Isolation and characterization of bioethanol producing wild yeasts from bio-wastes and co-products of sugar factories

Characterization and biocontrol potential of Wickerhamomyces subpelliculosus yeasts isolated from dates: Volatile compounds-mediated antifungal activity against mycotoxigenic Penicillium strains

Seven yeast strains were isolated from Tunisian dates. The strains were identified by sequence analysis of the D1/D2 domain of the nuclear large subunit (LSU) rRNA gene. Based on this all strains in the study were almost identical with that of the type strain of Wickerhamomyces subpelliculosus (CBS 5767) indicating that they belong to this species. All strains were characterized physiologically and biochemically. All strains grew in the presence of 50 % sucrose, 10 % sodium chloride and at 42 °C. The potential of these yeasts as biocontrol agent against mycotoxigenic Penicillium species inhabiting date, was evaluated. All yeast strains inhibited the growth of P. citrinum P10 and P. chrysogenum C17 previously isolated from dates, with inhibition percentages ranging between 43.6 % and 70.3 % on dual culture plate assays. Moreover, the volatile compounds (VCs) produced by these yeasts inhibited the mycelial growth rate and sporulation of both fungus strains, up to 76.5 and 100 %, respectively, on inverted culture plate assay. The VCs of W. subpelliculosus strains Y4 and Y24, which exhibit strong inhibitory activity against toxigenic Penicillium, were determined by head-space solid-phase microextraction (HS-SPME) combined with gas chromatography coupled with mass spectrometry (GC-MS) analysis. Results revealed significant levels of alcohols (27.36 % for Y4 and 23.35 % for Y24) and esters (66.19 % for Y4 and 75.82 % for Y24). Their significant bioactivity, along with the lack of reported adverse effects on consumer health or the environment, makes them a sustainable and effective alternative to synthetic fungicides for the biocontrol of mycotoxigenic Penicillium affecting stored dates.

Ethanol and 2-phenylethanol production by bee-isolated Meyerozyma caribbica strains

Investigating the biotechnological potential of wild microorganisms is paramount for optimizing bioprocesses. Given this premise, we looked for yeasts in Brazilian native stingless bees, considering the recognized potential of pollinating insect-associated microorganisms for the production of volatile organic compounds (VOCs). Two yeast strains of the species Meyerozyma caribbica were isolated from bees Scaptotrigona postica and evaluated for their fermentative capacity. Both yeasts were capable of fermenting sucrose (the main sugar used in the Brazilian ethanol industry) with over 90% efficiency and yields of up to 0.504 g/g. Through an experimental design analysis (CCD), it was verified that the ethanol productivity of these yeasts can also benefit from high concentrations of sucrose and low pH values, desirable traits for microorganisms in this biofuel production. At the same time, CCD analyses also showed the great capacity of these M. caribbica strains to produce another alcohol of broad biotechnological interest, 2-phenylethanol. Interestingly, the statistical analyses demonstrated that greater production of this compound can occur at high sugar concentrations and low availability of nitrogen sources, which can be easily achieved using residual low-cost feedstocks. Thus, our results suggest that these M. caribbica strains may be efficiently used in both ethanol and 2-phenylethanol production.

Isolation, screening and identification of ethanol producing yeasts from Ethiopian fermented beverages

The growing demand for renewable energy sources such as bioethanol is facing a lack of efficient ethanologenic microbes. This study aimed to isolate and screen ethanologenic yeasts from Ethiopian fermented beverages. A progressive screening and selection approach was employed. Selected isolates were evaluated for bioethanol production using banana peel waste as substrate. A total of 102 isolates were obtained. Sixteen isolates were selected based on their tolerance to stress conditions and carbohydrate fermentation and assimilation capacity. Most found moderately tolerant to 10 %, but slightly tolerant at 15 and 20 % (v/v) ethanol concentration. They yield 15.3 to 20.1 g/L and 9.1 ± 0.6 to 12.9 ± 1.3 g/L ethanol from 2 % (w/v) glucose and 80 g/L banana peel, respectively. Molecular characterization identified them as Saccharomyces cerevisiae strains. Results demonstrate insight about their potential role in the ethanol industry. Optimization of the fermentation conditions is recommended.

Diversity of dung beetle-associated yeasts from pristine environments of Botswana

Yeast-insect interactions are increasingly becoming an attractive source of discovery for previously unknown, unique, diverse, and industrially relevant yeast species. Despite a wealth of studies that have recently focused on yeasts in symbiotic association with Hymenopteran insects, yeasts associated with Coleopteran insects, such as lignocellulosic-rich dung-dependent beetles, remain poorly studied. Trends in yeast discovery suggest that species richness and diversity can be attributed to the ecological niche of the insect. Here, we considered the potential of dung beetles inhabiting the extreme environments of Botswana, characterized by desert-like conditions (semi-arid to arid and hot) as well as protected pristine environments, as possible attribute niches that can shape the extremophilic and diverse life history strategies of yeasts. We obtained a total of 97 phylogenetically diverse yeast isolates from six species of dung beetles from Botswana's unexplored environments, representing 19 species belonging to 11 genera. The findings suggest that the guts of dung beetles are a rich niche for non-Saccharomyces yeast species. Meyerozyma and Pichia were the most dominant genera associated with dung beetles, representing 55% (53 out of 97) of the yeast isolates in our study. Trichosporon and Cutaneotrichosporon genera represented 32% (31 out of 97) of the isolates. The remaining isolates belonged to Apiotrichum, Candida, Diutina, Naganishia, Rhodotorula, and Wickerhamiella genera (12 out of 97). We found out that about 62% (60 out of 97) of the isolates were potentially new species because of their low internal transcribed spacer (ITS) sequence similarity when compared to the most recent optimal species delineation threshold. A single isolate was unidentifiable using the ITS sequences. Using an in silico polymerase chain reaction-restriction fragment length polymorphism approach, we revealed that there was genetic diversity within isolates of the same species. Our results contribute to the knowledge and understanding of the diversity of dung beetle-associated yeasts.

Optimization of bioethanol production from sugarcane molasses by the response surface methodology using Meyerozyma caribbica isolate MJTm3

Purpose

Yeast strains tolerant to a wide range of stress conditions are needed for the production of bioethanol from substrates rich in sugar. In our earlier research findings, Meyerozyma caribbica isolate MJTm3 (OM329077) demonstrated remarkable stress tolerance and fermentative activity. The present study aimed to optimize six fermentation parameters to generate conducive fermentation conditions for ethanol production by M. caribbica isolate MJTm3.

Method

The response surface method (RSM) based on central composite design (CCD) was employed to optimize process conditions for higher bioethanol yield. The optimization process was carried out based on six independent parameters, namely temperature (25–35 °C), pH (5.5–6.5), inoculum size (10–20% (v/v)), molasses concentration (25–35 (w/v)), mixing rate (110–150 rpm), and incubation period (48–72-h). Analysis of ethanol concentration was done by HPLC equipped with a UV detector.

Result

The optimal conditions of the parameters resulting in a maximum predicted ethanol yield were as follows: pH 5.5, an inoculum size of 20%, a molasses concentration of 25 °Bx, a temperature of 30 °C, an incubation period of 72-h, and a mixing rate of 160 revolutions per minute (rpm). Using the above optimum conditions, the model predicted a bioethanol yield of 79%, 92% of the theoretical yield, a bioethanol concentration of 49 g L−1, and a productivity of 0.68 g L−1 h−1. A batch fermentation experiment was carried out to validate the predicted values and resulted in a bioethanol yield of 86%, 95% of theoretical yield, a bioethanol concentration of 56 g L−1, and productivity of 0.78 g L−1 h−1. On the other hand, the surface plot analysis revealed that the synergistic effect of the molasses concentration and the mixing rate were vital to achieving the highest bioethanol yield. These values suggested that the RSM with CCD was an effective method in producing the highest possible output of bioethanol from molasses in actual operation.

Conclusion

The study confirmed the potential of using M. caribbica isolate MJTm3 for bioethanol production from sugarcane molasses under the abovementioned optimal fermentation conditions.