Characterization of a plasmid-cured variant isolated from the lysogenic Lactobacillus helveticus CRL1179

MARTA GORRITI; JULIO VILLENA; BEATRIZ ESPECHE; M DYEN; ELVIRA HEBERT; RAÚL RAYA

San Miguel de Tucumán, Tucumán, Argentina

Simposio; . II International Symposium on Lactic acid bactéria- First Argentinian LAB Net Meeting; 2006

Centro de Referencia para Lactobacilos

Lactobacillus helveticus is a homofermentative, thermophilic lactic acid bacterium used commertially for the manufacture of hard cheeses. In this work, strain CRL 1179 was chosen as a model microorganism to optimize an electroporation protocol for L. helveticus, since there is as yet no a generalized method for transforming this bacterium. It was found that strain CRL 1179 is lysogenic, possesses two plasmids of approximately 7 and 10 kilobases  (Kb), and show an Fmc- phenotype, sice it coagulates nonfat milk after 16 hours. The temperate phage of CRL 1179, named jLhR3, could be induced to the lytic cycle with mitomicin C (0.2 ug/ml). Phage lysates could inhibit cell grow of sensitive cells, but no phage plaques could be observed. A plasmid-free derivative of CRL 1179, named C4, was isolated and characterized. Strain C4 has lost the 7 Kb plasmid and shows a phenotype of strong agglutination and an extended log phase (2-4 h) with regard to the original strain CRL 1179. In both strains the phenotype Fmc- could be attributed to a deficiency in the biosynthesis of purines, but not to the absence of a proteinase activity. All intents to electroporate CRL 1179 and C4 with plasmids pGK12 ans pSA3 has been so far unsatisfactory.