Lactic acid is the monomeric unit of polylactide (PLA), a bioplastic widely used in the packaging, automotive, food, and pharmaceutical industries. Previously, the yeast Komagataella phaffii was genetically modified for the production of lactate from glycerol. For this, the bovine L-lactate dehydrogenase- (LDH)-encoding gene was inserted and the gene encoding the pyruvate decarboxylase (PDC) was disrupted, resulting in the GLp strain. This showed a yield of 67% L-lactic acid and 20% arabitol as a by-product in batches with oxygen limitation. Following up on these results, the present work endeavored to perform a detailed study of the metabolism of this yeast, as well as perturbing arabitol synthesis in an attempt to increase lactic acid titers. The GLp strain was cultivated in a glycerol-limited chemostat at different dilution rates, confirming that the production of both lactic acid and arabitol is dependent on the specific growth rate (and consequently on the concentration of the limiting carbon source) as well as on the oxygen level. Moreover, disruption of the gene encoding arabitol dehydrogenase (ArDH) was carried out, resulting in an increase of 20% in lactic acid and a 50% reduction in arabitol. This study clarifies the underlying metabolic reasons for arabitol formation in K. phaffii and points to ways for improving production of lactic acid using K. phaffii as a biocatalyst.

Environmental pollutants are today a major concern and an intensely discussed topic on the global agenda for sustainable development. They include a wide range of organic compounds, such as pharmaceutical waste, pesticides, plastics, and volatile organic compounds that can be found in air, soil, water bodies, sewage, and industrial wastewater. In addition to impacting fauna, flora, and fungi, skin absorption, inhalation, and ingestion of some pollutants can also negatively affect human health. Fungi play a crucial role in the decomposition and cycle of natural and synthetic substances. They exhibit a variety of growth, metabolic, morphological, and reproductive strategies and can be found in association with animals, plants, algae, and cyanobacteria. There are fungal strains that occur naturally in soil, sediment, and water that have inherent abilities to survive with contaminants, making the organism important for bioassay applications. In this context, we reviewed the applications of fungal-based bioassays as a versatile tool for environmental monitoring.

Production of second-generation ethanol from lignocellulosic residues should be fueling the energy matrix in the near future. Lignocellulosic feedstock has received much attention as an alternative energy resource for biorefineries toward reducing the demand for fossil resources, contributing to a future sustainable bio-based economy. Fermentation of lignocellulosic hydrolysates poses many scientific and technological challenges as the drawback of Saccharomyces cerevisiae’s inability in fermenting pentose sugars (derived from hemicellulose). To overcome the inability of S. cerevisiae to ferment xylose and increase yeast robustness in the presence of inhibitory compound-containing media, the industrial S. cerevisiae strain SA-1 was engineered using CRISPR-Cas9 with the oxidoreductive xylose pathway from Scheffersomyces stipitis (encoded by XYL1, XYL2, and XYL3). The engineered strain was then cultivated in a xylose-limited chemostat under increasing dilution rates (for 64 days) to improve its xylose consumption kinetics under aerobic conditions. The evolved strain (DPY06) and its parental strain (SA-1 XR/XDH) were evaluated under microaerobic in the hemicellulosic hydrolysate. DPY06 exhibited 35% superior volumetric ethanol productivity compared to its parental strain.

Biorefineries require residual biomass as a raw material for their processes.Among all the possible products, 2G ethanol is undoubtedly the most studied and isprobably the most desired in environmental terms. Carbohydrate-rich feedstocks usedin biorefineries are mainly composed of polysaccharides, cellulose and hemicellulose(xylan), which initially require the action of hydrolytic enzymes to release theirconstituent monosaccharides, mostly glucose (from cellulose) and xylose (fromhemicellulose). The conversion of glucose into ethanol is carried out by the yeastSaccharomyces cerevisiae with an efficiency close to the theoretical maximum yield (>90%). Although it is the most widely used yeast in alcoholic fermentation processes, S.cerevisiae cannot metabolize xylose unless it undergoes genetic or evolutionaryengineering. However, in recent decades, wild yeasts with an innate capacity to fermentthis pentose and even hydrolyze the polysaccharides from lignocellulosic biomasseshave been isolated and characterized from natural environments. Facing this duality,we conducted a major literature review and presented the data both in favor ofengineering S. cerevisiae and the prospective use of wild yeasts in this chapter. Toanalyze the strengths of each strategy, this chapter also highlights the applications ofintegrated hydrolysis and fermentation processes and the possibility of simultaneouslygenerating xylitol as the second product in biorefineries.

Background: As global awareness regarding climate change and environmental pollution outcomes arise, eco-friendly and negative emission technologies emerge. Methods: In this scenario, polyhydroxyalkanoate (PHA)-accumulating microorganisms play an important role in the transition from the petrochemical-based non-biodegradable polymer to renewable, eco-friendly, and biocompatible materials. More specifically, CO2 can be converted to biopolymers through photosynthesis by cyanobacteria and algae, posing as a promising technology for renewable material, CO2, and petroleum-dependence mitigations. However, although many microorganisms can accumulate PHA intracellularly, limitations persist, such as the elevated cost and limited market availability. Results: Herein is presented a patent-based mapping on technological trends of PHAs production, including its production by microalgae and cyanobacteria using the Questel Orbit Intelligence software (version 1.9.8) in complement with the Espacenet Patent Search database. Conclusion: The inquiry on PHAs retrieved 34,243 patents filed since 1912, whereas 156 are related to their specific production by photosynthetic microorganisms, evidencing a prospective market for intellectual property.

A bstract: Simultaneous intracellular depolymerization of xylo-oligosaccharides (XOS) and acetate fermentation by engineered Saccharomyces cerevisiae offers an advance towards more cost-effective second-generation (2G) ethanol production. As xylan is one of the most abundant polysaccharides present in lignocellulosic residues, the transport and breakdown of XOS in an intracellular environment might bring a competitive advantage for recombinant strains in competition with contaminating microbes, which are always present in fermentation tanks; furthermore, acetic acid is a ubiquitous toxic component in lignocellulosic hydrolysates, deriving from hemicellulose and lignin breakdown. In the present work, the previously engineered S. cerevisiae strain, SR8A6S3, expressing NADPH-linked xylose reductase (XR), NAD ⁺ -linked xylitol dehydrogenase (XDH) (for xylose assimilation), as well as NADH-linked acetylating acetaldehyde dehydrogenase (AADH) and acetyl-CoA synthetase (ACS) (for an NADH-dependent acetate reduction pathway), was used as the host for expressing of two β-xylosidases, GH43-2 and GH43-7 , and a xylodextrin transporter, CDT-2 , from Neurospora crassa , yielding the engineered strain SR8A6S3-CDT ₂ -GH43 _2/7 . Both β-xylosidases and the transporter were introduced by replacing two endogenous genes, GRE3 and SOR1 , that encode aldose reductase and sorbitol (xylitol) dehydrogenase, respectively, which catalyse steps in xylitol production. Xylitol accumulation during xylose fermentation is a problem for 2G ethanol production since it reduces final ethanol yield. The engineered strain, SR8A6S3-CDT ₂ -GH43 _2/7 , produced ethanol through simultaneous co-utilization of XOS, xylose, and acetate. The mutant strain produced 60% more ethanol and 12% less xylitol than the control strain when a hemicellulosic hydrolysate was used as a mono- and oligosaccharide source. Similarly, the ethanol yield was 84% higher for the engineered strain using hydrolysed xylan compared with the parental strain. The consumption of XOS, xylose, and acetate expands the capabilities of S. cerevisiae for utilization of all of the carbohydrate in lignocellulose, potentially increasing the efficiency of 2G biofuel production. Highlights: Integration of XOS pathway in an acetate-xylose-consuming S. cerevisiae strain; Intracellular fermentation of XOS, acetate and xylose improved ethanol production; Deletion of both sor1 Δ and gre3 Δ reduced xylitol production.