Yeast Biofilm Research Articles

Effectiveness of sodium hypochlorite and benzalkonium chloride in reducing spoilage yeast biofilms on food contact surfaces

The study evaluates the effectiveness of sodium hypochlorite (NaOCl) and a commercial quaternary ammonium compound (QAC) against planktonic and biofilm-associated yeast (Candida tropicalis, C. krusei, C. kefyr, and Rhodotorula mucilaginosa) isolated from ultrafiltration modules in a clarified apple juice production facility. The results demonstrated that the efficacy of disinfection against planktonic yeast cells did not directly correlate with the effectiveness against biofilm-embedded cells. QAC proved to be more effective than NaOCl in reducing yeast biofilms, achieving a higher than 3-log10 reduction in cell counts. In contrast, NaOCl, even at its maximum permissible concentration for food-contact surfaces, exhibited limited efficacy against biofilms. Both disinfectants had limited success in preventing biofilm regrowth, indicating the potential for persistent contamination in food processing environments. Furthermore, both agents compromised biofilm structure, with QAC having a significantly more pronounced impact than NaOCl.

Phenolic Content, Antioxidant and Antimicrobial Properties of Hawthorn (Crataegus orientalis) Fruit Extracts Obtained via Carbohydrase-Assisted Extraction

The enzyme-assisted approaches for plant phenolics extraction are more eco-friendly methods compared to acid or alkaline hydrolysis. Carbohydrase enzymes can release free phenolics from plant materials by cleaving the glycosidic bonds between phenolic compounds and cell wall polymers. In this study, the efficiency of carbohydrase-assisted treatment approaches was evaluated to extract bioactive phenolics from hawthorn (Crataegus orientalis) fruit residues. Enzymatic treatment of the fruits was operated by using a crude cellulolytic enzyme cocktail from Rhizomucor miehei NRRL 5282 and a pectinase preparate from Aspergillus niger. Both cellulase and combined cellulase–pectinase treatments improved the total phenolic content (TPC) and antioxidant activity of extracts. The TPC increased to 1899 ± 27 mg gallic acid equivalents/100 g dry matter during the combined enzyme treatment, showing a strong correlation with the average antioxidant capacity determined by ferric-reducing antioxidant power (1.7-fold increment) and 2,2-diphenyl-1-picrylhydrazyl (1.15-fold increment) reagents. The major phenolics in enzyme-treated extracts were vanillic and ferulic acids, the concentrations of which increased 115.6-fold and 93.9-fold, respectively, during carbohydrase treatment. The planktonic growth of Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and Chromobacterium violaceum was slightly inhibited by the extracts with minimum inhibitory concentration values between 15.0 and 77.9 mg/mL, while the yeasts tested were quite resistant to the samples. B. subtilis and yeast biofilms were sensitive to the enzyme-treated extracts, which also showed quorum-sensing inhibitory effects against C. violaceum. The obtained bioactive hawthorn extracts hold potential as a natural source of antioxidants and antimicrobials.

The Impact of Cyclodextrins on the Physiology of Candida boidinii: Exploring New Opportunities in the Cyclodextrin Application.

Cyclodextrins, commonly used as excipients in antifungal formulations to improve the physicochemical properties and availability of the host molecules, have not been systematically studied for their effects and bioactivity without a complex active substance. This paper evaluates the effects of various cyclodextrins on the physiology of the test organism Candida boidinii. The research examines their impact on yeast growth, viability, biofilm formation and morphological changes. Native ACD, BCD, randomly methylated α- and β-CD and quaternary ammonium α-CD and β-CD were investigated in the 0.5-12.5 mM concentration range in both static and dynamic systems. The study revealed that certain cyclodextrins exhibited notable antifungal effects (up to ~69%) in dynamic systems; however, the biofilm formation was enhanced in static systems. The magnitude of these effects was influenced by several variables, including the size of the internal cavity, the concentration and structure of the cyclodextrins, and the contact time. Furthermore, the study found that CDs exhibited distinct effects in both static and dynamic systems, potentially related to their tendency to form aggregates. The findings suggest that cyclodextrins may have the potential to act as antifungal agents or growth promoters, depending on their structure and surrounding environments.

The arginine transporter Can1 negatively regulates biofilm formation in yeasts.

The arginine transporter Can1 is a multifunctional protein of the conventional yeast Saccharomyces cerevisiae. Apart from facilitating arginine uptake, Can1 plays a pivotal role in regulating proline metabolism and maintaining cellular redox balance. Here, we report a novel function of Can1 in the control of yeast biofilm formation. First, the S. cerevisiae CAN1 gene knockout strain displayed a significant growth delay compared to the wild-type strain. Our genetic screening revealed that the slow growth of the CAN1 knockout strain is rescued by a functional deficiency of the FLO8 gene, which encodes the master transcription factor associated with biofilm formation, indicating that Can1 is involved in biofilm formation. Intriguingly, the CAN1 knockout strain promoted the Flo11-dependent aggregation, leading to higher biofilm formation. Furthermore, the CAN1 knockout strain of the pathogenic yeast Candida glabrata exhibited slower growth and higher biofilm formation, similar to S. cerevisiae. More importantly, the C. glabrata CAN1 gene knockout strain showed severe toxicity to macrophage-like cells and nematodes. The present results could help to elucidate both the molecular mechanism underlying yeast biofilm formation and the role it plays. Future investigations may offer insights that contribute to development of antibiofilm agents.

Two promising Bacillus-derived antifungal lipopeptide leads AF4 and AF5 and their combined effect with fluconazole on the in vitro Candida glabrata biofilms.

Introduction: Candida species are endowed with the ability to produce biofilms, which is one of the causes of pathogenicity, as biofilms protect yeasts from antifungal drugs. Candida glabrata (Nakaseomyces glabrata) is one of the most prevalent pathogenic yeasts in humans and a biofilm producer. Methods: The study was aimed at evaluating the combined effects of two highly promising antifungal biomolecules (AF4 and AF5) lipopeptide in nature, chromatographically purified to homogeneity from Bacillus subtilis (B. subtilis) and the standard antifungal fluconazole (at different concentrations) to demonstrate C. glabrata biofilm formation inhibition. Biofilm production and inhibition were evaluated by quantification of the biofilm biomass and metabolic activity using crystal violet (CV) staining and XTT reduction assays, respectively. Microscopic techniques such as confocal scanning laser microscopy (CSLM) and scanning electron microscopy (SEM) were employed to visualize biofilm formation and inhibition. Results and Discussion: Compared to untreated and fluconazole-treated biofilms, an enhanced in vitro anti-biofilm effect of the antifungal lipopeptides AF4/AF5 alone and their combinations with fluconazole was established. The lipopeptides AF4/AF5 alone at 8 and 16μg/mL exhibited significant biomass and metabolic activity reductions. SEM and CSLM images provided evidence that the lipopeptide exposure results in architectural alterations and a significant reduction of C. glabrata biofilms, whereas (2', 7'-dichlorofluorescin diacetate (DCFDA) and propidium iodide (PI) analyses showed reactive oxygen species (ROS) generation along with membrane permeabilization. The estimation of exopolysaccharides (EPS) in AF4/AF5-treated biofilms indicated EPS reduction. The combinations of fluconazole (64/128μg/mL) and AF4/AF5 lipopeptide (16μg/mL) were found to significantly disrupt the mature (24h) biofilms as revealed by CSLM and SEM studies. The CSLM images of biofilms were validated using COMSTAT. The FTIR-analyses indicate the antibiofilm effects of both lipopeptides on 24h biofilms to support CSLM and SEM observations. The combinations of fluconazole (64/128μg/mL) and AF4/AF5 lipopeptide were found to disrupt the mature biofilms; the study also showed that the lipopeptides alone have the potentials to combat C. glabrata biofilms. Taken together, it may be suggested that these lipopeptide leads can be optimized to potentially apply on various surfaces to either reduce or nearly eradicate yeast biofilms.

Biofilm development of Candida boidinii and the effect of tyrosol on biofilm formation

ObjectivesThe applicability of a simple and high-throughput method for quantitative characterization of biofilm formation by Candida boidinii was tested in order to evaluate the effects of exogenous tyrosol on yeast growth and biofilm formation capacity.ResultsSignificant concentration-, temperature and time-dependent effect of tyrosol (2-(4-hydroxyphenyl)ethanol) was demonstrated, but it differentially affected the growth and biofilm formation (characterized by crystal violet staining and XTT-reduction assay) of Candida boidinii. Testing biofilm based on metabolic activity displayed sensitively the differences in the intensity of biofilm in terms of temperature, tyrosol concentration, and exposure time. At 22 °C after 24 h none of the tyrosol concentrations had significant effect, while at 30 °C tyrosol-mediated inhibition was observed at 50 mM and 100 mM concentration. After 48 h and 72 h at 22 °C, biofilm formation was stimulated at 6.25–25 mM concentrations, meanwhile at 30 °C tyrosol decreased the biofilm metabolic activity proportionally with the concentration.ConclusionsThe research concludes that exogenous tyrosol exerts unusual effects on Candida boidinii growth and biofilm formation ability and predicts its potential application as a regulating factor of various fermentations by Candida boidinii.

Development of yeast and microalgae consortium biofilm growth system for biofuel production

BackgroundThe current study aimed to develop a laboratory-scale biofilm photobioreactor system for biofuel production. Scope & ApproachDuring the investigation, Jute was discovered to be the best, cheap, hairy, open-pored supporting material for biofilm formation. Microalgae & yeast consortium was used in this study for biofilm formation. ConclusionThe study identified microalgae and yeast consortium as a promising choice and ideal partners for biofilm formation with the highest biomass yield (47.63 ± 0.93 g/m2), biomass productivity (4.39 ± 0.29 to 7.77 ± 0.05 g/m2/day) and lipid content (36%) over 28 days cultivation period, resulting in a more sustainable and environmentally benign fuel that could become a reality in the near future.

Pomegranate sarcotesta lectin (PgTeL) inhibits planktonic growth and disrupts biofilm formed by Cryptococcus neoformans.

We investigated the putative fungistatic and fungicidal activities of pomegranate sarcotesta lectin (PgTeL) against Cryptococcus neoformans B3501 (serotype D), specifically the ability of PgTeL to inhibit yeast capsule and biofilm formation in this strain. PgTeL showed a minimum inhibitory concentration of 172.0 μg ml-1, at which it did not exhibit a fungicidal effect. PgTeL concentrations of 4.0-256.0 μg ml-1 reduced biofilm biomass by 31.0-64.0%. Furthermore, 32.0-256.0 μg/mL PgTeL decreased the metabolic activity of the biofilm by 32.0-93.0%. Scanning electron microscopy images clearly revealed disruption of the biofilm matrix. Moreover, PgTeL disrupted preformed biofilms. At concentrations of 8.0-256.0 μg ml-1, PgTeL reduced metabolic activity in C. neoformans by 36.0-92.0%. However, PgTeL did not inhibit the ability of B3501 cells to form capsules under stress conditions. PgTeL inhibited biofilm formation and disrupted preformed biofilms, demonstrating its potential for use as an anticryptococcal agent.

Biotechnological applications of biofilms formed by osmotolerant and halotolerant yeasts.

Many microorganisms are capable of developing biofilms under adverse conditions usually related to nutrient limitation. They are complex structures in which cells (in many cases of different species) are embedded in the material that they secrete, the extracellular matrix (ECM), which is composed of proteins, carbohydrates, lipids, and nucleic acids. The ECM has several functions including adhesion, cellular communication, nutrient distribution, and increased community resistance, this being the main drawback when these microorganisms are pathogenic. However, these structures have also proven useful in many biotechnological applications. Until now, the most interest shown in these regards has focused on bacterial biofilms, and the literature describing yeast biofilms is scarce, except for pathological strains. Oceans and other saline reservoirs are full of microorganisms adapted to extreme conditions, and the discovery and knowledge of their properties can be very interesting to explore new uses. Halotolerant and osmotolerant biofilm-forming yeasts have been employed for many years in the food and wine industry, with very few applications in other areas. The experience gained in bioremediation, food production and biocatalysis with bacterial biofilms can be inspiring to find new uses for halotolerant yeast biofilms. In this review, we focus on the biofilms formed by halotolerant and osmotolerant yeasts such as those belonging to Candida, Saccharomyces flor yeasts, Schwannyomyces or Debaryomyces, and their actual or potential biotechnological applications. KEY POINTS: • Biofilm formation by halotolerant and osmotolerant yeasts is reviewed. • Yeasts biofilms have been widely used in food and wine production. • The use of bacterial biofilms in bioremediation can be expanded to halotolerant yeast counterparts.

Antimicrobial photodynamic therapy mediated by methylene blue-loaded polymeric micelles against Streptococcus mutans and Candida albicans biofilms.

Streptococcus mutans and Candida albicans can colonize the teeth, the oral cavity as biofilm and can cause oral infections. Thus, strategies to prevent and control oral biofilms are requested. The present study aims the development and characterization of methylene blue (MB)-loaded polymeric micelles for antimicrobial photodynamic therapy (aPDT) against Streptococcus mutans and Candida albicans biofilms METHODS: MB-loaded polymeric micelles were produced and characterized by particle size, polydispersity index, morphology, zeta potential, stability, MB release profile, and antimicrobial effect against S. mutans and C. albicans biofilms. MB-loaded polymeric micelles showed a reduced particle size, moderate polydisperse profile, spherical and neutral shape, which demonstrated to be promising features to allow micelles penetration into biofilms. Antimicrobial effect against bacterial and yeast biofilms was demonstrated once MB was irradiated by light under 660nm (aPDT). Furthermore, MB-loaded polymeric micelles showed significant inhibition of S. mutans and C. albicans biofilms. Furthermore, the treatment with MB-micelles incubated with high pre-incubation times (15 and 30min) were more effective than 5min. It can be explained by the time required for this nanosystem to penetrate the innermost layer of biofilms and release MB for aPDT. MB-loaded polymeric micelles can effectively decrease the bacteria and yeast viability and it may cause positive impacts in the clinical practice. Thus, the developed formulation showed potential in the treatment to remove oral biofilms, but clinical studies are needed to confirm its potential.

Synergistic Effect of Surfactants of Nocardia vaccinii IMV B-7405 and Essential Oils on Candida Genus Yeast

The increase in the number of resistant strains of Candida genus representatives, capable of forming biofilms on various surfaces, stimulates the search for new, alternative methods of combating them, one of which is the use of compounds of natural origin, such as essential oils. However, at the same time, their concentration should be minimal, which is due to the ability of essential oils to cause severe damage of the human’s central nervous system and aspiration pneumonia. This leads to the necessity of searching for new methods to reduce the concentration of essential oils and at the same time to preserve their properties, in particular, by their use in a mixture with other antimicrobial agents, which can be microbial surfactants. Previously, it was found that the degree of yeast biofilm destruction under the action of Nocardia vaccinii IMV B-7405 surfactants dependson the nature of the growth substrate and is the highest in the presence of preparations synthesized on purified glycerol. Aim. To study the synergism of antifungal activity and the role in the destruction of biofilms of a mixture of Nocardia vaccinii IMV B-7405 surfactants synthesized on glycerol of different quality and essential oils. Methods. N. vaccinii IMV B-7405 was grown in a medium containing purified glycerol or waste from biodiesel production at a concentration of 2% (v/v) as carbon sources. The surfactants were extracted from the supernatant of cultural liquid by a modified Folch mixture. The antimicrobial activity of essential oils, surfactants, and their mixtures was determined by the index of the minimum inhibitory concentration. To assess the synergistic effect of a mixture of surfactants with essential oils, the fractional inhibitory concentration index was used. The degree of biofilm destruction (%) was determined as the difference between the cell adhesion in untreated and treated with surfactants, essential oil, or their mixture wells of the polystyrene microplates. Results. It was found that the surfactants synthesized by N. vaccinii IMV B-7405 on both purified glycerol and waste from biodiesel production showed synergistic antifungal activity in mixtures with cinnamon and lemongrass essential oils. Thus, the minimum inhibitory concentrations against Candida albicans D-6, Candida utilis BVS-65, and Candida tropicalis RE-2 of a mixture of surfactants synthesized on purified glycerol with cinnamon and lemongrass essential oils were 1.8—7.5 and 3.7— 15 μg/mL, respectively, and were lower than in the case of using surfactants (30-60 μg/mL), cinnamon or lemongrass essential oil (156—312 μg/mL) alone. The use of a mixture of surfactants obtained on waste from biodiesel production and cinnamon or lemongrass essential oils made it possible to reduce the minimum inhibitory concentrations of the latter against studied yeast test cultures by 14—56 times. At the same time, the index of fractional inhibitory concentration did not exceed 0.5, which indicates the synergism of the antifungal activity of the mixture of these compounds. The destruction of Candida yeast biofilms under the action of surfactants synthesized on both purified glycerol and waste from biodiesel production in a mixture with cinnamon or lemongrass essential oils reached 60—67 and 67—77%, respectively, which is an average of 25—35% higher compared to the use of each monopreparation separately. Conclusions. The results presented in this paper confirm the previously obtained data that N. vaccinii IMV B-7405 surfactants, synthesized on both traditional substrates and toxic industrial wastes, have antimicrobial and antiadhesive synergistic action with essential oils, which allows us to consider them as potential components of the so-called «antifungal locks» in the fight against of Candida genus representatives.

Effect of NaOH concentration as activator on calcined eggshell and its application for yeast microbial fuel cell

Eggshells may be utilized as an advanced material. Yeast microbial fuel cells may benefit with calcined eggshell at carbon felt anodes. Stability issues and poor power density prohibit its wider usage. We determined the eggshell-to-NaOH ratio for calcined eggshell anode material. Calcined eggshell with a 1:4 eggshell-NaOH ratio had a high maximum power density (31 mW.m−2) and voltage stability of 45 mV after 30 days incubation. The addition of NaOH activator may also increase crystal size and crystallinity to 145 nm and 43.92 %, respectively, which may accelerate electron transport as evidenced by a decrease in the energy band gap from 5.6 to 5.2 eV, as determined by DFT analysis. The addition of NaOH activator during incubation increased the surface area to 181.2 m2.g−1, improving the anode's potential to host yeast biofilms. Calcined eggshell with a 1:4 eggshell-NaOH ratio is a good anode for yeast microbial fuel cells.

In Vitro Activity of a Hypochlorous Acid-Generating Electrochemical Bandage against Yeast Biofilms.

The antibiofilm activity of a hypochlorous acid (HOCl)-producing electrochemical bandage (e-bandage) was assessed against 14 yeast isolates in vitro. The evaluated e-bandage was polarized at +1.5 VAg/AgCl to allow continuous production of HOCl. Time-dependent decreases in the biofilm CFU counts were observed for all isolates with e-bandage treatment. The results suggest that the described HOCl-producing e-bandage could serve as a potential alternative to traditional antifungal wound biofilm treatments.

Effect of passive cell immobilization of co-cultured yeasts on the whey fermentation and alcohols production

Whey is one of the main residues of the dairy industry and its valorization by fermentation is an emergent practice that contributes to the circular economy and sustainable development. Whey fermentation with specialized yeast strains produces value-added biomolecules, such as fusel alcohols of high interest for the pharmaceutic, food and cosmetic industries due to their aromatic and flavor properties. The present study aimed to develop the whey fermentation with the yeasts Kluyveromyces marxianus and Debaryomyces hansenii immobilized on inert support, to increase cell density and 2-phenylethanol (2-PE) production. Biochar synthesized from wood feedstock, perlite and filter Kaldnes plastic rings were used as supports for the cell immobilization. They were selected based on their different nature and physical properties such as porous structure and rough surface, to study the effect of different supports on yeast biofilm development. Also, functional groups such as hydroxyl, carbonyl, siloxane, and aliphatic hydrocarbons were useful for the development of covalent bonds and electrostatic forces between cells-support. The yeast immobilization increased the 2-PE production, especially on the plastic rings and perlite, obtaining 0.56 ± 0.01 g/L of 2-PE for the suspended culture and up to 0.91 ± 0.01 g/L for the immobilized co-culture on filter Kaldnes plastic rings.

Virulence Mechanisms of Common Uropathogens and Their Intracellular Localisation within Urothelial Cells.

A recurrent urinary tract infection (UTI) is a common debilitating condition whereby uropathogens are able to survive within the urinary tract. In this study, we aimed to determine if the common uropathogens Escherichia coli, Enterococcus faecalis, and Group B Streptococcus possessed virulence mechanisms that enable the invasion of urothelial cells. Urothelial cells were isolated from women with detrusor overactivity and recurrent UTIs; the intracellular localisation of the uropathogens was determined by confocal microscopy. Uropathogens were also isolated from women with acute UTIs and their intracellular localisation and virulence mechanisms were examined (yeast agglutination, biofilm formation, and haemolysis). Fluorescent staining and imaging of urothelial cells isolated from women with refractory detrusor overactivity and recurrent UTIs demonstrated that all three uropathogens were capable of intracellular colonisation. Similarly, the bacterial isolates from women with acute UTIs were also seen to intracellularly localise using an in vitro model. All Enterococcus and Streptococcus isolates possessed a haemolytic capacity and displayed a strong biofilm formation whilst yeast cell agglutination was unique to Escherichia coli. The expression of virulence mechanisms by these uropathogenic species was observed to correlate with successful urothelial cell invasion. Invasion into the bladder urothelium was seen to be a common characteristic of uropathogens, suggesting that bacterial reservoirs within the bladder contribute to the incidence of recurrent UTIs.

The role of urease in the acid stress response and fimbriae expression in Klebsiella pneumoniae CG43.

Two urease operons were identified in Klebsiella pneumoniae CG43, ure-1 and ure-2. This study investigates whether a differential regulation of the expression of ure-1 and ure-2 exists and how urease activity influences the acid stress response and expression of type 1 and type 3 fimbriae. The ureA1 and ureA2 gene specific deletion mutants were constructed. Promoter activity was assessed using a LacZ reporter system. The sensitivity to acid stress was determined by assessing the survival after pH 2.5 treatment. The influence on type 1 and type 3 fimbriae expression was assessed using western blotting and mannose-sensitive yeast agglutination and biofilm formation assay, respectively. Bacterial growth analysis in mM9-U or modified Stuart broth revealed that ure-1 was the principal urease system, and ure-2 had a negative effect on ure-1 activity. Deletion of the fur or nac gene had no apparent effect on the activity of Pure1, Pure2-1, and Pure2-2. The Pure2-2 activity was enhanced by deletion of the hns gene. ureA1 deletion increased acid stress sensitivity, whereas the deleting effect of ureA2 was notable without hns. Deletion of ureA1 or ureA2 significantly induced the expression of type 1 fimbriae but decreased MrkA production and biofilm formation. ure-1 is the primary expression system in K. pneumoniae CG43, while ure-2 is active in the absence of hns. Impairment of urease activity increases the sensitivity to acid stress, and the accumulation of urea induces the expression of type 1 fimbriae but represses type 3 fimbriae expression.

Microbial biofilms in oenology

Biofilms are sessile microbial communities whose lifestyle confers specific properties. In recent years, they have attracted great interest in many research fields. Biofilms are indeed the cause of recurrent industrial problems, while microbial contaminations can finally impact the quality of a finished product or human health. However, these same properties can be interesting for several applications. Oenology is no exception, whether for potential damages to wine quality caused by biofilms or their beneficial effects through winemaking steps, from grape to bottle. This paper reviews yeast and bacterial biofilms in oenology, their nature, their negative effects, as well as the applications linked to their presence in wine and the mechanisms involved in their formation.

Arginine inhibits Saccharomyces cerevisiae biofilm formation by inducing endocytosis of the arginine transporter Can1.

Biofilms are formed by the aggregation of microorganisms into multicellular structures that adhere to surfaces. Biofilm formation by yeast is a critical issue in clinical and industrial fields because of the strong adhesion of yeast biofilm to abiotic surfaces and tissues. Here, we clarified the arginine-mediated inhibition of biofilm formation by yeast. First, we showed that arginine inhibits biofilm formation in fungi such as Saccharomyces cerevisiae, Candida glabrata, and Cladosporium cladosporioides, but not in bacteria. In regard to the underlying mechanism, biochemical analysis indicated that arginine inhibits biofilm formation by suppressing Flo11-dependent flocculation. Intriguingly, a strain with deletion of the arginine transporter-encoding CAN1 was insensitive to arginine-mediated inhibition of biofilm formation. Finally, Can1 endocytosis appeared to be required for the inhibitory mechanism of biofilm formation by arginine. The present results could help to elucidate the molecular mechanism of yeast biofilm formation and its control.

Efficacy assessment of different time cycles of nebulized hydrogen peroxide against bacterial and yeast biofilms

The prevention of healthcare-associated infections requires continuous effort. In order to achieve better practical results, the control of environmental microbial biofilms with effective disinfection strategies should be addressed. To test the efficacy of different time cycles of nebulized hydrogen peroxide (H2O2) against bacterial and yeast dry biofilms. The efficacies of a standard cycle (SC) and a fast cycle (FC) of nebulized H2O2 were compared. Microbial biofilms were grown on different material coupons. The metabolic activity of biofilms was determined by XTT assay, and the total biomass of biofilms was determined by crystal violet assay. Regarding the efficacy of nebulized H2O2 against biofilms, the mean reduction in metabolic activity for the SC was 55.2% [standard deviation (SD) 19.4%], compared with 50.4% (SD 17.7%) for the FC. The mean reduction in total biomass for the SC was 45.5% (SD 22.7%), compared with 46.7% (SD 21.7%) for the FC. No significant differences were found between the tested cycles and materials. H2O2 nebulization was found to exhibit good efficacy against healthcare-associated microbial dry biofilms. Moreover, similar efficacies were found between the SC and the FC.

Medium-chain fatty acids production from carbohydrates-rich wastewater through two-stage yeast biofilm processes without external electron donor addition: Biofilm development and pH impact

The production of medium-chain fatty acids (MCFAs) is considered promising for carbon resource recovery from waste streams. However, a large quantity of external electron donors are often required, causing great cost and environmental impact. Therefore, in this study, a two-stage technology was developed to produce MCFAs from carbohydrate-rich wastewater without external electron donor addition, with the biofilm development and pH impact being explored. Stage I aimed at converting organics into ethanol and a yeast biofilm reactor is innovatively applied. The results showed that the yeast biofilm could quickly form on carriers with steady-state thickness reaching 50–200 μm. However, the attachment of yeast biofilm was weak at the initial stage so that the violent turbulence should be avoided during operation. The polyurethane foam was the most suitable for yeast biofilm development among the tested carriers, as evidenced by the highest ethanol production, accounting for 74.2% of soluble organics. The Nakaseomyces was the main fungal genus in the steady-state biofilm, while lactic acid bacteria were also developed, resulting in lactate and acetate production. In Stage II, the yeast biofilm reactor effluent was applied for MCFA production at different pH (5–8). However, the MCFA production selectivity was significantly affected by pH, with 65.2% at pH of 5 but decreasing substantially to 3.0% at pH of 8. Both the microbial and electron transfer efficiency analysis suggested that mildly acidic pH can promote the electron transfer from ethanol toward the chain elongation process instead of its excessive oxidation. Thus, if conditions of online extraction or microbial tolerance permit, a lower pH should be recommended for Stage II in the developed technology as well as other ethanol-based MCFA production process. This is a conceptual study that eliminated external electron donor addition in MCFAs production and provide a sustainable and reliable way in carbon resources recovery.