Characterisation of non-conventional yeast Kluyveromyces marxianus in lignocellulosic hydrolysate
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Lignocellulosic biomass is a globally available non-edible renewable feedstock, the hydrolysate of which can be used in microbial cell factories for the production of industrially relevant compounds. However, a successful microbial host should possess certain traits as the environment of lignocellulosic hydrolysates is challenging. It requires the ability to consume or, preferably, co-consume different substrates (mainly xylose), and to tolerate growth-inhibiting compounds. This thesis is focused on characterisation of a thermotolerant fast-growing non-conventional yeast, Kluyveromyces marxianus, in a lignocellulosic hydrolysate derived from birch. Growth in shake flasks experiment was firstly assessed and appropriate hydrolysate dilution for further characterisation in bioreactors was chosen. For the fastest-growing eukaryote, K. marxianus performed surprisingly poorly in the bioreactor experiments with the maximum specific growth rate reaching only 0.03 h-1 and final biomass of 5 gdw/L. An important point to consider is the nature of the nitrogen source which is one of the key factors affecting the performance. In a different experiment with organic nitrogen – a solution of yeast extract and peptone – the yeast demonstrated higher specific growth rate (0.11 h-1), in contrast to the main experiment with ammonium sulphate. A known 2-PE producer, K. marxianus produced low amounts of 2-PE (up to 0.032 g/L was detected) which can also be linked to the nature of the nitrogen source used.
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