Polyhydroxyalkanoate production by Novosphingobium nitrogenifigens Y88T and Sphingobium scionense WP01T grown on radiata pine hydrolysates

In New Zealand, 90% of commercial forestry is made up of radiata pine which can provide sustainable and abundant source of lignocellulosic substrate.  Radiata pine being recalcitrant in nature requires pretreatment to expose cellulose for the enzymatic hydrolysis to fermentable sugars. Here, two different pretreatments - high-temperature mechanical pre-treatment (HTMP) and steam explosion in the presence of sulphur dioxide (SEW) were used to generate pulps which were enzymatically hydrolysed to produce corresponding hydrolysates. Without further de-toxification step, these hydrolysates were used as a simple carbon source to grow Novosphingobium nitrogenifigens Y88^T and Sphingobium scionense WP01^T. Both bacterial strains were isolated from soil samples where radiata pine logs are processed and therefore are naturally adapted to the softwood extractives and fermentation inhibitors produced during pretreatment. Polyhydroxyalkanoates (PHAs) a renewable alternative to petrochemical based plastics was produced at a reasonably high content when  WP01^T was grown on HTMP hydrolysate in a shake flask fermentation (32 %w/w PHA, Y_PHA/glucose =0.22 with a theoretical maximum yield of 46%). Interestingly, enzymatic hydrolysis of HTMP/SEW pulp and subsequent fermentation using WP01^T were scaled-up to 100 L without compromise on PHA yield. Gas chromatography and proton nuclear magnetic resonance spectroscopy indicated that the PHA produced was made up of polyhydroxybutyrate (PHB) with molecular weights ranging from 50–1600 kDa and polydispersities between 4.6 and 8.4.