Effect of oxygenation and temperature on glucose-xylose fermentation in Kluyveromyces marxianus CBS712 strain

Abstract

BackgroundThe yeast Kluyveromyces marxianus features specific traits that render it attractive for industrial applications. These include production of ethanol which, together with thermotolerance and the ability to grow with a high specific growth rate on a wide range of substrates, could make it an alternative to Saccharomyces cerevisiae as an ethanol producer. However, its ability to co-ferment C5 and C6 sugars under oxygen-limited conditions is far from being fully characterized.ResultsIn the present study, K. marxianus CBS712 strain was cultivated in defined medium with glucose and xylose as carbon source. Ethanol fermentation and sugar consumption of CBS712 were investigated under different oxygen supplies (1.75%, 11.00% and 20.95% of O2) and different temperatures (30°C and 41°C). By decreasing oxygen supply, independently from the temperature, both biomass production as well as sugar utilization rate were progressively reduced. In all the tested conditions xylose consumption followed glucose exhaustion. Therefore, xylose metabolism was mainly affected by oxygen depletion. Loss in cell viability cannot explain the decrease in sugar consumption rates, as demonstrated by single cell analyses, while cofactor imbalance is commonly considered as the main cause of impairment of the xylose reductase (KmXR) - xylitol dehydrogenase (KmXDH) pathway. Remarkably, when these enzyme activities were assayed in vitro, a significant decrease was observed together with oxygen depletion, not ascribed to reduced transcription of the corresponding genes.ConclusionsIn the present study both oxygen supply and temperature were shown to be key parameters affecting the fermentation capability of sugars in the K. marxianus CBS712 strain. In particular, a direct correlation was observed between the decreased efficiency to consume xylose with the reduced specific activity of the two main enzymes (KmXR and KmXDH) involved in its catabolism. These data suggest that, in addition to the impairment of the oxidoreductive pathway being determined by the cofactor imbalance, post-transcriptional and/or post-translational regulation of the pathway enzymes contributes to the efficiency of xylose catabolism in micro-aerobic conditions. Overall, the presented work provides novel information on the fermentation capability of the CBS712 strain that is currently considered as the reference strain of the genus K. marxianus.

Integrated Bioethanol Fermentation/Anaerobic Digestion for Valorization of Sugar Beet Pulp

“…Native yeast species able to ferment xylose include Scheffersomyces and Candida species, as well as some strains of K. marxianus [26]. Due to its natural ability to assimilate pentose and hexose sugars, K. marxianus could provide an alternative option to conventional yeasts for second-generation ethanol fermentation [27]. The metabolic diversity of their various strains makes these species interesting for several potential applications [28].…”

Dynamics of ethanol production from deproteinized whey by Kluyveromyces marxianus: An analysis about buffering capacity,thermal and nitrogen tolerance

“…2), which showed a thermotolerance to produce ethanol (end product) in these conditions. Thermotolerance has already been described to produce ethanol using K. marxianus (Lane and Morrissey 2010;Signori et al 2014). However, ethanol and biomass productions were influenced at 30°C by the changes in pH (Fig.…”

“…Thus, CW fermentation could be an interesting alternative to produce ethanol because of its high lactose content (Hungaro et al 2013;Song et al 2013). Still on current published reports, K. marxianus remains the popular inoculant agent utilized in ethanol fermentation of whey-based media (Table 1) because it presents the thermotolerance, fastest growth rate among eukaryotic organisms, the capacity to assimilate a wide range of sugars (which is an important aspect since different substrates may be combined) and secretion of lytic enzymes (Lane and Morrissey 2010;Signori et al 2014). However, despite this described thermotolerance, there are lack of studies on evaluating the metabolic tolerance such as nitrogen source influence to obtain the product of interest (end product) at the region of maximum metabolic activity of yeast (RMMA; ≈ pH: 4.5-6.0; T: 30-40°C), especially in fermentative systems focusing on ethanol production.…”

Ethanol Production by Alcohol Tolerant Yeasts Using Different Carbohydrate Sources

“…In a recent study, we found that nonSaccharomyces yeast species with 97-98% sequence homology to Pichia kudriavzevii, were capable of normal growth and metabolism in the presence of increasing amounts of ethanol (0-20% v/v) in the broth culture [13]. The paradigm shift towards the application of nonconventional yeast strains is evident with Kluyveromyces marxianus which was found to be to grow at extreme temperatures (45-52 degree Celsius °C) in additional to its inherent ability to utilise a wide range of carbon sources [14][15][16]. Attempts to produce ethanol with Pichia sp., has been attempted with sugarcane juice, glucose and galactose in India [7].…”