking and balance ability but not fatigue, knee extension strength, or body composition in adults with cerebral palsy: a pilot cross-sectional study.

Common secondary impairments associated with aging in adults with cerebral palsy (CP) decrease physical functions, including walking and balance ability, and increase the sense of fatigue. This motor dysfunction results in decreased physical activity (PA) and could be associated with obesity and sarcopenia. This study examined the association of daily PA levels with fatigue, physical function, and body composition in 22 adults with CP (age, 37.4 ±â€…14.7 years; Gross Motor Function Classification System level, I: 6, II: 16). The level of daily PA was divided into percent of sedentary behavior, light PA, and moderate-to-vigorous PA (%MVPA) per day. These outcomes were examined for correlation with the Fatigue Severity Scale, knee extension strength, comfortable and maximum walking speed, Timed-Up-and-Go-Test (TUG), and body fat percentage and skeletal muscle mass using Spearman's rank correlation coefficient. An additional partial correlation analysis with sex and age adjustment was performed. The %MVPA correlated positively with comfortable walking speed (rs = 0.424, P  = 0.049) and negatively with TUG (rs = -0.493, P  = 0.020). The partial correlation revealed associations of %MVPA with maximum walking speed (r = 0.604, P  = 0.022) and TUG (r = -0.604, P  = 0.022). The results show that among adults with CP, increased PA is associated with improvements in mobility but not in perceived fatigue or body composition, regardless of sex and age. Maintaining and improving %MVPA and walking and balance ability in adults with CP have a positive impact on each other, and potentially on overall health management.

MLPK function is not required for self-incompatibility in the S29 haplotype of Brassica rapa L.

KEY MESSAGE: S29 haplotype does not require the MLPK function for self-incompatibility in Brassica rapa. Self-incompatibility (SI) in Brassicaceae is regulated by the self-recognition mechanism, which is based on the S-haplotype-specific direct interaction of the pollen-derived ligand, SP11/SCR, and the stigma-side receptor, SRK. M locus protein kinase (MLPK) is known to be one of the positive effectors of the SI response. MLPK directly interacts with SRK, and is phosphorylated by SRK in Brassica rapa. In Brassicaceae, MLPK was demonstrated to be essential for SI in B. rapa and Brassica napus, whereas it is not essential for SI in Arabidopsis thaliana (with introduced SRK and SP11/SCR from related SI species). Little is known about what determines the need for MLPK in SI of Brassicaceae. In this study, we investigated the relationship between S-haplotype diversity and MLPK function by analyzing the SI phenotypes of different S haplotypes in a mlpk/mlpk mutant background. The results have clarified that in B. rapa, all the S haplotypes except the S29 we tested need the MLPK function, but the S29 haplotype does not require MLPK for the SI. Comparative analysis of MLPK-dependent and MLPK-independent S haplotype might provide new insight into the evolution of S-haplotype diversity and the molecular mechanism of SI in Brassicaceae.

Microbial mat compositions and localization patterns explain the virulence of black band disease in corals.

Black band disease (BBD) in corals is characterized by a distinctive, band-like microbial mat, which spreads across the tissues and often kills infected colonies. The microbial mat is dominated by cyanobacteria but also commonly contains sulfide-oxidizing bacteria (SOB), sulfate-reducing bacteria (SRB), and other microbes. The migration rate in BBD varies across different environmental conditions, including temperature, light, and pH. However, whether variations in the migration rates reflect differences in the microbial consortium within the BBD mat remains unknown. Here, we show that the micro-scale surface structure, bacterial composition, and spatial distribution differed across BBD lesions with different migration rates. The migration rate was positively correlated with the relative abundance of potential SOBs belonging to Arcobacteraceae localized in the middle layer within the mat and negatively correlated with the relative abundance of other potential SOBs belonging to Rhodobacteraceae. Our study highlights the microbial composition in BBD as an important determinant of virulence.

[Indentation of retinal pigment epithelium in polypoidal choroidal vasculopathy detected by retro-mode (scanning laser ophthalmoscopy)].

PURPOSE: To detect by Retro-mode (RM) imaging the nature and frequency of vascular indentation of the retinal pigment epithelium (RPE) due to polypoidal vessels and vascular networks in polypoidal choroidal vasculopathy (PCV). DESIGN: Retrospective cross-sectional study. PATIENTS AND METHODS: Thirty eyes of 29 Japanese patients with PCV diagnosed by ophthalmoscopy and indocyanine green angiography (IA) were retrospectively analyzed by RM imaging. We evaluated the ratio of detection of polypoidal and network vessels in PCV by RM, the main causes hindering vascular indentation of the RPE, and the relationship of the findings in IA(late phase) to RM imaging. RESULTS: In 13 out of the 30 eyes (43.3%) all of the polypoidal vessels of PCV were identified by RM imaging, whereas in 8 eyes (26.7%) only one part could be identified and none could be identified in the remaining 9 eyes (30%). Network vessels were detected completely in 15 eyes (50%), and partially in 5 eyes (16.7%)whereas none could be detected in the remaining 10 eyes (30.3%). In many cases the main causes of the hindered vascular indentation of the RPE were either serous retinal detachment and/or cystoid macular edema; fibrin, hemorrhagic pigment epithelial detachment, subretinal hemorrhages and pigment epithelial atrophy were also seen. Regarding the relationship of the findings of network vessels in IA (late phase) to RM imaging, RM imaging was superior or of equal value in finding network vessels in 14 (46.7%)of the 30 eyes. CONCLUSIONS: RM imaging detected polypoidal vessels and network vessels of PCV as vascular indentations of the RPE.

[Detection for retinal pigment epithelial lesions in fellow eye of age-related macular degeneration by retro-mode].

PURPOSE: Using the Retro-mode (RM), to detect drusen and other minute lesions of the retinal pigment epithelium (RPE) invisible in current imaging methods in the fellow eye of Japanese patients with exudative age-related macular degeneration(AMD). DESIGN: A retrospective cross-sectional study. PATIENTS AND METHODS: The fellow eyes of nineteen Japanese patients with unilateral exudative AMD were examined using RM imaging (F-10 fundus camera, Nidek), in contrast with fluorescein angiography, indocyanine green angiography, and optic coherence tomography (3D OCT-1000, Topcon Co). We were able to identify the type of drusen and minute granular lesions (MGLs) in the RPE. RESULTS: In all patients, RM imaging gave easier to identify images of all types of drusen than other current imaging methods. Moreover, MGLs of the RPE either adjacent to drusen or without drusen, invisible in other current methods, were detected by RM imaging. CONCLUSIONS: The RM provides clearer imaging of all kind of drusen, and MGLs of the RPE invisible with current methods. These MGLs are possible precursors of drusen.

Spatiotemporal Characteristics of Lateral Reactive Stepping in Individuals with Chronic Stroke.

We compared the spatiotemporal characteristics of lateral perturbation-induced reactive stepping in stroke subjects with those of age-matched controls. We subjected 12 stroke subjects and 17 healthy elderly controls to lateral stepping. We analyzed first-step spatiotemporal parameters during stepping and recorded the selected reactive step types at the stepping threshold. Stroke subjects showed a lower stepping threshold and more frequently used medial steps than controls. Stroke subjects also had a longer delay prior to foot-off in lateral steps when perturbed toward the nonparetic side, and in medial steps when perturbed toward both sides than controls. Thus, the time deficits in reactive stepping in individuals with stroke may be attributed to stroke-related sensorimotor impairments, indicating their limitations in balance control.

Differential regulation of degradation and immune pathways underlies adaptation of the ectosymbiotic nematode Laxus oneistus to oxic-anoxic interfaces.

Eukaryotes may experience oxygen deprivation under both physiological and pathological conditions. Because oxygen shortage leads to a reduction in cellular energy production, all eukaryotes studied so far conserve energy by suppressing their metabolism. However, the molecular physiology of animals that naturally and repeatedly experience anoxia is underexplored. One such animal is the marine nematode Laxus oneistus. It thrives, invariably coated by its sulfur-oxidizing symbiont Candidatus Thiosymbion oneisti, in anoxic sulfidic or hypoxic sand. Here, transcriptomics and proteomics showed that, whether in anoxia or not, L. oneistus mostly expressed genes involved in ubiquitination, energy generation, oxidative stress response, immune response, development, and translation. Importantly, ubiquitination genes were also highly expressed when the nematode was subjected to anoxic sulfidic conditions, together with genes involved in autophagy, detoxification and ribosome biogenesis. We hypothesize that these degradation pathways were induced to recycle damaged cellular components (mitochondria) and misfolded proteins into nutrients. Remarkably, when L. oneistus was subjected to anoxic sulfidic conditions, lectin and mucin genes were also upregulated, potentially to promote the attachment of its thiotrophic symbiont. Furthermore, the nematode appeared to survive oxygen deprivation by using an alternative electron carrier (rhodoquinone) and acceptor (fumarate), to rewire the electron transfer chain. On the other hand, under hypoxia, genes involved in costly processes (e.g., amino acid biosynthesis, development, feeding, mating) were upregulated, together with the worm's Toll-like innate immunity pathway and several immune effectors (e.g., bactericidal/permeability-increasing proteins, fungicides). In conclusion, we hypothesize that, in anoxic sulfidic sand, L. oneistus upregulates degradation processes, rewires the oxidative phosphorylation and reinforces its coat of bacterial sulfur-oxidizers. In upper sand layers, instead, it appears to produce broad-range antimicrobials and to exploit oxygen for biosynthesis and development.

Fidelity varies in the symbiosis between a gutless marine worm and its microbial consortium.

BACKGROUND: Many animals live in intimate associations with a species-rich microbiome. A key factor in maintaining these beneficial associations is fidelity, defined as the stability of associations between hosts and their microbiota over multiple host generations. Fidelity has been well studied in terrestrial hosts, particularly insects, over longer macroevolutionary time. In contrast, little is known about fidelity in marine animals with species-rich microbiomes at short microevolutionary time scales, that is at the level of a single host population. Given that natural selection acts most directly on local populations, studies of microevolutionary partner fidelity are important for revealing the ecological and evolutionary processes that drive intimate beneficial associations within animal species. RESULTS: In this study on the obligate symbiosis between the gutless marine annelid Olavius algarvensis and its consortium of seven co-occurring bacterial symbionts, we show that partner fidelity varies across symbiont species from strict to absent over short microevolutionary time. Using a low-coverage sequencing approach that has not yet been applied to microbial community analyses, we analysed the metagenomes of 80 O. algarvensis individuals from the Mediterranean and compared host mitochondrial and symbiont phylogenies based on single-nucleotide polymorphisms across genomes. Fidelity was highest for the two chemoautotrophic, sulphur-oxidizing symbionts that dominated the microbial consortium of all O. algarvensis individuals. In contrast, fidelity was only intermediate to absent in the sulphate-reducing and spirochaetal symbionts with lower abundance. These differences in fidelity are likely driven by both selective and stochastic forces acting on the consistency with which symbionts are vertically transmitted. CONCLUSIONS: We hypothesize that variable degrees of fidelity are advantageous for O. algarvensis by allowing the faithful transmission of their nutritionally most important symbionts and flexibility in the acquisition of other symbionts that promote ecological plasticity in the acquisition of environmental resources. Video Abstract.