Atypical citrate-fermenting Lactococcus lactis strains isolated from dromedary's milk

Area of Science:

• Microbiology
• Food Science
• Bacteriology

Background:

• Lactococcus lactis is a key dairy starter culture.
• Traditional strains are primarily derived from cow's milk.
• Novel strains with unique properties are sought for dairy applications.

Purpose of the Study:

• To isolate and characterize Lactococcus strains from dromedary milk with novel properties.
• To compare these strains to established dairy starters.
• To investigate the genetic basis of observed phenotypes.

Main Methods:

• Screening of dromedary milk for proteolytic Lactococcus isolates.
• Polymerase Chain Reaction (PCR) for gene identification (prtP).
• 16S rDNA sequencing for species identification.
• Phenotypic analysis for citrate fermentation (Cit+) and temperature tolerance (Ther+).
• Plasmid analysis using genetic approaches (inverse PCR).

Main Results:

• 74 proteolytic Lactococcus isolates were identified, harboring the prtP gene.
• 85% of these isolates exhibited citrate fermentation (Cit+) and were classified as Lactococcus lactis ssp. lactis biovar. diacetylactis.
• Several isolates showed tolerance to high temperatures (50°C) and alkaline pH.
• Four distinct plasmids (pTher, pPrt, pLac, pCit) were associated with specific phenotypes.
• Two types of pCit plasmids were identified, one containing a Leuconostoc cit cluster.

Conclusions:

• This study expands the known characteristics of Lactococcus lactis biovar. diacetylactis beyond citrate fermentation.
• The presence of a Leuconostoc-like cit cluster suggests potential horizontal gene transfer.
• Identified strains represent promising new dairy starter candidates with enhanced industrial properties.