hi see this attach is helpful 

Glycerol, 50 %, sterile

I recommend sterile glycerol (80%) gly and the rest sample and to store at freeze

 I prefer  Paraffin Method  

This is a simple and most economical method of maintaining pure cultures of bacteria and fungi. In this method, sterile liquid paraffin is poured over the slant (slope) of culture and stored upright at room temperature. The layer of paraffin ensures anaerobic conditions and prevents dehydration of the medium. This condition helps microorganisms or pure culture to remain in a dormant state and, therefore, the culture can be preserved form months to years (varies with species).

The advantage of this method is that we can remove some of the growth under the oil with a transfer needle, inoculate a fresh medium, and still preserve the original culture. The simplicity of the method makes it attractive, but changes in the characteristics of a strain can still occur.

For long term storage and genetic analysis , I recommended to utilize porous glass beads with cryopreservative for storage at low temperature. This commercially available "Microbank Bacterial and Fungal Preservation System" that offers the least possibility of disturbance to the stored organism, yet, permits ready and rapid access. See the link:

http://www.pro-lab.com/products-microbank.php?country=LV

Microbank system is OK of course but maybe they look for the chiepest way?

I recommend sterile glycerol (50%) or porous glass beads with cryopreservative

I used to work with Microbank system and store at -80C