Biotechnological production of poly(3-hydroxybutyrate) with<i>Wautersia eutropha</i>by application of green grass juice and silage juice as additional complex substrates

Abstract

Alternative inexpensive complex nitrogen- and phosphate sources from agriculture, green grass juice (GGJ) and silage juice (SJ), were added to cultivation medium in order to investigate their impact on growth of the well-known polyhydroxyalkanoate (PHA) accumulating strain Wautersia eutropha. The influence of these additives was directly compared with cultivations on defined minimal mineral medium (M) as well as on the same medium supplemented with more expensive complex additives: corn steep liquor (CSL) and casamino acids (CA). It turned out that the supplementation with most complex additives results in shortening of lag-phases of bacterial growth and in higher end-concentrations of residual biomass compared with M-medium. Finally, higher volumetric productivities for poly(3-hydroxybutyrate) (3-PHB) were achieved. The effect of the inexpensive additive SJ on volumetric productivity was similar to the result for the expensive CA (0.653 vs. 0.619 g L−1 h−1). The same was found for the biomass concentration (7.00 vs. 7.44 g L−1 respectively). Together with an economic appraisal presented in this study, the results suggest it is possible to make the sustainable process of microbial PHA-production more economically feasible. A survey of the thermal characteristics and molecular mass properties of the isolated polymers completes this work.