Creating Surface Properties Using a Palette of Hydrophobins

Renewable mycelium based composite - sustainable approach for lignocellulose waste recovery and alternative to synthetic materials - a review

The agricultural waste with lignocellulose origin is considered to be one of the major environmental pollutants which, because of their high nutritional value, represent an extremely rich resource with significant potential for the production of value added bio-products. This review discusses the applications of higher fungi to upcycle abundant agricultural by-products into more sustainable materials and to promote the transition to a circular economy. It focuses on the main factors influencing the properties and application of mycelium composites - the feedstock, the basidiomycete species and their interaction with the feedstock. During controlled solid state cultivation on various lignocellulose substrates, the basidiomycetes of class Agaricomycetes colonize their surfaces and form a three-dimensional mycelium net. Fungal mycelium secretes enzymes that break down lignocellulose over time and are partially replaced by mycelium. The mycelium adheres to the residual undegraded substrates resulting in the formation of a high-mechanical-strength bio-material called a mycelium based bio-composite. The mycelium based bio-composites are completely natural, biodegradable and can be composted after their cycle of use is completed. The physicochemical, mechanical, and thermodynamic characteristics of mycelium based bio-composites are competitive with those of synthetic polymers and allow them to be successfully used in the construction, architecture, and other industries.

Occurrence of filamentous fungi in drinking water: their role on fungal-bacterial biofilm formation

Water is indispensable to life and safe and accessible supply must be available to all. The presence of microorganisms is a threat to this commitment. Biofilms are the main reservoir of microorganisms inside water distribution systems and they are extremely ecologically diverse. Filamentous fungi and bacteria can coexist inside these systems forming inter-kingdom biofilms. This review has the goal of summarizing the most relevant and recent reports on the occurrence of filamentous fungi in water distribution systems along with the current knowledge and gaps about filamentous fungal biofilm formation. Special focus is given on fungal-bacterial interactions in water biofilms.

Putative hydrophobins of black poplar mushroom (Agrocybe cylindracea)

Hydrophobin proteins were extracted from Agrocybe cylindracea mycelia, the culture media (potato dextrose broth, PDB), and fruiting bodies. The putative hydrophobins obtained showed approximate sizes ranging from 8.0 to 25.0 kDa, dependent on their source. Multiple hydrophobin protein bands were detected in fruiting bodies. The hydrophobin yielded from aerial mycelia, or fruiting bodies, was approximately 6 mg/g dried weight. The crude extracts were examined for their properties in regards to surface modification, emulsification, and surface activity. Coating of hydrophobic Teflon sheet with crude extract made the surface significantly hydrophilic, whereas exposure of glass surfaces to extracts resulted in enhanced hydrophobicity. Crude extracts from culture media of A. cylindracea displayed emulsifying activity when mixed with hexane and could significantly reduce the surface tension of 60% ethanol and deionised water. The putative hydrophobin protein band from culture media (9.6 kDa), as analysed using LC-MS/MS, contained an amino acid fragment structurally similar to class I hydrophobin proteins from Basidiomycetes.

Development of anti-bacterial surfaces using a hydrophobin chimeric protein

The search for new approaches for developing antimicrobial surfaces is a challenge of great urgency to prevent and control microbial growth on surfaces. The strategy herein proposed relies on the design of a new, simple and general tool for creating antimicrobial surfaces, based on a hydrophobin chimeric protein which fuses the adhesive self-assembling class I hydrophobin Vmh2 from Pleurotus ostreatus to the human antimicrobial peptide LL-37. The recombinant LL37-Vmh2 protein displayed both the adhesive and the antimicrobic properties of its members, and when deposited on polystyrene surface, a positive effect due to the fusion was observed in terms of both efficacy and versatility of the coating. Indeed, the chimeric protein significantly enlarges the range of pathogens affected by Vmh2 layer rendering it able to inhibit three Gram-positive and two Gram-negative pathogens, selected among the renowned biofilm producer bacteria. Confocal Laser Scanning Microscopy analysis performed on Staphylococcus epidermidis biofilms formed on coated surfaces proved that, besides inhibiting biofilm formation, the LL37-Vmh2 coating also displayed biocidal activity, since dead cells were present in the biofilm layer. The reported results open new perspectives in various fields of application of LL37, and of antimicrobial peptides in general. LL37-Vmh2 increases the inventory of chimeric hydrophobins, further proving their effectiveness and versatility in surface functionalization.

From Graphite to Laccase Biofunctionalized Few-Layer Graphene: A "One Pot" Approach Using a Chimeric Enzyme

A chimeric enzyme based on the genetic fusion of a laccase with a hydrophobin domain was employed to functionalize few-layer graphene, previously exfoliated from graphite in the presence of the hydrophobin. The as-produced, biofunctionalized few-layer graphene was characterized by electrochemistry and Raman spectroscopy, and finally employed in the biosensing of phenols such as catechol and dopamine. This strategy paves the way for the functionalization of nanomaterials by hydrophobin domains of chimeric enzymes and their use in a variety of electrochemical applications.

Adhesion of filamentous fungi isolated from drinking water under different process conditions

Filamentous fungi (ff) are consistently recognized as drinking water (DW) inhabitants, typically harboured in biofilms. Their sessile behaviour is still poorly understood. This study aimed the evaluation of the influence of several abiotic factors (substratum, hydrodynamic conditions and nutrient availability) on biofilm formation by Penicillium brevicompactum and P. expansum isolated from DW. Fungal adhesion was quantified on high density polyethylene (HDPE) and polyvinyl chloride (PVC) surfaces using synthetic tap water (STW) and R2A broth, under stagnant or agitated (25 and 150 rpm) conditions. Fungal spore numbers were assessed after staining with Calcofluor White MR2 and epifluorescence microscopy. The surface charge and physicochemical properties of spores were characterized for a mechanistic understanding on the adhesion process. The adhesion kinetics of spores was represented accurately by the Logistic model, in which adhesion increased with time until a maximum level attained before spore germination (8 h after incubation). In general, P. brevicompactum demonstrated to adhere in a higher extent than P. expansum (12 × 10⁴ spores/cm²vs 1.7 × 10⁴ spores/cm²). Moreover, fungal adhesion was potentiated under stagnation and using R2A broth. HDPE and PVC allowed spore adhesion at similar extents. Adhesion predictions based on the extended Derjaguin, Landau, Verwey and Overbeek (XDLVO) theory corroborated the experimental results, highlighting the role of physicochemical surface properties on the adhesion of spores. These results allowed to refine a model for ff biofilm formation. The overall results help to understand key aspects determining the presence of P. brevicompactum and P. expansum biofilms in DW, where stagnant conditions and the presence of nutrients should be avoided to prevent ff biofilm formation.

Development of a biosensing platform based on a laccase-hydrophobin chimera

A simple and stable immobilization of a laccase from Pleurotus ostreatus was obtained through genetic fusion with a self-assembling and adhesive class I hydrophobin. The chimera protein was expressed in Pichia pastoris and secreted into the culture medium. The crude culture supernatant was directly used for coatings of polystyrene multi-well plates without additional treatments, a procedure that resulted in a less time-consuming and chemicals reduction. Furthermore, the gene fusion yielded a positive effect with respect to the wild-type recombinant enzyme in terms of both immobilization and stability. The multi-well plate with the immobilized chimera was used to develop an optical biosensor to monitor two phenolic compounds: L-DOPA ((S)-2-amino-3-(3,4-dihydroxyphenyl) propanoic acid) and caffeic acid (3-(3,4-dihydroxyphenyl)-2-propenoic acid); the estimation of which is a matter of interest in the pharmaceutics and food field. The method was based on the use of the analytes as competing inhibitors of the laccase-mediated ABTS oxidation. The main advantages of the developed biosensor are the ease of preparation, the use of small sample volumes, and the simultaneous analysis of multiple samples on a single platform.

Physico-Mechanical and Thermodynamic Properties of Mycelium-Based Biocomposites: A Review

Reducing the use of non-renewable resources is a key strategy of a circular economy. Mycelium-based foams and sandwich composites are an emerging category of biocomposites relying on the valorization of lignocellulosic wastes and the natural growth of the living fungal organism. While growing, the fungus cements the substrate, which is partially replaced by the tenacious biomass of the fungus itself. The final product can be shaped to produce insulating panels, packaging materials, bricks or new-design objects. Only a few pioneer companies in the world retain a significant know-how, as well as the ability to provide the material characterization. Moreover, several technical details are not revealed due to industrial secrecy. According to the available literature, mycelium-based biocomposites show low density and good insulation properties, both related to acoustic and thermal aspects. Mechanical properties are apparently inferior in comparison to expanded polystyrene (EPS), which is the major synthetic competitor. Nevertheless, mycelium-based composites can display an enormous variability on the basis of: fungal species and strain; substrate composition and structure; and incubation conditions. The aim of the present review is to summarize technical aspects and properties of mycelium-based biocomposites focusing on both actual applications and future perspectives.

Engineered Fusion Proteins for Efficient Protein Secretion and Purification of a Human Growth Factor from the Green Microalga Chlamydomonas reinhardtii

Light-driven recombinant protein (RP) production in eukaryotic microalgae offers a sustainable alternative to other established cell-culture systems. RP production via secretion into the culture medium enables simple product separation from the cells adding a layer of process value in addition to the algal biomass, which can be separately harvested. For the model microalga Chlamydomonas reinhardtii, a broad range of molecular tools have been established to enable heterologous gene expression; however, low RP production levels and unreliable purification from secretion concepts have been reported. Domesticated C. reinhardtii strains used for genetic engineering are often cell-wall deficient. These strains nevertheless secrete cell-wall components such as insoluble (hydroxy)proline-rich glycoproteins into the culture media, which hinder downstream purification processes. Here, we attempted to overcome limitations in secretion titers and improve protein purification by combining fusion partners that enhance RP secretion and enable alternative aqueous two-phase (ATPS) RP extraction from the culture medium. Protein fusions were strategically designed to contain a stably folded peptide, which enhanced secretion capacities and gave insights into (some) regulatory mechanisms responsible for this process in the algal host. The elevated protein titers mediated by this fusion were then successfully applied in combination with a fungal hydrophobin tag, which enabled protein purification from the complex microalgal extracellular environment by ATPS, to yield functional recombinant human epidermal growth factor (hEGF) from the algal host.

Pichia pastoris is a Suitable Host for the Heterologous Expression of Predicted Class I and Class II Hydrophobins for Discovery, Study, and Application in Biotechnology

The heterologous expression of proteins is often a crucial first step in not only investigating their function, but also in their industrial application. The functional assembly and aggregation of hydrophobins offers intriguing biotechnological applications from surface modification to drug delivery, yet make developing systems for their heterologous expression challenging. In this article, we describe the development of Pichia pastoris KM71H strains capable of solubly producing the full set of predicted Cordyceps militaris hydrophobins CMil1 (Class IA), CMil2 (Class II), and CMil3 (IM) at mg/L yields with the use of 6His-tags not only for purification but for their detection. This result further demonstrates the feasibility of using P. pastoris as a host organism for the production of hydrophobins from all Ascomycota Class I subdivisions (a classification our previous work defined) as well as Class II. We highlight the specific challenges related to the production of hydrophobins, notably the challenge in detecting the protein that will be described, in particular during the screening of transformants. Together with the literature, our results continue to show that P. pastoris is a suitable host for the soluble heterologous expression of hydrophobins with a wide range of properties.

The Physiological and Pathological Implications of the Formation of Hydrogels, with a Specific Focus on Amyloid Polypeptides

Hydrogels are water-swollen and viscoelastic three-dimensional cross-linked polymeric network originating from monomer polymerisation. Hydrogel-forming polypeptides are widely found in nature and, at a cellular and organismal level, they provide a wide range of functions for the organism making them. Amyloid structures, arising from polypeptide aggregation, can be damaging or beneficial to different types of organisms. Although the best-known amyloids are those associated with human pathologies, this underlying structure is commonly used by higher eukaryotes to maintain normal cellular activities, and also by microbial communities to promote their survival and growth. Amyloidogenesis occurs by nucleation-dependent polymerisation, which includes several species (monomers, nuclei, oligomers, and fibrils). Oligomers of pathological amyloids are considered the toxic species through cellular membrane perturbation, with the fibrils thought to represent a protective sink for toxic species. However, both functional and disease-associated amyloids use fibril cross-linking to form hydrogels. The properties of amyloid hydrogels can be exploited by organisms to fulfil specific physiological functions. Non-physiological hydrogelation by pathological amyloids may provide additional toxic mechanism(s), outside of membrane toxicity by oligomers, such as physical changes to the intracellular and extracellular environments, with wide-spread consequences for many structural and dynamic processes, and overall effects on cell survival.

Applications of Functional Amyloids from Fungi: Surface Modification by Class I Hydrophobins

Class I hydrophobins produced from fungi are amongst the first proteins recognized as functional amyloids. They are amphiphilic proteins involved in the formation of aerial structures such as spores or fruiting bodies. They form chemically robust layers which can only be dissolved in strong acids. These layers adhere to different surfaces, changing their wettability, and allow the binding of other proteins. Herein, the modification of diverse types of surfaces with Class I hydrophobins is reported, highlighting the applications of the coated surfaces. Indeed, these coatings can be exploited in several fields, spanning from biomedical to industrial applications, which include biosensing and textile manufacturing.

Recent Advances in Fungal Hydrophobin Towards Using in Industry

Fungal hydrophobin is a family of low molecular weight proteins consisting of four disulfide bridges and an extraordinary hydrophobic patch. The hydrophobic patch of hydrophobins and the molecules of gaseous CO2 may interact together and form the stable CO2-nanobubbles covered by an elastic membrane in carbonated beverages. The nanobubbles provide the required energy to provoke primary gushing. Due to the hydrophobicity of hydrophobin, this protein is used as a biosurfactant, foaming agent or encapsulating agent in food products and medicine formulations. Increasing demands for using of hydrophobins led to a challenge regarding production and purification of this product. However, the main issue to use hydrophobin in the industry is the regulatory affairs: yet there is no approved legislation for using hydrophobin in food and beverages. To comply with the legislation, establishing a consistent method for obtaining pure hydrophobins is necessary. Currently, few research teams in Europe are focusing on different aspects of hydrophobins. In this paper, an up-to-date collection of highlights from those special groups about the bio-chemical and physicochemical characteristics of hydrophobins have been studied. The recent advances of those groups concerning the production and purification, positive applications and negative function of hydrophobin are also summarised.

Hydrophobin-Based Surface Engineering for Sensitive and Robust Quantification of Yeast Pheromones

Detection and quantification of small peptides, such as yeast pheromones, are often challenging. We developed a highly sensitive and robust affinity-assay for the quantification of the α-factor pheromone of Saccharomyces cerevisiae based on recombinant hydrophobins. These small, amphipathic proteins self-assemble into highly stable monolayers at hydrophilic-hydrophobic interfaces. Upon functionalization of solid supports with a combination of hydrophobins either lacking or exposing the α-factor, pheromone-specific antibodies were bound to the surface. Increasing concentrations of the pheromone competitively detached the antibodies, thus allowing for quantification of the pheromone. By adjusting the percentage of pheromone-exposing hydrophobins, the sensitivity of the assay could be precisely predefined. The assay proved to be highly robust against changes in sample matrix composition. Due to the high stability of hydrophobin layers, the functionalized surfaces could be repeatedly used without affecting the sensitivity. Furthermore, by using an inverse setup, the sensitivity was increased by three orders of magnitude, yielding a novel kind of biosensor for the yeast pheromone with the lowest limit of detection reported so far. This assay was applied to study the pheromone secretion of diverse yeast strains including a whole-cell biosensor strain of Schizosaccharomyces pombe modulating α-factor secretion in response to an environmental signal.

Mechanism of Nonpolar Model Substances to Inhibit Primary Gushing Induced by Hydrophobin HFBI

In this work, the interactions of a well-studied hydrophobin with different types of nonpolar model substances and their impact on primary gushing is evaluated. The nature, length, and degree of saturation of nonpolar molecules are key parameters defining the gushing ability or inhibition. When mixed with hydrophobins, the nonpolar molecule-hydrophobin assembly acts as a less gushing or no gushing system. This effect can be explained in the framework of a competition effect between non-polar systems and CO2 to interact with the hydrophobic patch of the hydrophobin. Interactions of these molecules with hydrophobins are promoted as a result of the similar size of the nonpolar molecules with the hydrophobic patch of the protein, at the expense of the formation of nanobubbles with CO2. In order to prove the presence of interactions and to unravel the mechanisms behind them, a complete set of experimental techniques was used. Surface sensitive techniques clearly show the presence of the interactions, whose nature is not covalent nor hydrogen bonding according to infrared spectroscopy results. Interactions were also reflected by particle size analysis in which mixtures of particles displayed larger size than their pure component counterparts. Upon mixing with nonpolar molecules, the gushing ability of the protein is significantly disrupted.

Applications of hydrophobins: current state and perspectives

Hydrophobins are proteins exclusively produced by filamentous fungi. They self-assemble at hydrophilic-hydrophobic interfaces into an amphipathic film. This protein film renders hydrophobic surfaces of gas bubbles, liquids, or solid materials wettable, while hydrophilic surfaces can be turned hydrophobic. These properties, among others, make hydrophobins of interest for medical and technical applications. For instance, hydrophobins can be used to disperse hydrophobic materials; to stabilize foam in food products; and to immobilize enzymes, peptides, antibodies, cells, and anorganic molecules on surfaces. At the same time, they may be used to prevent binding of molecules. Furthermore, hydrophobins have therapeutic value as immunomodulators and can been used to produce recombinant proteins.

Hydrophobins as aqueous lubricant additive for a soft sliding contact

Two type II fungal hydrophobins, HFBI and FpHYD5, have been studied as aqueous lubricant additive at a nonpolar, compliant sliding contact (self-mated poly(dimethylsiloxane) (PDMS) contact) at two different concentrations, 0.1 mg/mL and 1.0 mg/mL. The two hydrophobins are featured as non-glycosylated (HFBI, m.w. ca. 7 kDa) vs glycosylated (FpHYD5, m.w. ca. 10 kDa) proteins. Far UV CD spectra of the two hydrophobins were very similar, suggesting overall structural similarity, but showed a noticeable difference according to the concentration. This is proposed to be related to the formation of multimers at 1.0 mg/mL. Despite 10-fold difference in the bulk concentration, the adsorbed masses of the hydrophobins onto PDMS surface obtained from the two solutions (0.1 and 1.0 mg/mL) were nearly identical, suggesting that a monolayer of the hydrophobins are formed from 0.1 mg/mL solution. PDMS-PDMS sliding interface was effectively lubricated by the hydrophobin solutions, and showed a reduction in the coefficient of friction by as much as ca. two orders of magnitude. Higher concentration solution (1.0 mg/mL) provided a superior lubrication, particularly in low-speed regime, where boundary lubrication characteristic is dominant via 'self-healing' mechanism. FpHYD5 revealed a better lubrication than HFBI presumably due to the presence of glycans and improved hydration of the sliding interface. Two type II hydrophobins function more favorably compared to a synthetic amphiphilic copolymer, PEO-PPO-PEO, with a similar molecular weight. This is ascribed to higher amount of adsorption of the hydrophobins to hydrophobic surfaces from aqueous solution.

The functional role of Cys3-Cys4 loop in hydrophobin HGFI

Hydrophobins are a large group of low-molecular weight proteins. These proteins are highly surface-active and can form amphipathic membranes by self-assembling at hydrophobic-hydrophilic interfaces. Based on physical properties and hydropathy profiles, hydrophobins are divided into two classes. Upon the analysis of amino acid sequences and higher structures, some models suggest that the Cys3-Cys4 loop regions in class I and II hydrophobins can exhibit remarkable difference in their alignment and conformation, and have a critical role in the rodlets structure formation. To examine the requirement for the Cys3-Cys4 loop in class I hydrophobins, we used protein fusion technology to obtain a mutant protein HGFI-AR by replacing the amino acids between Cys3 and Cys4 of the class I hydrophobin HGFI from Grifola frondosa with those ones between Cys3 and Cys4 of the class II hydrophobin HFBI from Trichoderma reesei. The gene of the mutant protein HGFI-AR was successfully expressed in Pichia pastoris. Water contact angle (WCA) and X-ray photoelectron spectroscopy (XPS) measurements demonstrated that the purified HGFI-AR could form amphipathic membranes by self-assembling at mica and hydrophobic polystyrene surfaces. This property enabled them to alter the surface wettabilities of polystyrene and mica and change the elemental composition of siliconized glass. In comparison to recombinant class I hydrophobin HGFI (rHGFI), the membranes formed on hydrophobic surfaces by HGFI-AR were not robust enough to resist 1 % hot SDS washing. Atomic force microscopy (AFM) measurements indicated that unlike rHGFI, no rodlet structure was observed on the mutant protein HGFI-AR coated mica surface. In addition, when compared to rHGFI, no secondary structural change was detected by Circular Dichroism (CD) spectroscopy after HGFI-AR self-assembled at the water-air interface. HGFI-AR could not either be deemed responsible for the fluorescence intensity increase of Thioflavin T (THT) and the Congo Red (CR) absorption spectra shift (after the THT(CR)/HGFI-AR mixed aqueous solution was drastically vortexed). Remarkably, replacement of the Cys3-Cys4 loop could impair the rodlet formation of the class I hydrophobin HGFI. So, it could be speculated that the Cys3-Cys4 loop plays an important role in conformation and functionality, when the class I hydrophobin HGFI self-assembles at hydrophobic-hydrophilic interfaces.

Functional analysis of hydrophobin genes in sexual development of Botrytis cinerea

Hydrophobins are small secreted fungal proteins that play roles in growth and development of filamentous fungi, i.e. in the formation of aerial structures and the attachment of hyphae to hydrophobic surfaces. In Botrytis cinerea, three hydrophobin genes have been identified. Studies by Mosbach et al. (2011) showed that hydrophobins are neither involved in conferring surface hydrophobicity to conidia and aerial hyphae of B. cinerea, nor are they required for virulence. The present study investigated the role of hydrophobins in sclerotium and apothecium development. Expression analysis revealed high expression of the Bhp1 gene during different stages of apothecium development. Two Bhp1 splice variants were detected that differ by an internal stretch of 13 amino acid residues. Seven different mutants in which either a single, two or three hydrophobin genes were knocked out, as well as two wild type strains of opposite mating types, were characterized for sclerotium and apothecium development. No aberrant morphology was observed in sclerotium development when single deletion mutants in hydrophobin genes were analyzed. Sclerotia of double knock out mutant ΔBhp1/ΔBhp3 and the triple knock out mutant, however, showed easily wettable phenotypes. For analyzing apothecium development, a reciprocal crossing scheme was setup. Morphological aberrations were observed in crosses with two hydrophobin mutants. When the double knock out mutant ΔBhp1/ΔBhp2 and the triple knock out mutant were used as the maternal parent (sclerotia), and fertilized with wild type microconidia, the resulting apothecia were swollen, dark brown in color and had a blotched surface. After initially growing upwards toward the light source, the apothecia in many cases collapsed due to loss of structural integrity. Aberrant apothecium development was not observed in the reciprocal cross, when these same mutants were used as the paternal parent (microconidia). These results indicate that the presence of hydrophobins in maternal tissue is important for normal development of apothecia of B. cinerea.

Emulsions with unique properties from proteins as emulsifiers

Many proteins are surface active molecules and form stable emulsions. In these emulsions, the protein covered oil droplets behave as sticky droplets even when they are ionically charged. As a result of the stickiness of the droplets the emulsions have gel-like properties. The stickiness is due to the multipolar nature of the proteins in contrast to the bipolar nature of surfactants or other amphiphilic compounds that form emulsions with repulsive droplets. Stable emulsions are also formed from particles like clays to which proteins are adsorbed. These hybrid compounds form even more stable emulsions with stronger elastic properties than clays and proteins on their own. These so called pickering emulsions have paste-like properties and do not flow. The scaffolding network of the crosslinked protein bilayers on the droplets is so strong that both the water and the oil can be removed from the emulsions by freeze drying without collapse of the scaffold. The resulting sponge can be used again for the uptake of both water and oil. Emulsions which are prepared from different proteins differ mainly in their elastic properties.

PfaH2: a novel hydrophobin from the ascomycete Paecilomyces farinosus

The pfah2 gene coding for a novel hydrophobin PfaH2 from the ascomycete Paecilomyces farinosus was identified during sequencing of random clones from a cDNA library. The corresponding protein sequence of PfaH2 deduced from the cDNA comprised 134 amino acids (aa). A 16 aa signal sequence preceded the N-terminus of the mature protein. PfaH2 belonged to the class Ia hydrophobins. The protein was isolated using trifluoroacetic acid extraction and purified via SDS-PAGE and high-performance liquid chromatography. The surface activity of the recently described PfaH1 and of PfaH2 was compared by the determination of contact angles (CAs) on glass slides and Teflon tape, and the CA of distilled water droplets was measured on glass slides coated with hydrophobin PfaH1 or PfaH2. Surprisingly, both hydrophobins adsorbed to hydrophilic surfaces and changed their physicochemical properties to a similar quantitative extent, although little aa sequence homology was found.

The antitumor activity of hydrophobin SC3, a fungal protein

The use of mushroom extracts has been common practice in traditional medicine for centuries, including the treatment of cancer. Proteins called hydrophobins are very abundant in mushrooms. Here, it was examined whether they have antitumor activity. Hydrophobin SC3 of Schizophyllum commune was injected daily intraperitoneally starting 1 day after tumor induction in two tumor mouse models (sarcoma and melanoma). SC3 reduced the size and weight of the melanoma significantly, but the sarcoma seemed not affected. However, microscopic analysis of the tumors 12 days after induction revealed a strong antitumor effect of SC3 on both tumors. The mitotic activity of the tumor decreased 1.6- (melanoma) to 2.3-fold (sarcoma), while the vital mass decreased 2.3- (melanoma) to 4.3-fold (sarcoma) compared to the control. Treatment did not cause any signs of toxicity. Behavior, animal growth, and weight of organs were similar to animals injected with vehicle, and no histological abnormalities were found in the organs. In vitro cell culture studies revealed no direct cytotoxic effect of SC3 towards sarcoma cells, while cytotoxic activity was observed towards melanoma cells at a high SC3 concentration. Daily treatment with SC3 did not result in detectable levels of anti-SC3 antibodies in the plasma. Instead, a cellular immune response was observed. Incubation of spleen cells with SC3 resulted in a 1.5- to 2.5-fold increase in interleukin-10 and TNF-α mRNA levels. In conclusion, the nontoxic fungal hydrophobin SC3 showed tumor-suppressive activity possibly via immunomodulation and may be of benefit as adjuvant in combination with chemotherapy and radiation.

Hydrophobin Vmh2-glucose complexes self-assemble in nanometric biofilms

Hydrophobins are small proteins secreted by fungi, which self-assemble into amphipathic membranes at air-liquid or liquid-solid interfaces. The physical and chemical properties of some hydrophobins, both in solution and as a biofilm, are affected by poly or oligosaccharides. We have studied the interaction between glucose and the hydrophobin Vmh2 from Pleurotus ostreatus by spectroscopic ellipsometry (SE), atomic force microscopy (AFM) and water contact angle (WCA). We have found that Vmh2-glucose complexes forms a chemically stable biofilm, obtained by drop deposition on silicon, 1.6 nm thick and containing 35 per cent of glucose, quantified by SE. AFM highlighted the presence of nanometric rodlet-like aggregates (average height, width and length being equal to 3.6, 23.8 and 40 nm, respectively) on the biofilm surface, slightly different from those obtained in the absence of glucose (4.11, 23.9 and 64 nm). The wettability of a silicon surface, covered by the organic layer of Vmh2-glucose, strongly changed: WCA decreased from 90° down to 17°.

The impact of recombinant fusion-hydrophobin coated surfaces on E. coli and natural mixed culture biofilm formation

The impact of increased surface hydrophobicity on biofilms regarding retardation, repulsion, or attraction was studied with hydrophobin modified glass substrata. Recombinantly produced fungal hydrophobins forming self-assembled monolayers were used as the surface coating. The adsorption dynamics of hydrophobins were analysed with a quartz crystal microbalance which showed the surface coating to be rapid and stable. The change of surface wettability was determined by water contact angle measurements and demonstrated an increase in hydrophobicity in range of 60-62°. The homogeneity of the monolayers was demonstrated by immunofluorescence microscopy. Atomic force microscopy was applied to visualise the uniform texture of the coated materials. The hydrophobin coatings had no impact on different biofilms in terms of spatial distribution, cell numbers, and population composition. In consequence, hydrophobicity might not represent an important parameter for biofilm formation. Nevertheless, recombinant hydrophobins are suitable for large scale surface modification and functionalization with bioactive molecules.