Riboflavin (vitamin B) is an essential nutrient for humans and animals that must be obtained from the diet. To ensure an optimal supply, riboflavin is used on a large scale as additive in the food and feed industries. Here, we describe a historical overview of the industrial process of riboflavin production starting from its discovery and the need to produce the vitamin in bulk at prices that would allow for their use in human and animal nutrition. Riboflavin was produced industrially by chemical synthesis for many decades. At present, the development of economical and eco-efficient fermentation processes, which are mainly based on Bacillus subtilis and Ashbya gossypii strains, has replaced the synthetic process at industrial scale. A detailed account is given of the development of the riboflavin overproducer strains as well as future prospects for its improvement.

Background Ashbya gossypii is a filamentous fungus that is currently exploited for the industrial production of riboflavin. The utilization of A. gossypii as a microbial biocatalyst is further supported by its ability to grow in low-cost feedstocks, inexpensive downstream processing and the availability of an ease to use molecular toolbox for genetic and genomic modifications. Consequently, A. gossypii has been also introduced as an ideal biotechnological chassis for the production of inosine, folic acid, and microbial oils. However, A. gossypii cannot use xylose, the most common pentose in hydrolysates of plant biomass.ResultsIn this work, we aimed at designing A. gossypii strains able to utilize xylose as the carbon source for the production of biolipids. An endogenous xylose utilization pathway was identified and overexpressed, resulting in an A. gossypii xylose-metabolizing strain showing prominent conversion rates of xylose to xylitol (up to 97% after 48 h). In addition, metabolic flux channeling from xylulose-5-phosphate to acetyl-CoA, using aheterologous phosphoketolase pathway, increased the lipid content in the xylose-metabolizing strain a 54% over the parental strain growing in glucose-based media. This increase raised to 69% when lipid accumulation was further boosted by blocking the beta-oxidation pathway.Conclusions Ashbya gossypii has been engineered for the utilization of xylose. We present here a proof-of-concept study for the production of microbial oils from xylose in A. gossypii, thus introducing a novel biocatalyst with very promising properties in developing consolidated bioprocessing to produce fine chemicals and biofuels from xylose-rich hydrolysates of plant biomass.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0685-9) contains supplementary material, which is available to authorized users.

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Recycling of poly­(ethylene terephthalate) (PET) wastes has become an urgent need since huge amounts of this plastic are accumulated in the environment. Unlike other chemical recycling methods, depolymerization of PET with supercritical ethanol is based on the use of a nontoxic green solvent. However, the viability of ethanolysis further depends on finding mild pressure and temperature conditions that do not interfere with the degradation efficiency. This challenge was faced in this study by performing ethanolysis of PET under unexplored pressure, temperature, reaction time, and weight ratio PET to ethanol (% wt) conditions. The variation of ethanolysis conditions revealed that besides the expected diethyl terephthalate (DET) and ethylene glycol (EG), other degradation products were also obtained, such as terephthalic acid (TPA). The exploration of the pathways involved allowed directing the process toward different degradation monomers by changing ethanolysis conditions. Long supercritical treatments completely degraded PET and essentially led to the formation of DET and EG since the primarily formed TPA reacted with ethanol under these conditions to produce further DET. Subcritical pressures and temperatures, short reaction times, and high % wt did not always result in complete degradation of PET but increased TPA formation, the main monomer regarded as the building block for PET repolymerization.

Summary Ashbya gossypii is a filamentous fungus that naturally overproduces riboflavin, and it is currently exploited for the industrial production of this vitamin. The utilization of A. gossypii for biotechnological applications presents important advantages such as the utilization of low‐cost culture media, inexpensive downstream processing and a wide range of molecular tools for genetic manipulation, thus making A. gossypii a valuable biotechnological chassis for metabolic engineering. A. gossypii has been shown to accumulate high levels of lipids in oil‐based culture media; however, the lipid biosynthesis capacity is rather limited when grown in sugar‐based culture media. In this study, by altering the fatty acyl‐CoA pool and manipulating the regulation of the main ∆9 desaturase gene, we have obtained A. gossypii strains with significantly increased (up to fourfold) de novo lipid biosynthesis using glucose as the only carbon source in the fermentation broth. Moreover, these strains were efficient biocatalysts for the conversion of carbohydrates from sugarcane molasses to biolipids, able to accumulate lipids up to 25% of its cell dry weight. Our results represent a proof of principle showing the promising potential of A. gossypii as a competitive microorganism for industrial biolipid production using cost‐effective feed stocks.