Efficient and rapid production of value-added chemicals from lignocellulosic biomass is an important step toward a sustainable society. Lactic acid, used for synthesizing the bioplastic polylactide, has been produced by microbial fermentation using primarily glucose. Lignocellulosic hydrolysates contain high concentrations of cellobiose and xylose. Here, we constructed a recombinant Saccharomyces cerevisiae strain capable of fermenting cellobiose and xylose into lactic acid. Specifically, genes (cdt-1, gh1-1, XYL1, XYL2, XYL3, and ldhA) coding for cellobiose transporter, β-glucosidase, xylose reductase, xylitol dehydrogenase, xylulokinase, and lactate dehydrogenase were integrated into the S. cerevisiae chromosomes. The resulting strain produced lactic acid from cellobiose or xylose with high yields. When fermenting a cellulosic sugar mixture containing 10 g/L glucose, 40 g/L xylose, and 80 g/L cellobiose, the engineered strain produced 83 g/L of lactic acid with a yield of 0.66 g lactic acid/g sugar (66% theoretical maximum). This study demonstrates initial steps toward the feasibility of sustainable production of lactic acid from lignocellulosic sugars by engineered yeast.

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Introduction Previous burn and traumatic injury studies have established that adrenergic signaling is increased after burn injury and may lead to an impairment of hematopoietic cell development in the bone marrow (BM). Nonetheless, mesenchymal stem cells (MSCs), which have gained momentum in regenerative medicine also play a predominant role in the BM niche. Understanding the propensity of the adrenergic receptor (AR) response by MSCs can be utilized for devising targeted therapies. However, the traditional plastic adherence procedure using ex vivo culture of BM cells for several weeks may skew the actual characteristics of MSCs. Our current study focused on isolating MSCs from freshly obtained BM in a murine scald burn model with a goal to characterize the expression pattern of native AR subgroups present on BM MSCs as compared to sham mice. Methods Eight, two-month-old adult female mice were subjected to a 15% total body 3rd degree burn or sham burn. The mice were sacrificed 7 days later. Femurs were removed and total bone marrow cells were flushed out. Multi parametric flow cytometry was used to gate for cells negative for hematopoietic cell markers (CD45, CD11B) and positive for MSC markers (CD105, CD106, SSEA, Ly6A) and AR subgroups (α1, α2, β1, β2, β3). We measured the number of BM MSCs, quantified the subtypes of ARs present on MSCs, and compared the ratio of AR antibody binding per total MSC population. Results Overall the frequency of MSCs per million total BM cells decreased by 48% post-burn injury with165,300 ± 194 in sham versus 110,000 ± 30 in burn displayed as bar graph in Panel A. Over 90% of MSCs consistently express β2 AR and only 10% express α2 AR subgroup in both scald and sham burn. Presence of other subgroups ranged from 50% to 80% of MSCs as seen in histograms to the right of dotted line in Panel B. Our AR propensity score based on AR mean fluorescence intensity adjusted to total number of MSCs present was increased by 2.8-fold for α1, 2.5-fold for β1, 1.6-fold for β3, and 1.3-fold for β2 AR subgroups (Panel C). These findings indicate burn injury not only decreases the frequency of BM MSCs but also increases the affinity of certain AR subgroups present on MSCs. Since BM MSCs are the major source of cytokines, chemokines and growth factors; detailed studies on AR mediated signaling in BM MSCs is warranted. Conclusions Polarization of AR signaling in BM MSCs by burn-induced catecholamines may have broader implications for comorbidities such as bone resorption and muscle wasting observed in human patients post burn trauma.