Isolation and Plasmid Characterization of a Lactobacillus Species Involved in the Manufacture of Fermented Sausage1

Abstract

Isolation and characterization of a Lactobacillus species capable of proper acid production in a sausage environment is described. The isolate from sausage, categorized as a lactobacillus in the subgenus Streptobacterium, was designated Lactobacillus sp. DR1. Growth occurred at 5 and 42°C but not at 45°C. Fructose, galactose, glucose, mannose, melibiose, N-acetylglucosamine, ribose, sucrose and trehalose were fermented. Gas production from glucose was not observed. In MRS glucose broth, D(−) and L(+) lactic acid were produced. Lactobacillus sp. DR1 contained a single cryptic plasmid of approximately 30 megadaltons (Mdal). In sausage fermentation trials, both Lactobacillus sp. DR1 and plasmid-free derivative DR1C lowered the pH to below 5.3 after 8 h in the smokehouse. Conjugation was demonstrated through the transfer of plasmid pAMβ1, which encodes erythromycin resistance, from Streptococcus lactis 2301β to Lactobacillus sp. DR1. Mutanolysin-generated protoplasts could be regenerated using 0.5 M ammonium chloride, lactose, maltose or sucrose as osmotic stabilizers. Regeneration frequencies ranged from less than 1.0% up to 35%; however, transformation of Lactobacillus sp. DR1 protoplasts by plasmid DNA in the presence of polyethylene glycol (PEG) was unsuccessful.