Pitocchi, Rossana (2024) Discovery and Characterization of New Biosurfactant Proteins for Bioremediation and Biomedical Applications. [Tesi di dottorato]

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Abstract

Proteins are intrinsically amphipathic molecules, even if their amphiphilic nature is affected by several factors such as protein folding or post-translational modifications. Hydrophobins and ceratoplatanins are the most studied surface-active proteins to date. They are both small fungal proteins, with high content of cysteines, that fulfill several functions in fungal life cycle. Hydrophobins are involved in the development of aerial development oh hyphae thanks to their capability to reduce surface tension, while ceratoplatanins can act both as virulence factor and as elicitors, besides possessing the ability to weaken cellulose fibers without enzymatic activity. Fungal biosurfactant proteins are still poorly characterized and exploited as class of biosurfactants. For this reason, one of the purposes of the present PhD project has been the isolation and characterization of new biosurfactant proteins from different fungal strains. The first work was conducted on two Fusarium solani strains isolated from a plastic dumpsite, collected by the Mycoteca Universitatis Taurinensins. From these fungi a protein has been extracted and identified as a new unknown protein, containing a cysteine-rich domain. Its characterization revealed that this protein forms aggregates, endowed with excellent emulsifying abilities. Moreover, other two already known hydrophobic proteins, named Vmh2 and PAC3, extracted from Pleurotus ostreatus and Acremonium sclerotigenum respectively, were herein characterized for the first time in terms of surfactant activities. Although many functional similarities, partial identification of PAC3 excludes that it does belong to the HPBs protein family. In addition, an already known BS protein, in particular the Ceratoplatanin extracted from Trichoderma harzianum, has been exploited for lignocellulosic valorization processes. This protein has proven able to efficiently pre-treat agrifood wastes, increasing the sugar conversion yield achievable after hydrolytic treatment. Another promising application that has been exploited in my PhD work, has regarded the functionalization of two different materials, to impart antimicrobial and antibiofilm properties. Polystyrene and Bacterial cellulose have been successfully functionalized with an engineered protein that fuses the adhesive protein of Vmh2 and the antimicrobial activity of the peptide GKY20. When adhered on cellulose, this protein has proven a good antimicrobial effect against Staphyloccoccus. aureus and S. epidermidis. Results here achieved, indicate that there are other classes of fungal proteins with surfactant abilities; these proteins offer a valid substitute for synthetic surfactants, because of the potential for industrial-scale utilization through genetic engineering.

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