Aerobic Growth Research Articles

A thermodynamic bottleneck in the TCA cycle contributes to acetate overflow in Staphylococcus aureus.

During aerobic growth, S. aureus relies on acetate overflow metabolism, a process where glucose is incompletely oxidized to acetate, for its bioenergetic needs. Acetate is not immediately captured as a carbon source and is excreted as waste by cells. The underlying factors governing acetate overflow in S. aureus have not been identified. Here, we show that acetate overflow is favored due to a thermodynamic bottleneck in the TCA cycle, specifically involving the oxidation of succinate to fumarate by succinate dehydrogenase. This bottleneck reduces flux through the TCA cycle, making it more efficient for S. aureus to generate ATP via acetate overflow metabolism. Additionally, the protein allocation cost of maintaining ATP flux through the restricted TCA cycle is greater than that of acetate overflow metabolism. Finally, we show that the TCA cycle bottleneck provides S. aureus the flexibility to redirect carbon towards maintaining redox balance through lactate overflow when oxygen becomes limiting, albeit at the expense of ATP production through acetate overflow. Overall, our findings suggest that overflow metabolism offers S. aureus distinct bioenergetic advantages over a thermodynamically constrained TCA cycle, potentially supporting its commensal-pathogen lifestyle.

Sodium transport and redox regulation in Saccharomyces cerevisiae under osmotic stress depending on oxygen availability

This study explores the molecular mechanisms behind the differential responses of Saccharomyces cerevisiae industrial strains (ATCC 9804 and ATCC 13007) to osmotic stress. We observed that, in contrast to ATCC 9804 strain, sodium flux in ATCC 13,007 is not N, N’-dicyclohexylcarbodiimide (DCCD)-sensitive under osmotic stress, suggesting a distinct ion homeostasis mechanism. Under aerobic conditions, osmotic stress increased reduced SH groups by 45% in ATCC 9804 and 34% in ATCC 13,007. In contrast, under microaerophilic conditions, both strains experienced a 50% reduction in thiol groups. Notably, ATCC 13,007 exhibited a 1.5-fold increase in catalase (CAT) activity under aerobic stress compared to standard conditions, while ATCC 9804 showed enhanced CAT activity due to SH group binding. Additionally, superoxide dismutase (SOD) activity was doubled during aerobic growth in both strains, with ATCC 13,007 showing a 1.5-fold higher SOD activity under osmotic stress. The results demonstrate that S. cerevisiae adapts to osmotic stress differently under aerobic and microaerophilic conditions, with aerobic conditions promoting Pma-Ena-Trk interplay, reduced thiol levels and increased catalase activity, while microaerophilic conditions demonstrate Pma-Nha-Trk interplay and shifts redox balance towards oxidized thiol groups and enhance superoxide dismutase activity. Understanding these mechanisms can aid in developing stress-resistant yeast strains for industrial applications.

Influence of Environmental Conditions on Bacterial Remediation of Oil-Contaminated Soil: A Case Study at Baiji Refinery

Total Petroleum Hydrocarbons (TPH) are a major environmental pollutant, posing serious risks to soil health and ecosystems. TPH contamination, often resulting from crude oil spills and industrial activities, significantly disrupts soil structure, reduces fertility, and hinders the growth of plants and soil-dwelling organisms. In the environment, TPH compounds persist due to their hydrophobic nature, leading to long-term ecological damage. They can infiltrate groundwater, compromising its purity and presenting health hazards to humans and wildlife. The existence of TPH in soil modifies the population of bacteria, reduces biodiversity, and impedes natural processes such as nutrient cycling. Effective bioremediation techniques, such as microbial degradation, are essential for mitigating the harmful impacts of TPH on soil and the broader environment. This study emphasizes the urgent need for sustainable remediation strategies to restore contaminated soils and protect ecological and human health. This study investigates the influence of environmental circumstances on bacteria employed for the remediation of soil polluted with crude oil, focusing on bacterial strains sourced from the Baiji refinery in Iraq. Microbial rehabilitation is an economical and environmentally sustainable method for decomposing hydrocarbons into simpler molecules, making it an effective method for soil bioremediation. The study monitored biodegradation over seven months, assessing the degradation efficiency of total petroleum hydrocarbons (TPH) using gas chromatography-mass spectrometry (GC-MS). Environmental factors, including temperature, moisture levels, and nutrient availability, were closely monitored to assess their impact on bacterial activity. Ideal moisture range for bacterial growth and hydrocarbon degradation is often cited as 40% to 60% of the soil's WHC. Too much water can reduce oxygen availability in the soil, inhibiting aerobic bacterial growth, while too little water can limit microbial metabolism. Temperature affects bacterial metabolism and the rate of hydrocarbon degradation. Most hydrocarbon-degrading bacteria thrive in mesophilic conditions. The ideal temperature range for TPH degradation by bacteria is generally between 25°C and 35°C. At temperatures below 15°C, microbial activity and degradation rates slow significantly, while temperatures above 40°C can inhibit bacterial growth or even kill the microbes. The results revealed that the moisture: 40%–60% of soil's water-holding capacity and temperature 25°C–35°C maintaining these conditions promotes the optimal breakdown of hydrocarbons in bioremediation efforts. The results revealed significant degradation of crude oil, with a reduction of 40 initial compounds in untreated samples to 25-35 compounds in treated samples. The biodegradation rates increased steadily over time, with a removal efficiency reaching 72.38% by the end of the experiment. Additionally, the study demonstrated that environmental conditions, particularly temperature and moisture, play a pivotal role in optimizing bacterial degradation activity. These findings underscore the potential of bacteria in bioremediation efforts and the necessity of optimal environmental conditions, such as controlled temperature, moisture content, and nutrient levels, are essential for maximizing the efficiency of crude oil degradation in contaminated soils.

Aerobic adaptation and metabolic dynamics of Propionibacterium freudenreichii DSM 20271: insights from comparative transcriptomics and surfaceome analysis.

The study of the response of Propionibacterium freudenreichii to aerobic growth is crucial for understanding how this bacterium adapts to different environments and produces essential compounds like vitamin B12. By investigating its physiological changes under aerobic conditions, we can gain insights into its metabolic adjustments and potential for enhanced growth. These findings not only deepen our understanding of P. freudenreichii's responses to oxygen availability but also offer valuable information for optimizing its growth in industrial applications. This research sheds light on the adaptive mechanisms of this bacterium, providing a foundation for further exploration and potential applications in various fields.

Essential genes for Haemophilus parainfluenzae survival and biofilm growth.

Haemophilus parainfluenzae (Hp) is a Gram-negative, highly prevalent, and abundant commensal in the human oral cavity, and an infrequent extraoral opportunistic pathogen. Hp occupies multiple niches in the oral cavity, including the supragingival plaque biofilm. Little is known about how Hp interacts with its neighbors in healthy biofilms nor its mechanisms of pathogenesis as an opportunistic pathogen. To address this, we identified the essential genome and conditionally essential genes in in vitro biofilms aerobically and anaerobically. Using transposon insertion sequencing (TnSeq) with a highly saturated mariner transposon library in two strains, the ATCC33392 type-strain (Hp 392) and oral isolate EL1 (Hp EL1), we show that the essential genomes of Hp 392 and Hp EL1 are composed of 395 (20%) and 384 (19%) genes, respectively. The core essential genome, consisting of 341 (17%) essential genes conserved between both strains, was composed of genes associated with genetic information processing, carbohydrate, protein, and energy metabolism. We also identified conditionally essential genes for aerobic and anaerobic biofilm growth, which were associated with carbohydrate and energy metabolism in both strains. RNAseq analysis determined that most genes upregulated during anaerobic growth are not essential for Hp 392 anaerobic survival. The completion of this library and analysis under these conditions gives us a foundational insight into the basic biology of H. parainfluenzae in differing oxygen conditions, similar to its in vivo habitat. This library presents a valuable tool for investigation into conditionally essential genes for an organism that lives in close contact with many microbial species in the human oral habitat.IMPORTANCEHaemophilus parainfluenzae is a highly abundant human commensal microbe, present in most healthy individuals where it colonizes the mouth. H. parainfluenzae correlates with good oral health and may play a role in preservation of healthy host status. Also, H. parainfluenzae can cause opportunistic infections outside of the oral cavity. To date, little is known about how H. parainfluenzae colonizes the human host, despite being such a frequent and abundant part of our human microbiome. Here, we demonstrate the creation and use of a powerful tool, a TnSeq library, used to identify genes necessary for both the outright growth of this organism and also genes conditionally essential for growth in varying oxygen status which it can encounter in the human host. This tool and these data serve as a foundation for further study of this relatively unknown organism that may play a role in preserving human health.

The role of Listeria monocytogenes PstA in β-lactam resistance requires the cytochrome bd oxidase activity.

PstA is a structurally conserved c-di-AMP-binding protein that is broadly present among Firmicutes bacteria. Furthermore, PstA binds c-di-AMP at high affinity and specificity, indicating an important role in the c-di-AMP signaling network. However, the molecular function of PstA remains elusive. Our findings reveal contrasting roles of PstA in β-lactam resistance depending on c-di-AMP-binding status. We also define physiological conditions for PstA function during aerobic growth. Future efforts can exploit these conditions to identify PstA interaction partners under β-lactam stress.

Cross-sectional study investigating the components and quality of colostrum and colostrum replacement products fed to Ontario dairy goat kids

Colostrum replacement products for use in goat kids are sourced from bovine colostrum and often used by producers to supplement or replace maternal colostrum to prevent infections. To compare the colostrum replacement products fed on-farm to caprine colostrum a cross-sectional study was undertaken. Ontario dairy goat producers were asked to collect first milking colostrum from their goats and samples of the reconstituted commercial replacement product currently in use. The frozen samples were thawed and submitted for testing of fat, protein and lactose content, IgG1 concentration and aerobic bacterial culture. Compared with caprine colostrum, the reconstituted replacement products were lower in protein (11.7%; P = 0.0007), and fat (4.6%; P < 0.0001) and higher in lactose (5.4%; P < 0.0001) on average. The average IgG1 concentration in goat colostrum (53.5 g/L; range: 16.6-1985.8) was significantly higher than in colostrum replacement products (33.7 g/L; range: 10.7-55.3) (P < 0.0001). The Brix cut-point for good quality goat colostrum (50 g/L) was calculated at 23% (sensitivity = 69.6%, specificity = 88.0%) for goat colostrum and 26% for the colostrum replacement product (sensitivity = 87.5%, specificity = 100%). The average aerobic count for goat colostrum was lower (2.95 log10 cfu/mL) than the colostrum replacement product samples that were cultured (3.85 log10 cfu/mL; P < 0.0001). Further investigation into colostrum replacement products, including on-farm storage of opened powdered product and mixing and storage of reconstituted product, is warranted. Variability in the levels of IgG1, aerobic bacterial growth and fat, protein and lactose content in colostrum replacement products also requires further exploration to determine their effects on kid health.

Does hydrogen peroxide help mitigate the incidence of Cutibacterium acnes in cervical spine surgeries?

Background: Surgical site infection (SSI) is a common yet serious complication of cervical spine surgery. While initially thought to be clinically insignificant, Cutibacterium acnes (C. acnes) is an important cause of infection. The purpose of this study was to investigate the ability of an hydrogen peroxide (H2O2) application during standard pre-surgical skin preparation to reduce the burden of C. acnes in patients undergoing cervical spine surgery. Methods: This was a retrospective review of prospectively collected data. Subjects were randomly assigned to either standard surgical preparation plus H2O2 (experimental) or without H2O2 (control). Pre-scrub, post-scrub, and dermal cultures were obtained to assess the C. acnes burden after cultures on an aerobic and anaerobic growth medium were held for 21 days. Multivariate analysis was conducted to determine factors associated with presence of C. acnes. Outcome measures included the results of intraoperative cultures and the development of a SSI within 90 days post-operatively. Results: Patients (n=86) undergoing elective two- or three-level fusion via anterior approach were included. Prior to application of the antiseptic solution, 65% (28/43) of the experimental cohort and 77% (33/43) of the control cohort had positive C. acnes cultures (p=0.34). Following application of antiseptic solution, there were no differences in positive C. acnes culture rates between the experimental and control cohorts in the epidermal (30% versus 28%, p=1.00) or dermal (40% versus 42%, p=1.00) cultures. No differences in the rates of C. acnes eradication from pre-antiseptic to post-antiseptic application occurred for epidermal (p= 1.00) or dermal (p= 1.00) skin layers. None of the factors were associated with positive C. acnes epidermal cultures on multivariable logistic regression analysis (p> 0.05). Conclusions: While there is potential for H2O2 to reduce the positive culture rate of C. acnes in cervical spine patients, no difference was seen when compared to standard surgical skin preparation.

Architecture of the RNF1 complex that drives biological nitrogen fixation.

Biological nitrogen fixation requires substantial metabolic energy in form of ATP as well as low-potential electrons that must derive from central metabolism. During aerobic growth, the free-living soil diazotroph Azotobacter vinelandii transfers electrons from the key metabolite NADH to the low-potential ferredoxin FdxA that serves as a direct electron donor to the dinitrogenase reductases. This process is mediated by the RNF complex that exploits the proton motive force over the cytoplasmic membrane to lower the midpoint potential of the transferred electron. Here we report the cryogenic electron microscopy structure of the nitrogenase-associated RNF complex of A. vinelandii, a seven-subunit membrane protein assembly that contains four flavin cofactors and six iron-sulfur centers. Its function requires the strict coupling of electron and proton transfer but also involves major conformational changes within the assembly that can be traced with a combination of electron microscopy and modeling.

Replacement of alkaline phosphate with flaxseed cake and its impact on mortadella's technological, oxidative, microbiological, and sensory aspects

SummaryThis study explored the replacement of alkaline phosphate (AP) with flaxseed cake (FC) in mortadella, assessing the impact on technological, oxidative, microbiological, and sensory properties. The inclusion of FC proved promising in maintaining emulsion stability, cooking loss, and water‐holding capacity and did not significantly affect colour characteristics, as indicated by the ΔE values (&lt;5). Sensory analysis validated the substitution, highlighting the absence of a sandy texture sensation and FC's ability to suppress sensory defects caused by the removal of AP. However, adding FC decreased texture parameters such as hardness and cohesiveness, which can be leveraged in formulating products for specific niches, like older adults. Adding FC did not favour mesophilic aerobic and lactic acid bacteria growth. Nevertheless, the TBARS values of the mortadellas with FC increased (peaking at 0.5 mg MDA kg−1), but the sensory detection limit was not reached even at the end of storage.

Cryopreserved bone flaps from decompressive craniectomies: a microbiological analysis.

Surgical site infection (SSI) is a serious complication after cranioplasty. Due to the relatively frequent occurrence of post-cranioplasty SSI, the utility of autologous bone flap swab cultures surrounding cryopreservation as a reliable predictor has been the subject of an ongoing debate. This bicentric study aims to contribute to this topic by conducting an in-depth analysis of bone flaps obtained via decompressive craniectomies. This study had three major aims: assessments of 1) bacterial contamination of bone flaps after decompressive craniotomy, 2) impact of cryoconservation on contamination rates and 3) potential effectiveness of anti-infective treatment to reduce the germ load prior to cranioplasty. Cryopreserved bone flaps from two centers were used. Microbiological cultivations of swabs prior to and after cryopreservation were taken and assessed for aerobic and anaerobic growth over a 14-day incubation period. Additionally, in a subset of bone flaps, swab testing was repeated after thorough rinsing with an anti-infectant (octenidine-phenoxyethanol) followed by saline. All 63 bone flaps (patients median age at surgery: 59years) were obtained via decompressive craniectomies. Swabs done prior to cryopreservation revealed a 54% infection rate with Propionibacterium acnes being the most common microorganism in 65% of those cases. After thorough disinfection of the preserved bone flaps, all but one case showed no bacterial growth in swab testing. Furthermore, no relevant risk factors for bacterial contamination could be identified. This retrospective study showed the common presence of bacterial growth in cryopreserved bone flaps before and after freezing. Rinsing with octenidine-phenoxyethanol and saline effectively prevented bacterial growth in a notable percentage of cases, suggesting a potential strategy to reduce contamination. However, persistent bacterial growth in some cases underscores the need for further research to optimize antiseptic measures during autologous cranioplasty.

Serine/Arginine-Rich Splicing Factor 7 Knockdown Inhibits Aerobic Glycolysis and Growth in HepG2 Cells by Regulating PKM2 Expression.

Serine/arginine-rich splicing factors (SRSFs), part of the serine/arginine-rich (SR) protein family, play a crucial role in precursor RNA splicing. Abnormal expression of SRSFs in tumors can disrupt normal RNA splicing, contributing to tumor progression. Notably, SRSF7 has been found to be upregulated in hepatocellular carcinoma (HCC), yet its specific role and molecular mechanisms in HCC pathogenesis are not fully understood. We investigated the expression and prognostic significance of SRSF7 in HCC using bioinformatics database analysis. In HepG2 cells, the expressions of SRSF7 and glycolytic enzymes were analyzed using qRT-PCR, and Western blot. Glucose uptake and lactate production were quantified using relevant reagent kits. Additionally, cell proliferation, clonogenicity, invasion, and apoptosis were evaluated using MTS assay, clonal formation assay, Transwell assay, and mitochondrial membrane potential assay, respectively. This study demonstrated significant overexpression of SRSF7 in HCC tissue, correlating with poor prognosis. Knockdown of SRSF7 in HepG2 cells resulted in inhibited proliferation, clonogenicity, and invasion, while apoptosis was enhanced. This knockdown also decreased glucose uptake and lactate production, along with a reduction in the expression of glucose transporter 1 (GLUT1) and lactate dehydrogenase A (LDHA). Furthermore, SRSF7 downregulation increased the pyruvate kinase muscle 1 (PKM1)/PKM2 ratio. The glycolytic boost due to PKM2 overexpression partially counteracted the effects of SRSF7 silencing on HepG2 cell growth. The knockdown of SRSF7 impairs aerobic glycolysis and growth in HepG2 cells by downregulating PKM2 expression.

ε-Polylysine treatment maintains sensory quality, texture, flavor, and inhibits aerobic bacteria growth in vacuum-packed fresh-cut lettuce

Quality deterioration and aroma loss of vacuum-packed fresh-cut lettuce during storage are important factors affecting its commercial value. In this study, the effects of ε-polylysine (ε-PL) on the quality and flavor attributes of vacuum-packed fresh-cut lettuce were studied. Fresh-cut lettuce was treated with different concentrations of ε-PL (0.2, 0.8, and 1.5 g L−1), vacuum-packed and stored at 4 °C for 12 d. The results showed that ε-PL treatment maintained the color and texture of fresh-cut lettuce, and reduced chlorophyll degradation and ascorbic acid loss. In addition, ε-PL treatment inhibited the growth of aerobic bacteria, and maintained or increased some aroma components such as (E)-2-hexenal, n-hexanol, hexanal, limonene, benzaldehyde. These results indicate that ε-PL treatment has potential practical application value in the preservation of vacuum-packed fresh-cut lettuce.

Effects of salinity on glycerol conversion and biological phosphorus removal by aerobic granular sludge

Industrial wastewater often has high levels of salt, either due to seawater or e.g. sodium chloride (NaCl) usage in the processing. Previous work indicated that aerobic granular sludge (AGS) is differently affected by seawater or saline water at similar osmotic strength. Here we investigate in more detail the impact of NaCl concentrations and seawater on the granulation and conversion processes for AGS wastewater treatment. Glycerol was used as the carbon source since it is regularly present in industrial wastewaters, and to allow the evaluation of microbial interactions that better reflect real conditions. Long-term experiments were performed to evaluate and compare the effect of salinity on granulation, anaerobic conversions, phosphate removal, and the microbial community. Smooth and stable granules as well as enhanced biological phosphorus removal (EBPR) were achieved up to 20 g/L NaCl or when using seawater. However, at NaCl levels comparable to seawater strength (30 g/L) incomplete anaerobic glycerol uptake and aerobic phosphate uptake were observed, the effluent turbidity increased, and filamentous granules began to appear. The latter is likely due to the direct aerobic growth on the leftover substrate after the anaerobic feeding period. In all reactor conditions, except the reactor with 30 g/L NaCl, Ca. Accumulibacter was the dominant microorganism. In the reactor with 30 g/L NaCl, the relative abundance of Ca. Accumulibacter decreased to ≤1 % and an increase in the genus Zoogloea was observed. Throughout all reactor conditions, Tessaracoccus and Micropruina, both actinobacteria, were present which were likely responsible for the anaerobic conversion of glycerol into volatile fatty acids. None of the glycerol metabolizing proteins were detected in Ca. Accumulibacter which supports previous findings that glycerol can not be directly utilized by Ca. Accumulibacter. The proteome profile of the dominant taxa was analysed and the results are further discussed. The exposure of salt-adapted biomass to hypo-osmotic conditions led to significant trehalose and PO43−-P release which can be related to the osmoregulation of the cells. Overall, this study provides insights into the effect of salt on the operation and stability of the EBPR and AGS processes. The findings suggest that maintaining a balanced cation ratio is likely to be more important for the operational stability of EBPR and AGS systems than absolute salt concentrations.

Effect of intestinal nitrate on growth of Klebsiella pneumoniae and its regulatory mechanism

To explore the effect of intestinal nitrates on the growth of Klebsiella pneumoniae and its regulatory mechanisms. K. pneumoniae strains with nitrate reductase narG and narZ single or double gene knockout or with NarXL gene knockout were constructed and observed for both aerobic and anaerobic growth in the presence of KNO3 using an automated bacterial growth analyzer and a spectrophotometer, respectively. The mRNA expressions of narG and narZ in K. pneumoniae in anaerobic cultures in the presence of KNO3 and the effect of the binary regulatory system NarXL on their expresisons were detected using qRT-PCR. Electrophoretic mobility shift assays (EMSA) and MST analysis were performed to explore the specific regulatory mechanisms of NarXL in sensing and utilizing nitrates. Competitive experiments were conducted to examine anaerobic growth advantages of narG and narZ gene knockout strains of K. pneumoniae in the presence of KNO3. The presence of KNO3 in anaerobic conditions, but not in aerobic conditions, promoted bacterial growth more effectively in the wild-type K. pneumoniae strain than in the narXL gene knockout strain. In anaerobic conditions, the narXL gene knockout strain showed significantly lowered mRNA expressions of narG and narZ (P < 0.0001). EMSA and MST experiments demonstrated that the NarXL regulator could directly bind to narG and narZ promoter regions. The wild-type K. pneumoniae strain in anaerobic cultures showed significantly increased expressions of narG and narZ mRNAs in the presence of KNO3 (P < 0.01), and narG gene knockout resulted in significantly attenuated anaerobic growth and competitive growth abilities of K. pneumoniae in the presence of KNO3 (P < 0.01). The binary regulatory system NarXL of K. pneumoniae can sense changes in intestinal nitrate concentration and directly regulate the expression of nitrate reductase genes narG and narZ to promote bacterial growth.

Growth-dependent cr(VI) reduction by Alteromonas sp. ORB2 under haloalkaline conditions: toxicity, removal mechanism and effect of heavy metals.

Bacterial reduction of hexavalent chromium (VI) to chromium (III) is a sustainable bioremediation approach. However, the Cr(VI) containing wastewaters are often characterized with complex conditions such as high salt, alkaline pH and heavy metals which severely impact the growth and Cr(VI) reduction potential of microorganisms. This study investigated Cr(VI) reduction under complex haloalkaline conditions by an Alteromonas sp. ORB2 isolated from aerobic granular sludge cultivated from the seawater-microbiome. Optimum growth of Alteromonas sp. ORB2 was observed under haloalkaline conditions at 3.5-9.5% NaCl and pH 7-11. The bacterial growth in normal culture conditions (3.5% NaCl; pH 7.6) was not inhibited by 100mg/l Cr(VI)/ As(V)/ Pb(II), 50mg/l Cu(II) or 5mg/l Cd(II). Near complete reduction of 100mg/l Cr(VI) was achieved within 24h at 3.5-7.5% NaCl and pH 8-11. Cr(VI) reduction by Alteromonas sp. ORB2 was not inhibited by 100mg/L As(V), 100mg/L Pb(II), 50mg/L Cu(II) or 5mg/L Cd(II). The bacterial cells grew in the medium with 100mg/l Cr(VI) contained lower esterase activity and higher reactive oxygen species levels indicating toxicity and oxidative stress. In-spite of toxicity, the cells grew and reduced 100mg/l Cr(VI) completely within 24h. Cr(VI) removal from the medium was driven by bacterial reduction to Cr(III) which remained in the complex medium. Cr(VI) reduction was strongly linked to aerobic growth of Alteromonas sp. The Cr(VI) reductase activity of cytosolic protein fraction was pronounced by supplementing with NADPH in vitro assays. This study demonstrated a growth-dependent aerobic Cr(VI) reduction by Alteromonas sp. ORB2 under complex haloalkaline conditions akin to wastewaters.

Efficacy of active and passive modified atmosphere packaging on quality preservation and storage life of pomegranate fruit and arils: A review

Pomegranate has nutritional value and health benefits due to its bioactive compounds and antioxidant properties. Fruit consumption is strongly recommended due to its high content of vitamins, fiber, minerals, and polyphenols. Supplying ready-to-eat pomegranate can be a beneficial technique to increase consumption with regard to its nutritional properties. However, maintaining nutritional quality and preventing microbial spoilage is a major challenge. Fruit quality is lost with visible symptoms such as weight loss, shriveling, husk scald, chilling injury, fungal rot, aril color degradation, and off-flavor during long-term storage. Therefore, it is very important to use appropriate strategies to maintain pomegranate whole fruit and aril quality. Gases around the product create a suitable environment for oxidative reactions and aerobic microorganism growth. Therefore, changing the atmosphere around the product can help maintain its quality. One of the effective methods to increase the postharvest life of products is to use modified atmosphere packaging (MAP), which reduces microbial spoilage and chilling injury, preserves the quality, and extends the shelf life by reducing the respiration rate. Modified atmosphere packaging, which uses natural atmospheric components (O2, CO2 and N2), has been widely accepted due to the lack of toxic residues on the product. This review discusses on recent research in terms of MAP application on quality properties and postharvest life of pomegranate fruit and arils during storage.

A comprehensive floc model for simulating simultaneous nitrification, denitrification, and phosphorus removal

A comprehensive floc model for simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) was designed, incorporating polyphosphate-accumulating organisms (PAOs), glycogen-accumulating organisms (GAOs), intrinsic half-saturation coefficients, and explicit external mass transfer terms. The calibrated model was able to effectively describe experimental data over a range of operating conditions. The estimated intrinsic half-saturation coefficients of oxygen values for ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, ordinary heterotrophic organisms (OHOs), PAOs, and GAOs were set at 0.08, 0.18, 0.03, 0.07, and 0.1 mg/L, respectively. Simulation suggested that low dissolved oxygen (DO) environments favor K-strategist nitrifying bacteria and PAOs. In SNDPR, virtually all influent and fermentation-generated volatile fatty acids were assimilated as polyhydroxyalkanoates by PAOs in the anaerobic phase. In the aerobic phase, PAOs absorbed 997 % and 171 % of the benchmark influent total phosphorus mass loading through aerobic growth and denitrification via nitrite. These high percentages were because they were calculated relative to the influent total phosphorus, rather than total phosphorus at the end of the anaerobic period. When considering simultaneous nitrification and denitrification, about 23.1 % of influent total Kjeldahl nitrogen was eliminated through denitrification by PAOs and OHOs via nitrite, which reduced the need for both oxygen and carbon in nitrogen removal. Moreover, the microbial and DO profiles within the floc indicated a distinct stratification, with decreasing DO and OHOs, and increasing PAOs towards the inner layer. This study demonstrates a successful floc model that can be used to investigate and design SNDPR for scientific and practical purposes.

A citric acid cycle-deficient Escherichia coli as an efficient chassis for aerobic fermentations.

Tricarboxylic acid cycle (TCA cycle) plays an important role for aerobic growth of heterotrophic bacteria. Theoretically, eliminating TCA cycle would decrease carbon dissipation and facilitate chemicals biosynthesis. Here, we construct an E. coli strain without a functional TCA cycle that can serve as a versatile chassis for chemicals biosynthesis. We first use adaptive laboratory evolution to recover aerobic growth in minimal medium of TCA cycle-deficient E. coli. Inactivation of succinate dehydrogenase is a key event in the evolutionary trajectory. Supply of succinyl-CoA is identified as the growth limiting factor. By replacing endogenous succinyl-CoA dependent enzymes, we obtain an optimized TCA cycle-deficient E. coli strain. As a proof of concept, the strain is engineered for high-yield production of four separate products. This work enhances our understanding of the role of the TCA cycle in E. coli metabolism and demonstrates the advantages of using TCA cycle-deficient E. coli strain for biotechnological applications.

Mitochondrial ATP generation is more proteome efficient than glycolysis.

Metabolic efficiency profoundly influences organismal fitness. Nonphotosynthetic organisms, from yeast to mammals, derive usable energy primarily through glycolysis and respiration. Although respiration is more energy efficient, some cells favor glycolysis even when oxygen is available (aerobic glycolysis, Warburg effect). A leading explanation is that glycolysis is more efficient in terms of ATP production per unit mass of protein (that is, faster). Through quantitative flux analysis and proteomics, we find, however, that mitochondrial respiration is actually more proteome efficient than aerobic glycolysis. This is shown across yeast strains, T cells, cancer cells, and tissues and tumors in vivo. Instead of aerobic glycolysis being valuable for fast ATP production, it correlates with high glycolytic protein expression, which promotes hypoxic growth. Aerobic glycolytic yeasts do not excel at aerobic growth but outgrow respiratory cells during oxygen limitation. We accordingly propose that aerobic glycolysis emerges from cells maintaining a proteome conducive to both aerobic and hypoxic growth.