SUMO E3 ligase SIZ1 connects sumoylation and reactive oxygen species homeostasis processes in Arabidopsis.

The ubiquitin-like modifying peptide SMALL UBIQUITIN-LIKE MODIFIER (SUMO) has become a known modulator of the plant response to multiple environmental stimuli. A common feature of many of these external stresses is the production of reactive oxygen species (ROS). Taking into account that SUMO conjugates rapidly accumulate in response to an external oxidative stimulus, it is likely that ROS and sumoylation converge at the molecular and regulatory levels. In this study, we explored the SUMO-ROS relationship, using as a model the Arabidopsis (Arabidopsis thaliana) null mutant of the major SUMO-conjugation enhancer, the E3 ligase SAP AND MIZ 1 (SIZ1). We showed that SIZ1 is involved in SUMO conjugate increase when primed with both exogenous and endogenous ROS. In siz1, seedlings were sensitive to oxidative stress imposition, and mutants accumulated different ROS throughout development. We demonstrated that the deregulation in hydrogen peroxide and superoxide homeostasis, but not of singlet O2 (1O2), was partially due to SA accumulation in siz1. Furthermore, transcriptomic analysis highlighted a transcriptional signature that implicated siz1 with 1O2 homeostasis. Subsequently, we observed that siz1 displayed chloroplast morphological defects and altered energy dissipation activity and established a link between the chlorophyll precursor protochlorophyllide and deregulation of PROTOCHLOROPHYLLIDE OXIDOREDUCTASE A (PORA), which is known to drive overproduction of 1O2. Ultimately, network analysis uncovered known and additional associations between transcriptional control of PORA and SIZ1-dependent sumoylation. Our study connects sumoylation, and specifically SIZ1, to the control of chloroplast functions and places sumoylation as a molecular mechanism involved in ROS homeostatic and signaling events.

Diagnostic accuracy and the first genotype-phenotype correlation in glycogen storage disease type V.

BACKGROUND: Glycogen storage disease type V (GSDV) is an autosomal recessive metabolic condition caused by pathogenic PYGM variants. This is an underdiagnosed condition as it presents with exercise intolerance in children. We reviewed the GSDV cases of a tertiary hospital center to assess diagnostic timing/accuracy, as well as potential clinical/analytical predictors of such factors. METHODS: We retrospectively reviewed all GSDV cases with follow-up in both Pediatric and Adult Metabolic Diseases consultations. We included 28 cases and assessed their hospital record for clinical information. RESULTS: Over 90% of our cases had late diagnoses, with more than 50% being diagnosed in adulthood despite symptom onset in preschool (very late diagnosis). Diagnostic age was lower in patients exhibiting myoglobinuria. Interestingly, patients with a positive family history of GSDV had similar rates of very late diagnoses, likely since the index case was already detected very late in life. Finally, we observe that the R50* variant is associated with increased myoglobinuria and CK elevation, in a dosage-dependent manner. CONCLUSION: We concluded that GSDV is severely underdiagnosed, and that some clinical and analytical aspects of the condition can be more indicative of this diagnosis. Furthermore, we propose for the first time a genotype-phenotype correlation in GSDV. IMPACT: GSDV is a pediatric-onset metabolic disorder that is mostly diagnosed late in the adult age and commonly misdiagnosed. We observed the first genotype-phenotype correlation in GSDV, regarding the common R50* variant. Awareness of GSDV for pediatricians and the overall medical community is vital.

An SPG7 mutation as a novel cause of monogenic progressive muscular atrophy.

BACKGROUND: Progressive muscular atrophy (PMA) is a rare adult-onset neurological disease that is characterized by isolated lower motor neuron degeneration. While it is still disputable whether PMA is a subtype of amyotrophic lateral sclerosis (ALS) or an isolated disorder, it is well-established as a clinically defined entity. About 5% of PMA cases are monogenic, and the implicated genes largely overlap with those causing monogenic ALS. CASE DESCRIPTION: Here we describe a 68-year-old female patient with progressive and asymmetric upper-limb weakness throughout an 18-month period, with muscle atrophy, dysphagia and slurring of speech. The lower limbs were unaffected, and there was no sign of upper motor neuron dysfunction. Comprehensive genetic testing for single nucleotide and copy-number variants revealed a pathogenic monoallelic variant c.1529C>T, p.(Ala510Val) in the SPG7 gene. DISCUSSION: Pathogenic biallelic SPG7 variants have been originally associated with hereditary spastic paraplegia, but other phenotypes are nowadays known to be linked to these variants, such as ALS. However, there is no report of this (or any) other SPG7 variant in association with PMA, whether it progressed to ALS or not. In conclusion, we present the first known case of PMA associated with a monoallelic SPG7 mutation.

High-throughput phenotyping of physiological traits for wheat resilience to high temperature and drought stress.

Interannual and local fluctuations in wheat crop yield are mostly explained by abiotic constraints. Heatwaves and drought, which are among the top stressors, commonly co-occur, and their frequency is increasing with global climate change. High-throughput methods were optimized to phenotype wheat plants under controlled water deficit and high temperature, with the aim to identify phenotypic traits conferring adaptative stress responses. Wheat plants of 10 genotypes were grown in a fully automated plant facility under 25/18 °C day/night for 30 d, and then the temperature was increased for 7 d (38/31 °C day/night) while maintaining half of the plants well irrigated and half at 30% field capacity. Thermal and multispectral images and pot weights were registered twice daily. At the end of the experiment, key metabolites and enzyme activities from carbohydrate and antioxidant metabolism were quantified. Regression machine learning models were successfully established to predict plant biomass using image-extracted parameters. Evapotranspiration traits expressed significant genotype-environment interactions (G×E) when acclimatization to stress was continuously monitored. Consequently, transpiration efficiency was essential to maintain the balance between water-saving strategies and biomass production in wheat under water deficit and high temperature. Stress tolerance included changes in carbohydrate metabolism, particularly in the sucrolytic and glycolytic pathways, and in antioxidant metabolism. The observed genetic differences in sensitivity to high temperature and water deficit can be exploited in breeding programmes to improve wheat resilience to climate change.

Tet3 ablation in adult brain neurons increases anxiety-like behavior and regulates cognitive function in mice.

TET3 is a member of the ten-eleven translocation (TET) family of enzymes which oxidize 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC). Tet3 is highly expressed in the brain, where 5hmC levels are most abundant. In adult mice, we observed that TET3 is present in mature neurons and oligodendrocytes but is absent in astrocytes. To investigate the function of TET3 in adult postmitotic neurons, we crossed Tet3 floxed mice with a neuronal Cre-expressing mouse line, Camk2a-CreERT2, obtaining a Tet3 conditional KO (cKO) mouse line. Ablation of Tet3 in adult mature neurons resulted in increased anxiety-like behavior with concomitant hypercorticalism, and impaired hippocampal-dependent spatial orientation. Transcriptome and gene-specific expression analysis of the hippocampus showed dysregulation of genes involved in glucocorticoid signaling pathway (HPA axis) in the ventral hippocampus, whereas upregulation of immediate early genes was observed in both dorsal and ventral hippocampal areas. In addition, Tet3 cKO mice exhibit increased dendritic spine maturation in the ventral CA1 hippocampal subregion. Based on these observations, we suggest that TET3 is involved in molecular alterations that govern hippocampal-dependent functions. These results reveal a critical role for epigenetic modifications in modulating brain functions, opening new insights into the molecular basis of neurological disorders.

Surgical guides for flapless dental implant placement and immediate definitive prosthesis installation by using selective laser melting and sintering for 3D metal and polymer printing: A clinical report.

Integration between the phases of computer-based guided dental implant surgery can be used to optimize oral rehabilitation. Two new surgical guides prepared by using the 3D metal and polymer printing technology are presented for immediate implant loading and definitive fixed prosthesis construction in flapless dental implant surgery. Nine implants and 2 fixed prostheses were installed in 2 completely edentulous adult patients by using a metallopolymer surgical guide with a metal central bar attached to a polymer seal or a metal guide. Virtual planning was used to design the 3D-printed surgical guides, which were then constructed by using selective laser sintering (SLM) and selective laser melting (SLS). The 3D-printed surgical guides oriented the surgical placement of the implants and were welded to the abutments and attached to the denture framework. The technique allowed implants and prostheses to be installed on the same day.

Accuracy Evaluation of the Computer-Designed Selective Laser Sintering Surgical Guide for Flapless Immediate Loading Dental Implants Surgery in Edentulous Jaws.

This study was designed to evaluate the accuracy of a novel computer-designed and selectively laser sintered surgical guide for flapless dental implant placement in the edentulous jaw. Fifty dental implants were placed in 11 patients with at least 1 totally edentulous jaw. Initially, cone-beam computed tomography (CBCT) was performed in each patient to define the virtual position of the dental implants based on the assessment of bone availability and the proposed dental prosthesis. After virtual planning, 3D surgical guides were printed using selective laser sintering. CBCT was repeated after the surgery, and the pre- and postoperative images were overlapped in computer-assisted design software to compare the planned and actual positions of the dental implants using a 1-sample t test. The mean ± angular standard deviation between the long axes of the planned and final dental implant positions was 4.58° ± 2.85°; the linear deviation in the coronal position was 0.87 ± 0.49 mm and in the apical region of the dental implants was 1.37 ± 0.69 mm. These differences were statistically significant (P < .001). The proposed modifications reduced the deviations, resulting in an improvement in the technique. We were able to place implants and temporary prostheses using the present protocol, taking into account the differences between the planned and final positions of the dental implants.

Photoprotection and optimization of sucrose usage contribute to faster recovery of photosynthesis after water deficit at high temperatures in wheat.

Plants are increasingly exposed to events of elevated temperature and water deficit, which threaten crop productivity. Understanding the ability to rapidly recover from abiotic stress, restoring carbon assimilation and biomass production, is important to unravel crop climate resilience. This study compared the photosynthetic performance of two Triticum aestivum L. cultivars, Sokoll and Paragon, adapted to the climate of Mexico and UK, respectively, exposed to 1-week water deficit and high temperatures, in isolation or combination. Measurements included photosynthetic assimilation rate, stomatal conductance, in vitro activities of Rubisco (EC 4.1.1.39) and invertase (INV, EC 3.2.1.26), antioxidant capacity and chlorophyll a fluorescence. In both genotypes, under elevated temperatures and water deficit (WD38°C), the photosynthetic limitations were mainly due to stomatal restrictions and to a decrease in the electron transport rate. Chlorophyll a fluorescence parameters clearly indicate differences between the two genotypes in the photoprotection when subjected to WD38°C and showed faster recovery of Paragon after stress relief. The activity of the cytosolic invertase (CytINV) under these stress conditions was strongly related to the fast photosynthesis recovery of Paragon. Taken together, the results suggest that optimal sucrose export/utilization and increased photoprotection of the electron transport machinery are important components to limit yield fluctuations due to water shortage and elevated temperatures.

DCMC as a Promising Alternative to Bentonite in White Wine Stabilization. Impact on Protein Stability and Wine Aromatic Fraction.

Protein haze in white wine is one of the most common non-microbial defects of commercial wines, with bentonite being the main solution utilized by the winemaking industry to tackle this problem. Bentonite presents some serious disadvantages, and several alternatives have been proposed. Here, an alternative based on a new cellulose derivative (dicarboxymethyl cellulose, DCMC) is proposed. To determine the efficiency of DCMC as a bentonite alternative, three monovarietal wines were characterized, and their protein instability and content determined by a heat stability test (HST) and the Bradford method, respectively. The wines were treated with DCMC to achieve stable wines, as shown by the HST, and the efficacy of the treatments was assessed by determining, before and after treatment, the wine content in protein, phenolic compounds, sodium, calcium, and volatile organic compounds (VOCs) as well as the wine pH. DCMC applied at dosages such as those commonly employed for bentonite was able to reduce the protein content in all tested wines and to stabilize all but the Moscatel de Setúbal varietal wine. In general, DCMC was shown to induce lower changes in the wine pH and phenolic content than bentonite, reducing the wine calcium content. Regarding which VOCs are concerned, DCMC produced a general impact similar to that of bentonite, with differences depending on wine variety. The results obtained suggest that DCMC can be a sustainable alternative to bentonite in protein white wine stabilization.

Use of Oak and Cherry Wood Chips during Alcoholic Fermentation and the Maturation Process of Rosé Wines: Impact on Phenolic Composition and Sensory Profile.

There is a lack of knowledge about the use of different wood species on rosé wine production. Thus, this work focused on the impact of the addition of wood chips from oak and cherry trees during the alcoholic fermentation and maturation process on rosé wine characteristics. Therefore, phenolic composition and sensory characteristics were monitored during the rosé wines' production. The use of wood chips during alcoholic fermentation induced a significant increase of phenolic content in rosé musts. During rosé wine maturation, the wood chip contact induced significantly higher values of colored anthocyanins, color intensity, and polymeric pigments, and significantly lower values of color hue in the corresponding rosé wines. In terms of sensory profile, a tendency for lower scores of "overall appreciation" were attributed to control rosé wine, while significantly higher scores for "color intensity" descriptor were attributed to all rosé wines matured in contact with wood chips. For the majority of phenolic parameters and individual phenolic compounds quantified, a clear and specific influence of the use of oak and cherry wood chips was not detected, except for (+)-catechin, where the rosé wines produced in contact with cherry chips showed the highest values. This study provides relevant information for winemakers about the impact of the use of wood chips on rosé wine quality.

Molecular modeling studies on the interactions of 7-methoxytacrine-4-pyridinealdoxime, 4-PA, 2-PAM, and obidoxime with VX-inhibited human acetylcholinesterase: a near attack conformation approach.

7-methoxytacrine-4-pyridinealdoxime (7-MEOTA-4-PA, named hybrid 5C) is a compound formerly synthesized and evaluated in vitro, together with 4-pyridine aldoxime (4-PA) and commercial reactivators of acetylcholinesterase (AChE). This compound was designed with the purpose of being a prophylactic reactivator, capable of interacting with different subdomains of the active site of AChE. To investigate these interactions, theoretical results from docking were first compared with experimental data of hybrid 5C, 4-PA, and two commercial oximes, on the reactivation of human AChE (HssAChE) inhibited by VX. Then, further docking studies, molecular dynamics simulations, and molecular mechanics Poisson-Boltzmann surface area calculations, were carried out to investigate reactivation performances, considering the near attack conformation (NAC) approach, prior to the nucleophilic substitution mechanism. Our results helped to elucidate the interactions of such molecules with the different subdomains of the active site of HssAChE. Additionally, NAC poses of each oxime were suggested for further theoretical studies on the reactivation reaction.

Novichoks: The Dangerous Fourth Generation of Chemical Weapons.

"Novichoks" is the name given to the controversial chemical weapons supposedly developed in the former Soviet Union between the 1970s and the 1990s. Designed to be undetectable and untreatable, these chemicals became the most toxic of the nerve agents, being very attractive for both terrorist and chemical warfare purposes. However, very little information is available in the literature, and the Russian government did not acknowledge their development. The intent of this review is to provide the IJMS readers with a general overview on what is known about novichoks today. We briefly tell the story of the secret development of these agents, and discuss their synthesis, toxicity, physical-chemical properties, and possible ways of treatment and neutralization. In addition, we also wish to call the attention of the scientific community to the great risks still represented by nerve agents worldwide, and the need to keep constant investments in the development of antidotes and ways to protect against such deadly compounds.

Chemical characteristics of grapes cv. Syrah (Vitis vinifera L.) grown in the tropical semiarid region of Brazil (Pernambuco state): influence of rootstock and harvest season.

BACKGROUND: Obtaining two or more successive annual vintages from the same vineyard is characteristic of regions with a tropical climate, such as the Submédio of the São Francisco Valley, Brazil. The present study aimed to characterize the chemical composition of grapes in four production cycles (i.e. two calendar years) when considering the interaction between cv. Syrah and two rootstocks. For a broad characterization, two methodologies for the extraction of phenolic compounds were used, as well as different methods of analysis. RESULTS: The results obtained showed that there was an influence of rootstock and harvest season. Grapes from vines grafted onto IAC 313 contained higher concentrations of total condensed tannins (skins) and flavanols than grapes from vines grafted onto 1103P. However, the grape samples from the vines grafted onto 1103P contained higher levels of monomeric anthocyanins than the grape samples from the vines grafted onto IAC 313. The first harvest season was characterized by higher concentrations of most phenolic compounds than the second harvest season. CONCLUSION: In the present study, it was possible to confirm that, in the semiarid region of Brazil, the interaction between the cultivar Syrah and the different rootstocks, as well as the climatic conditions in each harvest season, influenced the composition of the grapes, mainly in relation to phenolic compounds. © 2019 Society of Chemical Industry.

Acacia, cherry and oak wood chips used for a short aging period of rosé wines: effects on general phenolic parameters, volatile composition and sensory profile.

BACKGROUND: There is a restricted knowledge about the potential impact of the use of different wood chip species on the rosé wine aging process. Thus, the aim of this work was to evaluate the general phenolic parameters, aroma composition and sensory profile of rosé wines during a short maturation (20 aging days) in contact with wood chips from oak, acacia and cherry. In addition, the different wood chips were added to a rosé wine without a previous clarification process (unfined wine) and to a rosé wine submitted to a clarification process (fined wine). RESULTS: For the brief maturation time considered, the use of different wood chips induced a tendency for an increase of phenolic content, in particular for unfined rosé wine aged in contact with acacia chips. For volatile composition, the differentiation was clearer for aldehyde compounds group. Regarding sensorial overall appreciation the panel test preferred the unfined rosé wine aged in contact with acacia wood chips. CONCLUSIONS: The results show that, in general, the use of different wood chip species (acacia, cherry and oak) for a brief maturation time of rosé wines could play an important role in rosé wine characteristics, in particular in their phenolic composition. © 2019 Society of Chemical Industry.

Potential of two delivery systems for nisin topical application to dental plaque biofilms in dogs.

BACKGROUND: Periodontal disease (PD) is caused by the development of a microbial biofilm (dental plaque) in the periodontium, affecting approximately 80% of dogs. Several bacterial species present in the canine oral cavity can be implicated in the development of this disease, including Enterococcus spp. To decrease antibiotic administration, a possible control strategy for dog's enterococcal PD may involve the use of the antimicrobial peptide (AMP) nisin. Nisin's inhibitory activity was evaluated against a collection of previously characterized enterococci obtained from the oral cavity of dogs with PD (n = 20), as well as the potential of a guar-gum gel and a veterinary toothpaste as topical delivery systems for this AMP. The Minimum Inhibitory (MIC) and Bactericidal Concentrations (MBC) and the Minimum Biofilm Eradication (MBEC) and Inhibitory Concentrations (MBIC) were determined for nisin and for the supplemented guar-gum gel. For the supplemented veterinary toothpaste an agar-well diffusion assay was used to evaluate its inhibitory potential. RESULTS: Nisin was effective against all isolates. Independently of being or not incorporated in the guar-gum gel, its inhibitory activity on biofilms was higher, with MBIC (12.46 ± 5.16 and 13.60 ± 4.31 µg/mL, respectively) and MBEC values (21.87 ± 11.33 and 42.34 ± 16.61 µg/mL) being lower than MIC (24.61 ± 4.64 and 14.90 ± 4.10 µg/mL) and MBC (63.09 ± 13.22 and 66.63 ± 19.55 µg/mL) values. The supplemented toothpaste was also effective, showing inhibitory activity against 95% of the isolates. CONCLUSIONS: The inhibitory ability of nisin when incorporated in the two delivery systems was maintained or increased, demonstrating the potential of these supplemented vehicles to be applied to PD control in dogs.

Effect of Lachancea thermotolerans on the Formation of Polymeric Pigments during Sequential Fermentation with Schizosaccharosmyces pombe and Saccharomyces cerevisiae.

Anthocyanins in red grape musts may evolve during the winemaking process and wine aging for several different reasons; colour stability and evolution is a complex process that may depend on grape variety, winemaking technology, fermentative yeast selection, co-pigmentation phenomena and polymerization. The condensation of flavanols with anthocyanins may occur either with the flavylium ion or with the hemiacetal formation in order to produce oligomers and polymers. The kinetics of the reaction are enhanced by the presence of metabolic acetaldehyde, promoting the formation of pyranoanthocyanin-type dimers or flavanol-ethyl-anthocyanin structures. The experimental design carried out using white must corrected with the addition of malvidin-3-O-glucoside and flavanols, suggests that non-Saccharomyces yeasts are able to provide increased levels of colour intensity and larger polymeric pigment ratios and polymerization indexes. The selection of non-Saccharomyces genera, in particular Lachancea thermotolerans and Schizosaccharomyces pombe in sequential fermentation, have provided experimental wines with increased fruity esters, as well as producing wines with potential pigment compositions, even though there is an important reduction of total anthocyanins.

Synthesis, Biological Evaluation, and Docking Studies of Novel Bisquaternary Aldoxime Reactivators on Acetylcholinesterase and Butyrylcholinesterase Inhibited by Paraoxon.

Nerve agents and oxon forms of organophosphorus pesticides act as strong irreversible inhibitors of two cholinesterases in the human body: acetylcholinesterase (AChE; EC 3.1.1.7) and butyrylcholinesterase (BChE; EC 3.1.1.8), and are therefore highly toxic compounds. For the recovery of inhibited AChE, antidotes from the group of pyridinium or bispyridinium aldoxime reactivators (pralidoxime, obidoxime, HI-6) are used in combination with anticholinergics and anticonvulsives. Therapeutic efficacy of reactivators (called "oximes") depends on their chemical structure and also the type of organophosphorus inhibitor. Three novel oximes (K131, K142, K153) with an oxime group in position four of the pyridinium ring were designed and then tested for their potency to reactivate human (Homo sapiens sapiens) AChE (HssACHE) and BChE (HssBChE) inhibited by the pesticide paraoxon (diethyl 4-nitrophenyl phosphate). According to the obtained results, none of the prepared oximes were able to satisfactorily reactivate paraoxon-inhibited cholinesterases. On the contrary, extraordinary activity of obidoxime in the case of paraoxon-inhibited HssAChE reactivation was confirmed. Additional docking studies pointed to possible explanations for these results.

Dehydration rate determines the degree of membrane damage and desiccation tolerance in bryophytes.

Desiccation tolerant (DT) organisms are able to withstand an extended loss of body water and rapidly resume metabolism upon rehydration. This ability, however, is strongly dependent on a slow dehydration rate. Fast dehydration affects membrane integrity leading to intracellular solute leakage upon rehydration and thereby impairs metabolism recovery. We test the hypothesis that the increased cell membrane damage and membrane permeability observed under fast dehydration, compared with slow dehydration, is related to an increase in lipid peroxidation. Our results reject this hypothesis because following rehydration lipid peroxidation remains unaltered, a fact that could be due to the high increase of NO upon rehydration. However, in fast-dried samples we found a strong signal of red autofluorescence upon rehydration, which correlates with an increase in ROS production and with membrane leakage, particularly the case of phenolics. This could be used as a bioindicator of oxidative stress and membrane damage.

Finite Element Evaluation of Stable Fixation in Combined Mandibular Fractures.

PURPOSE: The fixation of combined mandibular fractures, especially symphyseal-condylar fractures, although occurring commonly and having a higher complication rate in the clinic, is rarely investigated regarding predictable therapeutic approaches. Thus this study's aim was to assess different forms of condylar fixation when combined with symphyseal fracture fixation. MATERIALS AND METHODS: Using finite element models, we analyzed the stress distribution that occurs when a condylar fracture is fixed with 1 miniplate, 2 miniplates, or a trapezoidal condylar miniplate and when a symphyseal fracture is fixed with 2 parallel plates, 2 perpendicular plates, or 2 lag screws. The null hypothesis was that there would be no differences among the different fixation techniques. RESULTS: The results showed a stress concentration in the anterior region of the condyle, close to the sigmoid notch. Moreover, adequate fixation in the symphysis could result in less tension at the condylar region. Therefore, when the symphysis was fixed with a lag-screw technique, condylar fixation was less required, showing a more adequate stress distribution when the condyle was fixed with 1 or 2 plates. Conversely, when the symphyseal fixation was less effective, by use of perpendicular plates, there was a change in the stress distribution at the condylar region, altering fixation behavior and resulting in more tension and displacement in the condyle, especially when a trapezoidal plate was used. CONCLUSIONS: A lag screw and parallel double plates appear to be suitable for symphyseal fixation, whereas 2 straightly positioned plates and a trapezoidal plate are suitable for condylar fixation. However, the combination of perpendicular plates in symphyseal fixation and a trapezoidal plate in condylar fixation showed an altered stress distribution.

Photosynthesis in estuarine intertidal microphytobenthos is limited by inorganic carbon availability.

The effects of dissolved inorganic carbon (DIC) availability on photosynthesis were studied in two estuarine intertidal microphytobenthos (MPB) communities and in the model diatom species Phaeodactylum tricornutum. Kinetics of DIC acquisition, measured with a liquid-phase oxygen electrode, showed higher K(1/2)(DIC) (0.31 mM) and Vm (7.78 nmol min(-1) µg (Chl a)(-1)) for MPB suspensions than for P. tricornutum (K(1/2)(DIC) = 0.23 mM; Vm = 4.64 nmol min(-1) µg (Chl a)(-1)), suggesting the predominance of species with lower affinity for DIC and higher photosynthetic capacity in the MPB. The net photosynthetic rate of the MPB suspensions reached saturation at a DIC concentration of 1-1.5 mM. This range was lower than the concentrations found in the interstitial water of the top 5-mm sediment layer, suggesting no limitation of photosynthesis by DIC in the MPB communities. Accordingly, carbon isotope discrimination revealed a moderate activity of CO2-concentrating mechanisms in the MPB. However, addition of NaHCO3 to intact MPB biofilms caused a significant increase in the relative maximum photosynthetic electron transport rate (rETR max) measured by imaging pulse-amplitude modulated chlorophyll a fluorescence. These results suggest local depletion of DIC at the photic layer of the sediment (the first few hundred µm), where MPB cells accumulate during diurnal low tides. This work provides the first direct experimental evidence of DIC limitation of photosynthesis in highly productive intertidal MPB communities.