What do we know about the yeast strains from the Brazilian fuel ethanol industry?

Abstract

The production of fuel ethanol from sugarcane-based raw materials in Brazil is a successful example of a large-scale bioprocess that delivers an advanced biofuel at competitive prices and low environmental impact. Two to three fed-batch fermentations per day, with acid treatment of the yeast cream between consecutive cycles, during 6-8 months of uninterrupted production in a nonaseptic environment are some of the features that make the Brazilian process quite peculiar. Along the past decades, some wild Saccharomyces cerevisiae strains were isolated, identified, characterized, and eventually, reintroduced into the process, enabling us to build up knowledge on these organisms. This information, combined with physiological studies in the laboratory and, more recently, genome sequencing data, has allowed us to start clarifying why and how these strains behave differently from the better known laboratory, wine, beer, and baker's strains. All these issues are covered in this minireview, which also presents a brief discussion on future directions in the field and on the perspectives of introducing genetically modified strains in this industrial process.

Vinasse from Sugarcane Ethanol Production: Better Treatment or Better Utilization?

“…The high-density cell culture and simple composition of sugarcane juice allow a quick fermentation cycle (6-10 h) and low cell growth rates (Della-Bianca et al, 2013). The upstream steps include a sulfitation process, which enrich the downstream products with sulfur compounds, especially sulfate species (Della-Bianca et al, 2013). After fermentation, the fermented juice is processed into an ethanol stream and a liquid-rich by-product-vinasse.…”

Promoter engineering of the Saccharomyces cerevisiae RIM15 gene for improvement of alcoholic fermentation rates under stress conditions

“…Effects of P PCK1 -RIM15 on alcoholic fermentation under more severe conditions The high viability of the P PCK1 -RIM15 cells after single-batch fermentation suggested that this strain may be beneficial for use in repetitive fermentation in which yeast cells are harvested after batch fermentation and reused in the next batch (8,9). To test this possibility, we repeated 7-day batch fermentation tests 10 times (70 days of fermentation in total) and measured carbon dioxide emission during the initial 3 days (E3) in the third (E3 3 ) and 10th (E3 10 ) cycles (Fig.…”

“…A loss-of-function mutation in Rim15p (rim15 5055insA ) found specifically in K7 and related strains (3) couples a decrease in stress tolerance with an increase in the fermentation rate through impairment of stress-induced anabolic synthesis of storage and structural carbohydrates and redirection of glucose into glycolysis (6). Stress-sensitive sake yeast strains are suitable for sake fermentation in which yeast cells are not subjected to severe osmotic stress due to the simultaneous saccharification and fermentation (SSF) process of rice starch (7) and are usually not recycled from one batch to another, unlike brewing of lager-type beer or production of bioethanol (8,9). However, to guarantee alcoholic fermentation under more stressful and/or repetitive fermentation conditions, other attempts should be made to control the activity of Rim15p, which plays pivotal roles in acquisition of stress responses (10e13) and inhibition of alcoholic fermentation (3,6,14e16).…”

Morphophysiological and molecular characterization of wild yeast isolates from industrial ethanol process

“…Contrariwise, some isolates were found to derive from genetic modifications, a clonal differentiation that occurs during the fermentation process. This mainly occurs due to the unique large-scale fed-batch process, which utilizes acid cell recycling and submits the cells under a great deal of stress (Della-Bianca et al, 2013). Yeast isolates subjected to harsh conditions tend to develop genetic-induced physiological traits that make them more resistant, including the activation of genes responsible for cell wall integrity and oxidative stress response (Elsztein et al, 2011).…”