Accumulation Of Organic Acids Research Articles

Transcriptional factor MdESE3 controls fruit acidity by activating genes regulating malic acid content in apple.

Acidity is a key factor controlling fruit flavor and quality. In a previous study, combined transcriptome and methylation analyses identified a P3A-type ATPase from apple (Malus domestica), MdMa11, which regulates vacuolar pH when expressed in Nicotiana benthamiana leaves. In this study, the role of MdMa11 in controlling fruit acidity was verified in apple calli, fruits, and plantlets. In addition, we isolated an AP2 domain-containing transcription factor, designated MdESE3, based on yeast one-hybrid (Y1H) screening using the MdMa11 promoter as bait. A subcellular localization assay indicated that MdESE3 localized to the nucleus. Analyses of transgenic apple calli, fruits, and plantlets, as well as tomatoes, demonstrated that MdESE3 enhances fruit acidity and organic acid accumulation. Meanwhile, chromatin immunoprecipitation quantitative PCR (ChIP-qPCR), luciferase (LUC) transactivation assays, and GUS reporter assays indicated that MdESE3 could bind to the ethylene-responsive element (ERE; 5'-TTTAAAAT-3') upstream of the MdMa11 transcription start site, thereby activating its expression. Furthermore, MdtDT, MdDTC2, and MdMDH12 expression increased in apple fruits and plantlets overexpressing MdESE3 and decreased in apple fruits and plantlets where MdESE3 was silenced. The ERE was found in MdtDT and MdMDH12 promoters, but not in the MdDTC2 promoter. The Y1H, LUC transactivation assays, and GUS reporter assays indicated that MdESE3 could bind to the MdtDT and MdMDH12 promoters and activate their expression. Our findings provide valuable functional validation of MdESE3 and its role in the transcriptional regulation of MdMa11, MdtDT, and MdMDH12 and malic acid accumulation in apple.

The interaction between Aspergillus brasiliensis and exposed copper circuits in the space microgravity environment

In the space station, filamentous fungi are one of the main potential hazards causing short circuits or corrosion failure of printed circuit boards (PCBs). A 90-day fungal corrosion test was carried out on the China Space Station (CSS), focusing on the interaction between A. brasiliensis and exposed copper circuits. The results showed that the mycelial morphology, ultrastructure, and organic acid accumulation of the test fungi exhibited significant changes in the space microgravity environment. Aspergillus brasiliensis tended to excrete higher levels of oxalic acid in space as a defense mechanism against copper toxicity, which could exacerbate localized corrosion of copper metal.

Autophagy-regulated ethylene synthesis mediates fruit ripening by affecting the accumulation of lycopene, sugars and organic acids in tomato

Autophagy is a universal cellular process in eukaryotes that plays a critical role in plant growth and stress response. However, the role of autophagy in fruit ripening is largely unknown. Here, we demonstrated that most autophagy-related genes (ATGs) were up-regulated during tomato (Solanum lycopersicum L.) fruit ripening. By using mutants of different autophagy pathway genes (ATG6, ATG10, ATG18a), we revealed that the deficiency of autophagy delayed the ripening of fruit. Compared with wild-type (WT), the production of ethylene was significantly reduced and the accumulation of lycopene was delayed in atg mutants during fruit ripening. We also observed the contents of glucose and fructose were both significantly decreased in atg mutants compared with WT, while the content of organic acids showed the opposite trend. Additionally, the negative regulator of ethylene production, APETALA2a (AP2a), interacted with ATG8 through a specific ATG8-interacting motif (AIM) and could be degraded through the autophagy pathway. These results demonstrate that autophagy plays a critical role in fruit ripening by regulating ethylene production and the accumulation of pigments, sugars and organic acids in tomato.

Study on biodegradation of polyurethane coating on PCB by Aspergillus brasiliensis in space

Polyurethane (PU) is a commonly used conformal coating for printed circuit boards (PCBs). Filamentous fungi present in the space station environment are capable of degrading PU coatings, thereby posing a threat to the safety of electronic components. Therefore, we conducted a 90-day interaction test between Aspergillus brasiliensis and PU-coated PCBs in the China Space Station (CSS) and a controlled environment on the ground. This research aimed to investigate the alterations in the physiological properties of A. brasiliensis on PCB surfaces and the deterioration behavior of PU coating systems in the space microgravity environment. The results show that many fungal parameters, such as growth, morphology, cell ultrastructure, and low molecular weight organic acids (LMWOA) accumulation showed strong changes after spaceflight compared to ground controls. Distinct corrosion morphological features were found in the internal coatings by FIB/SEM analysis, suggesting the existence of a particular deterioration mechanism in the microgravity environment, which requires further investigation.

Carboxylic acid accumulation and secretion contribute to the alkali-stress tolerance of halophyte Leymus chinensis.

Leymus chinensis is a dominant halophytic grass in alkalized grasslands of Northeast China. To explore the alkali-tolerance mechanism of L. chinensis, we applied a widely targeted metabolomic approach to analyze metabolic responses of its root exudates, root tissues and leaves under alkali-stress conditions. L. chinensis extensively secreted organic acids, phenolic acids, free fatty acids and other substances having -COOH or phosphate groups when grown under alkali-stress conditions. The buffering capacity of these secreted substances promoted pH regulation in the rhizosphere during responses to alkali stress. L. chinensis leaves exhibited enhanced accumulations of free fatty acids, lipids, amino acids, organic acids, phenolic acids and alkaloids, which play important roles in maintaining cell membrane stability, regulating osmotic pressure and providing substrates for the alkali-stress responses of roots. The accumulations of numerous flavonoids, saccharides and alcohols were extensively enhanced in the roots of L. chinensis, but rarely enhanced in the leaves, under alkali-stress conditions. Enhanced accumulations of flavonoids, saccharides and alcohols increased the removal of reactive oxygen species and alleviated oxygen damage caused by alkali stress. In this study, we revealed the metabolic response mechanisms of L. chinensis under alkali-stress conditions, emphasizing important roles for the accumulation and secretion of organic acids, amino acids, fatty acids and other substances in alkali tolerance.

Integrated bacterial transcriptome and host metabolome analysis reveals insights into "Candidatus Liberibacter asiaticus" population dynamics in the fruit pith of three citrus cultivars with different tolerance.

"Candidatus Liberibacter asiaticus" (CLas), the causal agent of citrus Huanglongbing (HLB), is able to multiply to a high abundance in citrus fruit pith. However, little is known about the biological processes and phytochemical substances that are vital for CLas colonization and growth in fruit pith. In this study, CLas-infected fruit pith of three citrus cultivars ("Shatangju" mandarin, "Guanxi" pomelo, and "Shatian" pomelo) exhibiting different tolerance to CLas were collected and used for dual RNA-Seq and untargeted metabolome analysis. Comparative transcriptome analysis found that the activation of the CLas noncyclic TCA pathway and pathogenic-related effectors could contribute to the colonization and growth of CLas in fruit pith. The pre-established Type 2 prophage in the CLas genome and the induction of its CRISPR/cas system could enhance the phage resistance of CLas and, in turn, facilitate CLas population growth in fruit pith. CLas infection caused the accumulation of amino acids that were correlated with tolerance to CLas. The accumulation of most sugars and organic acids in CLas-infected fruit pith, which could be due to the phloem blockage caused by CLas infection, was thought to be beneficial for CLas growth in localized phloem tissue. The higher levels of flavonoids and terpenoids in the fruit pith of CLas-tolerant cultivars, particularly those known for their antimicrobial properties, could hinder the growth of CLas. This study advances our understanding of CLas multiplication in fruit pith and offers novel insight into metabolites that could be responsible for tolerance to CLas or essential to CLas population growth.IMPORTANCECitrus Huanglongbing (HLB, also called citrus greening disease) is a highly destructive disease currently threatening citrus production worldwide. HLB is caused by an unculturable bacterial pathogen, "Candidatus Liberibacter asiaticus" (CLas). However, the mechanism of CLas colonization and growth in citrus hosts is poorly understood. In this study, we utilized the fruit pith tissue, which was able to maintain the CLas at a high abundance, as the materials for dual RNA-Seq and untargeted metabolome analysis, aiming to reveal the biological processes and phytochemical substances that are vital for CLas colonization and growth. We provided a genome-wide CLas transcriptome landscape in the fruit pith of three citrus cultivars with different tolerance and identified the important genes/pathways that contribute to CLas colonization and growth in the fruit pith. Metabolome profiling identified the key metabolites, which were mainly affected by CLas infection and influenced the population dynamic of CLas in fruit pith.

The Potential of Pediococcus acidilactici Cell-Free Supernatant as a Preservative in Food Packaging Materials.

This study delves into the production and antimicrobial characteristics of cell-free supernatants from Pediococcus acidilactici (CFSs-Pa). Antimicrobial activity was initially observed in CFS-Pa harvested after 12 h of incubation and increased up to the late stationary phase at 48 h. The increase in antimicrobial activity did not align with total protein content, pointing to other factors linked to the accumulation of organic acids, particularly lactic acid. The SDS-PAGE analysis also indicated that the expected proteinaceous compound (pediocin) was not observed in CFS-Pa. Further investigations suggested that the antimicrobial properties of CFS-Pa were exclusively due to organic acids. The MIC values confirmed potent antimicrobial activity, particularly at a 10% dilution of CFS-Pa in MRS broth. The time-kill assays demonstrated bactericidal activity against EHEC, Listeria monocytogenes, and Staphylococcus aureus by 12 h, 18 h, and 24 h using a 10% dilution of CFS-Pa. Additionally, CFS-Pa exhibited dose-dependent antioxidant activity, requiring a 70% (v/v) concentration to inhibit DPPH scavenging activity by 50%. All the experimental results suggested potential applications of CFS-Pa in food preservation. An attempt to incorporate CFS-Pa into bacterial cellulose (BC) for edible food packaging demonstrated promising antimicrobial results, particularly against L. monocytogenes and S. aureus, with room for optimization.

Integrated transcriptome and metabolome analysis provides insights into blue light response of Flammulina filiformis

Blue light promotes primordium differentiation and fruiting body formation of mushroom. However, the blue light response mechanism of mushroom remains unclear. In this study, mycelium of Flammulina filiformis was exposed to blue light, red light and dark conditions, and then the comparative metabolome and transcriptome analysis was applied to explore metabolic regulation mechanism of F. filiformis under blue light and red light conditions. The yield of the fruiting body of F. filiformis under blue light condition was much higher than that under dark and red light conditions. Metabolome analysis showed that blue light treatment reduced the concentrations of many low molecular weight carbohydrates in the pilei, but it promoted the accumulation of some low molecular weight carbohydrates in the stipes. Blue light also decreased the accumulation of organic acids in the stipes. Blue light treatment reduced the levels of tyrosine and tryptophan in the stipes, but it largely promoted the accumulation of lysine in this organ. In the stipes of F. filiformis, blue light shifted metabolite flow to synthesis of lysine and carbohydrates through inhibiting the accumulation of aromatic amino acids and organic acids, thereby enhancing its nutritional and medicinal values. The transcriptome analysis displayed that blue light enhanced accumulation of lysine in fruiting body of F. filiformis through downregulation of lysine methyltransferase gene and L-lysine 6-monooxygenase gene. Additionally, in the stipes, blue light upregulated many hydrolase genes to improve the ability of the stipe to biodegrade the medium and elevated the growth rate of the fruiting body.

Fever-like temperature impacts on Staphylococcus aureus and Pseudomonas aeruginosa interaction, physiology, and virulence both in vitro and in vivo

BackgroundStaphylococcus aureus (SA) and Pseudomonas aeruginosa (PA) cause a wide variety of bacterial infections and coinfections, showing a complex interaction that involves the production of different metabolites and metabolic changes. Temperature is a key factor for bacterial survival and virulence and within the host, bacteria could be exposed to an increment in temperature during fever development. We analyzed the previously unexplored effect of fever-like temperatures (39 °C) on S. aureus USA300 and P. aeruginosa PAO1 microaerobic mono- and co-cultures compared with 37 °C, by using RNAseq and physiological assays including in vivo experiments.ResultsIn general terms both temperature and co-culturing had a strong impact on both PA and SA with the exception of the temperature response of monocultured PA. We studied metabolic and virulence changes in both species. Altered metabolic features at 39 °C included arginine biosynthesis and the periplasmic glucose oxidation in S. aureus and P. aeruginosa monocultures respectively. When PA co-cultures were exposed at 39 °C, they upregulated ethanol oxidation-related genes along with an increment in organic acid accumulation. Regarding virulence factors, monocultured SA showed an increase in the mRNA expression of the agr operon and hld, pmsα, and pmsβ genes at 39 °C. Supported by mRNA data, we performed physiological experiments and detected and increment in hemolysis, staphyloxantin production, and a decrease in biofilm formation at 39 °C. On the side of PA monocultures, we observed an increase in extracellular lipase and protease and biofilm formation at 39 °C along with a decrease in the motility in correlation with changes observed at mRNA abundance. Additionally, we assessed host–pathogen interaction both in vitro and in vivo. S. aureus monocultured at 39οC showed a decrease in cellular invasion and an increase in IL-8—but not in IL-6—production by A549 cell line. PA also decreased its cellular invasion when monocultured at 39 °C and did not induce any change in IL-8 or IL-6 production. PA strongly increased cellular invasion when co-cultured at 37 and 39 °C. Finally, we observed increased lethality in mice intranasally inoculated with S. aureus monocultures pre-incubated at 39 °C and even higher levels when inoculated with co-cultures. The bacterial burden for P. aeruginosa was higher in liver when the mice were infected with co-cultures previously incubated at 39 °C comparing with 37 °C.ConclusionsOur results highlight a relevant change in the virulence of bacterial opportunistic pathogens exposed to fever-like temperatures in presence of competitors, opening new questions related to bacteria-bacteria and host–pathogen interactions and coevolution.

Reduced Growth in Eustoma under High Nutrient and Phytotoxic Organic Acid Concentrations and Recovery through Hot Water Conditioning of Continuously Cropped Soil

Stunted vegetative growth and delayed or absent flowering are commonly observed in eustoma (Eustoma grandiflorum) when cultivated continuously in the same greenhouse soil. These effects are likely caused by the excessive accumulation of soluble salts and/or phytotoxic organic acids in the soil. This study aimed to clarify the mechanism of continuous cropping obstacles and formulate prevention measures of eustoma. Seedlings of eustoma ‘Croma III White’ were grown hydroponically with 0%, 25%, 50%, 75%, 100% (full), 125%, 150%, 175%, or 200% strength of Johnson’s solution. Plant height, leaf area, and shoot dry weight increased steadily as solution strength increased from 25% to 125% [solution electrical conductivity (EC) of 2.4 dS⋅m−1] and then gradually decreased as solution strength further increased from 125% to 200% (solution EC of 3.8 dS⋅m−1). When grown hydroponically in 200% strength Johnson’s solution, plant height, leaf area, and root length increased with increasing equimolar mixtures of organic acids, including maleic acid, benzoic acid, malic acid, and hydroxybenzoic acid, up to 1.2 to 1.6 mM and decreased thereafter. Node number and the percentage of flower bud visibility declined beyond 1.6 mM organic acid mixtures. Plants with 2.0 and 2.4 mM organic acid mixtures had the lowest net photosynthetic rate, stomatal conductance, transpiration, and intercellular carbon dioxide concentration. Plants had normal growth and produced flower buds when the continuously cropped soil was preconditioned with 100 °C reverse-osmosis water before planting.

Biomass conversion and radiocaesium (Rad-Cs) leaching behaviors of radioactive grass in anaerobic wet fermentation systems: Effects of pre-treatments

Persistent concerns regarding environmental hazards arise from the difficulty in disposing of radioactive plant-based wastes originating from the nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FNPP) in Japan in 2011. In this study, three anaerobic digestion (AD) strategies were proposed: Sole anaerobic wet fermentation, and wet fermentations with either alkaline-heat or ultrasonic pre-treatment, which were employed for long-term anaerobic treatment of a genuine radioactive grass stemming from the FNPP accident. The objectives of this work are to investigate the effects of pre-treatments on biomass conversion efficiency and to gain insight into the leaching behavior of radiocaesium (Rad-Cs) within AD processes. Experimental results indicate that by introducing alkaline-heat and ultrasonic pre-treatments to AD systems, the removal efficiencies of total solids (TS) from the raw grass increased by 60.8 % and 42.5 %, respectively, compared to sole wet fermentation. Pre-treatments have been shown to enhance the stability of AD systems, both in terms of enhancing methane production and mitigating pH fluctuations triggered by the accumulation of organic acids. Remarkably, even though the Rad-Cs leaching rate was highest when the AD system was fed with the alkaline-heat pre-treated grass, it remained unsatisfactory at only 5.77 %. We inadvertently isolated a soil-like component from the raw grass, and analyzed both its proportion in the raw grass and the radioactivity intensity. The results indicate that although the soil constituted only 9.51 % TS of the raw grass, it accounted for a significant 81.35 % of the total radioactivity. The soil, which has a pronounced affinity for ionic Cs, being mixed into the raw grass, was identified as the primary factor limiting the leaching efficiency of Rad-Cs throughout both the pre-treatment and wet fermentation phases.

Spermidine or spermine pretreatment regulates organic metabolites and ions homeostasis in favor of white clover seed germination against salt toxicity

White clover is widely cultivated as a leguminous forage or ground cover plant worldwide. However, soil salinization decreases its yield and quality. Aims of the present experiment were to elucidate the impact of seed pretreatment with spermidine (Spd) or spermine (Spm) on amylolysis, Na+/K+ accumulation, and metabolic homeostasis during germination. Seed was soaked in distilled water (control), Spd or Spm solution and then germinated under optimal or salt stress conditions for 7 days. Results showed that germination vigor, germination percentage, or seed vigour index of seeds pretreatment with Spd increased by 7%, 11%, or 70% when compared with water-pretreated seeds under salt stress, respectively. Germination percentage or seed vigour index of seeds pretreatment with Spm increased by 17% or 78% than water-pretreated seeds under saline condition, respectively. In response to salt stress, accelerated amylolysis via activation of β-amylase activity was induced by Spd or Spm pretreatment. Spd or Spm pretreatment also significantly enhanced accumulation of diverse amino acids, organic acids, sugars, and other metabolites (putrescine, myo-inositol, sorbitol, daidzein etc.) associated with enhanced osmotic adjustment, antioxidant capacity, and energy supply during germination under salt stress. In addition, Spd or Spm pretreatment not only significantly reduced salt-induced K+ loss and overaccumulation of Na+, but also improved the ratio of K+ to Na+, contributing to Na+ and K+ balance in seedlings. In response to salt stress, seeds pretreatment with Spd or Spm up-regulated transcription level of NHX2 related to enhancement in compartmentation of Na+ from cytoplasm to vacuole, thus reducing Na+ toxicity in cytoplasm. Spm priming also uniquely up-regulated transcription levels of SKOR, HKT1, and HAL2 associated with K+ and Na + homeostasis and decline in cytotoxicity under salt stress.

Aluminum Supplementation Mediates the Changes in Tea Plant Growth and Metabolism in Response to Calcium Stress.

Tea plants are more sensitive to variations in calcium concentration compared to other plants, whereas a moderate aluminum concentration facilitates the growth and development of tea plants. Aluminum and calcium show a competitive interaction with respect to the uptake of elements, consequently exerting physiological effects on plants. To further explore these interactions, in this study, we used the solution culture method to treat tea plants with two calcium concentrations (0.8 mM and 5.6 mM) and three aluminum concentrations (0 mM, 0.4 mM, and 1 mM). We then determined the influence of the combined treatments on root growth and quality compound accumulation in the tissues by a combination of phenotype, gene expression, and metabolite analyses. Moderate aluminum supplementation (0.4 mM) alleviated the inhibition of root growth caused by high calcium stress. High calcium stress significantly inhibited the accumulation of most amino acids (e.g., Glutamic acid, Citulline, and Arginine) and organic acids (e.g., a-ketoglutaric acid) in the roots, stems, and leaves, whereas aluminum deficiency significantly increased most amino acids in the roots and leaves (except Serine, Alanine, and Phenylalanine in the roots and Ser in the leaves), with a more than two-fold increase in Arg and Lysine. High calcium stress also induced the accumulation of secondary metabolites such as epigallocatechin gallate and procyanidin in the roots, whereas aluminum supplementation significantly reduced the contents of flavonol glycosides such as quercetin, rutin, myricitrin, and kaempferitrin, as well as caffeine, regardless of calcium concentration. Aluminum supplementation reversed some of the changes in the contents of leaf metabolites induced by calcium stress (e.g., 4-dihydroquercetin, apigenin C-pentoside, phenethylamine, and caffeine). Overall, calcium stress caused severe growth inhibition and metabolic disorders in tea plants, which could be reversed by aluminum supplementation, particularly in maintaining the root tips and the accumulation of secondary metabolites. These results provide a theoretical basis for improving calcium-aluminum nutrient management to promote tea plant growth and quality.

Root phosphoenolpyruvate carboxylase activity is essential for Sorghum bicolor tolerance to ammonium nutrition

Phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) is an enzyme family with pivotal roles in plant carbon and nitrogen metabolism. A main role for non-photosynthetic PEPC is as anaplerotic enzyme to load tricarboxylic acid (TCA) cycle with carbon skeletons that compensate the intermediates diverted for biomolecule synthesis such as amino acids. When plants are grown under ammonium (NH4+) nutrition, the excessive uptake of NH4+ often provokes a stress situation. When plants face NH4+ stress, N assimilation is greatly induced and thus, requires the supply of carbon skeletons coming from TCA cycle. In this work, we addressed the importance of root PEPC and TCA cycle for sorghum (Sorghum bicolor L. Moench), a C4 cereal crop, grown under ammonium nutrition. To do so, we used RNAi sorghum lines that display a decrease expression of SbPPC3 (Ppc3 lines), the main root PEPC isoform, and reduced root PEPC activity. SbPPC3 silencing provoked ammonium hypersensitivity, meaning lower biomass accumulation in Ppc3 respect to WT plants when growing under ammonium nutrition. The silenced plants presented a deregulation of primary metabolism as highlighted by the accumulation of NH4+ in the root and the alteration of normal TCA functioning, which was evidenced by the accumulation of organic acids in the root under ammonium nutrition. Altogether, our work evidences the importance of non-photosynthetic PEPC, and root TCA cycle, in sorghum to deal with high external NH4+ availability.

Widely targeted metabolomics analysis reveals the formation of nonvolatile flavor qualities during oolong tea manufacturing: a case study of Jinguanyin.

The manufacturing processes of oolong tea significantly impact its nonvolatile components, leading to the emergence of distinct flavor attributes. Understanding the dynamic changes in nonvolatile components during the manufacturing stages of the Jinguanyin (JGY) cultivar is crucial for unraveling the potential mechanism behind flavor formation. Comprehensive metabolomics and sensomics analyses were conducted to investigate the dynamic changes in nonvolatile components throughout various phases of oolong tea processing, focusing on the JGY cultivar. A total of 1,005 nonvolatile metabolites were detected, with 562 recognized as significant differential metabolites during various phases of oolong tea processing. Notably, the third turning-over, third setting, and high-temperature treatments exhibited the most significant effects on the nonvolatile metabolites of oolong tea. JGY finished tea demonstrated a characteristic flavor profile, marked by mellowness, sweetness in aftertaste, and a significant Yin rhyme. This flavor profile was collectively promoted by the accumulation of amino acids and organic acids, the decrease in flavonols (3-O-glycosides) and sugar substances, the alteration of phenolic acids, and the stabilization of caffeine. This study contribute to the understanding of the formation of oolong tea flavor qualities. The dynamic changes observed in various types of nonvolatile compounds during oolong tea processing shed light on the intricate interplay of metabolites and their influence on the final flavor characteristics.

Organic acid and sugar components accumulation and flavor associated metabolites dynamic changes in yellow- and white-fleshed seedless loquats (Eriobotrya japonica)

Triploid loquats are divided into yellow- and white-fleshed cultivars. To better understand taste variations in triploid loquat fruits, we used a UPLC-ESI-QTRAP-MS/MS-based widely targeted metabolomic analysis to examine the metabolic composition of two different color fleshed triploid loquats with a sample size of 54 and external validation method within a confidence level of P＜0.05. We identified key flavor-related differentially accumulated metabolites using the variable importance in projection (VIP) value (VIP ≥ 1.0) and fold change ≥ 2 or ≤ 0.5. Furthermore, the results of the HPLC analysis showed that white-fleshed loquats had a low malic acid content. We also performed the UPLC-MS/MS system to investigate the carotenoids contents and lipidome in four triploid cultivars. In the fruits of white-fleshed varieties, the carotenoids contents were significantly downregulated, but the contents of most glycerolphospholipids were increased. Our results reveal the metabolomic changes between the yellow- and white-fleshed cultivars.

Anaerobic digestion of whole cells and post-extracted algae residues of Scenedesmus obliquus in immobilized batch reactor

Conventional anaerobic digesters are operated by mixing microbes with substrates under anaerobic conditions to generate biomethane (bioCH4). After anaerobic digestion (AD), digestates are inseparable from spent microbes and in some cases, the digester fails due to the accumulation of organic acids. This study demonstrates an immobilized bacteria reactor system adopting digested sludge (DS) encapsulated in calcium-alginate to digest algae and post-extracted algae residue (PEAR). This has not been reported elsewhere. From this study, it was established that a mixing speed of 100 rpm and 10 days of AD at a temperature of 37 °C are the best conditions for stable encapsulation of DS, while at a concentration of 4% w/v sodium alginate, bioCH4 was maximized. Relative to the conventional approach, 24% and 58% more bioCH4 was produced, digesting algae and PEAR of Scenedesmus obliquus, respectively. Spent encapsulated DS was reused and a performance of 85% was achieved, based on the bioCH4 production employing spent encapsulated DS compared to fresh encapsulated DS. Improved bioCH4 production from the immobilized reactor suggests that alga-to-biofuel can be more economically viable while separability of digestates at the end of AD indicates a reduction in waste generation and digestates can be processed for other uses such as animal feed or fertilizer.

Vacuolar proteomic analysis reveals tonoplast transporters for accumulation of citric acid and sugar in citrus fruit.

Vacuole largely dictates the fruit taste and flavor, as most of the sugars and organic acids are stored in the vacuoles of the fruit. However, difficulties associated with vacuole separation severely hinder identification and characterization of vacuolar proteins in fruit species. In this study, we established an effective approach for separating vacuoles and successfully purified vacuolar protein from six types of citrus fruit with varying patterns of sugar and organic acid contents. By using label-free LC-MS/MS proteomic analysis, 1443 core proteins were found to be associated with the essential functions of vacuole in citrus fruit. Correlation analysis of metabolite concentration with proteomic data revealed a transporter system for the accumulation of organic acid and soluble sugars in citrus. Furthermore, we characterized the physiological roles of selected key tonoplast transporters, ABCG15, Dict2.1, TMT2, and STP7 in the accumulation of citric acid and sugars. These findings provide a novel perspective and practical solution for investigating the transporters underlying the formation of citrus taste and flavor.

Optimization of apple fruit flavor by MdVHP1-2 via modulation of soluble sugar and organic acid accumulation

For fleshy fruits, the content and ratio of organic acids and soluble sugars are key factors for their flavor. Therefore, a better understanding of soluble sugar and organic acid accumulation in vacuoles is essential to the improvement of fruit quality. Vacuolar-type inorganic pyrophosphatase (V-PPase) has been found in various plants with crucial functions based on the hydrolysis of PPi. However, the effects of V-PPase on the soluble sugar and organic acid accumulation in apple fruit remain unclear. In this study, MdVHP1-2, a V-PPase protein in the vacuolar membrane, was identified. The results showed a positive correlation between the expression of MdVHP1-2 and the sugar/acid ratio during ripening of apple fruits. A series of transgenic analyses showed that overexpression of MdVHP1-2 significantly elevated the contents of soluble sugars and organic acids as well as the sugar/acid ratio in apple fruits and calli. Additionally, transient interference induced by MdVHP1-2 expression inhibited the accumulation of soluble sugars and organic acids in apple fruits. In summary, this study provides insight into the mechanisms by which MdVHP1-2 modulates fruit flavor through mediation of soluble sugar and organic acid accumulation, thereby facilitating improvement of the overall quality of apple and other fruits.

Whole-Genome Analysis of Termite-Derived Bacillus velezensis BV-10 and Its Application in King Grass Silage.

Bacillus velezensis (B. velezensis) is a cellulose-degrading strain that has the potential as an additive in fermented feed. B. velezensis BV-10 was isolated and screened from the termite gut. We sequenced the whole genome of this new source of B. velezensis to reveal its potential for use in cellulose degradation. Whole-genome sequencing of B. velezensis BV-10 showed that it has a circular chromosome of 3929792 bp containing 3873 coding genes with a GC content of 45.51% and many genes related to cellulose, hemicellulose, and lignin degradation. King grass silage was inoculated with B. velezensis BV-10 and mixed with other feed additives to assess the effect of B. velezensis BV-10 on the fermentation quality of silage. Six treatment groups were established: the control, B. velezensis BV-10, molasses, cellulase, B. velezensis BV-10 plus molasses, and B. velezensis BV-10 plus cellulase groups. After 30 days of silage-fermentation testing, B. velezensis BV-10 was found to rapidly reduce the silage pH value and significantly reduce the acid-detergent fiber (ADF) content (p < 0.05). The addition of B. velezensis BV-10 plus molasses and cellulase in fermented feed significantly reduced the silage neutral-detergent fiber and ADF content and promoted organic-acid accumulation (p < 0.05). The above results demonstrate that B. velezensis BV-10 promotes the fermentation quality of silage and that this effect is greater when other silage-fermentation additives are included. In conclusion, genes involved in cellulose degradation in B. velezensis BV-10 were identified by whole-genome sequencing and further experiments explored the effects of B. velezensis BV-10 and different feed additives on the fermentation quality of king grass silage, revealing the potential of Bacillus velezensis as a new silage additive.