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Hyaluronic acid (HA) is a biopolymer of repeating units of glucuronic acid and N-acetylglucosamine. Its market was valued at USD 8.9 billion in 2019. Traditionally, HA has been obtained from rooster comb-like animal tissues and fermentative cultures of attenuated pathogenic streptococci. Various attempts have been made to engineer a safe micro-organism for HA synthesis; however, the HA titres obtained from these attempts are in general still lower than those achieved by natural, pathogenic producers. In this scenario, ways to increase HA molecule length and titres in already constructed strains are gaining attention in the last years, but no recent publication has reviewed the main genetic strategies applied to improve HA production on heterologous hosts. In light of that, we hereby compile the advances made in the engineering of micro-organisms to improve HA synthesis.

The study of the epigenetic regulation of gene function has reached pivotal importance in life sciences in the last decades. The mechanisms and effects of processes such as DNA methylation, histone posttranslational modifications and non-coding RNAs, as well as their impact on chromatin structure and dynamics, are clearly involved in physiology homeostasis in plants, animals and microorganisms. In the fungal kingdom, studies on the model yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe contributed enormously to the elucidation of the eukaryote epigenetic landscape. Epigenetic regulation plays a central role in the expression of virulence attributes of human pathogens such as Candida albicans. In this article, we review the most recent studies on the effects of drugs capable of altering epigenetic states and on the impact of chromatin structure-related genes deletion in filamentous fungi. Emphasis is given on plant and insect pathogens, endophytes, secondary metabolites and cellulases/xylanases producing species.

The methylotrophic yeast Hansenula polymorpha, known as a non-conventional yeast, is used for the last 30 years for the production of recombinant proteins, including enzymes, vaccines, and biopharmaceuticals. Although a large number of reviews have been published elucidating the applications of this yeast as a cell factory, the latest was released about 10 years ago. Therefore, this review aimed at summarizing available information on the use of H. polymorpha as a host for recombinant protein production in the last decade. Examples of chemicals and virus-like particles produced using this yeast also are discussed. Firstly, the aspects that feature this yeast as a host for recombinant protein production are highlighted including the techniques available for its genetic manipulation as well as strategies for cultivation in bioreactors. Special attention is given to the novel genomic editing tools, mainly CRISPR/Cas9 that was recently established in this yeast. Finally, recent examples of using H. polymorpha as an expression platform are presented and discussed. The production of human Parathyroid Hormone (PTH) and Staphylokinase (SAK) in H. polymorpha are described as case studies for process establishment in this yeast. Altogether, this review is a guideline for this yeast utilization as an expression platform bringing a thorough analysis of the genetic aspects and fermentation protocols used up to date, thus encouraging the production of novel biomolecules in H. polymorpha.

Humicola grisea var. thermoidea (Hgvt) is a thermophilic ascomycete that produces lignocellulolytic enzymes and it is proposed for the conversion of agricultural residues into useful byproducts. Drugs that inhibit the DNA methyltransferases (DNMTs) activity are employed in epigenetic studies but nothing is known about a possible effect on the production of fungal enzymes. We evaluated the effect of 5-aza-2'-deoxycytidine (5-Aza; a chemical inhibitor of DNMTs activity) on the secreted enzyme activity and on the transcription of cellulase and xylanase genes from Hgvt grown in agricultural residues and in glucose. Upon cultivation on wheat bran (WB), the drug provoked an increase in the xylanase activity at 96 h. When Hgvt was grown in glucose (GLU), a repressor of Hgvt glycosyl hydrolase genes, 5-Aza led to increased transcript accumulation for the cellobiohydrolases and for the xyn2 xylanase genes. In WB, 5-Aza enhanced the expression of the transcription factor CreA gene. Growth on WB or GLU, in presence of 5-Aza, led to a significant increase in transcripts of the pH-response regulator PacC gene. To our knowledge, this is the first report on the effect of a DNMT inhibitor in the production of fungal plant cell wall degradation enzymes.