Preservation of Penicillium Species by Lyophilization

Abstract

The maintenance and production of reliable pure cultures with desirable quality is a key operation and the first significant stage in the success of fungal identification. This study assessed spawn preservation and lyophilization (freeze drying) of cultures, for a long time. The sampling was done during the years 2008-2010. Samples were processed in fungal research laboratory of First Fungal Culture Bank of Pakistan (FCBP), Institute of Agricultural Sciences, University of the Punjab, Lahore, Pakistan. Lyophilization has been used to stabilize living cells and fungal isolates, to dehydrate vast range of materials, including foodstuffs, pharmaceuticals, biotechnology products, vaccines, and diagnostic and biological materials, to improve the storage and the quality of DNA after extraction. Long-term maintenance of Penicillium species is essential for detailed studies. Fifty Penicillium species were isolated from different sources by direct and dilution method, and then preserved by spawn and lyophilization technique. Fungal isolates were purified and identified based on their morphology. The viability and purity of the fungal species by fungal spawn and lyophilized material (fungal spawn and fungal mat) were monitored immediately after storage at 1, 2 and 3 months at 4 ^oC. Each fungal isolate was considered viable if the rate of growth present was the same as that of the original culture and if the morphology of the colony matched the fungal identification documented for each species. All lyophilized Penicillium species were found viable at 1-3 months of storage recovered each time from both type of lyophilized material, fungal spawn and fungal mat and showed the initial colony characteristics and growth rates. Neither stabilizer nor skimmed milk was used in fungal material to protect it from sticking with the walls of the container. Modified method of Penicillium spawn preservation by lyoplilization has been found cost effective in contrast to liquid nitrogen preservation. It was concluded that lyophilization is simple, inexpensive, reliable and effective method for the long term preservation of Penicillium isolates.