4 strains of E. coli are used in these studies: JM101 for M13 infection and isolation, XL1BMRF'for M13 or pUC-based DNA transformation, and ED8767 for cosmid DNA transformation. To maintain their respective F' episomes necessary for M13 viral infection, JM101 is streaked onto a M9 minimal media plate and XL1BMRF' is streaked onto an LB plate containing tetracycline. ED8767 is streaked onto an LB plate. These plates are incubated at 37degC overnight. For each strain, 3 ml. of appropriate liquid.. - [Read Bacterial Cell Maintenance Protocol]
This method is advantageous for saving the occasional cultures that become contaminated. Yeast contaminated cultures will appear cloudy when slightly shaken and lymphocytes will not cluster together as much as normal. If cultures are suspect, a drop of culture can be streaked on a YPD media plate to check for growth of yeast colonies, or a 5 ml sample can be taken to Barnes Diagnostic Center for identification of yeast strain. - [Read Removal of Yeast Contamination from Lymphoblast Cultures Protocol]
Phage are streaked onto a medium to obtain an independent isolate prior to preparing a new lysate. This is done to reduce the likelihood of working with lysates which have become contaminated, and/or have accumulated mutations. - [Read Streaking Lambda Phages Protocol]
Some yeast strains are unstable (e. g., small YAC-bearing strains) and need to be repurified by streaking on an agar plate and then verifying the genetic content of the isolated colony before proceeding. In cases where the strain is unstable, plan to streak the cells onto the selective medium to retain the desired stock, (however, most strains can be streaked onto the complete medium, YPD). - [Read Streaking Yeast Stocks Protocols]