Shorter Lag Phase Research Articles

Improvement of Asterarcys quadricellulare biomass solubilization and subsequent biogas production via pretreatment approaches: structural changes and kinetic modeling evaluation.

This study investigated the effect of enzymatic and hydrothermal pretreatment approaches on the solubilization of organic matter, structure, and biogas yield from microalgal biomass. The soluble chemical oxygen demand (sCOD) concentration increased by 1.21-3.30- and 5.54-6.60-fold compared to control by enzymatic and hydrothermal pretreatments respectively. The hydrothermal pretreatment affected the structural changes in the microalgal biomass markedly; nonetheless, increased enzymatic concentration also had a definite effect on it as determined by qualitative approaches like scanning electron microscopy and Fourier transform infrared spectroscopy. Also, the hydrothermal pretreatment (100°C for 30min) resulted in the highest biogas production potential (P) of 765.37 mLg-1 VS at a maximum biogas production rate (Rm) of 22.66 mLg-1day-1 with a very short lag phase (λ) of 0.07days. The biogas production of pretreated microalgal biomass particularly at higher enzyme dose (20%, 24h) and higher hydrothermal pretreatment temperature (120°C, 30min) showed a significant but weak correlation (R = 0.53) with sCOD, thus demonstrating that the less organic matter was used up for the biogas production. The modified Gompertz model explained the anaerobic digestion of microalgal biomass more accurately and had a better fit to the experimental data comparatively because of the low root mean square error (3.259-16.728), residual sum of squares (78.887-177.025), and Akaike's Information Criterion (38.605-62.853).

Third Generation Lactic Acid Production by Lactobacillus pentosus from the Macroalgae Kappaphycus alvarezii Hydrolysates

The evaluation of macroalgae as a new raw material for diverse bioprocesses is of great interest due to their fast growth rate and low environmental impact. Lactic acid has a high value in the bio-based industry and is mainly produced via fermentation. The anaerobic lactic acid fermentation of Kappaphycus alvarezii hydrolysates using the high-producing strain Lactobacillus pentosus was evaluated for detoxified and non-treated hydrolysates prepared from concentrated algal biomass and dilute acid solution mixtures. A novel hydrolysate detoxification procedure, combining activated charcoal and over-liming, for 5-hydroxymethylfurfural (HMF) removal was used. L. pentosus was found to successfully ferment detoxified and untreated hydrolysates produced in up to 30% and 20% w/v solutions, respectively. Significant production rates (1.88 g/L.h) and short lag phases were achieved in bioreactor fermentation operating at 37 °C and pH 6 with 150 rpm impeller velocity. A 0.94 g/g yield from fermentable sugars (galactose and glucose) was achieved, indicating that K. alvarezii could be used as a raw material for lactic acid production, within the context of Third Generation (3G) biorefinery.

Modeling the Growth of Six Listeria monocytogenes Strains in Smoked Salmon Pâté

In this study, the growth of six L. monocytogenes strains isolated from different fish products was quantified and modeled in smoked salmon pâté at a temperature ranging from 2 to 20 °C. The experimental data obtained for each strain was fitted to the primary growth model of Baranyi and Roberts to estimate the following kinetic parameters: lag phase (λ), maximum specific growth rate (μmax), and maximum cell density (Nmax). Then, the effect of storage temperature on the obtained μmax values was modeled by the Ratkowsky secondary model. In general, the six L. monocytogenes strains showed rapid growth in salmon pâté at all storage temperatures, with a relatively short lag phase λ, even at 2 °C. The growth behavior among the tested strains was similar at the same storage temperature, although significant differences were found for the parameters λ and μmax. Besides, the growth variations among the strains did not follow a regular pattern. The estimated secondary model parameter Tmin ranged from -4.25 to -3.19 °C. This study provides accurate predictive models for the growth of L. monocytogenes in fish pâtés that can be used in shelf life and microbial risk assessment studies. In addition, the models generated in this work can be implemented in predictive modeling tools and repositories that can be reliably and easily used by the fish industry and end-users to establish measures aimed at controlling the growth of L. monocytogenes in fish-based pâtés.

Changes in the metabolome of probiotics during the stationary phase increase resistance to lyophilization

In the probiotics manufacturing process, lyophilization damages the cell membrane of microorganisms, reducing their viability and delaying reactivation of their cellular metabolism. The growth phase of microorganisms at the time of lyophilization is thought to significantly affect their viability during storage and reactivation in the intestine. However, no study has systematically investigated the differences in overcoming mechanisms in microorganisms harvested at different growth phases against lyophilization. Therefore, in this study, we comparatively assessed the resistance mechanism of Bifidobacterium animalis ssp. lactis and Lacticaseibacillus rhamnosus harvested at exponential and stationary growth phases. We found that B. animalis ssp. lactis and L. rhamnosus harvested at the stationary phase had shorter lag phase in growth and higher survival rates during storage than those harvested at the exponential phase. As a result of metabolome analysis, the cells harvested at the stationary phase accumulated trehalose and arabinose, which function as cryoprotectants and protect cells from lyophilization-induced damage. These findings could provide a basis for establishing a manufacturing protocol for lyophilized probiotics that can be rapidly reactivated in the intestine to achieve optimal metabolic activity and induce health benefits.

Liquid-Droplet-Mediated ATP-Triggered Amyloidogenic Pathway of Insulin-Derived Chimeric Peptides: Unraveling the Microscopic and Molecular Processes.

Disease-associated progression of protein dysfunction is typically determined by an interplay of transition pathways leading to liquid-liquid phase separation (LLPS) and amyloid fibrils. As LLPS introduces another layer of complexity into fibrillization of metastable proteins, a need for tunable model systems to study these intertwined processes has emerged. Here, we demonstrate the LLPS/fibrillization properties of a family of chimeric peptides, ACC1-13Kn, in which the highly amyloidogenic fragment of insulin (ACC1-13) is merged with oligolysine segments of various lengths (Kn, n = 8, 16, 24, 32, 40). LLPS and fibrillization of ACC1-13Kn are triggered by ATP through Coulombic interactions with Kn fragments. ACC1-13K8 and ACC1-13K16 form fibrils after a short lag phase without any evidence of LLPS. However, in the case of the three longest peptides, ATP triggers instantaneous LLPS followed by the disappearance of droplets occurring in-phase with the formation of amyloid fibrils. The kinetics of the phase transition and the stability of mature co-aggregates are highly sensitive to ionic strength, indicating that electrostatic interactions play a pivotal role in selecting the LLPS-fibrillization transition pathway. Densely packed ionic interactions that characterize ACC1-13Kn-ATP fibrils render them highly sensitive to hydrostatic pressure due to solvent electrostriction, as demonstrated by infrared spectroscopy. Using atomic force microscopy imaging of rapidly frozen samples, we demonstrate that early fibrils form within single liquid droplets, starting at the droplet/bulk interface through the formation of single bent fibers. A hypothetical molecular scenario underlying the emergence of the LLPS-to-fibrils pathway in the ACC1-13Kn-ATP system has been put forward.

Minimizing the Lag Phase of Cupriavidus necator Growth under Autotrophic, Heterotrophic, and Mixotrophic Conditions.

Cupriavidus necator has the unique metabolic capability to grow under heterotrophic, autotrophic, and mixotrophic conditions. In the current work, we examined the effect of growth conditions on the metabolic responses of C. necator. In our lab-scale experiments, autotrophic growth was rapid, with a short lag phase as the exponential growth stage was initiated in 6 to 12 h. The lag phase extended significantly (>22 h) at elevated O2 and CO2 partial pressures, while the duration of the lag phase was independent of the H2 or N2 partial pressure. Under heterotrophic conditions with acetate as the organic substrate, the lag phase length was short (<12 h), but it increased with increasing acetate concentrations. When glucose and glycerol were provided as the organic substrate, the lag phase was consistently long (>12 h) regardless of the examined substrate concentrations (up to 10.0 g/L). In the transition experiments, C. necator cells showed rapid transitions from autotrophic to heterotrophic growth in less than 12 h and vice versa. Our experimental results indicate that C. necator can rapidly grow with both autotrophic and heterotrophic substrates, while the lag time substantially increases with nonacetate organic substrates (e.g., glucose or glycerol), high acetate concentrations, and high O2 and CO2 partial pressures. IMPORTANCE The current work investigated the inhibition of organic and gaseous substrates on the microbial adaption of Cupriavidus necator under several metabolic conditions commonly employed for commercial polyhydroxyalkanoate production. We also proposed a two-stage cultivation system to minimize the lag time required to change over between the heterotrophic, autotrophic, and mixotrophic pathways.

Comparative Study of the Effect of Temperature and pH on the Growth of Bio-flavor Producing Microorganisms Kluyveromyces marxianus and Ceratocystis fimbriata

Kluyveromyces marxianus and Ceratocystis fimbriata are two potential microorganisms that have been reported to produce fruity and floral aroma compounds during fermentation. In the present investigation, an in vitro comparative study was conducted using a liquid medium to investigate the effect of temperature from 20±2°C to 45±2°C and pH from 3 to 8 on the growth of both microorganisms. The results showed that the optimum growth of K. marxianus was found at 30°C while C. fimbriata showed the highest growth at 20°C. Similarly, the optimum growth of K. marxianus was found at pH 4.5 while C. fimbriata showed the highest growth at pH 6.5. The comparative analysis suggested that K. marxianus has a shorter lag phase and shows better growth at ambient temperature and pH compared to C. fimbriata. Thus, it is concluded that K. marxianus can be a better choice for the industrial production of bio-flavors.

Deciphering the contribution of PerR to oxidative stress defense system in Clostridium tyrobutyricum

AbstractAs a next‐generation probiotic, Clostridium tyrobutyricum, which is considered obligate anaerobe, has been extensively considered a promising candidate for future use to promote health benefits. The industrial applications were limited by its weak tolerance to oxygen stress during fermentation. Here, we enhanced the oxidative stress tolerance of C. tyrobutyricum L319 by deleting the peroxide response regulator gene perR using an endogenous CRISPR‐Cas system. The mutant strain exhibited greatly improved growth when exposed to oxygen, which also showed a shortened lag phase compared with the control strain. Consistently, a concomitant increase in butyric acid productivity from 0.08 to 0.13 g/L/h in the presence of oxygen was observed. Decreased intracellular ROS level sand NAD+/NADH ratios were also observed in the mutant strain. Furthermore, transcriptome and binding target analysis revealed that genes encoding transcriptional regulators and proteins related to redox balance were upregulated. Changes in carbohydrate, amino acid and purine metabolisms upon oxygen exposure were also observed. Importantly, phylogenomic analysis indicated that PerR may be a universal engineering target in diverse Clostridium species. These findings will contribute to the development of robust C. tyrobutyricum strains for efficient butyric acid production in the food industry.

The Effect of Atranes on the Growth of &lt;i&gt;Rhodococcus qingshengii&lt;/i&gt; VKM Ac-2784D in the Presence of Various Carbon Sources and on Its Ability to Degrade Naphthalene

Abstract—Rhodococcus qingshengii VKM Ac-2784D isolated from the rhizosphere of Elytrigia repens, is a promising oil degrader. To increase its biotechnological potential, the effect of atranes (potential growth stimulants) on its growth and naphthalene degradation was studied. The effect of the studied atranes on R. qingshengii VKM Ac-2784D was shown to depend on the nature of the carbon source: addition of atranes had practically no effect on the growth rate of bacteria in the rich BTN medium; in the media 8E and 8E with glucose, it baused short-term activation of growth, characterized by a shorter lag phase. In the presence of naphthalene, atranes had a predominantly negative effect on the growth of R. qingshengii VKM Ac-2784D. The studied atranes had a negative effect on the rate of naphthalene decomposition by R. qingshengii VKM Ac-2784D, and also decreased the cell wall hydrophobicity and the synthesis of extracellular biosurfactants. It may therefore be assumed that the studied compounds will have a negative effect on the rate of naphthalene decomposition by this microorganism.

Деструкция фталевых кислот штаммом Paenarthrobacter sp. SA101, выделенным из сточных вод химического предприятия

Phthalic and terephthalic acids (PA and TPA) are widely used in the chemical industry as plasticizers, for the production of polymer materials, and therefore are common eco-pollutants. The ability of the strain Paenarthrobacter sp. SA101, isolated from a sample of a chemical plant wastewater (Perm), to growth on high concentrations of PA and TPA was studied. It was shown that strain SA101 is capable of efficient growth on these substrates at concentrations up to 20 g/l, which is shown for the representatives of the genus Paenarthrobacter for the first time. Higher strain growth parameters were recorded in media with PA, than in media with TPA: the maximum value of OD600 (1.64), the highest specific growth rate (0.073±0.003 h-1) and the shortest lag phase were observed in a medium with 10 g/l of PA. The highest specific growth rate (0.04±0.002 h‑1) and the maximum value of OD600 (1.6) were observed with 20 g/l of TPA, however, the lag phase of growth was longer than in the medium with 10 g/l of TPA. The strain SA101 was able to utilize 76% of PA in 39 hours and 74.2% of TPA in 71 hours of cultivation, when using these substrates at a concentration of 10 g/l. The cells of the strain SA101 contain a plasmid with a molecular weight of ~ 100 bp. The strain SA101 is promising for the development of biotechnological methods for cleaning phthalate-contaminated soils and industrial effluents.

Effects of platelets activated by different agonists on fibrin formation and thrombin generation

Activated platelets possess procoagulant activity expressing on their surface phosphatidylserine (PS), a substrate for assembling coagulation complexes. We examined the effects of platelets activated by different agonists on fibrin formation and thrombin generation and compared these effects with each other and with PS expression. Modified plasma recalcification assay was developed to assess platelet effects on fibrin formation. Washed human platelets were left intact or activated by A23187 ionophore, collagen, arachidonic acid, ADP or TRAP (Thrombin Receptor Activating Peptide) and spun down in 96-well plates. Plasma was then added, recalcified, and fibrin formation was monitored by light absorbance. Platelets prepared in the same way were tested for their effect on thrombin generation. PS expression was evaluated by flow cytometry using annexin V staining. Platelets significantly accelerated fibrin formation and thrombin generation. They shortened lag phase and increased maximum rate of plasma clotting, and increased peak and maximum rate of thrombin generation. In both tests platelets were presumably activated by endogenous thrombin formed in plasma after triggering coagulation reactions. However, pretreatment with exogenous agonists additionally increased platelet procoagulant activity. It reached the maximum after incubation with A23187, being lower with collagen and arachidonic acid and minimum with ADP and TRAP (the latter might be ineffective due to competition with endogenous thrombin). The effects of platelets activated by different agonists on fibrin formation and thrombin generation correlate with each other and correspond to PS expression on their surface.

Mixed culture chain elongation for consumption of acetate and ethanol in anaerobic fermentation: The impact of salt type, dosage and acclimation

Microbial chain elongation is a newly developed carboxylate platform-based bioprocess, which often encounters high salinity stress due to saline feedstock and pH adjustment. In this study, we systematically investigated the effects of salt types (Na+, K+, and NH4+), dosage, and salinity acclimation on microbial chain elongation, and identified the microbial community by high throughput 16S rRNA gene sequencing. The results showed that a high level of Na+ and NH4+ (12.5 g/L of cations) exerted seriously inhibitory effects without chain elongating activity, while K+ had the slightest inhibition only with a little longer lag phase and lower products yield. The chain elongating products yields and the selectivity of caproate decreased with the increasing Na+ concentration, and 8.6 g/L of Na+ was found to be the threshold value for un-acclimated inoculum used for chain elongation. The acclimation to high saline conditions greatly promoted the consumption of acetate and ethanol with a shorter lag phase, and recovered a robust elongating activity for butyrate production. Furthermore, the high throughput 16S rRNA gene sequencing analysis results indicated that six genera, such as Clostridium IV and Clostridium sensu stricto, closely relating chain elongation process were depressed by high salinity, and the salinity acclimation helped to enrich the functional microbes. These findings could provide useful information for engineering microbial chain elongation process under saline conditions.

Improvement of the catalytic performance of glycerol kinase from Bacillus subtilis by chromosomal site-directed mutagenesis.

Glycerol kinase is the key enzyme in glycerol metabolism, and its catalytic efficiency has an important effect on glycerol utilization. Based on an analysis of the glycerol utilization pathway and regulation mechanism in B. subtilis, we conducted site-directed mutagenesis of the key glycerol kinase gene (glpK) on the chromosome to improve the glycerol utilization efficiency of Bacillus subtilis. Recombinant wild-type Bacillus subtilis glycerol kinase (BsuGlpKWT) and two mutants (BsuGlpKM270I and BsuGlpKS71V) were successfully overexpressed in Escherichia coli BL21(DE3) and purified by Ni-IDA metal chelate chromatography. The specific activity of the BsuGlpKM270I mutant (62.6U/mg) was significantly higher (296.2%) than that of wild-type BsuGlpKWT (15.8U/mg). By contrast, the mutant BsuGlpKS71V (4.89U/mg) exhibited lower (69.1%) activity than BsuGlpKWT, which suggested that variant S71V exhibited reduced catalytic efficiency for the substrate. Furthermore, the mutant strain B. subtilis M270I was constructed using a markerless delivery system, and exhibited a higher specific growth rate (improved by 11.3%, from 0.453 ± 0.012 to 0.511 ± 0.017h-1) and higher maximal biomass (cell dry weight increased by 16%, from 0.577 ± 0.033 to 0.721 ± 0.015g/L) than the parental strain with a shortened lag phase (2 ~ 4h shorter) in M9 minimal medium with glycerol. These results indicate that the mutated glpK resulted in improved glycerol utilization, which has broad application prospects.

Microscale Colocalization of Cascade Enzymes Yields Activity Enhancement.

Colocalization of cascade enzymes is broadly discussed as a phenomenon that can boost the cascade reaction throughput, although a direct experimental verification is often challenging. This is mainly due to difficulties in establishing proper size regimes and in the analytical quantification of colocalization effect with adequate experimental systems and simulations. In this study, by taking advantage of reversible DNA-directed colocalization of enzymes on microspheres, we established a cascade system that can be used to directly evaluate the colocalization effect with exactly the same experimental settings except for the state of enzyme dispersion. In the regime of highly dilute microspheres of particular sizes, the colocalized cascade shows enhanced activity compared with the freely diffusing cascade, as evidenced by a shortened lag phase in the time-course production. Reaction-diffusion modeling reveals that the enhancement can be ascribed to the initial accumulation of intermediate substrate around the colocalized enzymes and is found to be carrier-size-dependent. This work demonstrates the dependence of the colocalization effect of enzyme cascades on an interplay of nano- and microscales, lending theoretical support to the rational design of highly efficient multienzyme catalysts.

Exopolysaccharides production from marine Bacillus strains and their antioxidant and bio-flocculant capacities.

Microbial exopolysaccharides (EPS) have gained high scientific concern due to their exceptional physicochemical features and high industrial applicability. Owing to their biotechnological importance, the present study was designed to screen and isolate the EPS-producing Bacillus strains based on their growth potential on specific media and colony morphologies. The bacterial isolates Bacillus subtilis Bs1-01, Bacillus licheniformis Bl1-02, and Bacillus brevis Bb1-04 showed excellent EPS production due to their shortened lag phase and abundant biomass production. Shake-flask fermentation valued the maximum production yield of 50.19 ± 1.14g/L by Bl1-02 after 72h incubation (about 3.40 times higher than that of Bacillus thuringiensis Bt1-05). The basic component analysis revealed the improved amount of total carbohydrate, reducing sugar ends, and protein contents by Bl1-02 strain. Structural characteristics and functional groups of the EPS characterized by Fourier transform infrared spectroscopy demonstrated that all EPS were in close agreement to each other due to the presence of similar chemical bonds and functional groups. EPS from Bl1-02 strain showed stronger and more stable bio-emulsifying and hygroscopicity activities (12.23%). The crude EPS exhibited potent antioxidant properties which were examined against reducing potential (H2O2 scavenging) and total antioxidant tests. Among bio-flocculation activities of EPS at different concentrations, Bs1-01 strain produced EPS at a concentration of 60mg/mL was observed to show the maximum value of 79.20%. In conclusion, the EPS from marine Bacillus strains showed excellent functional properties suggesting potential industrial applications that demand separate investigations.

Identification of Kic1p and Cdc42p as Novel Targets to Engineer Yeast Acetic Acid Stress Tolerance

Robust yeast strains that are tolerant to multiple stress environments are desired for an efficient biorefinery. Our previous studies revealed that zinc sulfate serves as an important nutrient for stress tolerance of budding yeast Saccharomyces cerevisiae. Acetic acid is a common inhibitor in cellulosic hydrolysate, and the development of acetic acid-tolerant strains is beneficial for lignocellulosic biorefineries. In this study, comparative proteomic studies were performed using S. cerevisiae cultured under acetic acid stress with or without zinc sulfate addition, and novel zinc-responsive proteins were identified. Among the differentially expressed proteins, the protein kinase Kic1p and the small rho-like GTPase Cdc42p, which is required for cell integrity and regulation of cell polarity, respectively, were selected for further studies. Overexpression of KIC1 and CDC42 endowed S. cerevisiae with faster growth and ethanol fermentation under the stresses of acetic acid and mixed inhibitors, as well as in corncob hydrolysate. Notably, the engineered yeast strains showed a 12 h shorter lag phase under the three tested conditions, leading to up to 52.99% higher ethanol productivity than that of the control strain. Further studies showed that the transcription of genes related to stress response was significantly upregulated in the engineered strains under the stress condition. Our results in this study provide novel insights in exploring zinc-responsive proteins for applications of synthetic biology in developing a robust industrial yeast.

Leveraging quorum sensing system for automatic coordination of Escherichia coli growth and lactic acid biosynthesis

PurposeOverproduction of desired metabolites usually sacrifices cell growth. Here we report that quorum sensing (QS) can be exploited to coordinate cell growth and lactic acid production in Escherichia coli.MethodsWe engineered two QS strains: one strain overexpressing acyl-homoserine lactone (AHL) synthesis genes (“ON”), the other strain overexpressing both AHL synthesis and degradation gene (aiiA) (“ON to semi-OFF”). To clarify the impact of the QS system on lactic acid production, D-lactate dehydrogenase gene ldhA was deleted from the E. coli genome, and Enhanced Green Fluorescence Protein (eGFP) was used as the reporter.ResultsCompared to the “ON” strain, the “ON to semi-OFF” strain showed delayed log growth and decreased egfp expression at stationary phase. When egfp was replaced by ldhA for lactic acid production, compared to the wild-type strain, the “ON to semi-OFF” strain demonstrated 231.9% and 117.3% increase in D-lactic acid titer and space-time yield, respectively, while the “ON” strain demonstrated 83.6%, 31%, and 36% increase in growth rate, maximum OD600, and glucose consumption rate, respectively. Quantitative real-time PCR revealed that both ldhA and the genes for phosphotransferase system were up-regulated in ldhA-overexpressing “ON” strain compared to the strain only harboring QS system. Moreover, the “ON” strain showed considerable increase in glucose consumption after a short lag phase. Compared to the reference strain harboring only ldhA gene in vector, both the “ON” and “ON to semi-OFF” strains demonstrated synchronization between cell growth and D-lactic acid production.ConclusionsCollectively, QS can be leveraged to coordinate microbial growth and product formation.

An investigation for improving dry anaerobic digestion of municipal solid wastes by adding biochar derived from gasification of wood pellets

In this study, the effect of biochar addition derived from a downdraft fixed-bed gasifier on the performances of dry anaerobic digestion of the Organic Fraction of Municipal Solid Waste (OFMSW) was investigated at a high organic load of (1) the source segregated OFMSW (16 and 26% TS) and (2) the source segregated OFMSW replaced with 15% garden waste (22.2% TS). Adding biochar effectively enhanced the rate and yield of biomethane (up to 36.6%), controlled acidification, and shortened lag phase in both feedstocks at high organic loads up to 136.9 gVS/L. Execution of dry anaerobic digestion for source-separated OFMSW without acidification can only be achieved by more than 30 g/L biochar dosage, which is better to run in a semi-solid state (16% TS). However, the synergistic effects at higher biochar doses were not palpable. OFMSW with a higher C/N ratio yielded more limited benefits, as inhibitory volatile fatty acids were further controlled in the early days. This study could promise the integration of gasification and dry anaerobic digestion to enhance the biogas production efficiency at high organic loads, although more researches should be done under continuous conditions.

Increasing calcium phosphate aqueous solubility and spontaneous supersaturation combining citrate and gluconate with perspectives for functional foods

Uptake of calcium from food depends on solubility of calcium salts in the intestines, and precipitation of calcium phosphates decreases bioaccessibility of food calcium. Citrate as a high affinity complex binder for calcium was found spontaneously to create strongly supersaturated solutions by rapid dissolution of calcium hydrogen phosphate characterized by short lag phases for precipitation. Gluconate with weaker affinity for calcium binding showed longer lag phases for precipitation from supersaturated solutions. For citrate/gluconate combinations, the highest degree of supersaturation with longest lag phases for precipitation were found by trial-and-error experiments for a citrate/gluconate ratio of 1:10 for dissolution of calcium hydrogen phosphate resulting in supersaturation factors around three and without precipitation for more than a month. The aim of the present study was to provide a physicochemical explanation of this robust supersaturation. Calcium speciation based on electrochemical calcium activity measurement identified a low [Ca2+]·[HCitr2−] product as critical for supersaturation.

Effect of genus Clostridium abundance on mixed-culture fermentation converting food waste into biohydrogen

This study examined the effect of various inocula on mixed-culture dark fermentative H2 production from food waste. Heat-treated and frozen H2-producing granular sludge (HPG) grown with monomeric sugars showed a higher H2 yield, production rate, and acidogenic efficiency along with a shorter lag phase than heat-treated methanogenic sludge. Among three different methods of methanogenic sludge inoculation, inoculation after centrifugation showed better H2 production performance. Propionic acid production and homoacetogenesis were regarded as major H2-consuming pathways when methanogenic sludge was used, whereas only homoacetogenesis was found in HPG-inoculated fermentation. During fermentation, the abundance of Clostridium increased greater than 48-fold for methanogenic sludge and greater than 108-fold for HPG, respectively. The initial abundance of Clostridium showed a linear relationship with the H2 production rate and lag-phase time. The use of inoculum with a high abundance of Clostridium is essential for H2 production from food waste.