Selection of lysine-excreting mutants from Aureobasidium pullulans

✍ Scribed by Chengbin Wu; Beth Reed-Hamer; Dr. Thomas P. West

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 268 KB
• Volume: 35
• Category: Article
• ISSN: 0233-111X
• DOI: 10.1002/jobm.3620350115

✦ Synopsis

A method to select lysine-excreting mutants from the fungus Aureobasidium pullulans was devised. This method involved the use of bacterial auxotroph indicator solid medium where mutant colonies were detected by their ability to support the satellite growth of an Escherichia coli lysine auxotrophic strain in the medium. Utilizing this procedure and a lysine bioassay, two mutants were identified that were capable of producing approximately double the concentration of lysine in the culture medium relative to their parent strain.

Lysine is an essential amino acid that is usually limiting in many foods and feeds. A possible remedy to the problem of limiting lysine levels in foods and feeds is to treat them with lysine-excreting mutants that could elevate lysine content following fermentation. Numerous studies investigating the selection of lysine-excreting mutants from bacteria for this purpose have been reported. The three types of procedures used to select such bacterial mutants include resistance to lysine analogues (SANDS and HANKIN 1974, SATIAWIHARDJA et ul. 1993), growth on medium containing excess threonine and the use of auxotrophic mutants that excrete lysine during cell starvation (KISS and STEPHANOPOULOS 1992). In contrast, the isolation of such mutants from fungi has remained virtually unexplored. In this study, a procedure to select lysine-excreting mutants of the imperfect fungus Aureobasi- dium pullulans was devised. The procedure involved identifying possible fungal lysineexcreting mutant colonies growing on the indicator solid medium by their ability to support the satellite growth of a lysine-requiring Escherichia coli strain present in the medium. Two A. pullulans mutants were identified by this procedure and were confirmed to excrete lysine into the culture medium using a lysine bioassay.