Volkmar Passoth

Throughout evolution, the human brain has continued to develop. The size of the modern brain means it demands a huge amount of energy. Despite this, the human digestive system has become less efficient. As a result, humans need food technology to be able to access the nutrients from raw food materials. Food biotechnology uses the metabolic abilities of organisms, mainly microorganisms, to make these nutrients available.

Nowadays, the food production industry is one of those that uses most fossil resources and releases most greenhouse gases. As the global population grows, so does the need for food and addressing this issue poses several challenges.

To meet the demand for animal products, huge amounts of plant protein are produced for animal feed, and parts of this cultivation take place on former rainforest land. One way to make food production more efficient is to decrease the proportion of animal-derived food consumed. However, plant proteins are often not as easily digested as animal proteins, and plants produce anti-nutrients. Vegetable oil is another important resource that is increasingly used for food and animal feed. It is also used for production of biofuels and chemicals. The consequent demand is connected to deforestation. High levels of food waste also create a significant challenge.

Microorganisms have the potential to modify proteins and make them easier to digest. They can also break down anti-nutrients, thereby preventing negative health effects. Furthermore, microorganisms can be used for biopreservation, thereby decreasing waste, by inhibiting other microbes that are pathogenic or produce toxins, or simply degrade food and animal feed.

In our research, we try to develop production systems where microbial fermentation is used to improve the quality of food and animal feed. One important aim is to understand the physiology of the microorganisms involved so that we can optimise their performance. Microorganisms are incredibly diverse, meaning their metabolism has an extremely broad spectrum of biochemical reactions, and thus can convert unusual compounds into food. For instance, there are over 2000 different known yeast species and only a handful are closely related to baker’s yeast.

For several years, we have been investigating the conversion of inedible plant materials such as straw and wood residues into food. Our main focus is on oleaginous yeasts, which are yeasts that can accumulate up to 80% of their biomass as lipids with a quality similar to vegetable oil. The yeasts we study are able to use sugars and other compounds that are released when straw or wood residues are hydrolysed, enabling them to make wood and straw edible. These yeasts produce other interesting compounds such as carotenoids and biosurfactants (compounds that lower surface tension) that can be used for food production and as chemicals.

Food biotechnology can lead to improvements in other areas of the field. When studying the physiology of oleaginous yeasts, we might even be able to learn something about our own physiology. Fungi are the closest relatives of animals and are important model organisms. So, not only might studying oleaginous yeasts save the rainforest, it might teach us how to treat food-related diseases like obesity.

Oleaginous yeasts for food, feed, biochemicals and biofuels, and as model organisms

Oleaginous yeasts are the most rapid lipid producers among all known organisms and can accumulate up to 80% of their biomass as lipids within a few days. This yeast oil has a similar quality as vegetable oil and can replace it in principle in all potential applications- as food and feed component, or raw material for biodiesel and biochemicals’ production. Many of these yeasts can utilise residues of agriculture or forestry (lignocellulose hydrolysates), crude glycerol (residue from biodiesel production) or organic acids as carbon source.

During the recent years, we have performed successful research on a variety of oleaginous yeasts. We have established methods for cultivation under controlled conditions, to obtain high amounts of lipids from a variety of lignocellulosic hydrolysates and crude glycerol. We have established spectroscopy- based methods for the determination of the intracellular lipid content, as well as methods for the extraction and quantification of carotenoids. We were involved in studies about the production system of yeast lipids- shortening production time, i.e. more rapid lipid production was identified as crucial factor of microbial lipid production, as well as crude glycerol conversion from biodiesel production. A variety of yeast strains has been investigated for rapid lipid production; usually species of Rhodotorula were faster and more efficient than those of Lipomyces. Mixing crude glycerol with hemicellulose hydrolysate had an activating effect on lipid accumulation in Rhodotorula species. We have tested oleaginous yeasts as component in fish feed, replacing vegetable oil, and did not find any negative effects on fish wellbeing, growth and quality. Using long- and short- read sequencing technologies, we could reconstruct the genomes of strains of Rhodotorula toruloides and Rhodotorula babjevae to the chromosomal level, which is the basis to develop those yeasts as microbial cell factories. Known genomes are also crucial to understand physiology and evolution of these yeasts-  to develop them as model eukaryotic cells for for instance diseases related to lipid metabolism, such as obesity and cancer.

Microbial fermentation for improved animal feed and biopreservation

Fermentation can improve the nutritional characteristics of grain, pulse- and even lignocellulose- based feed material. It can also prevent spoilage by undisirable microorganisms. Microfungi can be protein- and lipid sources in fermented food and animal, especially fish feed. We are currently working on the establishment on novel fermented foods based on Faba beans and oat in the frame of a Horizon research program. In previous projects we were analysing the microbial populations in a variety of feed fermentations, and specifically investigated the physiology of the biocontrol yeast Wickerhamomyces anomalus (previous names: Hansenula anomala, Pichia anomala). In our fermentations, we have seen a reduction of the antinutrient phytate, and an inhibition of moulds and Enterobacteriaceae. We have even seen that biopreservation of both cereal grain and wheat straw can increase ethanol production from this material.

Novel ethanol production yeasts

When investigating the microbial population in a Swedish ethanol plant we found that Brettanomyces bruxellensis (synonyme Dekkera bruxellensis) had outcompeted the originally inocculated production organism Saccharomyces cerevisiae. Nevertheless, production was obviously not negatively influenced, B. bruxellensis can thus be seen as production organism. This was in a way challenging the dogma about competitivness of S. cerevisiae in ethanol processes. We are investigating physiology and genome of this yeast, to understand its exceptional stress tolerance.

I was also working on the physiology and genetics of the xylose- fermenting yeast Scheffersomyces stipitis (previous name Pichia stipitis). This yeast has, apart from its exceptional ability to ferment xylose to ethanol, an interesting response to oxygen limitation. We even found that this yeast has some antifungal activity.

Our group runs a variety of national and international collaborations. We belong to the Horizon consortium HealtFerm (https://healthferm.eu/), with 23 partners from whole EU. The program investigates innovative pulse and cereal-based food fermentations together with the health effects and consumer perception of novel fermented foods. We are partners in two NordFors-projects. SAFE (https://www.nordforsk.org/projects/sustainable-aquaculture-feed-based-novel-biomass-wood-products-safe) investigates the potential of oleaginous yeasts and thraustochytrids for developing salmon feed from wood based materials. It involves partners from Norway, Estonia and Sweden. MUSA is a recently funded project on the valorisation of spent mushroom substrate, with partners from Norway, Estonia and several Swedish institutions. We are also active in the COST action Yeast4Bio (https://yeast4bio.eu/)

M.Sc. in biology at Greifswald University (Germany- and the oldest Swedish university during almost 200 years) 1992

PhD in microbiology at Aachen University 1998

Post-doc at Lund University (Group of Prof. Bärbel Hahn-Hägerdal, Marie-Curie Grant) 1998- 2000

Post-doc at Greifswald University (Molecular Biologist in the group "Molecular Cardiology") 2001-2002

Assistant Professor at SLU Uppsala 2002-2005

Associate Professor at SLU Uppsala 2005-2020

Professor for food biotechnology at SLU Uppsala since 2020

• Main supervisor for two active PhD-students: Giselle Martín-Hernandez and Yashaswini Nagavara Nagaraj.
• Co-supervisor for three active PhD-projects: Christian Sigtryggsson, Johanna Östlund, Alejandra Fernandez Castaneda
• Main supervisor of four PhD-students, who obtained their degree:
  Jule Brandenburg (defence 2021)
  Mikołaj Chmielarz (defence 2021)
  Ievgeniia Tiukova (defence 2014)
  Johanna Blomqvist (defence 2011)

Martín-Hernandez GC, Chmielarz M, Müller B, Brandt C, Hölzer M, Viehweger A, Passoth V (2023). Enhanced glycerol assimilation and lipid production in Rhodotorula toruloides CBS14 upon addition of hemicellulose primarily correlates with early transcription of energy-metabolism-related genes. Biotechnol Biofuels Bioprod 16, 42. 10.1186/s13068-023-02294-3

Passoth V, Brandenburg J, Chmielarz M, Martín-Hernandez GC, Nagaraj Y, Müller B, Blomqvist J 2023. Oleaginous yeasts for biochemicals, biofuels and food from lignocellulose-hydrolysate and crude glycerol. Yeast in press. https://doi.org/10.1002/yea.3838

Nagaraj YN, Burkina V, Okmane L, Blomqvist J, Rapoport A, Sandgren M, Pickova J, Sampels S, Passoth V (2022) Identification, quantification and kinetic study of carotenoids and lipids in Rhodotorula toruloides CBS14 cultivated on wheat straw hydrolysate. Fermentation 8, 300. https://doi.org/10.3390/fermentation8070300 

Martín-Hernandez GC, Müller B, Brandt C, Hölzer M, Viehweger A, Passoth V (2022). Near chromosome-level genome assembly and annotation of Rhodotorula babjeveae strains reveals high intraspecific divergence. J Fungi 8, 323. https://doi.org/10.3390/jof8040323

Martín-Hernandez GC, Müller B, Chmielarz M, Brandt C, Hölzer M, Viehweger A, Passoth V (2021). Chromosome-level genome assembly and transcriptome-based annotation of the oleaginous yeast Rhodotorula toruloides CBS 14. Genomics 113, 4022-4026. https://doi.org/10.1016/j.ygeno.2021.10.006

Brandenburg J, Blomqvist J, Shapaval V, Kohler A, Sampels S, Sandgren M, Passoth V (2021) Oleaginous yeasts respond differently to carbon sources present in lignocellulose hydrolysate. Biotechnol Biofuels 14, 124. https://doi.org/10.1186/s13068-021-01974-2 

Chmielarz M, Blomqvist J, Sampels S, Sandgren M, Passoth V (2021) Microbial lipid production from crude glycerol and hemicellulosic hydrolysate with oleaginous yeasts. Biotechnol Biofuels 14, 65. https://doi.org/10.1186/s13068-021-01916-y

Blomqvist J, Pickova J, Tilami SK, Sampels S, Mikkelsen N, Brandenburg J, Sandgren M, Passoth V (2018). Oleaginous yeast as a component in fish feed. Sci Rep. 8, 15945. https://www.nature.com/articles/s41598-018-34232-x

Brandenburg J, Poppele I, Blomqvist J, Puke M, Pickova J, Sandgren M, Rapoport A, Vedernikovs N, Passoth V (2018) Bioethanol and lipid production from the enzymatic hydrolysate of wheat straw after furfural extraction. Appl Microbiol Biotechnol 102, 6269-6277. https://doi.org/10.1007/s00253-018-9081-7

Huyben D, Boqvist S, Passoth V, Renström L, Bengtsson UA, Andréoletti O, Kiessling A, Lundh T, Vågsholm I (2018). Screening of intact yeasts and cell extracts to reduce Scrapie prions during biotransformation of food waste. Acta Vet Scandinavia 60: 9

Karlsson H, Ahlgren S, Sandgren M, Passoth V, Wallberg O, Hansson PA (2017). Greenhouse gas performance of biochemical biodiesel production from straw- soil organic carbon changes and time-dependent climate impact. Biotechnol Biofuels 10, 273

Huyben D, Nyman A, Vidakovic A, Passoth V, Moccia R, Kiessling A, Dicksved J, Lundh T (2017). Effects of dietary inclusion of the yeasts Saccharomyces cerevisiae and Wickerhamomyces anomalus on gut microbiota of rainbow trout. Aquaculture 473, 528-537. doi http://dx.doi.org/10.1016/j.aquaculture.2017.03.024

Katongole CB, Bakeeva A, Passoth V, Lindberg JE (2017). Effect of solid-state fermentation with Arxula adeninivorans or Hypocrea jecorina (anamorph Trichoderma reesei) on hygienic quality and in-vitrodigestibility of banana peels by mono-gastric animals. Livestock Science 199, 14-21

Karlsson H, Ahlgren S, Sandgren M, Passoth V, Wallberg O, Hansson PA (2016). A systems analysis of biodiesel production from wheat straw using oleaginous yeast: process design, mass and energy balances. Biotechnol Biofuels 9, 229

Brandenburg J, Blomqvist J, Pickova J, Bonturi N, Sandgren M, Passoth V. (2016). Lipid production from hemicellulose with Lipomyces starkeyi in a pH regulated fed batch cultivation. Yeast 33, 451-462. doi: 10.1002/yea.3160.