Biochemical evaluation, molecular characterization and identification of novel yeast strains isolated from Brazilian savannah fruits, chicken litter and a sugar and alcohol mill with biotechnological potential for biofuel and food industries

Physiological evaluation of yeast strains under anaerobic conditions using glucose, fructose, or sucrose as the carbon source

The aim of this study was to evaluate the physiology of 13 yeast strains by assessing their kinetic parameters under anaerobic conditions. They included Saccharomyces cerevisiae CAT-1 and 12 isolated yeasts from different regions in Brazil. The study aimed to enhance understanding of the metabolism of these strains for more effective applications. Measurements included quantification of sugars, ethanol, glycerol, and organic acids. Various kinetic parameters were analyzed, such as specific substrate utilization rate (qS), maximum specific growth rate (μmax), doubling time, biomass yield, product yield, maximum cell concentration, ethanol productivity (PEth), biomass productivity, and CO2 concentration. S. cerevisiae CAT-1 exhibited the highest values in glucose for μmax (0.35 h-1), qS (3.06 h-1), and PEth (0.69 gEth L-1 h-1). Candida parapsilosis Recol 37 did not fully consume the substrate. In fructose, S. cerevisiae CAT-1 stood out with higher values for μmax (0.25 h-1), qS (2.24 h-1), and PEth (0.60 gEth L-1 h-1). Meyerozyma guilliermondii Recol 09 and C. parapsilosis Recol 37 had prolonged fermentation times and residual substrate. In sucrose, only S. cerevisiae CAT-1, S. cerevisiae BB9, and Pichia kudriavzevii Recol 39 consumed all the substrate, displaying higher PEth (0.72, 0.51, and 0.44 gEth L-1 h-1, respectively) compared to other carbon sources.

The marula and elephant intoxication myth: assessing the biodiversity of fermenting yeasts associated with marula fruits (Sclerocarya birrea)

The inebriation of wild African elephants from eating the ripened and rotting fruit of the marula tree is a persistent myth in Southern Africa. However, the yeasts responsible for alcoholic fermentation to intoxicate the elephants remain poorly documented. In this study, we considered Botswana, a country with the world's largest population of wild elephants, and where the marula tree is indigenous, abundant and protected, to assess the occurrence and biodiversity of yeasts with a potential to ferment and subsequently inebriate the wild elephants. We collected marula fruits from over a stretch of 800 km in Botswana and isolated 106 yeast strains representing 24 yeast species. Over 93% of these isolates, typically known to ferment simple sugars and produce ethanol comprising of high ethanol producers belonging to Saccharomyces, Brettanomyces, and Pichia, and intermediate ethanol producers Wickerhamomyces, Zygotorulaspora, Candida, Hanseniaspora, and Kluyveromyces. Fermentation of marula juice revealed convincing fermentative and aromatic bouquet credentials to suggest the potential to influence foraging behaviour and inebriate elephants in nature. There is insufficient evidence to refute the aforementioned myth. This work serves as the first work towards understanding the biodiversity marula associated yeasts to debunk the myth or approve the facts.

Isolation, Identification, Optimization of Baker’s Yeast from Natural Sources, Scale-Up Production Using Molasses as a Cheap Carbohydrate Source, and Evaluation for Bread Production

(1) Background: Bangladesh must has to spend a large amount of foreign currency to import commercial baker’s yeast every year. We could save money by finding a potential Saccharomyces cerevisiae from natural sources compatible with commercial baker’s yeast production. (2) Methods: Grapes, rice, pineapples were collected, processed, and inoculated on YMA plates and incubated at 30 °C for 48 h. Then 11 single morphologically well-formed colonies were isolated, purified, and identified, three as S. cerevisiae, three as S. rouxii, three as S. bisporus, and two as S. exigus based on standard cultural, morphological, and biochemical characteristics. Identified S. cerevisiae (designated as G2, P5 and R3) were then assessed for CO2 production as a measure of their baking potential during bread production and compared with two commercial strains (designated as C1 and C2). (3) Results: Isolate-G2 produced the maximum of 1830 mm3 of gas, whereas C1, C2, R3, and P5 produced 1520, 1680, 770, and 610 mm3 gas, respectively. No strain produced H2S which is associated with an off-flavor and unpleasant taste. These isolates showed maximum cell density at a pH range of 4–5.5 in 4–16% molasses broth at 30 °C after 4 days of incubation and maximum 4.75 × 109, 7.9 × 108, 1.472 × 1010, 2.08 × 1010 and 5.24 × 109 CFU mL−1 were produced by C1, C2, G2, P5 and R3, respectively. Isolate-G2 was found to have the most potential, whereas isolate-R3 and P5 have satisfactory potential. (4) Conclusions: G2 could be a good candidate for commercial trials.

Effects of the carbon source on the physiology and invertase activity of the yeast Saccharomyces cerevisiae FT858

Saccharomyces cerevisiae FT858 is an industrial yeast strain with high fermentative efficiency, but marginally studied so far. The aim of this work was to evaluate the biotechnological potential of S. cerevisiae FT858 through kinetic growth parameters, and the influence of the concentration of the substrate on the synthesis of the invertase enzyme. Invertases have a high biotechnological potential and their production through yeast is strongly influenced by the sugars in the medium. S. cerevisiae FT858 has an excellent biotechnological potential compared to the industrial yeast reference S. cerevisiae CAT-1, as it presented a low glycerol yield on the substrate (Y _GLY/S) and a 10% increase in ethanol yield on sucrose in cultures with sucrose at 37 °C. The substrate concentration directly interfered in invertase production and the enzymatic expression underwent strong regulation through glucose concentration in the culture medium and S. cerevisiae CAT-1 presented constitutive behavior for the invertase enzyme.

Evaluation of the Fermentative Capacity of Saccharomyces cerevisiae CAT-1 and BB9 Strains and Pichia kudriavzevii BB2 at Simulated Industrial Conditions

The search for promising yeasts that surpass the fermentative capacity of commercial strains, such as Saccharomyces cerevisiae CAT-1, is of great importance for industrial ethanol processes in the world. Two yeasts, Pichia kudriavzevii BB2 and Saccharomyces cerevisiae BB9, were evaluated in comparison to the industrial yeast S. cerevisiae CAT-1. The objective was to evaluate the performance profile of the three studied strains in terms of growth, substrate consumption, and metabolite formation, aiming to determine their behaviour in different media and pH conditions. The results showed that under cultivation conditions simulating the medium used in the industrial process (must at 22° Brix at pH 3.0) the highest ethanol productivity was 0.41 g L^-1 h^-1 for S. cerevisiae CAT-1, compared to 0.11 g L^-1 h^-1 and 0.16 g L^-1 h^-1 for P. kudriavzevii and S. cerevisiae BB2, respectively. S. cerevisiae CAT-1 produced three times more ethanol in must at pH 3.0 (28.30 g L^-1) and in mineral medium at pH 3.0 (29.17 g L^-1) and 5.0 (30.70 g L^-1) when compared to the value obtained in sugarcane must pH 3.0 (9.89 g L^-1). It was concluded that S. cerevisiae CAT-1 was not limited by the variation in pH in the mineral medium due to its nutritional composition, guaranteeing better performance of the yeast even in the presence of stressors. Only S. cerevisiae CAT-1 expressed he constitutive invertase enzyme, which is responsible for hydrolysing the sucrose contained in the must.

Effects of the carbon source and the interaction between carbon sources on the physiology of the industrial Saccharomyces cerevisiae CAT-1

During industrial fermentation, wild isolates are able to persist and even predominate in the bioreactors. Saccharomyces cerevisiae CAT-1 was one of these isolates and now is one of the yeasts mostly used in industrial ethanol processes in Brazil due to its efficient fermentation capacity. Despite it, the strain's physiology has been marginally studied so far. Since strains of the same species may have different responses to a specific cultivation condition, this work aimed to evaluate the physiology of S. cerevisiae CAT-1 in batch cultures using different carbon sources (glucose, fructose, sucrose, maltose, and galactose) as a sole carbon source and in binary mixtures, at 30 and 37 °C. The results showed that the fructose, sucrose, and maltose were the sugars that presented the highest ethanol yields on the substrate (0.40 g_ethanol g_substrate^-1) at both temperatures. Galactose was the sugar that the yeast had the lowest affinity given the lowest maximum specific growth rate (0.28 h^-1). Despite the influence of a variety of mechanisms for sugar transport, the cells consume first substrates with fewer metabolic steps to catabolism and are susceptible to adaptive evolution depending on the availability of substrate.

Physiology of yeast strains isolated from Brazilian biomes in a minimal medium using fructose as the sole carbon source reveals potential biotechnological applications

The aim of this study was to evaluate the kinetic parameters and the production of metabolites of 13 novel yeasts isolated from a distillery and fruits, and Saccharomyces cerevisiae CAT-1, cultivated in fructose-based medium. The yeasts with the highest µ _max were obtained from must, Pichia kudriavzevii BB2, P. kudriavzevii BB1, and S. cerevisiae BB9 (0.47-0.49 h^-1). S. cerevisiae CAT-1 (3.02 g gDCM^-1 h^-1), S. cerevisiae BB9 (3.01 g gDCM^-1 h^-1), and Candida glabrata Recol 41 (2.52 g gDCM^-1 h^-1) stood out in terms of µ _S. C. parapsilosis Recol 29, and Rhodotorula mucilaginosa Recol 03 strains showed the highest Y _X/S (0.30 and 0.28 gDCM g^-1, respectively). C. glabrata Recol 10 and S. cerevisiae BB9 strains stood out for their higher substrate conversion rates into ethanol (0.44 and 0.41 gEth gS^-1, respectively). R. mucilaginosa Recol 03 presented the poorest performance in substrate consumption (0.87 g gDCM^-1 h^-1), while the strains isolated from must and C. glabrata Recol 10 showed the highest ethanol production and the C. parapsilosis Recol 29 showed the highest biomass conversion.