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Background Xylose is a most prevalent sugar available in hemicellulose fraction of lignocellulosic biomass (LCB) and of great interest for the green economy. Unfortunately, most of the cell factories cannot inherently metabolize xylose as sole carbon source. Yarrowia lipolytica is a non-conventional yeast to produce industrially important metabolites, and it is able to metabolize a large variety of substrates including both hydrophilic and hydrophobic carbon sources. However, Y. lipolytica lacks effective metabolic pathway for xylose uptake and only scarce information is available on utilization of xylose. For the economically feasible of LCB-based biorefineries, effective utilization of both pentose and hexose sugars is obligatory. Results In the present study, succinic acid (SA) production from xylose by Y. lipolytica was examined. To this end, Y. lipolytica PSA02004 strain was engineered by overexpressing pentose pathway cassette comprising of xylose reductase ( XR ), xylitol dehydrogenase ( XDH ) and xylulose kinase ( XK ) gene. The recombinant strain exhibited a robust growth on xylose as sole carbon source and accumulated SA (3.8 g/L) with a yield of 0.19 g/g in shake flask studies. Substrate inhibition studies revealed a marked negative impact on cell growth and product formation above 60 g/L xylose concentration. The modelling based on inhibition kinetics revealed that Aiba model showed better fit with experimental data, which resulted the correlation coefficient (R 2 ) of 0.82 and inhibition constant (K I ) 88.9 g/L. The batch cultivation of recombinant strain in bioreactor resulted in a maximum biomass concentration of 7.3 g/L and SA titer of 11.2 g/L with the yield of 0.18 g/g. Similar results in term of cell growth and SA production were obtained with xylose-rich hydrolysate derived from sugarcane bagasse. The fed-batch fermentation yielded biomass concentration of 11.8 g/L (OD 600 : 56.1) and SA titer of 22.3 g/L with a gradual decrease in pH below 4.0. Acetic acid was obtained as a main byproduct in all the fermentations. Conclusion The recombinant strain displayed potential bioconversion of xylose to succinic acid. Further this study provided a new insight on conversion of LCB into value-added products. To the best of our knowledge, this is the first study on SA production by Y. lipolytica using xylose as a sole carbon source.

Background: Xylitol is a commercially important chemical with multiple applications in food and pharmaceutical industries. According to the US Department of Energy, xylitol is among the twelve platform chemicals that can be produced from biomass. The chemical method for xylitol synthesis is however expensive and energy intensive. In contrast, the biological route involving microbial cell factories offers a potential cost-effective alternative process. The bioprocess occurs under ambient conditions and makes use of biocatalysts which can be sourced from renewable carbon coming from a variety of cheap feedstocks classified as wastes. Result: In this study, biotransformation of xylose to xylitol was investigated using Yarrowia lipolytica an oleaginous yeast grown on glycerol/glucose screening of primary carbon source, media optimisation in shake flask, scale up in bioreactor and downstream processing of xylitol were carried out. With the two step medium optimization involving central composite design and artificial neural network coupled with genetic algorithm, the yeast amassed 53.2 g/L of xylitol using glycerol and xylose with a bioconversion yield of 0.97 g/g. Similar results were obtained when pure glycerol was substituted with crude glycerol from biodiesel industry (titer: 50.5 g/L; yield: 0.92 g/g). Even when xylose from lignocellulosic hydrolysate was used as opposed to pure xylose, a xylitol yield of 0.54 g/g was achieved. Xylitol was successfully crystallized from fermented broth using pure glycerol/xylose and crude glycerol /xylose with a recovery of 35 and 39.45%, respectively. Conclusion: To the best of the author’s knowledge, this is the first study demonstrating the potential of Y. lipolytica as microbial cell factory for xylitol synthesis from inexpensive feedstocks. The results obtained are competitive with other xylitol producing organisms.

The CH2Cl2 crude extract and a fraction enriched with halogenated monoterpenes of the Brazilian red alga Plocamium brasiliense were evaluated for cytotoxicity and against the virus HSV-1. The extract showed low cytotoxicity compared with the fraction containing monoterpenes. The crude extract showed, in vitro, a high reduction of infectivity of the virus HSV-1.

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