Lactic Acid Permeability of Aquaporin-9 Enables Cytoplasmic Lactate Accumulation via an Ion Trap

(1) Background: Human aquaporin-9 (AQP9) conducts several small uncharged metabolites, such as glycerol, urea, and lactic acid. Certain brain tumors were shown to upregulate AQP9 expression, and the putative increase in lactic acid permeability was assigned to severity. (2) Methods: We expressed AQP9 and human monocarboxylate transporter 1 (MCT1) in yeast to determine the uptake rates and accumulation of radiolabeled l-lactate/l-lactic acid in different external pH conditions. (3) Results: The AQP9-mediated uptake of l-lactic acid was slow compared to MCT1 at neutral and slightly acidic pH, due to low concentrations of the neutral substrate species. At a pH corresponding to the pKa of l-lactic acid, uptake via AQP9 was faster than via MCT1. Substrate accumulation was fundamentally different between AQP9 and MCT1. With MCT1, an equilibrium was reached, at which the intracellular and extracellular l-lactate/H+ concentrations were balanced. Uptake via AQP9 was linear, theoretically yielding orders of magnitude of higher substrate accumulation than MCT1. (4) Conclusions: The selectivity of AQP9 for neutral l-lactic acid establishes an ion trap for l-lactate after dissociation. This may be physiologically relevant if the transmembrane proton gradient is steep, and AQP9 acts as the sole uptake path on at least one side of a polarized cell.

Optimization of Nitrogen Demand in Vegetables by Different Impacts on Autotrophic and Heterotrophic Nitrification

Aims The understanding of the interactions between N transformations and N uptake by plants in greenhouse soils with large N accumulation is still not clear. The aim is to understand the plant- soil interactions (vegetables) on N transformations with respect to N supply. Methods 15N tracing studies were conducted in two greenhouse soils to simultaneously quantify soil gross N transformation and plant N uptake rates using the Ntraceplant tool. Results There were significant feedbacks between vegetable N uptake and soil gross N transformation rates, whether soil N accumulation occurred or not. Plant NO3– uptake rates (UNO3) were higher than the NH4+ uptake rates (UNH4), which is consistent with the NO3–-preference of the vegetable plants studied. While UNH4 was still responsible for 6-49% of total N uptake rates, significantly negative relationships between UNH4 and NH4+ immobilization rate and autotrophic nitrification rate (ONH4) were observed. ONH4 was significantly inhibited in the presence of plants and decreased with time. ONH4 (1.11 mg N kg-1 d-1) was much lower than UNO3 (8.29 mg N kg-1 d-1) in the presence of plants. However, heterotrophic nitrification rate (ONrec), which ranged from 0.10 to 8.11 mg N kg-1 d-1 was significantly stimulated and was responsible for 5-97% of NO3– production in all plant treatments, providing additional NO3– to meet N requirements of plants and microorganisms.Conclusions The management of organic N fertilizers should be improved to stimulate inorganic N production via heterotrophic nitrification in greenhouse cultivation.

Application of Synthetic Peptide CEP1 Increases Nutrient Uptake Rates Along Plant Roots

The root system of a plant provides vital functions including resource uptake, storage, and anchorage in soil. The uptake of macro-nutrients like nitrogen (N), phosphorus (P), potassium (K), and sulphur (S) from the soil is critical for plant growth and development. Small signaling peptide (SSP) hormones are best known as potent regulators of plant growth and development with a few also known to have specialized roles in macronutrient utilization. Here we describe a high throughput phenotyping platform for testing SSP effects on root uptake of multiple nutrients. The SSP, CEP1 (C-TERMINALLY ENCODED PEPTIDE) enhanced nitrate uptake rate per unit root length in Medicago truncatula plants deprived of N in the high-affinity transport range. Single structural variants of M. truncatula and Arabidopsis thaliana specific CEP1 peptides, MtCEP1D1:hyp4,11 and AtCEP1:hyp4,11, enhanced uptake not only of nitrate, but also phosphate and sulfate in both model plant species. Transcriptome analysis of Medicago roots treated with different MtCEP1 encoded peptide domains revealed that hundreds of genes respond to these peptides, including several nitrate transporters and a sulfate transporter that may mediate the uptake of these macronutrients downstream of CEP1 signaling. Likewise, several putative signaling pathway genes including LEUCINE-RICH REPEAT RECPTOR-LIKE KINASES and Myb domain containing transcription factors, were induced in roots by CEP1 treatment. Thus, a scalable method has been developed for screening synthetic peptides of potential use in agriculture, with CEP1 shown to be one such peptide.

Regulation of Kidney Mitochondrial Function by Caloric Restriction

Caloric restriction (CR) prevents obesity, promotes healthy aging, and increases resilience against several pathological stimuli in laboratory rodents. At the mitochondrial level, protection promoted by CR in the brain and liver is related to higher calcium uptake rates and capacities, avoiding Ca2+-induced mitochondrial permeability transition. Dietary restriction has also been shown to increase kidney resistance against damaging stimuli such as ischemia/reperfusion, but if these effects are related to similar mitochondrial adaptations had not yet been uncovered. Here, we characterized changes in mitochondrial function in response to six months of CR in rats, measuring bioenergetic parameters, redox balance and calcium homeostasis. CR promoted an increase in mitochondrial oxygen consumption rates under non-phosphorylating and uncoupled conditions. While CR prevents mitochondrial reactive oxygen species production in many tissues, in kidney we found that mitochondrial H2O2 release was enhanced, although levels of carbonylated proteins and methionine sulfoxide were unchanged. Surprisingly, and opposite to the effects observed in brain and liver, mitochondria from CR animals are more prone to Ca2+-induced mitochondrial permeability transition. CR mitochondria also displayed higher calcium uptake rates, which were not accompanied by changes in calcium efflux rates, nor related to altered inner mitochondrial membrane potentials or the amounts of the mitochondrial calcium uniporter (MCU). Instead, increased mitochondrial calcium uptake rates in CR kidneys correlate with a loss of MICU2, an MCU modulator. Interestingly, MICU2 is also modulated by CR in liver, suggesting it has a broader diet-sensitive regulatory role controlling mitochondrial calcium homeostasis. Together, our results highlight the organ-specific bioenergetic, redox, and ionic transport effects of CR. Specifically, we describe the regulation of the expression of MICU2 and its effects on mitochondrial calcium transport as a novel and interesting aspect of the metabolic responses to dietary interventions.

Vitreoscilla Haemoglobin: A Tool to Reduce Overflow Metabolism

Overflow metabolism is a phenomenon extended in nature, ranging from microbial to cancer cells. Accumulation of overflow metabolites pose a challenge for large-scale bioprocesses. Yet, the causes of overflow metabolism are not fully clarified. In this work, the underlying mechanisms, reasons and consequences of overflow metabolism in different organisms have been summarized. The reported effect of aerobic expression of Vitreoscilla haemoglobin (VHb) in different organisms are revised. The use of VHb to reduce overflow metabolism is proposed and studied through flux balance analysis in E. coli at a fixed maximum substrate and oxygen uptake rates. Simulations showed that the presence of VHb increases the growth rate, while decreasing acetate production, in line with the experimental measurements. Therefore, aerobic VHb expression is considered a potential tool to reduce overflow metabolism in cells.

Assessing the impact of educational methods on influenza vaccine uptake and patient knowledge and attitudes: a randomised controlled trial

Introduction: Although influenza vaccination reduces rates of pneumonia, hospitalisation and mortality, influenza vaccination uptake remains low in older patients. The primary aim was to compare individualised counselling with educational pamphlets alone in improving influenza vaccination uptake. The secondary aims were to evaluate knowledge and attitudes towards influenza vaccination and factors influencing uptake. Methods: A randomised controlled study was conducted in two government polyclinics with 160 participants per arm. Patients aged 65 years and above attending for doctor consultation were recruited. All participants received an educational pamphlet on influenza vaccination. The intervention group received additional face-to-face counselling. Participants filled a pre- and postintervention questionnaire assessing knowledge of influenza and attitudes towards the vaccine. Follow-up calls and verification of electronic records was done at three months to determine actual vaccine uptake. Results: At three months, 16 (10%) patients in the intervention group and 20 (12.5%) patients in the control group had completed influenza vaccination (p = 0.48). Factors positively associated with vaccine uptake were willingness to receive vaccination immediately after intervention (adjusted odds ratio [OR] 12.15, 95% confidence interval [CI] 4.42–33.38), and male gender (adjusted OR 2.96, 95% CI 1.23–7.12). Individualised counselling was more effective in improving knowledge (p < 0.01). Overall knowledge scores did not influence actual vaccine uptake rates. (adjusted OR 1.10 [0.90–1.3]). Conclusion: Both arms of patient education increased uptake of influenza vaccination. Individualised counselling was not superior to pamphlets alone in improving uptake. Performing vaccination at the initial point of contact improves actual uptake rates.

Extending the Cultivation Period of Undaria pinnatifida by Using Regional Strains with Phenotypic Differentiation along the Sanriku Coast in Northern Japan

The Sanriku district is one of the largest Undaria pinnatifida (Wakame) cultivation areas in Japan. However, the production has steadily declined in recent years due to the high retirement rate among fishers. Extending the cultivation period is a potential way to improve productivity by decentralizing the workforce through the production process. We aimed to investigate the phenotypic differentiation between regional strains of U. pinnatifida collected from Matsushima Bay (MAT) and Hirota Bay (HRT) in the Sanriku district through a cultivation trial to verify the application for the purpose of extending the cultivation period. The growth of MAT was better than that of HRT when the cultivation started earlier (i.e., 9 and 19 October 2014); in contrast, HRT outperformed MAT when the cultivation started later (6 November and 12 December 2014). The yield of MAT reached over the standard amount in the Sanriku district in February. On the other hand, the yield of HRT reached over this value in April. Furthermore, the photosynthetic performance and nutrient uptake rates differed between MAT and HRT, indicating that the differences may result in maturation characteristics. According to these results, the combined use of MAT and HRT would be a valuable strategy by which to extend the cultivation period.

Development of a plasmid stabilization system in Vibrio natriegens for the high production of 1,3-propanediol and 3-hydroxypropionate

Vibrio natriegens is a promising industrial chassis with a super-fast growth rate and high substrate uptake rates. V. natriegens was previously engineered to produce 1,3-propanediol (1,3-PDO) from glycerol by overexpressing the corresponding genes in a plasmid. However, antibiotic selection pressure for plasmid stability was not satisfactory and plasmid loss resulted in reduced productivity of the bioprocess. In this study, we developed an antibiotic-free plasmid stabilization system for V. natriegens. The system was achieved by shifting the glpD gene, one of the essential genes for glycerol degradation, from the chromosome to plasmid. With this system, engineered V. natriegens can stably maintain a large expression plasmid during the whole fed-batch fermentation and accumulated 69.5 g/L 1,3-PDO in 24 h, which was 23% higher than that based on antibiotic selection system. This system was also applied to engineering V. natriegens for the production of 3-hydroxypropionate (3-HP), enabling the engineered strain to accumulate 64.5 g/L 3-HP in 24 h, which was 30% higher than that based on antibiotic system. Overall, the developed strategy could be useful for engineering V. natriegens as a platform for the production of value-added chemicals from glycerol. Graphic Abstract