Blakeslea trispora (Mucorales) has economic importance because of its ability to produce large amounts of beta-carotene. To shed light on the actual point of induction and to shorten the following production process, germination and growth of its two mating types, (-) and (+), were observed separately, and the mating point was investigated in lab scale experiments. The (-) mating type showed much faster germination than the (+) type on solid medium and in Erlenmeyer flasks. However, after a first period, the (-) mating type grew clearly slower than the (+) type. In addition, the (-) type branched more vividly than the (+) type. A ratio of 30:1 of (-) and (+) type at an age of 20 h was found to achieve highest beta-carotene yields. Our results provide a comprehensive overview of Blakeslea trispora growth and its product synthesis.

BackgroundIn recent years the production of biobased biodegradable plastics has been of interest of researchers partly due to the accumulation of non-biodegradable plastics in the environment and to the opportunity for new applications. Commonly investigated are the polyhydroxyalkanoates (PHAs) poly(hydroxybutyrate) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHB-V). The latter has the advantage of being tougher and less brittle. The production of these polymers in bacteria is well established but production in yeast may have some advantages, e.g. the ability to use a broad spectrum of industrial by-products as a carbon sources.ResultsIn this study we increased the synthesis of PHB-V in the non-conventional yeast Arxula adeninivorans by stabilization of polymer accumulation via genetic modification and optimization of culture conditions. An A. adeninivorans strain with overexpressed PHA pathway genes for β-ketothiolase, acetoacetyl-CoA reductase, PHAs synthase and the phasin gene was able to accumulate an unexpectedly high level of polymer. It was found that an optimized strain cultivated in a shaking incubator is able to produce up to 52.1% of the DCW of PHB-V (10.8 g L−1) with 12.3%mol of PHV fraction. Although further optimization of cultivation conditions in a fed-batch bioreactor led to lower polymer content (15.3% of the DCW of PHB-V), the PHV fraction and total polymer level increased to 23.1%mol and 11.6 g L−1 respectively. Additionally, analysis of the product revealed that the polymer has a very low average molecular mass and unexpected melting and glass transition temperatures.ConclusionsThis study indicates a potential of use for the non-conventional yeast, A. adeninivorans, as an efficient producer of polyhydroxyalkanoates.

Organic synthetic polymers such as polyacrylamide derivates, polyethylenimine, Na polyacrylates e.t.c. have received much attention as flocculating substances used in waste water treatment. There is an urgent need for the production of effective flocculants to replace mechanical separation methods or, at least, to optimize them. Biological safety and decomposition are essential pre-requisits for utilizing flocculants produced by microbial processes (e.g. discontinuous and continuous cultivation of bacteria or yeasts). The extracted polymers consisting of proteins, lipids, nucleic acids and polysaccharides are capable of being degraded easily by microbiological reactions because they are natural compounds. The induction phase of excreting cellularic biopolymen is the crucial stage. In the special literature, low p 0 2 levels associated with a high concentration of the carbon source, limitation of N, P and trace elements have been recommended for the induction of excreting exopolymers. In order to ensure suniciant induction, we preferred a special procedure, the main characteristic of it being changed between limitation and excessive supply of components essential for the growth of microorganisms. The quality control ofexopolysaccharides for flocculation was determined by turbidimetric methods and sedimentation tests with caoline as a standard substance. For the initial investigations Acetobacter methanoficus and Methyfobaclerium rhodesianum were used.

Solid-state fermentation (SSF) technology has been rapidly developed for the past 10 years as a production platform for secondary metabolites, biofuels, food, and pharmaceuticals. Yet, the main drawback of SSF is the local temperature rise of up to 20 K, which potentially reduces the strain activity and inactivates heat sensible products. Due to the low heat capacity and thermal conductivity of mixtures of air with plant material, in comparison to aqueous suspensions in submerged fermentations, heat from metabolic processes is less efficiently dissipated. The exact knowledge of the metabolic heat generation during SSF processes is crucial to guide strategies against overheating. In this work, a simple method using a cost-efficient multichannel instrument is proposed, which allows the determination of heat generation during SSF processes. This method was successfully tested and validated with Blakeslea trispora producing β-carotene during growth on barley. Additionally, the consequences of the generated metabolic heat during SSF on temperature rise and water evaporation were discussed. Finally, changes in growth and product concentration could also be detected by the heat signal, implying the potential as a timesaving screening method.

SriiiiinaryThe two-step cultivation of microorg;uiisms described in part I of this series will be expl;iined by referring to its application to the production of SCP on the basis of sucrose/molasses ;LS carbon sources. The inactivation of the yeast Candida utilis is carried out thermally, and the specific death rate was determined to be between 119 x lo-' s-l and 324 x 10-4 .TI, respectively. With this new procedure the apparent productivity could be increased by 96.6%, the yield coefficient of molasses increased b y 5.8% and of sucrose by 12.9%. The crude protein content of the product in the case of sucrose rose by 104?/,. The variability of process design is demonstrated. Int,rodiiction&rally tliffeiwit procedures have been developed for the production of S W [ 1,2]. In all cases process engineering implied the following configuration : Fermentation Evaporation 2. Separation DryingOn the basis of this fundamental configuration there are some variants which are characterized by a special procedure in the fermentation step. Esnniples are t he PEKILO-process (fungus cultivation, steril condition of fermentation) [3] and SC'P-procluction using pure oxygen [4]. Our proposal explained in this paper (basic principles in [5]) uses also special procedure in the fermentationstep. Fernientationis implemented in two steps in such a way that there are active and inactivated cells coexisting in the second fermentat ion step. The new procetliire should be demonstrated by the protluction of SCP. Naterial and XethodsCandida rrtilis ZIMET 43849 was used.The fermentations were carried out in a xymow-fermenter of the type LFS 112.As carbon sources pure sucrose and molasses (with 50% of sucrose) mere used. The nutrition solution had the following composition: