Microbial formulation: DOM-project approaches on the stabilisation of
biocontrol bacteria and yeast.
Sebastian Håkansson*, Åsa Schoug, Petter Melin, Jens Levenfors and Johan Schnürer
DOM (Domestication of Microorganisms), Dept. of Microbiology, Swedish University of
Agricultural Sciences (SLU), SE-750 07, Uppsala, Sweden.
*sebastian.hakansson@mikrob.slu.se
Formulation of microbial biomass in order to achieve maximal stability and cell viability is a
complex task and can be performed in a multitude of ways. The optimal formulation will be
very dependent on the type of microorganism and the intended application and it is therefore
necessary to perform an optimisation in each specific case. However, increased knowledge of
general and fundamental formulation parameters will lead to faster as well as more time- and
cost efficient formulation development.
Within the DOM-project, we work with both liquid and dry formulations of a variety of active
biocontrol microorganisms. Fermentation optimizations and preconditioning studies are areas
of focus, as well as drying process development and optimization. Currently, the formulation
platforms in use are freeze-drying (lyophilization), vacuum drying and fluidized bed drying.
Within DOM and its collaboration partners, several necessary analytical techniques of
importance for formulation development are available. These include Magic Angle Spinning
Nuclear Magnetic Resonance (MAS-NMR), gas chromatography/mass spectronomy (GCMS) and high pressure liquid chromatography (HPLC) for identification and quantification of
accumulated intracellular compatible solutes. We also have instruments for measuring total
water contents (Karl-Fisher titration) and water activities, which are crucial parameters of dry
formulations. In addition, we have access to Differential Scanning Calorimetry (DSC) and
isothermal calorimetry (IC) to measure important physico-chemical properties of formulation
media and dry products.
Examples of the DOM formulation work will be presented, encompassing both gram-negative
(Pseudomonas spp.) [1] and gram-positive (Lactobacilli) bacteria [2] as well as the biocontrol
yeast Pichia anomala [3]. We have substantially improved formulation survival for several of
our model microorganism for both freeze- and vacuum drying and have performed direct
comparisons of several formulation techniques for the yeast P. anomala. The approaches
chosen for different drying protectants and process optimizations in various cases will be
discussed. Finally, the aims for future work with new microbial species and the development
of vacuum drying technology will be presented.
1.
2.
3.
Hökeberg, M., B. Gerhardson, and L. Johnsson, Biological control of cereal seed-borne diseases by
seed bacterization with greenhouse-selected bacteria. European Journal of Plant Pathology, 1997.
103(1): p. 25-33.
Schoug, S., et al., Freeze-drying of Lactobacillus coryniformis Si3-effects of sucrose concentration, cell
density, and freezing rate on cell survival and thermophysical properties. Cryobiology, 2006. 53(1): p.
119-27.
Melin, P., S. Håkansson, and J. Schnurer, Optimisation and comparison of liquid and dry formulations
of the biocontrol yeast Pichia anomala J121. Appl Microbiol Biotechnol, 2007. 73(5): p. 1008-16.