Background: Here we describe a novel cultivation method, called EnBase™, or enzyme-based-substratedelivery, for the growth of microorganisms in millilitre and sub-millilitre scale which yields 5 to 20 times higher cell densities compared to standard methods. The novel method can be directly applied in microwell plates and shake flasks without any requirements for additional sensors or liquid supply systems. EnBase is therefore readily applicable for many high throughput applications, such as DNA production for genome sequencing, optimisation of protein expression, production of proteins for structural genomics, bioprocess development, and screening of enzyme and metagenomic libraries.

BackgroundBioprocess development of recombinant proteins is time consuming and laborious as many factors influence the accumulation of the product in the soluble and active form. Currently, in most cases the developmental line is characterised by a screening stage which is performed under batch conditions followed by the development of the fed-batch process. Performing the screening already under fed-batch conditions would limit the amount of work and guarantee that the selected favoured conditions also work in the production scale.ResultsHere, for the first time, high throughput multifactorial screening of a cloning library is combined with the fed-batch technique in 96-well plates, and a strategy is directly derived for scaling to bioreactor scale. At the example of a difficult to express protein, an RNase inhibitor, it is demonstrated that screening of various vector constructs and growth conditions can be performed in a coherent line by (i) applying a vector library with promoters and ribosome binding sites of different strength and various fusion partners together with (ii) an early stage use of the fed-batch technology. It is shown that the EnBase® technology provides an easy solution for controlled cultivation conditions in the microwell scale. Additionally the high cell densities obtained provide material for various analyses from the small culture volumes. Crucial factors for a high yield of the target protein in the actual case were (i) the fusion partner, (ii) the use of of a mineral salt medium together with the fed-batch technique, and (iii) the preinduction growth rate. Finally, it is shown that the favorable conditions selected in the microwell plate and shake flask scales also work in the bioreactor.ConclusionsCultivation media and culture conditions have a major impact on the success of a screening procedure. Therefore the application of controlled cultivation conditions is pivotal. The consequent use of fed-batch conditons from the first screening phase not only shortens the developmental line by guarantying that the selected conditions are relevant for the scale up, but in our case also standard batch cultures failed to select the right clone or conditions at all.

Native wheat, barley, rice, maize, wx maize, and potato starch species were modified by depolymerization in 1-allyl-3-methylimidazolium chloride ([AMIM]Cl) ionic liquid (IL) using oil bath or microwave heating. Reactions were catalyzed with p-toluenesulfonic acid (p-TsOH). Reaction times varied depending on the starch species and its concentration, the heating method, and volume of the reaction mixture. Depolymerization products were analyzed with HPLC-ELSD. All starch species mostly degraded into water-soluble 1500-2000 Da-sized starch oligomers. Glucose and other short-chained sugars did not precipitate along with starch oligomers due to their high solubility in IL. This property was utilized in the purification of commercial maltodextrins. Produced water-soluble, low MW starch oligomers might be used, e.g., in bacterial cultivations as a glucose source.

Recombinant protein synthesis in Pichia pastoris is generally controlled by the strong methanol inducible AOX1 promoter which is repressed by glucose and glycerol. In shake flasks, commonly one or two methanol pulses are added per day for induction. Such pulse feeding procedure leads to carbon starvation phases, which may enhance proteolytic activities and, therefore, cause product losses. Starvation between the methanol pulses could be avoided with a continuous enzymatic feed of glucose from a glucose-based polymer. The amount of glucose was low enough to prevent AOX1 repression by glucose. Energy and carbon were continuously supplied for cell maintenance resulting in significantly increased cell densities and product activities, as shown here at the example of a fungal lipase expressed in P. pastoris. A threefold improvement in measured product activity was obtained by applying enzymatic glucose feed and a further improvement was achieved by applying a defined mixture of ammonium compounds. The strategy described here simplifies the general procedure in shaken cultures by allowing the direct continuation of the cultivation from glucose to the methanol-based production phase without a medium change. It is easily applicable to multiwell plates and thus beneficial for high throughput applications.

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