Pichia anomala:cell physiology and biotechnology relative to other yeasts

Pichia anomala is a most interesting yeast species, from a number of environmental, industrial and medical aspects. This yeast has been isolated from very diverse natural habitats (e.g. in foods, insects, wastewaters etc.) and it also exhibits wide metabolic and physiological diversity. Some of the activities of P. anomala, particularly its antimicrobial action, make it a very attractive organism for biological control applications in the agri-food sectors of industry. Being a ‘robust’ organism, it additionally has potential to be exploited in bioremediation of environmental pollutants. This paper provides an overview of cell physiological characteristics (growth, metabolism, stress responses) and biotechnological potential (e.g. as a novel biocontrol agent) of P. anomala and compares such properties with other yeast species, notably Saccharomyces cerevisiae, which remains the most exploited industrial microorganism. We await further basic knowledge of P. anomala cell physiology and genetics prior to its fuller commercial exploitation, but the exciting biotechnological potential of this yeast is highlighted in this paper

125th anniversary review: fuel alcohol: current production and future challenges

Global research and industrial development of liquid transportation biofuels are moving at a rapid pace. This is mainly due to the significant roles played by biofuels in decarbonising our future energy needs, since they act to mitigate the deleterious impacts of greenhouse gas emissions to the atmosphere that are contributors of climate change. Governmental obligations and international directives that mandate the blending of biofuels in petrol and diesel are also acting as great stimuli to this expanding industrial sector. Currently, the predominant liquid biofuel is bioethanol (fuel alcohol) and its worldwide production is dominated by maize-based and sugar cane-based processes in North and South America, respectively. In Europe, fuel alcohol production employs primarily wheat and sugar beet. Potable distilled spirit production and fuel alcohol processes share many similarities in terms of starch bioconversion, fermentation, distillation and co-product utilisation, but there are some key differences. For example, in certain bioethanol fermentations, it is now possible to yield consistently high ethanol concentrations of ~20% (v/v). Emerging fuel alcohol processes exploit lignocellulosic feedstocks and scientific and technological constraints involved in depolymerising these materials and efficiently fermenting the hydrolysate sugars are being overcome. These so-called secondgeneration fuel alcohol processes are much more environmentally and ethically acceptable compared with exploitation of starch and sugar resources, especially when considering utilisation of residual agricultural biomass and biowastes. This review covers both first and second-generation bioethanol processes with a focus on current challenges and future opportunities of lignocellulose-to-ethanol as this technology moves from demonstration pilot-plants to full-scale industrial facilities

Yeasts

Yeasts are a group of eukaryotic microfungi with a well-defined cell wall whose growth is either entirely unicellular or a combination of hyphal and unicellular reproduction. The approximately 1500 known yeast species belong to two distinct fungal phyla, the Ascomycota and the Basidiomycota. Within each these phyla, yeasts can be found in several subphyla or classes, reflecting the enormous diversity of their evolutionary origins and biochemical properties. In nature, yeasts are found mainly in association with plants or animals but are also present in soil and aquatic environments. Yeasts grow rapidly and have simple nutritional requirements, for which reason they have been used as model systems in biochemistry, genetics and molecular biology. They were the first microorganisms to be domesticated for the production of beer, bread or wine, and they continue to be used for the benefit of humanity in the production of many important health care and industrial commodities, including recombinant proteins, biopharmaceuticals, biocontrol agents and biofuels. The best-known yeast is the species Saccharomyces cerevisiae, which may be regarded as the world’s foremost industrial microbe

Influence of cell surface characteristics on adhesion of Saccharomyces cerevisiae to the biomaterial hydroxylapatite

The influence of the physicochemical properties of biomaterials on microbial cell adhesion is well known, with the extent of adhesion depending on hydrophobicity, surface charge, specific functional groups and acid–base properties. Regarding yeasts, the effect of cell surfaces is often overlooked, despite the fact that generalisations may not be made between closely related strains. The current investigation compared adhesion of three industrially relevant strains of Saccharomyces cerevisiae (M-type, NCYC 1681 and ALY, strains used in production of Scotch whisky, ale and lager, respectively) to the biomaterial hydroxylapatite (HAP). Adhesion of the whisky yeast was greatest, followed by the ale strain, while adhesion of the lager strain was approximately 10-times less. According to microbial adhesion to solvents (MATS) analysis, the ale strain was hydrophobic while the whisky and lager strains were moderately hydrophilic. This contrasted with analyses of water contact angles where all strains were characterised as hydrophilic. All yeast strains were electron donating, with low electron accepting potential, as indicated by both surface energy and MATS analysis. Overall, there was a linear correlation between adhesion to HAP and the overall surface free energy of the yeasts. This is the first time that the relationship between yeast cell surface energy and adherence to a biomaterial has been described

Saccharomyces cerevisiae in the production of fermented beverages

Alcoholic beverages are produced following the fermentation of sugars by yeasts, mainly (but not exclusively) strains of the species, Saccharomyces cerevisiae. The sugary starting materials may emanate from cereal starches (which require enzymatic pre‐hydrolysis) in the case of beers and whiskies, sucrose‐rich plants (molasses or sugar juice from sugarcane) in the case of rums, or from fruits (which do not require pre‐hydrolysis) in the case of wines and brandies. In the presence of sugars, together with other essential nutrients such as amino acids, minerals and vitamins, S. cerevisiae will conduct fermentative metabolism to ethanol and carbon dioxide (as the primary fermentation metabolites) as the cells strive to make energy and regenerate the coenzyme NAD+ under anaerobic conditions. Yeasts will also produce numerous secondary metabolites which act as important beverage flavour congeners, including higher alcohols, esters, carbonyls and sulphur compounds. These are very important in dictating the final flavour and aroma characteristics of beverages such as beer and wine, but also in distilled beverages such as whisky, rum and brandy. Therefore, yeasts are of vital importance in providing the alcohol content and the sensory profiles of beverages. This Introductory Chapter reviews, in general, the growth, physiology and metabolism of S. cerevisiae in alcoholic beverage fermentations

<i>Saccharomyces cerevisiae</i> in the production of whisk(e)y

Whisk(e)y is a major global distilled spirit beverage. Whiskies are produced from cereal starches that are saccharified, fermented and distilled prior to spirit maturation. The strain of Saccharomyces cerevisiae employed in whisky fermentations is crucially important not only in terms of ethanol yields, but also for production of minor yeast metabolites which collectively contribute to development of spirit flavour and aroma characteristics. Distillers must therefore pay very careful attention to the strain of yeast exploited to ensure consistency of fermentation performance and spirit congener profiles. In the Scotch whisky industry, initiatives to address sustainability issues facing the industry (for example, reduced energy and water usage) have resulted in a growing awareness regarding criteria for selecting new distilling yeasts with improved efficiency. For example, there is now a desire for Scotch whisky distilling yeasts to perform under more challenging conditions such as high gravity wort fermentations. This article highlights the important roles of S. cerevisiae strains in whisky production (with particular emphasis on Scotch) and describes key fermentation performance attributes sought in distiller’s yeast, such as high alcohol yields, stress tolerance and desirable congener profiles. We hope that the information herein will be useful for whisky producers and yeast suppliers in selecting new distilling strains of S. cerevisiae, and for the scientific community to stimulate further research in this area

Hydrolytic effects of acid and enzymatic pre-treatment on the anaerobic biodegradability of <i>Ascophyllum nodosum</i> and <i>Laminaria digitata</i> species of brown seaweed

Abundant marine biomass in coastal regions has continued to attract increasing attention in recent times as a possible source of renewable energy. This study aimed to evaluate the effects of hydrolytic pre-treatment for the purpose of enhancing biogas yield of Laminaria digitata and Ascophyllum nodosum species found on the west coast of Scotland. Results show that L. digitata, in its natural and untreated form, appears to be more readily hydrolysable than A. nodosum. Two treatments were assessed: acid only and acid followed by enzyme. Both treatments enhanced the hydrolysis of both seaweed species, with acid-enzyme treatment providing a better performance

The future of bioethanol

Yeasts have been domesticated by mankind before horses. After the mastering of alcoholic fermentation for centuries, yeasts have become the protagonist of one of the most important biotechnological industries worldwide: the production of bioethanol. This chapter will initially present some important challenges to be overcome in this industry, both in first and second generation biofuel production. Then, it will briefly revisit some advances obtained in recent years. Finally, it will present and discuss some opportunities, in the scope of metabolic engineering and synthetic biology, that will likely be present in the future of bioethanol

Fermentation of stalk juices from different Nigerian sorghum cultivars to ethanol

For improved production of ethanol from sorghum stalk juice fermentation, cultivation location and cultivar type are important factors to consider. In the present study, SSV2 and KSV8 sorghum cultivars were cultivated in Kano and Kaduna states in Nigeria that exhibit notably different rain precipitation and diurnal temperatures. The crude stalk juices (without pre-treatment or nutrient supplementation) were extracted from these sorghum samples and fermented with a distiller’s strain of the yeast, Saccharomyces cerevisiae. Sugar consumption and alcohol production were determined by HPLC and GC-MS, respectively. When it was grown in the Kaduna site, SSV2 was identified as the highest yielding sorghum cultivar from which we extracted the maximum levels of extractable sugars (161.50 g l-1 ) that yielded favourable ethanol levels of 80.56 g l-1 following fermentation. Our findings show that relatively colder and wetter cultivation sites are preferred for sorghum stalk juice destined for bioethanol production.<br/