Stress response and adaptation mechanisms in Kluyveromyces marxianus.

Kluyveromyces marxianus is a non-Saccharomyces yeast that has gained importance due to its great potential to be used in the food and biotechnology industries. In general, K. marxianus is a known yeast for its ability to assimilate hexoses and pentoses; even this yeast can grow in disaccharides such as sucrose and lactose and polysaccharides such as agave fructans. Otherwise, K. marxianus is an excellent microorganism to produce metabolites of biotechnological interest, such as enzymes, ethanol, aroma compounds, organic acids, and single-cell proteins. However, several studies highlighted the metabolic trait variations among the K. marxianus strains, suggesting genetic diversity within the species that determines its metabolic functions; this diversity can be attributed to its high adaptation capacity against stressful environments. The outstanding metabolic characteristics of K. marxianus have motivated this yeast to be a study model to evaluate its easy adaptability to several environments. This chapter will discuss overview characteristics and applications of K. marxianus and recent insights into the stress response and adaptation mechanisms used by this non-Saccharomyces yeast.

Optimizing cellulose fraction for enhanced utility: Comparative pre-treatment of Agave tequilana Weber var. blue bagasse fiber for sustainable applications.

In recent decades, natural fibers have emerged as an alternative to synthetic fibers due to their renewable nature, lower environmental impact, and comparable strength properties. Agave bagasse, a byproduct of agave juice extraction in Mexico, stands out for its potential in various industrial applications, notably biocomposite production. Bagasse is rich in cellulose, along with hemicellulose and lignin. Cellulose is the most suitable to be converted into valuable products, and it is versatile, renewable, and biodegradable. An effective pre-treatment is crucial to enrich its fraction. This study aims to determine the optimal pre-treatment conditions for the agave bagasse. Three different pre-treatments were tested, acid (H2SO4), enzymatic (Cellic® HTec2 enzymatic preparation), and sequence of acid-enzymatic (sulfuric acid and Cellic® HTec2), to determine which pre-treatment got the optimal cellulose fraction increase. The acid pre-treatment was conducted over three time ranges (5, 10, and 15 min) at different acid concentrations (1%, 1.5%, and 2%). Enzymatic reactions were conducted over 24 h, testing three different enzyme concentrations (1.5%, 3%, 4.5%). The sequential pre-treatment utilized the optimal conditions derived from the acid experiments (1.5% H2SO4 for 10 min), followed by enzymatic reactions carried out over three different durations (6, 12, and 24 h). The findings revealed that a 1.5% acid concentration applied for 10 min was the most efficient pre-treatment method. This pre-treatment resulted in a 1.9-fold increase in the cellulose fraction while reducing hemicellulose content by 30%. The hemicellulose reduction was confirmed through Fourier Transform IR spectroscopy (FTIR) analysis, complemented by scanning electron microscopy (SEM) observations highlighting physical alterations in the fiber structure. Furthermore, thermogravimetric analysis (TGA) demonstrated improved thermal stability, suggesting potential use in biocomposites. Future research should evaluate the environmental impact of optimized pre-treatment methods for agave bagasse.

Application of dielectric spectroscopy to unravel the physiological state of microorganisms: current state, prospects and limits.

Microbial physiology is an essential characteristic to be considered in the research and industrial use of microorganisms. Conventionally, the study of microbial physiology has been limited to carrying out qualitative and quantitative analysis of the role of individual components in global cell behaviour at a specific time and under certain growth conditions. In this framework, groups of observable cell physiological variables that remain over time define the physiological states. Recently, with advances in omics techniques, it has been possible to demonstrate that microbial physiology is a dynamic process and that, even with low variations in environmental culture conditions, physiological changes in the cell are provoked. However, the changes cannot be detected at a macroscopic level, and it is not possible to observe these changes in real time. As an alternative to solve this inconvenience, dielectric spectroscopy has been used as a complementary technique to monitor on-line cell physiology variations to avoid long waiting times during measurements. In this review, we discuss the state-of-the-art application of dielectric spectroscopy to unravel the physiological state of microorganisms, its current state, prospects and limitations during fermentation processes. Key points • Summary of the state of the art of several issues of dielectric spectroscopy. • Discussion of correlation among dielectric properties and cell physiological states. • View of the potential use of dielectric spectroscopy in monitoring bioprocesses.

Dielectric property measurements as a method to determine the physiological state of Kluyveromyces marxianus and Saccharomyces cerevisiae stressed with furan aldehydes.

Cell physiology parameters are essential aspects of biological processes; however, they are difficult to determine on-line. Dielectric spectroscopy allows the on-line estimation of viable cells and can provide important information about cell physiology during culture. In this study, we investigated the dielectric property variations in Kluyveromyces marxianus SLP1 and Saccharomyces cerevisiae ERD yeasts stressed by 5-hydroxymethyl-2-furaldehyde and 2-furaldehyde during aerobic growth. The dielectric properties of cell permittivity, specific membrane capacitance (Cm), and intracellular conductivity (σIn) were considerably affected by furan aldehydes in the same way that the cell population, viability, cell size, substrate consumption, organic acid production, and respiratory parameters were. The yeasts stressed with furan aldehydes exhibited three physiological states (φ): adaptation, replicating, and nonreplicating states. During the adaptation state, there were small and stable signs of permittivity, Cm, and σIn; additionally, no cell growth was observed. During the replicating state, cell growth was restored, and the cell viability increased; in addition, the permittivity and σIn increased rapidly and reached their maximum values, while the Cm decreased. In the nonreplicating state, the permittivity and σIn were stable, and Cm decreased to its minimum value. Our results demonstrated that knowing dielectric properties allowed us to obtain information about the physiological state of the cells under control and stressed conditions. Since the permittivity, Cm, and σIn are directly associated with the physiological state of the yeast, these results should contribute to a better understanding of the stress response of yeasts and open the possibility to on-line monitor and control the physiological state of the cell in the near future.

Performance evaluation of Pichia kluyveri, Kluyveromyces marxianus and Saccharomyces cerevisiae in industrial tequila fermentation.

Traditionally, industrial tequila production has used spontaneous fermentation or Saccharomyces cerevisiae yeast strains. Despite the potential of non-Saccharomyces strains for alcoholic fermentation, few studies have been performed at industrial level with these yeasts. Therefore, in this work, Agave tequilana juice was fermented at an industrial level using two non-Saccharomyces yeasts (Pichia kluyveri and Kluyveromyces marxianus) with fermentation efficiency higher than 85 %. Pichia kluyveri (GRO3) was more efficient for alcohol and ethyl lactate production than S. cerevisiae (AR5), while Kluyveromyces marxianus (GRO6) produced more isobutanol and ethyl-acetate than S. cerevisiae (AR5). The level of volatile compounds at the end of fermentation was compared with the tequila standard regulation. All volatile compounds were within the allowed range except for methanol, which was higher for S. cerevisiae (AR5) and K. marxianus (GRO6). The variations in methanol may have been caused by the Agave tequilana used for the tests, since this compound is not synthesized by these yeasts.

Induction of xylanases by sugar cane bagasse at different cell densities of Cellulomonas flavigena.

The effect of cell density on xylanolytic activity and productivity of Cellulomonas flavigena was evaluated under two different culturing conditions: fed-batch culture with discontinuous feed of sugar cane bagasse (SCB; condition 1) and glycerol fed-batch culture followed by addition of SBC as xylanases inducer (condition 2). The enzymatic profile of xylanases was similar in both systems, regardless of the initial cell density at time of induction. However, the xylanolytic activity changed with initial cell density at the time of induction (condition 2). The maximum volumetric xylanase activity increased with increased initial cell density from 4 to 34 g l(-1) but decreased above this value. The largest total volumetric xylanase productivity under condition 2 (1.3 IU ml(-1) h(-1)) was significantly greater compared to condition 1 (maximum 0.6 IU ml(-1) h(-1)). Consequently, induction of xylanase activity by SCB after growing of C. flavigena on glycerol at intermediate cell density can be a feasible alternative to improve activity and productivity of xylanolytic enzymes.