Screening, identification, and low-energy ion modified breeding of a yeast strain producing high level of 3-hydroxypropionic acid.

3-Hydroxypropionic acid (3HP) is an important platform chemical with a wide range of applications. The biological preparation of this compound is safe and low cost. In this study, orchard soil and human waste were used as raw materials to screen microbial strains that could produce 3HP in selective medium containing varying amounts of propionic acid. A yeast strain that can use propionic acid as substrate and produce 48.96 g/L 3HP was screened. Morphological observation, physiological and biochemical identification, and 26s rDNA sequencing identified the IS451 strain as Debaryomyces hansenii. The low-energy ion N+ , with the energy of 10 keV and a dose of 70 × 2.6 × 1013  ions/cm2 , was implanted into the IS451 strain. The mutant strain WT39, whose 3HP titer reached 62.42 g/L, was obtained. The strain exhibited genetic stability and tolerance to high concentrations of propionic acid and was considered to have broad application prospects.

Coupling two sizes of CSTR-type bioreactors for sequential lactic acid and xylitol production from hemicellulosic hydrolysates of vineshoot trimmings.

This study develops a system for the efficient valorisation of hemicellulosic hydrolysates of vineshoot trimmings. By connecting two reactors of 2L and 10L, operational conditions were set up for the sequential production of lactic acid and xylitol in continuous fermentation, considering the dependence of the main metabolites and fermentation parameters on the dilution rate. In the first bioreactor, Lactobacillus rhamnosus consumed all the glucose to produce lactic acid at 31.5°C, with 150rpm and 1L of working volume as the optimal conditions. The residual sugars were employed for the xylose to xylitol bioconversion by Debaryomyces hansenii in the second bioreactor at 30°C, 250rpm and an air-flow rate of 2Lmin(-1). Several steady states were reached at flow rates (F) in the range of 0.54-5.33mLmin(-1), leading to dilution rates (D) ranging from 0.032 to 0.320h(-1) in Bioreactor 1 and from 0.006 to 0.064h(-1) in Bioreactor 2. The maximum volumetric lactic acid productivity (Q(P LA)=2.908gL(-1)h(-1)) was achieved under D=0.266h(-1) (F=4.44mLmin(-1)); meanwhile, the maximum production of xylitol (5.1gL(-1)), volumetric xylitol productivity (Q(P xylitol)=0.218gL(-1)h(-1)), volumetric rate of xylose consumption (Q(S xylose)=0.398gL(-1)h(-1)) and product yield (0.55gg(-1)) were achieved at an intermediate dilution rate of 0.043h(-1) (F=3.55mLmin(-1)). Under these conditions, ethanol, which was the main by-product of the fermentation, was produced in higher amounts (1.9gL(-1)). Finally, lactic acid and xylitol were effectively recovered by conventional procedures.

Kinetic modelling of the sequential production of lactic acid and xylitol from vine trimming wastes.

A mathematical model describing the kinetics of the sequential production of lactic acid and xylitol from detoxified-concentrated vine trimming hemicellulosic hydrolysates by Lactobacillus rhamnosus and Debaryomyces hansenii, respectively, was developed from the basic principles of mass balance in two stages considering as main reactions: (1) glucose and xylose consumption by L. rhamnosus; and (2) xylitol and arabitol production by D. hansenii. The model allows to evaluate the yields and productivities under microaerobic and oxygen restricted conditions (in particular the effects caused by purging the oxygen with nitrogen), which were particularly important during the xylose to xylitol bioconversion by yeasts. The model was tested using experimental data obtained from detoxified-concentrated hemicellulosic hydrolysates, after CaCO3 addition in both types of fermentation processes, without purges (microaerobic conditions) or purging oxygen with nitrogen (oxygen-limited conditions) after sampling in order to reduce the oxygen dissolved. L. rhamnosus was removed by microfiltration before adding D. hansenii at the beginning of the second stage. Mass balance-based and logistic functions were successfully applied to develop the model of the system which properly predicts the consumption of sugars as well as the metabolites produced and yields. The dynamics of fermentation were also adequately described by the developed model.

Development of culture media containing spent yeast cells of Debaryomyces hansenii and corn steep liquor for lactic acid production with Lactobacillus rhamnosus.

To develop a cost-effective fermentation medium, biomass of Debaryomyces hansenii coming from xylitol production and corn steep liquor was evaluated for lactic acid production by Lactobacillus rhamnosus in glucose-containing media. Glucose consumption and lactic acid generation were followed using a variety of media made with different nutrient supplementation. Under selected conditions, media containing glucose, biomass of D. hansenii and corn steep liquor as unique components led to product yields similar to those obtained in a fully supplemented medium.