The diversity of lipases from psychrotrophic strains of Pseudomonas : a novel lipase from a highly lipolytic strain of Pseudomonas fluorescens

Strains of Pseudomonas fluorescens and Ps. fragi are the predominant psychrotrophs found in raw milk and may cause spoilage due to the secretion of hydrolytic enzymes such as lipase and protease. The diversity of lipases has been examined in Pseudomonas isolates from raw milk which represent different taxonomic groups (phenons). Significant diversity was found using both DNA hybridization and immunoblotting techniques, which has implications for the development of a diagnostic test. The lipase-encoding gene ( lipA ) was cloned from one strain, C9, of Ps. fluorescens biovar V. In contrast to previously reported lipase sequences from Ps. fluorescens , the gene encodes a lipase of M_r 33 kDa. Alignment of all known Pseudomonas and Burkholderia lipase amino acid sequences indicates the existence of two major groups, one of M_r approximately 30 kDa comprising sequences from Ps. fragi , Ps. aeruginosa , Ps. fluorescens C9 and Burkholderia , and one of approximately 50 kDa comprising Ps. fluorescens lipases. The lipase from C9 does not contain a signal peptide and is presumed to be secreted via a signal peptide-independent pathway. The lipA gene of strain C9 was disrupted by insertional mutagenesis. The mutant retained its lipolytic phenotype, strongly suggesting the presence of a second lipase in this strain.