Application of whey retentate as complex nitrogen source for growth of the polyhydroxyalkanoate producer Hydrogenophaga pseudoflava strain DSM1023

Polyhydroxyalkanoates, microbial polyesters produced in vivo starting from renewable resources, are considered the future materials of choice to compete recalcitrant petro-chemical plastic on the polymer market. In order to make polyhydroxyalkanoates market-fit, (techno)economics of their production need to be improved. Among the multifarious factors affecting costs of polyhydroxyalkanoate production, increased volumetric productivity is of utmost importance. Improving microbial growth kinetics and increasing cell density are strategies leading to a high concentration of catalytically active biomass within a short time; after changing cultivation conditions, these cells can accumulate polyhydroxyalkanoates as intracellular products. The resulting increase of volumetric productivity for polyhydroxyalkanoates can be realized by supplying complex nitrogen sources to growing microbial cultures. In the present study, the impact of different expensive and inexpensive complex nitrogen sources, in particular whey retentate, on the growth and specific growth rates of Hydrogenophaga pseudoflava was tested. Based on a detailed kinetic process analysis, the study demonstrates that especially whole (not hydrolyzed) whey retentate, an amply available surplus material from dairy industry, displays positive effects on cultivations of H. pseudoflava in defined media (increase of concentration of catalytically active biomass after 26.25 h of cultivation by about 50%, increase of specific growth rate μ from 0.28 to 0.41 1/h during exponential growth), while inhibiting effects (inhibition constant K i = 6.1 g/L) of acidically hydrolyzed whey retentate need to be overcome. Considering the huge amounts of surplus whey accruing especially in Europe, the combined utilization of whey permeate (carbon source) and whey retentate (complex nitrogen source) for biopolyester production can be considered a viable bioeconomic strategy for the next future.

Improved Laccase Production by Trametes pubescens MB89 in Distillery Wastewaters

Various culture parameters were optimised for laccase synthesis by Trametes pubescens MB89, including pH, carbon source, nitrogen source, lignocellulosic supplements, and reported inducers. Glucose, in conjunction with a complex nitrogen source at pH 5.0, resulted in the highest laccase yield. Adding ethanol, copper, or 2,5-xylidine prior to inoculation further improved laccase concentrations. The addition of 2,5-xylidine was further investigated with multiple additions applied at varying times. This novel application substantially improved laccase production when applied regularly from inoculation and during the growth phase, and also countered glucose repression of laccase synthesis. Single and multiple factor changes were studied in three distillery wastewaters and a wine lees. A synergistic increase in laccase synthesis was observed with the addition of glucose, copper, and 2,5-xylidine. Single addition of 2,5-xylidine proved most beneficial with distillery wastewaters, while copper addition was most beneficial when using the wine lees as a culture medium.

Bacteriocin Production with Lactobacillus amylovorus DCE 471 Is Improved and Stabilized by Fed-Batch Fermentation

ABSTRACT Amylovorin L471 is a small, heat-stable, and hydrophobic bacteriocin produced by Lactobacillus amylovorus DCE 471. The nutritional requirements for amylovorin L471 production were studied with fed-batch fermentations. A twofold increase in bacteriocin titer was obtained when substrate addition was controlled by the acidification rate of the culture, compared with the titers reached with constant substrate addition or pH-controlled batch cultures carried out under the same conditions. An interesting feature of fed-batch cultures observed under certain culture conditions (constant feed rate) is the apparent stabilization of bacteriocin activity after obtaining maximum production. Finally, a mathematical model was set up to simulate cell growth, glucose and complex nitrogen source consumption, and lactic acid and bacteriocin production kinetics. The model showed that bacterial growth was dependent on both the energy and the complex nitrogen source. Bacteriocin production was growth associated, with a simultaneous bacteriocin adsorption on the producer cells dependent on the lactic acid accumulated and hence the viability of the cells. Both bacteriocin production and adsorption were inhibited by high concentrations of the complex nitrogen source.