Initial Inoculum Concentration Research Articles

Enhancing the Antioxidant Potential of Weissella confusa PP29 Probiotic Media through Incorporation of Hibiscus sabdariffa L. Anthocyanin Extract.

Lactic acid bacteria (LAB) produce important metabolites during fermentation processes, such as exopolysaccharides (EPS), which represent powerful natural antioxidants. On the other hand, H. sabdariffa L. anthocyanin extracts protect LAB and support their development. This study uncovers for the first time, the antioxidant profile of Weissella confusa PP29 probiotic media and focuses on elevating its impressive antioxidant attributes by synergistically integrating H. sabdariffa L. anthocyanin extract. The multifaceted potential of this innovative approach is explored and the results are remarkable, allowing us to understand the protective capacity of the fermented product on the intestinal mucosa. The total phenolic content was much lower at the end of the fermentation process compared to the initial amount, confirming their LAB processing. The DPPH radical scavenging and FRAP of the fermented products were higher compared to ascorbic acid and antioxidant extracts, while superoxide anion radical scavenging and lipid peroxidation inhibitory activity were comparable to that of ascorbic acid. The antioxidant properties of the fermented products were correlated with the initial inoculum and anthocyanin concentrations. All these properties were preserved for 6 months, demonstrating the promising efficacy of this enriched medium, underlining its potential as a complex functional food with enhanced health benefits.

Drug resistance patterns and genotype associations of Trichomonas gallinae in meat pigeons (Columba livia): insights from Guangdong Province, China.

Avian trichomoniasis, caused by the protozoan parasite Trichomonas gallinae, is a prevalent and economically significant disease in pigeons. This study investigated the drug resistance of T. gallinae isolates in Guangdong Province, China. The results revealed that 25.3% (20/79) of the isolates were resistant to one or more of the four nitroimidazole drugs tested, namely, metronidazole, dimetridazole, secnidazole, and tinidazole. Secnidazole elicited the highest resistance rate (19.0%; 15/79), followed by tinidazole (17.7%; 14/79), metronidazole (17.7%; 14/79), and dimetridazole (13.9%; 11/79). An enormous majority of the resistant isolates (70.0%; 14/20) exhibited resistance to multiple drugs. Additionally, the resistance rate was significantly higher in isolates from birds aged < 30 days (53.3%; 8/15) than in those from older birds (23.1%; 12/52). Moreover, no drug resistance was detected in female pigeons. The genotype of the isolated strain was also associated with drug resistance. Specifically, 50.0% (15/30) of ITS-B genotypes exhibited resistance to drugs, while only 10.2% (5/49) of ITS-A genotypes demonstrated resistance. This study also found the growth characteristics of different Trichomonas isolates to be influenced by their genotypes and initial inoculum concentrations. These findings underscore the urgent need for effective measures to control and prevent drug-resistant T. gallinae infections in pigeons, thus ensuring the stable development of the pigeon industry.

Biotransformation of Deoxynivalenol by a Dual-Member Bacterial Consortium Isolated from Tenebrio molitor Larval Feces.

In this study, a dual-member bacterial consortium with the ability to oxidize deoxynivalenol (DON) to 3-keto-DON, designated SD, was first screened from the feces of Tenebrio molitor larvae. This consortium consisted of Pseudomonas sp. SD17-1 and Devosia sp. SD17-2, as determined by 16S rRNA-based phylogenetic analysis. A temperature of 30 °C, a pH of 8.0-9.0, and an initial inoculum concentration ratio of Devosia to Pseudomonas of 0.1 were optimal single-factor parameters for the DON oxidation activity of the bacterial consortium SD. Genome-based bioinformatics analysis revealed the presence of an intact PQQ biosynthesis operon (pqqFABCDEG) and four putative pyrroloquinoline quinone (PQQ)-dependent alcohol dehydrogenase (ADH) genes in the genomes of Pseudomonas strain SD17-1 and Devosia strain SD17-2, respectively. Biochemical analyses further confirmed the PQQ-producing phenotype of Pseudomonas and the DON-oxidizing enzymatic activities of two of four PQQ-dependent ADHs in Devosia. The addition of PQQ-containing a cell-free fermentation supernatant from Pseudomonas activated DON-oxidizing activity of Devosia. In summary, as members of the bacterial consortium SD, Pseudomonas and Devosia play indispensable and complementary roles in SD's oxidation of DON. Specifically, Pseudomonas is responsible for producing the necessary PQQ cofactor, whereas Devosia expresses the PQQ-dependent DON dehydrogenase, together facilitating the oxidation of DON.

Climate change and food safety: Temperature impact on the attachment of Escherichia coli pathogroups on cress leaf

AbstractClimate change and its worldwide effects are undeniable. Temperature increase due to climate change may affect foodborne pathogen survival on fresh produce. This study aimed to present an evaluation of climate change impact regarding temperature rise situations, on attachment of different pathogenic Escherichia coli strains on cress grown under controlled conditions. EHEC O157:H7, EAEC O104:H4 and EPEC O26 were inoculated with initial inoculum concentration of 8 log MPN/mL at different stages during growth to observe how inoculation time (7, 14, 21 and 28 days post sowing; dps) and route (seed and leaves) affect pathogen load on fresh produce. This study revealed that temperature increase designed according to mitigation scenarios for climate change (+2, +4 and +6 °C) did not cause any considerable change in pathogen persistence on leaf at 30 dps (~4.5 to 7 log MPN/g). In plants contaminated at later stage (21 and 28 dps), higher bacterial populations were obtained for all temperatures studied. Our results show that E. coli translocated towards leaf portions from seed and established significant amount of pathogen load on leaf (~4 to 5.3 log MPN/g). Also, inoculated bacteria have tightly bound to leaf (~3.5 to 7 log MPN/g) and cannot be eliminated by washing. Although persistence of E. coli O157:H7, O104:H4 and O26 did not differ significantly according to temperature, the bacterial load on the leaves was above infectious dose for humans.

A Systematic Quantitative Determination of the Antimicrobial Efficacy of Grape Seed Extract against Foodborne Bacterial Pathogens

Concerns regarding the role of antimicrobial resistance (AMR) in disease outbreaks are growing due to the excessive use of antibiotics. Moreover, consumers are demanding food products that are minimally processed and produced in a sustainable way, without the use of chemical preservatives or antibiotics. Grape seed extract (GSE) is isolated from wine industry waste and is an interesting source of natural antimicrobials, especially when aiming to increase sustainable processing. The aim of this study was to obtain a systematic understanding of the microbial inactivation efficacy/potential of GSE against Listeria monocytogenes (Gram-positive), Escherichia coli and Salmonella Typhimurium (Gram-negative) in an in vitro model system. More specifically, for L. monocytogenes, the effects of the initial inoculum concentration, bacterial growth phase and absence of the environmental stress response regulon (SigB) on the GSE microbial inactivation potential were investigated. In general, GSE was found to be highly effective at inactivating L. monocytogenes, with higher inactivation achieved for higher GSE concentrations and lower initial inoculum levels. Generally, stationary phase cells were more resistant/tolerant to GSE as compared to exponential phase cells (for the same inoculum level). Additionally, SigB appears to play an important role in the resistance of L. monocytogenes to GSE. The Gram-negative bacteria under study (E. coli and S. Typhimurium) were less susceptible to GSE as compared to L. monocytogenes. Our findings provide a quantitative and mechanistic understanding of the impact of GSE on the microbial dynamics of foodborne pathogens, assisting in the more systematic design of natural antimicrobial-based strategies for sustainable food safety.

Advanced treatment of secondary effluent from wastewater treatment plant by a newly isolated microalga Desmodesmus sp. SNN1.

Secondary effluents contain considerable amounts of nitrogen and phosphorous, which if dumped untreated can cause eutrophication of the receiving water bodies. Microalgae can remove these nutrients and other pollutants from the wastewater effluents and play an effective role in the secondary effluent treatment. In this study, six microalgae strains (SNN1, SNN2, SNN3, SNN4, SNS1, and SNS2) were isolated and screened from the water and mud of Yingxue Lake of Shandong Jianzhu University, and their efficiencies for the removal of COD, NH4 +-N, TN, and TP in the secondary effluent were assessed. By comparing the growth performances and nutrient removal ability of algal strains in domestic sewage, we found that SNN1 (identified and named as Desmodesmus sp. SNN1) has the highest efficiency for biomass accumulation and sewage purification. Hence, the algal strain SNN1 was selected for further screening and optimization experiments. The strain showed higher biomass yield and better nutrient removal rate when the pH of secondary effluent was 9.0 and the initial inoculum concentration (optical density at 680 nm) of algal strain was 0.4. After 12 days of treatment, the concentrations of COD, NH4 +-N, TN, and TP in the secondary effluent were 31.79, 0.008, 8.631, and 0.069 mg/L, respectively. Therefore, SNN1 with the removal rates of 52.69% (COD), 99.99% (NH4 +-N), 89.09% (TN), and 94.64% (TP) displayed its high potential in nutrient removal. In addition, it also yielded 5.30 mg/L of chlorophyll a and 168.33 mg/L of lipids. These results demonstrated that this strain exhibited an effective treatment capacity for secondary effluent and microalgal oil production. This study is helpful to provide a strategy for the resource utilization of secondary effluent and the conservation of freshwater resources required by microalgae culture.

Role of extracellular polymeric substance in flocculation of Chlorococcum sphacosum cultivated with different initial inoculum concentrations in municipal wastewater

Initial inoculum concentration of microalgae has been proposed to affect wastewater treatment performance. However, it is unclear whether the initial inoculum concentration affects the flocculation efficiency of microalgae. Efficient flocculation of microalgae, after all, was critical to cost-effective large-scale wastewater treatment. Here, it was found that the flocculation efficiency of Chlorococcum sphacosum significantly decreased from 59.46 % to 23.73 % following the increase of microalgal initial inoculum concentration from 50 mg/L to 800 mg/L. Extracellular polymeric substance (EPS) concentration also reduced significantly. Moreover, the proportion of some surface groups, such as hydrophobic amino acid tryptophan, α-helix, and C(C/H), in EPS of the microalga also reduced simultaneously. The correlation analysis and variance partitioning analysis (VPA) indicated that both EPS concentration and composition characteristics had outstanding contributions to microalgal flocculation. It was speculated that the change of EPS concentration and hydrophobic component ratio derived from the variation in microalgal inoculum concentrations was one of the main driving factors for variations in flocculation efficiency. This investigation was valuable for understanding the flocculation mechanism of microalgae.

Inoculum for the cultivation of Methylosinus sporium

This research assessed the effect of the amount of inoculum on the specific growth rate of Methylosinus sporium culture. Methanotrophs were inoculated in different quantities onto media of the same composition and volume. Seven different initial inoculum concentrations were obtained in duplicate. Samples were cultured for 31 hours, during which sampling and optical density measurements were carried out. In accordance with the fact that the optical density is directly proportional to the concentration of microorganisms in the sample, the specific growth rate was calculated. The research revealed an interval from 6.5 to 24 hours, during which the culture demonstrates a stable growth rate of 0.06 h-1, at an inoculation dose at which the optical density of the nutrient medium with the added inoculum is 0.030-0.121.

ANAEROBIC CO-DIGESTION OF SUGARCANE VINASSE AND ELEPHANT GRASS JUICE FOR BIOMETHAN PRODUCTION

In the present study, biogas production was investigated by co-digesting elephant grass juice (EGJ) and sugarcane vinasse using batch reactor. Some factors that influence biomethane production were observed, including initial pH, inoculum concentration and proportions of each substrate. Two tests were carried out. In Experiment I, the following proportions (%v/v sugarcane vinasse/elephant grass juice) were tested: A - 25/75, B - 50/50, C - 75/25, D - 100/0, E - 0/100. In Experiment II, the effect of adding alkalizer to the condition that showed the highest methane production (in Experiment I) was also evaluated. In the Experiment I, the highest accumulated production was observed for the proportion 1:1 corresponding to 50% of EGJ and 50% of vinasse (370.94 mLCH4/gVS). Experiment II showed the higher values of accumulated methane production of 1,364.1 mLCH4/gVS. Regarding addition of alkalizing, a maximum production of 836.18 mLCH4/gVS was obtained in the experimental condition with 50% EGJ and 50% vinasse, but with the lowest addition of alkalizer tested (0.05 g HCO3/gCOD). In general, the use of elephant grass caused the acidification of the reactors and was unfavorable for biogas production.

Volatile organic compounds produced by Bacillus velezensis L1 as a potential biocontrol agent against postharvest diseases of wolfberry.

Volatile organic compounds (VOCs) produced by antagonistic microorganisms have good biocontrol prospects against postharvest diseases. Infection caused by Alternaria iridiaustralis and 10 other significant fungal diseases can be successfully inhibited by VOCs produced by an identified and screened endophytic strain L1 (Bacillus velezensis). This study revealed the in vivo and in vitro biocontrol effects of VOCs released by B. velezensis L1 on A. iridiaustralis, a pathogenic fungus responsible for rot of wolfberry fruit. The inhibition rates of VOCs of B. velezensis L1 on the mycelial growth of A. iridiaustralis in vitro were 92.86 and 90.30%, respectively, when the initial inoculum concentration on the plate was 1 × 109 colony forming unit (CFU)/ml. Spore germination and sporulation were 66.89 and 87.96%, respectively. VOCs considerably decreased the wolfberry’s disease index and decay incidence in vivo. Scanning electron microscopy revealed that the morphological and structural characteristics of A. iridiaustralis could be altered by VOCs. Ten VOCs were identified through headspace-gas chromatography-ion mobility spectrometry. Pure chemical tests revealed that 2.3-butanedione had the strongest antifungal effects, totally inhibiting A. iridiaustralis in wolfberry fruit at a 60 μl/L concentration. The theory underpinning the potential application of VOCs from B. velezensis is provided herein. This is also the first study to document the antifungal capabilities of the B. velezensis strain on postharvest wolfberry fruit. GRAPHICAL ABSTRACT

Two stage treatability and biokinetic study of dairy wastewater using bacterial consortium and microalgae

Purpose of present research work is to perform nutrient removal and evaluate bio-kinetic coefficients of a two-stage dairy wastewater treatment process in batch reactor using bacterial consortium and microalgae Chlorella pyrenoidosa. The research work was performed in laboratory-scale batch reactor. Primary treated real life dairy wastewater after a treatment with a consortium of bacterial population containing carbon oxidation and nitrification bacteria was taken as the feed material for algal treatment process using microalgae C. pyrenoidosa strain. Nitrate nitrogen which was formed during bacterial nitrification still remaining in bacterial pre-treated dairy wastewater along with phosphorus that have been removed by algal treatment using microalgae of C. pyrenoidosa. The present investigation was done for bacterial and algal treatment of dairy plant effluent in a lab-scale batch reactor with acclimatized seeds of both carbon oxidation, nitrification bacteria, microalgae C. pyrenoidosa and also to evaluate various biokinetic coefficients. Around 95% ammonium nitrogen and soluble chemical oxygen demand (SCOD), around 99.67% and 90.25% of Nitrate nitrogen (NO3−-N) and Phosphorus (PO43-- P) removal were achieved corresponding to initial ammonium nitrogen and SCOD of 55 and 720 mg/L, nitrate nitrogen and phosphorus concentration of 54 and 16 mg/L respectively, with an initial inoculum concentration of bacterial consortium of 15%; corresponding to 1500 mg/L and microalgae C. pyrenoidosa of 0.8% v/v; corresponding to 80 mg/L after 24 h and 8 days of detention period in batch reactor respectively. Kinetic study was also carried out to obtain bio-kinetic coefficient for SCOD, ammonium nitrogen, nitrate nitrogen and phosphorus removal using bacterium and microalgae C. pyrenoidosa.

Initial and Final Cell Concentrations Significantly Influence the Maximum Growth Rate of Listeria monocytogenes in Published Literature Data for Whole Intact Fresh Produce

Listeria monocytogenes has shown the ability to grow on fresh uncut produce; however, the factors that control growth are not well understood. Peer-reviewed journal articles (n = 29) meeting the inclusion criteria and related to the growth of L. monocytogenes on fresh produce were found through university library databases and Google Scholar searches. Growth models were fit to each of the extracted 130 data sets to estimate log CFU per day rates of growth by using the DMFit tool. Multiple linear stepwise regression models for factors influencing growth rate were developed using R software. Factors included were temperature, nutrient level of inoculation buffer, initial cell concentration, final cell concentration, inoculation method, container permeability, and surface characteristics. The full model produced adjusted R2, Akaike information criterion, and root mean square error values of 0.41, 488, and 1.61, respectively. Stepwise regression resulted in a reduced model with parameters for incubation temperature, inoculation buffer type, initial and final cell concentrations, container characteristics, and produce surface characteristics. Model fit statistics improved slightly in the reduced model. A further reduced three-parameter model included storage temperature and initial and final cell concentrations, with interaction terms. This three-parameter model had adjusted R2, Akaike information criterion, and root mean square error values of 0.66, 417, and 1.24, respectively. Incubation temperature (P = 1.00E-09) initial cell concentration (P = 3.05E-12), and final cell concentration (P = 4.17E-09) all had highly significant effects on maximum growth rate. Our findings show the importance of inoculum concentration and produce microbial carrying capacity on the estimated growth rate and highlight the overall importance that temperature has on growth rate. Future experiments should consider initial inoculum concentration carefully when conducting growth studies for L. monocytogenes on whole produce.

Aspects of Mannheimia haemolytica cryopreservation

Mannheimia haemolytica causes severe pneumonia and septicemia in ruminant animals. The study aims to create an effective protective media for the long‐term storage of microbial cultures of M. haemolytica in a veterinary laboratory. The protective nutrient media were based on Hottinger's nutrient broth. Glycerol and ethylene glycol were used as cryoprotectants. Two protective media were obtained. Medium #1 consisted of nutrient broth (90%) and glycerin (10%), and medium #2 had nutrient broth (90%) and ethylene glycol (10%) in it. A homogeneous suspension 1.0 McFarland units turbidity was prepared from a pure culture of microorganisms (3.0 x 108 CFU/ml). The suspension was added to ampoules with an appropriate protective medium. The inoculated media were placed in a cryogenic storage dewar in liquid nitrogen at ‐196 ° C. The viability of M. haemolytica was determined by inoculation on blood agar and counting the number of living bacteria. The initial inoculum concentration of M. haemolytica was 3.0x107 CFU/ml. After 18‐20 hours of cultivation, it becomes 7.0x109 CFU/ml. The survival and safety of bacteria depend on the cryoprotectant. The results of the experiment showed that 10% glycerol provides 98.6% survival of M. haemolytica. The number of viable cells after cryopreservation was 6.9x109 CFU/ml. Ethylene glycol showed a 95.7% survival rate. The number of viable cells after cryopreservation was 6.7x109 CFU/ml. Without cryoprotectant, M. haemolytica showed a 40.0% survival rate with only 2.8x109 CFU/ml viable cells after defrosting. M. haemolytica causes turbidity and sediment formation at the bottom of the tube on Hottinger broth. After growing on semi‐liquid media (semi‐liquid agar with the addition of glucose or serum), bacteria show bipolar staining in smears. On Hottinger broth, with the addition of 10% defibrinated ram blood M. haemolytica formed small dewy colonies with an even edge without a hemolysis zone. The final species identification was performed by the proteomic method using MALDI‐TOF‐SM. All used media keep microorganisms' cultures in a stable, viable state. Thus, they can be successfully used for the storage of bacteria at low‐temperature conditions.

Utilization of sugarcane molasses as the main carbon source for the production of polyhydroxyalkanoates from Enterobacter cloacae

Polyhydroxyalkanoates (PHAs) are biodegradable polymers that otherwise exhibit many properties similar to that of conventional, non-biodegradable plastics. Hence, they are considered as potential substitutes for non-biodegradable plastics. But industrial production and commercialization of PHA have been hindered greatly due to the high cost requirements, especially those involved in the provision of suitable carbon sources. In this study, sugarcane molasses was used as a cheap carbon source for PHA production using a wild strain of Enterobacter cloacae isolated from sugarcane extract. This isolate was selected for PHA production based on Sudan Black B staining, and it was subsequently identified by performing BLASTn using its 16S rRNA sequence (GenBank accession number: ON314993). The PHA yield was studied under varying conditions of initial pH, molasses concentration and inoculum concentration. The highest yield of 4.13 - 4.98 g/L or 48 - 56% PHA was obtained after 48-60 h incubation at initial pH 7, molasses concentration 4% and inoculum concentration 2%. After downstream processing, the extracted PHA was characterized by FTIR spectroscopy. It is concluded that E. cloacae has the potential to utilize sugarcane molasses as a cheap carbon source to yield impressive amounts of PHA, and that it should be considered a candidate for further studies and for the cheaper industrial production of PHA.

Alginate encapsulated nanobio-hybrid system enables improvement of photocatalytic biohydrogen production in the presence of oxygen

Bacterial encapsulation for the generation of fuels and other valuable chemicals through fermentation emerges as a novel biotechnological strategy that provides significant advantages over the use of free cells. In the present study, we established an optimal alginate encapsulated TiO2/Escherichia coli hybrid system by varying the initial concentrations of alginate (2–5%) and initial inoculum concentration (OD600 0.5–2.5) to form the hydrogel beads for efficient production of hydrogen in the presence of oxygen with the given visible-light intensity of 2000 W m−2. The maximum hydrogen production of 2.8 mmol H2/mmol glucose was obtained with hydrogel beads consisting of 4% sodium alginate and initial inoculum with a cell density of 1.5 OD600. Natural sunlight could also be used to produce hydrogen under the same optimized condition. The optimization of the encapsulated nano bio-hybrid system with respect to alginate and inoculum concentration allows for the enhancement of hydrogen production even in the presence of oxygen.

Growth of 'Candidatus Liberibacter asiaticus' in Commercial Grapefruit Juice-Based Media Formulations Reveals Common Cell Density-Dependent Transient Behaviors.

The phloem-restricted, insect-transmitted bacterium 'Candidatus Liberibacter asiaticus' (CLas) is associated with huanglongbing (HLB), the most devastating disease of citrus worldwide. The inability to culture CLas impairs the understanding of its virulence mechanisms and the development of effective management strategies to control this incurable disease. Previously, our research group used commercial grapefruit juice (GJ) to prolong the viability of CLas invitro. In the present study, GJ was amended with a wide range of compounds and incubated under different conditions to optimize CLas growth. Remarkably, results showed that CLas growth ratios were inversely proportional to the initial inoculum concentration. This correlation is probably regulated by a cell density-dependent mechanism, because diluting samples between subcultures allowed CLas to resume growth. Moreover, strategies to reduce the cell density of CLas, such as subculturing at short intervals and incubating samples under flow conditions, allowed this bacterium to multiply and reach maximum growth as early as 3 days after inoculation, although no sustained exponential growth was observed under any tested condition. Unfortunately, cultures were only transient, because CLas lost viability over time; nevertheless, we obtained populations of about 105 genome equivalents/ml repeatedly. Finally, we established an ex vivo system to grow CLas within periwinkle calli that could be used to propagate bacterial inoculum in the lab. In this study we determined the influence of a comprehensive set of conditions and compounds on CLas growth in culture. We hope our results will help guide future efforts toward the long-sought goal of culturing CLas axenically.

'Candidatus Liberibacter' Pathosystems at the Forefront of Agricultural and Biological Research Challenges.

'Candidatus Liberibacter' Pathosystems at the Forefront of Agricultural and Biological Research Challenges.

Production of bacterial cellulose films by Gluconoacetobacter xylinus for lipase immobilization

Bacterial cellulose (BC), a microbial polysaccharide, has chemically equivalent structure to plant cellulose with unbranched pellicle structure of only glucose monomers. Due to the unique nanostructure, BC has great potential in enzyme immobilization. In this study, the effects of different cultivation conditions including rotational speed, initial inoculum concentration and medium pH on the film-like cellulosic biomass formation of Gluconacetobacter xylinus JCM 9730 were examined. The resultant BC films were then studied for its feasibility in the immobilization of lipase, a widely used enzyme in biotechnological and industrial processes including food, pharmaceutical, chemical and paper industries. Results showed that increasing in rotational speed from 0 rpm to 200 rpm converted cellulose-producing cells to non-cellulose-producing ones, leading to a significant decline in BC film formation. The increase in initial inoculum size from 0.01 g/L to 0.1 g/L reduced sugar concentration and surface area of the medium, and therefore inhibiting the formation of film-like cellulosic biomass. In addition, the optimum pH range of Acetobacter species from 5.4 – 6.3 was found not optimal for BC film formation. The highest amount of film-like cellulosic biomass of 19.01 g/L was obtained under static condition (0 rpm) with initial cell concentration of 0.04 g/L and initial pH of 4.0. The BC film samples were then acetylated with acetic anhydride/iodine system to convert the hydroxyl groups to less hydrophilic acetyl groups and were used for lipase immobilization. Results showed that lipase immobilized on acetylated BC still maintained its lipid hydrolytic activity. It can be hence concluded that BC films produced by G. xylinus JCM 9730 were potential for lipase immobilization.

Integrated hydrothermal assisted green synthesis of ZnO nano discs and their water purification efficiency together with antimicrobial activity

The water microbial contamination is very common and different techniques are in practice for the decontamination purpose. The advance oxidation processes are being employed to mortify pathogens polluting drinking water. Heterogeneous photocatalysis under sunlight irradiation is a cost effective and remarkably proficient method for water purification. Zinc Oxide (ZnO) is a biocompatible material that has promising photo–oxidant activity. In this study, ZnO has been synthesized using Aloe vera (Av) extract assisted with hydrothermal approach. The nano disc structure of ZnO was characterized by XRD SEM, TEM, AFM, EDX, and FTIR techniques. The optical properties of ZnO@Av NDs (nano discs) evaluated by DRS and PL revealed their sunlight harvesting capability, as the calculated band gap value was 2.8 eV. The surface area and surface charge were measured by BET (5.34 m2g-1) and Zeta potential (+7.46 mV). The antibacterial activity of ZnO@Av NDs was studied against Salmonella typhimurium as a function of various process variables i.e., photocatalyst loading, sunlight exposure time, and bacterial inoculum size. The bactericidal reaction parameters were optimized statistically by Response Surface Methodology (RSM) on exposure to direct sunlight (average solar flux was 650 KWh/m2) at pH 7. As optimized conditions, 100 μL initial inoculum concentration of S. typhimurium was treated with 60 μg/mL of ZnO@Av NDs suspension under sunlight irradiation of 5 h, antibacterial index obtained was 6.8. The MIC and MBC for ZnO@Av NDs against S. typhimurium were 50 μL and 100 μL, respectively. It has been observed that ZnO@Av NDs lower the optical density of water that contains S. typhimurium. The photocatalytic purification of water using ZnO@Av NDs is safe and cost-effective method under sunlight irradiation, which could possibly be employed for the wastewater purification.

Volatile organic compounds produced by Pseudomonas fluorescens ZX as potential biological fumigants against gray mold on postharvest grapes

Volatile organic compounds (VOCs) produced by antagonistic microorganisms have the potential for controlling postharvest diseases on fruit and vegetables. In this study, the biocontrol efficacy of VOCs emitted by Pseudomonas fluorescens ZX was determined in vitro and in vivo against gray mold, caused by Botrytis cinerea, on grapes. In vitro, application of VOCs produced by bacterial suspension of P. fluorescens ZX at initial inoculum concentration of 1 × 109 colony-forming units (CFU)/mL inhibited B. cinerea mycelial growth from 52 to 23 mm and spore germination from 88.56 to 39.67%. In vivo tests indicated that, for grapes, disease incidence and disease index were markedly reduced by VOCs from P. fluorescens ZX incubated on NA plates, in NB, and on healthy grapes. Pre-fumigation with VOCs could inhibit development of gray mold on grapes. Furthermore, P. fluorescens ZX-producing VOCs exhibited favorable effects on postharvest natural decay of grapes. In vitro testing of selected pure chemicals demonstrated that dimethyl trisulfide (20 μL/L), dimethyl disulfide (40 μL/L), geranyl formate (640 μL/L), acetic acid (160 μL/L), butyric acid (320 μL/L), 2-methylbutyric acid (160 μL/L), isobutyric acid (160 μL/L) and isovaleric acid (320 μL/L) could completely inhibit mycelial growth of B. cinerea on PDA plates. These eight substances also exerted a strong inhibitory effect on gray mold on grapes. Additionally, SEM analysis showed that VOCs could affect the morphological and structural characteristics of B. cinerea both in vitro and in vivo. Collectively, VOCs produced by P. fluorescens ZX are promising for biocontrol of gray mold on grapes through fumigant action.