Role of cultivation media in the development of yeast strains for large scale industrial use

Improvement of cell growth in green algae Chlamydomonas reinhardtii through co-cultivation with yeast Saccharomyces cerevisiae

PURPOSE

CO2 fixation methods using green algae have attracted considerable attention because they can be applied for the fixation of dilute CO2 in the atmosphere. However, green algae generally exhibit low CO2 fixation efficiency under atmospheric conditions. Therefore, it is a challenge to improve the CO2 fixation efficiency of green algae under atmospheric conditions. Co-cultivation of certain microalgae with heterotrophic microorganisms can increase the growth potential of microalgae under atmospheric conditions. The objective of this study was to determine the culture conditions under which the growth potential of green algae Chlamydomonas reinhardtii is enhanced by co-culturing with the yeast Saccharomyces cerevisiae, and to identify the cause of the enhanced growth potential.

RESULTS

When C. reinhardtii and S. cerevisiae were co-cultured with an initial green algae to yeast inoculum ratio of 1:3, the cell concentration of C. reinhardtii reached 133 × 105 cells/mL on day 18 of culture, which was 1.5 times higher than that of the monoculture. Transcriptome analysis revealed that the expression levels of 363 green algae and 815 yeast genes were altered through co-cultivation. These included genes responsible for ammonium transport and CO2 enrichment mechanism in green algae and the genes responsible for glycolysis and stress responses in yeast.

CONCLUSION

We successfully increased C. reinhardtii growth potential by co-culturing it with S. cerevisiae. The main reasons for this are likely to be an increase in inorganic nitrogen available to green algae via yeast metabolism and an increase in energy available for green algae growth instead of CO2 enrichment.

Emergence of Orchestrated and Dynamic Metabolism of Saccharomyces cerevisiae

Microbial metabolism is a fundamental cellular process that involves many biochemical events and is distinguished by its emergent properties. While the molecular details of individual reactions have been increasingly elucidated, it is not well understood how these reactions are quantitatively orchestrated to produce collective cellular behaviors. Here we developed a coarse-grained, systems, and dynamic mathematical framework, which integrates metabolic reactions with signal transduction and gene regulation to dissect the emergent metabolic traits of Saccharomyces cerevisiae. Our framework mechanistically captures a set of characteristic cellular behaviors, including the Crabtree effect, diauxic shift, diauxic lag time, and differential growth under nutrient-altered environments. It also allows modular expansion for zooming in on specific pathways for detailed metabolic profiles. This study provides a systems mathematical framework for yeast metabolic behaviors, providing insights into yeast physiology and metabolic engineering.

Sustainable metabolic engineering requires a perfect trifecta

The versatility of cellular metabolism in converting various substrates to products inspires sustainable alternatives to conventional chemical processes. Metabolism can be engineered to maximize the yield, rate, and titer of product generation. However, the numerous combinations of substrate, product, and organism make metabolic engineering projects difficult to navigate. A perfect trifecta of substrate, product, and organism is prerequisite for an environmentally and economically sustainable metabolic engineering endeavor. As a step toward this endeavor, we propose a reverse engineering strategy that starts with product selection, followed by substrate and organism pairing. While a large bioproduct space has been explored, the top-ten compounds have been synthesized mainly using glucose and model organisms. Unconventional feedstocks (e.g. hemicellulosic sugars and CO2) and non-model organisms are increasingly gaining traction for advanced bioproduct synthesis due to their specialized metabolic modes. Judicious selection of the substrate-organism-product combination will illuminate the untapped territory of sustainable metabolic engineering.

Yeast lacking the sterol C-5 desaturase Erg3 are tolerant to the anti-inflammatory triterpenoid saponin escin

Escin is a mixture of over 30 glycosylated triterpenoid (saponin) structures, extracted from the dried fruit of horse chestnuts. Escin is currently used as an anti-inflammatory, and has potential applications in the treatment of arthritis and cancer. Engineered yeast would enable production of specific bioactive components of escin at industrial scale, however many saponins have been shown to be toxic to yeast. Here we report that a Saccharomyces cerevisiae strain specifically lacking the sterol C-5 desaturase gene ERG3, exhibits striking enhanced tolerance to escin treatment. Transcriptome analyses, as well as pre-mixing of escin with sterols, support the hypothesis that escin interacts directly with ergosterol, but not as strongly with the altered sterols present in erg3Δ. A diverse range of saponins are of commercial interest, and this research highlights the value of screening lipidome mutants to identify appropriate hosts for engineering the industrial production of saponins.

Application of Adaptive Laboratory Evolution in Lipid and Terpenoid Production in Yeast and Microalgae

Due to the complexity of metabolic and regulatory networks in microorganisms, it is difficult to obtain robust phenotypes through artificial rational design and genetic perturbation. Adaptive laboratory evolution (ALE) engineering plays an important role in the construction of stable microbial cell factories by simulating the natural evolution process and rapidly obtaining strains with stable traits through screening. This review summarizes the application of ALE technology in microbial breeding, describes the commonly used methods for ALE, and highlights the important applications of ALE technology in the production of lipids and terpenoids in yeast and microalgae. Overall, ALE technology provides a powerful tool for the construction of microbial cell factories, and it has been widely used in improving the level of target product synthesis, expanding the range of substrate utilization, and enhancing the tolerance of chassis cells. In addition, in order to improve the production of target compounds, ALE also employs environmental or nutritional stress strategies corresponding to the characteristics of different terpenoids, lipids, and strains.

Endochitinase and Chitobiosidase Production by Marine Aeromonas caviae CHZ306: Establishment of Nitrogen Supplementation

Aeromonas caviae CHZ306, a marine-derived bacterium isolated from zooplankton, can use chitin (a polymer of a β-(1,4)-linked N-acetyl-D-glucosamine) as a carbon source. The chitin is hydrolyzed by chitinolytic enzymes, namely endochitinases and exochitinases (chitobiosidase and N-acetyl-glucosaminidase). Indeed, the chitinolytic pathway is initiated by the coexpression of the enzymes endochitinase (EnCh) and chitobiosidase (ChB); however, few studies, including biotechnological production of these enzymes, have been reported, although chitosaccharide are helpful in several industries, such as cosmetics. This study demonstrates the potential to maximize the simultaneous EnCh and ChB production by nitrogen supplementation on culture media. Twelve different nitrogen supplementation sources (inorganic and organic) previously analyzed in elemental composition (carbon and nitrogen) were tested and evaluated in the Erlenmeyer flask culture of A. caviae CHZ306 for EnCh and ChB expression. None of the nutrients inhibited bacterial growth, and the maximum activity in both EnCh and ChB was observed at 12 h, using corn-steep solids and peptone A. Corn-steep solids and peptone A were then combined at three ratios (1:1, 1:2, and 2:1) to maximize the production. The high activities for EnCh (30.1 U.L−1) and ChB (21.3 U.L−1) were obtained with 2:1 corn-steep solids and peptone A, corresponding to more than 5- and 3-fold enhancement, respectively, compared to the control condition.

ACtivE: Assembly and CRISPR-Targeted in Vivo Editing for Yeast Genome Engineering Using Minimum Reagents and Time

Thanks to its sophistication, the CRISPR/Cas system has been a widely used yeast genome editing method. However, CRISPR methods generally rely on preassembled DNAs and extra cloning steps to deliver gRNA, Cas protein, and donor DNA. These laborious steps might hinder its usefulness. Here, we propose an alternative method, Assembly and CRISPR-targeted in vivo Editing (ACtivE), that only relies on in vivo assembly of linear DNA fragments for plasmid and donor DNA construction. Thus, depending on the user's need, these parts can be easily selected and combined from a repository, serving as a toolkit for rapid genome editing without any expensive reagent. The toolkit contains verified linear DNA fragments, which are easy to store, share, and transport at room temperature, drastically reducing expensive shipping costs and assembly time. After optimizing this technique, eight loci proximal to autonomously replicating sequences (ARS) in the yeast genome were also characterized in terms of integration and gene expression efficiencies and the impacts of the disruptions of these regions on cell fitness. The flexibility and multiplexing capacity of the ACtivE were shown by constructing a β-carotene pathway. In only a few days, >80% integration efficiency for single gene integration and >50% integration efficiency for triplex integration were achieved on Saccharomyces cerevisiae BY4741 from scratch without using in vitro DNA assembly methods, restriction enzymes, or extra cloning steps. This study presents a standardizable method to be readily employed to accelerate yeast genome engineering and provides well-defined genomic location alternatives for yeast synthetic biology and metabolic engineering purposes.

Growth ability, carbon source utilization and biochemical features of the new specie Zalaria obscura

This research investigated the characteristics of Zalaria obscura LS31012019 in terms of growth ability in different media (SDB, YPD and TSB) and temperatures (22, 25 and 37 °C), utilization of several carbon sources (Glucose, Fructose, Lactose, Sucrose, Xylose, Glycerol and Mannitol at 5, 2 and 1%) and several biochemical features (total protein content, Glutathione, pigments), in comparison with those of the phylogenetically related Aureobasidium pullulans ATCC 15233. The best growth of Z. obscura LS31012019 was obtained in YPD at 25 °C with the highest OD value (0.45) after 144 h of incubation, similar to that of A. pullulans ATCC 15233 (0.48). Glucose resulted the preferred carbon source for both the considered yeasts but also sucrose resulted in efficacy supporting the growth of Z. obscura LS31012019 and A. pullulans ATCC 15233, for their ability in converting sucrose to glucose and fructose and the latter into glucose. Interestingly, Z. obscura LS31012019 utilized also glycerol and mannitol. The biochemical analysis showed the similarity of protein profile in Z. obscura LS31012019 and A. pullulans ATCC 15233 (from 90 to 20 kDa) and a reduced GSH content (0.321 and 0.233 µmol/mg). The pigments extraction with hexane generated a yellow oleaginous pellet in both the strains, while a yellow solid matrix more intensely coloured in A. pullulans ATTC 15233 was visible with the following solvent extractions. Overall, our data showed that Z. obscura LS31012019 can grow in different media and temperatures and utilize carbon sources apart from glucose and sucrose, shifting to a non-fermentative metabolism. These results improve the information regarding the characteristics of Z. obscura, opening a new field of investigation for the possible application of new species of black yeasts in human application.

Isopropanol biosynthesis from crude glycerol using fatty acid precursors via engineered oleaginous yeast Yarrowia lipolytica

Background

Isopropanol is widely used as a biofuel and a disinfectant. Chemical preparation of isopropanol destroys the environment, which makes biological preparation of isopropanol necessary. Previous studies focused on the use of expensive glucose as raw material. Therefore, the microbial cell factory that ferments isopropanol with cheap raw materials will provide a greener way to produce isopropanol.

Results

This study converted crude glycerol into isopropanol using Y. lipolytica. As a microbial factory, the active natural lipid and fatty acid synthesis pathway endows Y. lipolytica with high malonyl-CoA production capacity. Acetoacetyl-CoA synthase (nphT7) and isopropanol synthesis genes are integrated into the Y. lipolytica genome. The nphT7 gene uses the accumulated malonyl-CoA to synthesize acetoacetyl-CoA, which increases isopropanol production. After medium optimization, the best glycerol medium was found and resulted in a 4.47-fold increase in isopropanol production. Fermenter cultivation with pure glycerol medium resulted in a maximum isopropanol production of 1.94 g/L. In a crude glycerol fermenter, 1.60 g/L isopropanol was obtained, 82.53% of that achieved with pure glycerol. The engineered Y. lipolytica in this study has the highest isopropanol titer reported.

Conclusions

The engineered Y. lipolytica successfully produced isopropanol by using crude glycerol as a cheap carbon source. This is the first study demonstrating the use of Y. lipolytica as a cell factory to produce isopropanol. In addition, this is also a new attempt to accumulate lipid synthesis precursors to synthesize other useful chemicals by integrating exogenous genes in Y. lipolytica.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01890-6.

Analysis of glucose and xylose metabolism in new indigenous Meyerozyma caribbica strains isolated from corn residues

Aiming to broaden the base of knowledge about wild yeasts, four new indigenous strains were isolated from corn residues, and phylogenetic-tree assemblings on ITS and LSU regions indicated they belong to Meyerozyma caribbica. Yeasts were cultivated under full- and micro-aerobiosis, starting with low or high cell-density inoculum, in synthetic medium or corn hydrolysate containing glucose and/or xylose. Cells were able to assimilate both monosaccharides, albeit by different metabolic routes (fermentative or respiratory). They grew faster in glucose, with lag phases ~ 10 h shorter than in xylose. The hexose exhaustion occurred between 24 and 34 h, while xylose was entirely consumed in the last few hours of cultivation (44-48 h). In batch fermentation in synthetic medium with high cell density, under full-aerobiosis, 18-20 g glucose l^-1 were exhausted in 4-6 h, with a production of 6.5-7.0 g ethanol l^-1. In the xylose medium, cells needed > 12 h to consume the carbohydrate, and instead of ethanol, cells released 4.4-6.4 g l^-1 xylitol. Under micro-aerobiosis, yeasts were unable to assimilate xylose, and glucose was more slowly consumed, although the ethanol yield was the theoretical maximum. When inoculated into the hydrolysate, cells needed 4-6 h to deplete glucose, and xylose had a maximum consumption of 57%. Considering that the hydrolysate contained ~ 3 g l^-1 acetic acid, it probably has impaired sugar metabolism. Thus, this study increases the fund of knowledge regarding indigenous yeasts and reveals the biotechnological potential of these strains.

Engineering Yeast for De Novo Synthesis of the Insect Repellent Nepetalactone

While nepetalactone, the active ingredient in catnip, is a potent insect repellent, its low in planta accumulation limits its commercial viability as an alternative repellent. Here we describe for the first time de novo nepetalactone synthesis in Saccharomyces cerevisiae, enabling sustainable and scalable production. Nepetalactone production required introducing eight exogenous genes including the cytochrome P450 geraniol-8-hydroxylase, the bottleneck of the heterologous pathway. Combinatorial assessment of geraniol-8-hydroxylase and cytochrome P450 reductase variants, and copy-number variations were used to overcome this bottleneck. We found that several reductases improved hydroxylation activity and increasing geraniol-8-hydroxylase gene copy number improved 8-hydroxygeraniol titers. The accumulation of an unwanted metabolite implied inefficient channeling of carbon through the pathway. With the native yeast old yellow enzymes previously shown to use monoterpene intermediates as substrates, both homologues were deleted. These deletions increased 8-hydroxygeraniol yield, resulting in 3.10 mg/L/OD₆₀₀ of nepetalactone from simple sugar in microtiter plates. This optimized pathway will benefit the development of high yielding strains for the scale up production of nepetalactone.

Recombinant protein production in Pichia pastoris: From transcriptionally redesigned strains to bioprocess optimization and metabolic modelling

Pichia pastoris is one of the most widely used host for the production of recombinant proteins. Expression systems that rely mostly on promoters from genes encoding alcohol oxidase 1 or glyceraldehyde-3-phosphate dehydrogenase have been developed together with related bioreactor operation strategies based on carbon sources such as methanol, glycerol, or glucose. Although, these processes are relatively efficient and easy to use, there have been notable improvements over the last twenty years to better control gene expression from these promoters and their engineered variants. Methanol-free and more efficient protein production platforms have been developed by engineering promoters and transcription factors. The production window of P. pastoris has been also extended by using alternative feedstocks including ethanol, lactic acid, mannitol, sorbitol, sucrose, xylose, gluconate, formate, or rhamnose. Herein, the specific aspects that are emerging as key parameters for recombinant protein synthesis are discussed. For this purpose, a holistic approach has been considered to scrutinize protein production processes from strain design to bioprocess optimization, particularly focusing on promoter engineering, transcriptional circuitry redesign. This review also considers the optimization of bioprocess based on alternative carbon sources and derived co-feeding strategies. Optimization strategies for recombinant protein synthesis through metabolic modelling are also discussed.

Heterologous production of cellulose- and starch-degrading hydrolases to expand Saccharomyces cerevisiae substrate utilization: Lessons learnt

Selected strains of Saccharomyces cerevisiae are used for commercial bioethanol production from cellulose and starch, but the high cost of exogenous enzymes for substrate hydrolysis remains a challenge. This can be addressed through consolidated bioprocessing (CBP) where S. cerevisiae strains are engineered to express recombinant glycoside hydrolases during fermentation. Looking back at numerous strategies undertaken over the past four decades to improve recombinant protein production in S. cerevisiae, it is evident that various steps in the protein production "pipeline" can be manipulated depending on the protein of interest and its anticipated application. In this review, we briefly introduce some of the strategies and highlight lessons learned with regards to improved transcription, translation, post-translational modification and protein secretion of heterologous hydrolases. We examine how host strain selection and modification, as well as enzyme compatibility, are crucial determinants for overall success. Finally, we discuss how lessons from heterologous hydrolase expression can inform modern synthetic biology and genome editing tools to provide process-ready yeast strains in future. However, it is clear that the successful expression of any particular enzyme is still unpredictable and requires a trial-and-error approach.

Intensification of p-coumaric acid heterologous production using extractive biphasic fermentation

p-coumaric acid (p-CA) can be produced from D-glucose by an engineered S. cerevisiae strain. p-CA has antimicrobial properties and retro-inhibition activity. Moreover, p-CA is a hydrophobic compound, limiting its accumulation in fermentation broth. To overcome these issues all at once, a liquid-liquid extraction in-situ product recovery process using oleyl alcohol as extractant has been implemented in order to continuously extract p-CA from the broth. Media and pH impacts on strain metabolism were assessed, highlighting p-CA decarboxylase endogenous activity. Biphasic fermentations allowed an increase in p-CA respiratory production rates at both pH assessed (13.65 and 9.45 mg L^-1.h^-1 at pH 6 and 4.5, respectively) compared to control ones (10.5 and 7.5 mg L^-1.h^-1 at pH 6 and 4.5, respectively). Biphasic fermentation effects on p-CA decarboxylation were studied showing that continuous removal of p-CA decreased its decarboxylation into 4-vinylphenol at pH 4.5 (57 mg L^-1 in biphasic fermentation vs 173 mg L^-1 in control one).

Development of wheat bran hydrolysate as Komagataella phaffii medium for heterologous protein production

Developing a Komagataella phaffii (K. phaffii, named as Pichia pastoris formerly) medium using wheat bran hydrolysate (WBH) is a potential approach for wheat bran utilization and heterologous protein by K. phaffii because K. phaffii is used as protein producer by researchers and engineers widely. In this research, the detoxification process of WBH was optimized to obtain the final procedure as pH adjusting to 10 by calcium hydroxide addition, then, 2.0 g/L active carbon absorption followed by 1 h shaking and 3,600 × g centrifugation for 10 min, finally, 3.75 mmol/L sodium thiosulfate addition for 10 min shaking followed by 3,600 × g centrifugation for 10 min. Recombinant K. phaffii-xynB harboring xylanase B gene from Aspergillus niger ATCC 1015 under alcohol oxidase 1 promoter (P_AOX1) was cultivated in detoxified WBH expressing 1059.8 U/mL xylanase B which was 90.9% of that in complex medium from Pichia protocols. These researches built a solid base for detoxified WBH as a low-cost medium of K. phaffii to express heterologous protein, also provided a bright outlet for wheat bran utilization.

Novel auto-selection systems for transformation selection of Saccharomyces cerevisiae in rich complex media

The most widely used strategy for selection of yeast transformed with episomal plasmids comprises the use of auxotrophic yeast strains in combination with vectors containing complementing prototrophic marker genes. Another approach uses heterologous genes or cassettes which, if present in the vector, render the otherwise sensitive yeast strain resistant to antibiotics. In addition, auto-selection systems for Saccharomyces cerevisiae have been developed that eliminate the requirement for synthetic drop-out media or the use of antibiotics for transformation selection and subsequent plasmid maintenance in expression cultures. Here we describe a combination of host strain and vector system introducing a novel concept of auto-selection systems that allows for easy and robust propagation of host cells deleted in essential genes in supplemented media before being transformed with rescuing plasmids. With that, our approach is favorable over commonly used selection strategies and has major advantage over other auto-selection systems. Our approach complements the auto-selection toolbox already available for S. cerevisiae, thus contributing a novel system that enables the use of complex peptone-based media for protein expression and metabolic engineering approaches. We therefore expect that this new strategy will be of general interest to the yeast research community in academia and industry.

Improving the Utilization of Isomaltose and Panose by Lager Yeast Saccharomyces pastorianus

Approximately 25% of all carbohydrates in industrial worts are poorly, if at all, fermented by brewing yeast. This includes dextrins, β-glucans, arabinose, xylose, disaccharides such as isomaltose, nigerose, kojibiose, and trisaccharides such as panose and isopanose. As the efficient utilization of carbohydrates during the wort’s fermentation impacts the alcohol yield and the organoleptic traits of the product, developing brewing strains with enhanced abilities to ferment subsets of these sugars is highly desirable. In this study, we developed Saccharomyces pastorianus laboratory yeast strains with a superior capacity to grow on isomaltose and panose. First, we designed a plasmid toolbox for the stable integration of genes into lager strains. Next, we used the toolbox to elevate the levels of the α-glucoside transporter Agt1 and the major isomaltase Ima1. This was achieved by integrating synthetic AGT1 and IMA1 genes under the control of strong constitutive promoters into defined genomic sites. As a result, strains carrying both genes showed a superior capacity to grow on panose and isomaltose, indicating that Ima1 and Agt1 act in synergy to consume these sugars. Our study suggests that non-GMO strategies aiming to develop strains with improved isomaltose and panose utilization could include identifying strains that overexpress AGT1 and IMA1.

Adaptive evolution of sulfite tolerance in Brettanomyces bruxellensis

Brettanomyces bruxellensis is considered one of the most problematic microbes associated with wine production. Sulfur dioxide is commonly used to inhibit the growth of B. bruxellensis and limit the potential wine spoilage. Brettanomyces bruxellensis wine isolates can grow at higher concentrations of this preservative than isolates from other sources. Thus, it has been suggested that the use of sulfite may have selected for B. bruxellensis strains better adapted to survive in the winemaking environment. We utilized laboratory adaptive evolution to determine the potential for this to occur. Three B. bruxellensis strains, representative of known genetic variation within the species, were subjected to increasing sublethal sulfur dioxide concentrations. Individual clones isolated from evolved populations displayed enhanced sulfite tolerance, ranging from 1.6 to 2.5 times higher than the corresponding parental strains. Whole-genome sequencing of sulfite-tolerant clones derived from two of the parental strains revealed structural variations affecting 270 genes. The region containing the sulfite efflux pump encoding gene, SSU1, showed clear copy number variants in all sequenced clones. Regardless of parental strain genetic background, SSU1 copy number changes were reproducibly associated with one SSU1 haplotype. This work clearly demonstrates adaptive evolution of B. bruxellensis when exposed to sublethal sulfites and suggests that, similar to Saccharomyces cerevisiae wine yeast, the mechanism responsible involves the gene SSU1.

Engineering oxygen-independent biotin biosynthesis in Saccharomyces cerevisiae

An oxygen requirement for de novo biotin synthesis in Saccharomyces cerevisiae precludes the application of biotin-prototrophic strains in anoxic processes that use biotin-free media. To overcome this issue, this study explores introduction of the oxygen-independent Escherichia coli biotin-biosynthesis pathway in S. cerevisiae. Implementation of this pathway required expression of seven E. coli genes involved in fatty-acid synthesis and three E. coli genes essential for the formation of a pimelate thioester, key precursor of biotin synthesis. A yeast strain expressing these genes readily grew in biotin-free medium, irrespective of the presence of oxygen. However, the engineered strain exhibited specific growth rates 25% lower in biotin-free media than in biotin-supplemented media. Following adaptive laboratory evolution in anoxic cultures, evolved cell lines that no longer showed this growth difference in controlled bioreactors, were characterized by genome sequencing and proteome analyses. The evolved isolates exhibited a whole-genome duplication accompanied with an alteration in the relative gene dosages of biosynthetic pathway genes. These alterations resulted in a reduced abundance of the enzymes catalyzing the first three steps of the E. coli biotin pathway. The evolved pathway configuration was reverse engineered in the diploid industrial S. cerevisiae strain Ethanol Red. The resulting strain grew at nearly the same rate in biotin-supplemented and biotin-free media non-controlled batches performed in an anaerobic chamber. This study established an unique genetic engineering strategy to enable biotin-independent anoxic growth of S. cerevisiae and demonstrated its portability in industrial strain backgrounds.

A buffered media system for yeast batch culture growth

Background

Fungi are premier hosts for the high-yield secretion of proteins for biomedical and industrial applications. The stability and activity of these secreted proteins is often dependent on the culture pH. As yeast acidifies the commonly used synthetic complete drop-out (SD) media that contains ammonium sulfate, the pH of the media needs to be buffered in order to maintain a desired extracellular pH during biomass production. At the same time, many buffering agents affect growth at the concentrations needed to support a stable pH. Although the standard for biotechnological research and development is shaken batch cultures or microtiter plate cultures that cannot be easily automatically pH-adjusted during growth, there is no comparative study that evaluates the buffering capacity and growth effects of different media types across pH-values in order to develop a pH-stable batch culture system.

Results

We systematically test the buffering capacity and growth effects of a citrate-phosphate buffer (CPB) from acidic to neutral pH across different media types. These media types differ in their nitrogen source (ammonium sulfate, urea or both). We find that the widely used synthetic drop-out media that uses ammonium sulfate as nitrogen source can only be effectively buffered at buffer concentrations that also affect growth. At lower concentrations, yeast biomass production still acidifies the media. When replacing the ammonium sulfate with urea, the media alkalizes. We then develop a medium combining ammonium sulfate and urea which can be buffered at low CPB concentrations that do not affect growth. In addition, we show that a buffer based on Tris/HCl is not effective in maintaining any of our media types at neutral pH even at relatively high concentrations.

Conclusion

Here we show that the buffering of yeast batch cultures is not straight-forward and addition of a buffering agent to set a desired starting pH does not guarantee pH-maintenance during growth. In response, we present a buffered media system based on an ammonium sulfate/urea medium that enables relatively stable pH-maintenance across a wide pH-range without affecting growth. This buffering system is useful for protein-secretion-screenings, antifungal activity assays, as well as for other pH-dependent basic biology or biotechnology projects.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02191-5.

Optimization of Synthetic Media Composition for Kluyveromyces marxianus Fed-Batch Cultivation

The Kluyveromyces marxianus yeast recently has gained considerable attention due to its applicability in high-value-added product manufacturing. In order to intensify the biosynthesis rate of a target product, reaching high biomass concentrations in the reaction medium is mandatory. Fed-batch processes are an attractive and efficient way how to achieve high cell densities. However, depending on the physiology of the particular microbial strain, an optimal media composition should be used to avoid by-product synthesis and, subsequently, a decrease in overall process effi-ciency. Thus, the aim of the present study was to optimise the synthetic growth medium and feeding solution compositions (in terms of carbon, nitrogen, phosphorous, magnesium, and calcium concentrations) for high cell density K. marxianus fed‑batch cultivations. Additionally, the biomass yields from the vitamin mixture and other macro/microelements were identified. A model predictive control algorithm was successfully applied for a fed-batch cultivation control. Biomass growth and substrate consumption kinetics were compared with the mathematical model predictions. Finally, 2‑phenylethanol biosynthesis was induced and its productivity was estimated. The determined optimal macronutrient ratio for K. marxianus biomass growth was identified as C:N:P = 1:0.07:0.011. The maximal attained yeast biomass concentration was close to 70 g·L-1 and the 2-PE biosynthesis rate was 0.372 g·L−1·h−1, with a yield of 74% from 2-phenylalanine.

Increasing the Production of β-Glucan from Saccharomyces carlsbergensis RU01 by Using Tannic Acid

In this study, we increased β-glucan production from brewer’s yeast, Saccharomyces carlsbergensis RU01, by using tannic acid. High-pressure freezing and transmission electron microscopy (HPF-TEM) revealed that the yeast cell wall obtained from yeast malt (YM) medium supplemented with 0.1% w/v tannic acid was thicker than that of yeast cultured in YM medium alone. The production of β-glucan from S. carlsbergensis RU01 was optimized in 3% w/v molasses and 0.1% w/v diammonium sulfate (MDS) medium supplemented with 0.1% w/v tannic acid. The results showed that MDS medium supplemented with 0.1% w/v tannic acid significantly increased the dry cell weight (DCW), and the β-glucan production was 0.28±0.01% w/v and 11.99±0.04% w/w. Tannic acid enhanced the β-glucan content by up to 42.23%. β-Glucan production in the stirred tank reactor (STR) was 1.4-fold higher than that in the shake flask (SF) culture. Analysis of the β-glucan composition by Fourier transform infrared (FTIR) spectroscopy showed that the β-glucan of S. carlsbergensis RU01 cultured in MDS medium supplemented with 0.1% w/v tannic acid had a higher proportion of polysaccharide than that of the control. In addition, β-glucans from brewer’s yeast can be used as prebiotic and functional foods for human health and in animal feed.

Impact of media components from different suppliers on enterokinase productivity in Pichia pastoris

Background

The aim of this study was to provide an information about the homogeneity on the level of enterokinase productivity in P. pastoris depending on different suppliers of the media components.

Results

In previous studies, we performed the optimisation process for the production of enterokinase by improving the fermentation process. Enterokinase is the ideal enzyme for removing fusion partners from target recombinant proteins. In this study, we focused our optimization efforts on the sources of cultivation media components. YPD media components were chosen as variables for these experiments. Several suppliers for particular components were combined and the optimisation procedure was performed in 24-well plates. Peptone had the highest impact on enterokinase production, where the difference between the best and worst results was threefold. The least effect on the production level was recorded for yeast extract with a 1.5 fold difference. The worst combination of media components had a activity of only 0.15 U/ml and the best combination had the activity of 0.88 U/ml, i.e., a 5.87 fold difference. A substantially higher impact on the production level of enterokinase was observed during fermentation in two selected media combinations, where the difference was almost 21-fold.

Conclusions

Results demonstrated in the present study show that the media components from different suppliers have high impact on enterokinase productivity and also provide the hypothesis that the optimization process should be multidimensional and for achieving best results it is important to perform massive process also in terms of the particular media component supplier .

High-throughput screening for high-efficiency small-molecule biosynthesis

Systems metabolic engineering faces the formidable task of rewiring microbial metabolism to cost-effectively generate high-value molecules from a variety of inexpensive feedstocks for many different applications. Because these cellular systems are still too complex to model accurately, vast collections of engineered organism variants must be systematically created and evaluated through an enormous trial-and-error process in order to identify a manufacturing-ready strain. The high-throughput screening of strains to optimize their scalable manufacturing potential requires execution of many carefully controlled, parallel, miniature fermentations, followed by high-precision analysis of the resulting complex mixtures. This review discusses strategies for the design of high-throughput, small-scale fermentation models to predict improved strain performance at large commercial scale. Established and promising approaches from industrial and academic groups are presented for both cell culture and analysis, with primary focus on microplate- and microfluidics-based screening systems.

Whole-Cell Biotransformation of 1,12-Dodecanedioic Acid from Coconut Milk Factory Wastewater by Recombinant CYP52A17SS Expressing Saccharomyces cerevisiae

Biotransformation of fatty acids from renewable wastewater as feedstock to value-added chemicals is a fascinating commercial opportunity. α,ω-Dicarboxylic acids (DCAs) are building blocks in many industries, such as polymers, cosmetic intermediates, and pharmaceuticals, and can be obtained by chemical synthesis under extreme conditions. However, biological synthesis can replace the traditional chemical synthesis using cytochrome P450 enzymes to oxidize fatty acids to DCAs. Saccharomyces cerevisiae BY(2R)/pYeDP60-CYP52A17SS (BCM), a transgenic strain expressing the galactose-inducible CYP52A17SS cytochrome P450 enzyme, was able to grow in a coconut milk factory wastewater (CCW) medium and produced 12-hydroxydodecanoic acid (HDDA) and 1,12-dodecanedioic acid (DDA). The supplementation of CCW with 10 g/L yeast extract and 20 g/L peptone (YPCCW) markedly increased the yeast growth rate and the yields of 12-HDDA and 1,12-DDA, with the highest levels of approximately 60 and 38 µg/L, respectively, obtained at 30 °C and pH 5. The incubation temperature and medium pH strongly influenced the yeast growth and 1,12-DDA yield, with the highest 1,12-DDA formation at 30 °C and pH 5–5.5. Hence, the S. cerevisiae BCM strain can potentially be used for producing value-added products from CCW.

Metabolic engineering strategies for butanol production in Escherichia coli

The global market of butanol is increasing due to its growing applications as solvent, flavoring agent, and chemical precursor of several other compounds. Recently, the superior properties of n-butanol as a biofuel over ethanol have stimulated even more interest. (Bio)butanol is natively produced together with ethanol and acetone by Clostridium species through acetone-butanol-ethanol fermentation, at noncompetitive, low titers compared to petrochemical production. Different butanol production pathways have been expressed in Escherichia coli, a more accessible host compared to Clostridium species, to improve butanol titers and rates. The bioproduction of butanol is here reviewed from a historical and theoretical perspective. All tested rational metabolic engineering strategies in E. coli to increase butanol titers are reviewed: manipulation of central carbon metabolism, elimination of competing pathways, cofactor balancing, development of new pathways, expression of homologous enzymes, consumption of different substrates, and molecular biology strategies. The progress in the field of metabolic modeling and pathway generation algorithms and their potential application to butanol production are also summarized here. The main goals are to gather all the strategies, evaluate the respective progress obtained, identify, and exploit the outstanding challenges.

Engineering Cell Wall Integrity Enables Enhanced Squalene Production in Yeast

Microbial production of many lipophilic compounds is often limited by product toxicity to host cells. Engineering cell walls can help mitigate the damage caused by lipophilic compounds by increasing tolerance to those compounds. To determine if the cell wall engineering would be effective in enhancing lipophilic compound production, we used a previously constructed squalene-overproducing yeast strain (SQ) that produces over 600 mg/L of squalene, a model membrane-damaging lipophilic compound. This SQ strain had significantly decreased membrane rigidity, leading to increased cell lysis during fermentation. The SQ strain was engineered to restore membrane rigidity by activating the cell wall integrity (CWI) pathway, thereby further enhancing its squalene production efficiency. Maintenance of CWI was associated with improved squalene production, as shown by cell wall remodeling through regulation of Ecm33, a key regulator of the CWI pathway. Deletion of ECM33 in the SQ strain helped restore membrane rigidity and improve stress tolerance. Moreover, ECM33 deletion suppressed cell lysis and increased squalene production by approximately 12% compared to that by the parent SQ strain. Thus, this study shows that engineering of the yeast cell wall is a promising strategy for enhancing the physiological functions of industrial strains for production of lipophilic compounds.

Low-cost media statistical design for laccase rPOXA 1B production in P. pastoris

Laccases (E.C. 1.10.3.2) are multicopper oxidases of great importance in the industry due to their non-specificity and high oxidative potential. Laccases are useful to bleach synthetic dyes, oxidize phenolic compounds and degrade pesticides, among others. Hence, the objective of this work was to optimize low cost culture media for recombinant (rPOXA 1B) laccase production from Pleurotus ostreatus in Pichia pastoris. To this end, low cost nitrogen sources were studied, such as malt extract, isolated soy protein and milk serum. Following, two central composite designs (CCD) were performed. In CCD-1 different concentrations of glucose USP (0–13.35 gL^-1), protein isolated soy protein (5–25 gL^-1), malt extract (3.5–17.5 gL^-1) and (NH₄)₂SO₄ (1.3–6.5 gL^-1) were evaluated. In CCD-2 only different concentrations of glucose USP (7.9–22 gL^-1) and isolated soy protein (15.9–44.9 gL^-1) were evaluated. CCD-2 results led to a One Factor Experimental design (OFED) to evaluate higher isolated soy protein (20–80 gL^-1) concentrations. In all designs, (CCD-1, CCD-2 and OFED) CuSO₄ (0.16 gL^-1) and chloramphenicol (0.1 gL^-1) concentrations remained unchanged. For the OFED after sequential statistical optimization, an enzyme activity of 12,877.3 ± 481.2 UL⁻¹ at 168 h was observed. rPOXA 1B activity increased 30.54 % in comparison with CCD-2 results. Final composition of optimized media was: 20 gL^-1 glucose USP, 50 gL^-1 isolated soy protein 90 % (w/w), 11.74 gL^-1 malt extract, and 4.91 gL^-1 (NH₄)₂SO₄. With this culture media, it was possible to reduce culture media costs by 89.84 % in comparison with improved culture media previously described by our group.

Biochemical analysis of cellobiose catabolism in Candida pseudointermedia strains isolated from rotten wood

We isolated two Candida pseudointermedia strains from the Atlantic rain forest in Brazil, and analyzed cellobiose metabolization in their cells. After growth in cellobiose medium, both strains had high intracellular β-glucosidase activity [~ 200 U (g cells)^-1 for 200 mM cellobiose and ~ 100 U (g cells)^-1 for 2 mM pNPβG] and negligible periplasmic cellobiase activity. During batch fermentation, the strain with the best performance consumed all the available cellobiose in the first 18 h of the assay, producing 2.7 g L^-1 of ethanol. Kinetics of its cellobiase activity demonstrated a high-affinity hydrolytic system inside cells, with K_m of 12.4 mM. Our data suggest that, unlike other fungal species that hydrolyze cellobiose extracellularly, both analyzed strains transport it to the cytoplasm, where it is then hydrolyzed by high-affinity intracellular β-glucosidases. We believe this study increases the fund of knowledge regarding yeasts from Brazilian microbiomes.

Quantitative Trait Nucleotides Impacting the Technological Performances of Industrial Saccharomyces cerevisiae Strains

The budding yeast Saccharomyces cerevisiae is certainly the prime industrial microorganism and is related to many biotechnological applications including food fermentations, biofuel production, green chemistry, and drug production. A noteworthy characteristic of this species is the existence of subgroups well adapted to specific processes with some individuals showing optimal technological traits. In the last 20 years, many studies have established a link between quantitative traits and single-nucleotide polymorphisms found in hundreds of genes. These natural variations constitute a pool of QTNs (quantitative trait nucleotides) that modulate yeast traits of economic interest for industry. By selecting a subset of genes functionally validated, a total of 284 QTNs were inventoried. Their distribution across pan and core genome and their frequency within the 1,011 Saccharomyces cerevisiae genomes were analyzed. We found that 150 of the 284 QTNs have a frequency lower than 5%, meaning that these variants would be undetectable by genome-wide association studies (GWAS). This analysis also suggests that most of the functional variants are private to a subpopulation, possibly due to their adaptive role to specific industrial environment. In this review, we provide a literature survey of their phenotypic impact and discuss the opportunities and the limits of their use for industrial strain selection.

Proteome response of two natural strains of Saccharomyces cerevisiae with divergent lignocellulosic inhibitor stress tolerance

Strains of Saccharomyces cerevisiae with improved tolerance to plant hydrolysates are of utmost importance for the cost-competitive production of value-added chemicals and fuels. However, engineering strategies are constrained by a lack of understanding of the yeast response to complex inhibitor mixtures. Natural S. cerevisiae isolates display niche-specific phenotypic and metabolic diversity, encoded in their DNA, which has evolved to overcome external stresses, utilise available resources and ultimately thrive in their challenging environments. Industrial and laboratory strains, however, lack these adaptations due to domestication. Natural strains can serve as a valuable resource to mitigate engineering constraints by studying the molecular mechanisms involved in phenotypic variance and instruct future industrial strain improvement to lignocellulosic hydrolysates. We, therefore, investigated the proteomic changes between two natural S. cerevisiae isolates when exposed to a lignocellulosic inhibitor mixture. Comparative shotgun proteomics revealed that isolates respond by regulating a similar core set of proteins in response to inhibitor stress. Furthermore, superior tolerance was linked to NAD(P)/H and energy homeostasis, concurrent with inhibitor and reactive oxygen species detoxification processes. We present several candidate proteins within the redox homeostasis and energy management cellular processes as possible targets for future modification and study. Data are available via ProteomeXchange with identifier PXD010868.

Exploring the xylose paradox in Saccharomyces cerevisiae through in vivo sugar signalomics of targeted deletants

BACKGROUND

There have been many successful strategies to implement xylose metabolism in Saccharomyces cerevisiae, but no effort has so far enabled xylose utilization at rates comparable to that of glucose (the preferred sugar of this yeast). Many studies have pointed towards the engineered yeast not sensing that xylose is a fermentable carbon source despite growing and fermenting on it, which is paradoxical. We have previously used fluorescent biosensor strains to in vivo monitor the sugar signalome in yeast engineered with xylose reductase and xylitol dehydrogenase (XR/XDH) and have established that S. cerevisiae senses high concentrations of xylose with the same signal as low concentration of glucose, which may explain the poor utilization.

RESULTS

In the present study, we evaluated the effects of three deletions (ira2∆, isu1∆ and hog1∆) that have recently been shown to display epistatic effects on a xylose isomerase (XI) strain. Through aerobic and anaerobic characterization, we showed that the proposed effects in XI strains were for the most part also applicable in the XR/XDH background. The ira2∆isu1∆ double deletion led to strains with the highest specific xylose consumption- and ethanol production rates but also the lowest biomass titre. The signalling response revealed that ira2∆isu1∆ changed the low glucose-signal in the background strain to a simultaneous signalling of high and low glucose, suggesting that engineering of the signalome can improve xylose utilization.

CONCLUSIONS

The study was able to correlate the previously proposed beneficial effects of ira2∆, isu1∆ and hog1∆ on S. cerevisiae xylose uptake, with a change in the sugar signalome. This is in line with our previous hypothesis that the key to resolve the xylose paradox lies in the sugar sensing and signalling networks. These results indicate that the future engineering targets for improved xylose utilization should probably be sought not in the metabolic networks, but in the signalling ones.

Multi-Factorial-Guided Media Optimization for Enhanced Biomass and Lipid Formation by the Oleaginous Yeast Cutaneotrichosporon oleaginosus

The non-conventional, oleaginous yeast Cutaneotrichosporon oleaginosus is flagged as an industrial cell factory for generation of oleochemicals and biofuels due to its substrate flexibility and high triglyceride yields. In this study, we employed a computational Response Surface Methodology to guide and streamline the experimental media optimization matrix with 12 nitrogen and 10 carbon sources in order to provide for high biomass and lipid accumulation toward an industrially relevant fermentation process. The resulting data provide new insights into C. oleaginosus physiology under variable nutritional states. Accordingly, the lipid content % (lipid weight/yeast dry weight) is controlled by a defined interplay between carbon and nitrogen. In our experimental setup, the highest biomass (18.4 ± 2.20 g/L) and lipid yield (9 ± 0.34 g/L; 49.74 ± 5.16% g lipid weight/g yeast dry cell weight) were obtained with lactose and yeast extract as carbon and nitrogen sources at an elemental weight ratio of 120:1, respectively. Interestingly, with ammonium salts as a N-source, the intracellularly accumulated triglycerides increasingly contain saturated fatty acids, which provides a new route to generate tailored fatty acid profiles for specific oleochemicals or food applications. Our data indicate that a metabolic ceiling for lipid accumulation in C. oleaginosus is obtained with the correct carbon and nitrogen source mixture.

Novel Yeast Strains for the Efficient Saccharification and Fermentation of Starchy By-Products to Bioethanol

The use of solid starchy waste streams to produce value-added products, such as fuel ethanol, is a priority for the global bio-based economy. Despite technological advances, bioethanol production from starch is still not economically competitive. Large cost-savings can be achieved through process integration (consolidated bioprocessing, CBP) and new amylolytic microbes that are able to directly convert starchy biomass into fuel in a single bioreactor. Firstly, CBP technology requires efficient fermenting yeast strains to be engineered for amylase(s) production. This study addressed the selection of superior yeast strains with high fermentative performances to be used as recipient for future CBP engineering of fungal amylases. Twenty-one newly isolated wild-type Saccharomyces cerevisiae strains were screened at 30 °C in a simultaneous saccharification and fermentation (SSF) set up using starchy substrates at high loading (20% w/v) and the commercial amylases cocktail STARGEN™ 002. The industrial yeast Ethanol Red™ was used as benchmark. A cluster of strains produced ethanol levels (up to 118 g/L) significantly higher than those of Ethanol Red™ (about 109 g/L). In particular, S. cerevisiae L20, selected for a scale-up process into a 1-L bioreactor, confirmed the outstanding performance over the industrial benchmark, producing nearly 101 g/L ethanol instead of 94 g/L. As a result, this strain can be a promising CBP host for heterologous expression of fungal amylases towards the design of novel and efficient starch-to-ethanol routes.

Growth of Candida norvegensis (strain Levazoot 15) with different energy, nitrogen, vitamin, and micromineral sources

To examine the growth of Candida norvegensis (strain Levazoot 15), four experiments were conducted with different sources of energy, nitrogen, vitamins, and microminerals. Optical density was used as an indirect measure of strain growth in a fully randomized factorial design, in which principal factor A was the source of energy, nitrogen, vitamins, or microminerals and principal factor B was the measurement time point (0, 20, or 40 h). The results showed that the yeast strain used glucose (primarily sucrose and lactose) as the energy source and tryptone as the nitrogen source. The addition of B-complex vitamins or microminerals was not necessary for strain growth. It is concluded that the strain Levazoot 15 preferentially utilizes glucose as a source of energy, tryptone as a source of nitrogen and manganese as a mineral source, and that no vitamin source was necessary for growth.

Lachancea thermotolerans, a Yeast Symbiont of Yellowjackets, Enhances Attraction of Three Yellowjacket Species (Hymenoptera: Vespidae) to Fruit Powder

Previously, we showed that the symbiotic yeast Lachancea thermotolerans (Filippov) (Saccharomycetales: Saccharomycetaceae) is attractive to its Vespula (Hymenoptera: Vespidae) yellowjacket hosts when grown on media supplemented with grape juice. We hypothesized that "Concerto", a commercial strain of this yeast, could be combined with fruit powder to form a shelf-stable bait for trapping yellowjackets. Using molecular techniques, we first confirmed that Concerto yeast is indeed the species L. thermotolerans. We then tested whether: 1) Concerto yeast produces volatiles similar to those produced by L. thermotolerans isolated from yellowjackets, 2) Concerto yeast enhances attraction of yellowjackets to fruit powder, 3) a Concerto yeast/fruit powder bait interacts synergistically with a yellowjacket semiochemical lure, and 4) a synthetic analog blend of Concerto-produced volatiles attracts yellowjackets. Using gas chromatography-mass spectrometry, we demonstrated that the chemical composition of Concerto-produced volatiles closely resembles that produced by a yellowjacket-isolated strain of L. thermotolerans. In field experiments, addition of Concerto to fruit powder doubled its attractiveness to yellowjackets. Addition of the Concerto/fruit powder bait to a heptyl butyrate-based wasp lure revealed a weak additive effect. A three-component synthetic analog blend of volatiles identified from the Concerto/fruit powder bait attracted Vespula pensylvanica (Saussure), but no other yellowjacket species. Our results suggest that commercial L. thermotolerans in combination with fruit powder could be used as a yellowjacket bait, and that addition of yeast-produced volatiles to a commercial wasp lure may improve its attractiveness to V. pensylvanica. Further research should determine why the synthetic volatile blend failed to attract Vespula species other than V. pensylvanica.

Augmenting Pentose Utilization and Ethanol Production of Native Saccharomyces cerevisiae LN Using Medium Engineering and Response Surface Methodology

Economics of ethanol production from lignocellulosic biomass depends on complete utilization of constituent carbohydrates and efficient fermentation of mixed sugars present in biomass hydrolysates. Saccharomyces cerevisiae, the commercial strain for ethanol production uses only glucose while pentoses remain unused. Recombinant strains capable of utilizing pentoses have been engineered but with limited success. Recently, presence of endogenous pentose assimilation pathway in S. cerevisiae was reported. On the contrary, evolutionary engineering of native xylose assimilating strains is promising approach. In this study, a native strain S. cerevisiae LN, isolated from fruit juice, was found to be capable of xylose assimilation and mixed sugar fermentation. Upon supplementation with yeast extract and peptone, glucose (10%) fermentation efficiency was 78% with ~90% sugar consumption. Medium engineering augmented mixed sugars (5% glucose + 5% xylose) fermentation efficiency to ~50 and 1.6% ethanol yield was obtained with concomitant sugar consumption ~60%. Statistical optimization of input variables Glucose (5.36%), Xylose (3.30%), YE (0.36%), and peptone (0.25%) with Response surface methodology led to improved sugar consumption (74.33%) and 2.36% ethanol within 84 h. Specific activities of Xylose Reductase and Xylitol Dehydrogenase exhibited by S. cerevisiae LN were relatively low. Their ratio indicated metabolism diverted toward ethanol than xylitol and other byproducts. Strain was tolerant to concentrations of HMF, furfural and acetic acid commonly encountered in biomass hydrolysates. Thus, genetic setup for xylose assimilation in S. cerevisiae LN is not merely artifact of xylose metabolizing pathway and can be augmented by adaptive evolution. This strain showed potential for commercial exploitation.

Probiotic effect of Pichia pastoris X-33 produced in parboiled rice effluent and YPD medium on broiler chickens

In a previous paper we showed that the yeast Pichia pastoris X-33 grown in parboiled rice effluent supplemented with glycerol byproduct from the biodiesel industry improved the quality of the effluent. In this paper we show the validation of this yeast (PPE) as probiotic for broilers. Its effect on feed efficiency and immunomodulation was compared with the same yeast grown in yeast peptone dextrose medium (PPY), with Saccharomyces boulardii (SBY) and with the controls fed unsupplemented feed (CON). One-day-old female chicks were vaccinated against infectious bursal disease (IBD) and the titers of anti-IBD antibodies were measured by ELISA. PPE group had the highest mean titres on days 14 and 28 (p<0,05), and at 28 days, 64% of the animals showed seroconvertion. The PPE group also showed the best weight gains at 42 days of age, that, on days 7, 14 and 21 were 19%, 15%, and 8.7% higher, respectively, than the control group. The best feed conversion, 8.2% higher than the control group, was obtained by PPY at 42 days. Histopathological studies did not detect any undesirable effects in the supplemented animals. We concluded that Pichia pastoris X-33 when grown in effluents of the rice parboiling industry supplemented with glycerol byproduct from the biodiesel has probiotic properties for poultry.

Notable mixed substrate fermentation by native Kodamaea ohmeri strains isolated from Lagenaria siceraria flowers and ethanol production on paddy straw hydrolysates

BACKGROUND

Bioethanol obtained by fermenting cellulosic fraction of biomass holds promise for blending in petroleum. Cellulose hydrolysis yields glucose while hemicellulose hydrolysis predominantly yields xylose. Economic feasibility of bioethanol depends on complete utilization of biomass carbohydrates and an efficient co-fermenting organism is a prerequisite. While hexose fermentation capability of Saccharomyces cerevisiae is a boon, however, its inability to ferment pentose is a setback.

RESULTS

Two xylose fermenting Kodamaea ohmeri strains were isolated from Lagenaria siceraria flowers through enrichment on xylose. They showed 61% glucose fermentation efficiency in fortified medium. Medium engineering with 0.1% yeast extract and peptone, stimulated co-fermentation potential of both strains yielding maximum ethanol 0.25 g g^-1 on mixed sugars with ~ 50% fermentation efficiency. Strains were tolerant to inhibitors like 5-hydroxymethyl furfural, furfural and acetic acid. Both K. ohmeri strains grew well on biologically pretreated rice straw hydrolysates and produced ethanol.

CONCLUSIONS

This is the first report of native Kodamaea sp. exhibiting notable mixed substrate utilization and ethanol fermentation. K. ohmeri strains showed relevant traits like utilizing and co-fermenting mixed sugars, exhibiting excellent growth, inhibitor tolerance, and ethanol production on rice straw hydrolysates.