Title: Deletion and acquisition of genomic content during early stage adaptation of Pseudomonas aeruginosa to a human host environment Rau MH, Marvig RL, Ehrlich GD, Molin S, Jelsbak L Ref: Environ Microbiol, 14:2200, 2012 : PubMed
Adaptation of bacterial pathogens to a permanently host-associated lifestyle by means of deletion or acquisition of genetic material is usually examined through comparison of present-day isolates to a distant theoretical ancestor. This limits the resolution of the adaptation process. We conducted a retrospective study of the dissemination of the P.aeruginosa DK2 clone type among patients suffering from cystic fibrosis, sequencing the genomes of 45 isolates collected from 16 individuals over 35 years. Analysis of the genomes provides a high-resolution examination of the dynamics and mechanisms of the change in genetic content during the early stage of host adaptation by this P.aeruginosa strain as it adapts to the cystic fibrosis (CF) lung of several patients. Considerable genome reduction is detected predominantly through the deletion of large genomic regions, and up to 8% of the genome is deleted in one isolate. Compared with in vitro estimates the resulting average deletion rates are 12- to 36-fold higher. Deletions occur through both illegitimate and homologous recombination, but they are not IS element mediated as previously reported for early stage host adaptation. Uptake of novel DNA sequences during infection is limited as only one prophage region was putatively inserted in one isolate, demonstrating that early host adaptation is characterized by the reduction of genomic repertoire rather than acquisition of novel functions. Finally, we also describe the complete genome of this highly adapted pathogenic strain of P.aeruginosa to strengthen the genetic basis, which serves to help our understanding of microbial evolution in a natural environment.
Title: Secretion of Serratia liquefaciens phospholipase from Escherichia coli Givskov M, Molin S Ref: Molecular Microbiology, 8:229, 1993 : PubMed
The Serratia liquefaciens phospholipase (PhlA) is secreted to the medium from its natural host. Here we present results which indicate that, when cloned and expressed in Escherichia coli, secretion can be mediated by a putative host-encoded pathway, expression of which is controlled by FlhD (formerly FlbB), the master regulator of the flagellar/chemotaxis regulon. In the absence of this secretion pathway, the synthesized phospholipase accumulates inside the host cell where it forms a complex with the PhlB protein. PhlB, which is encoded from the promoter distal gene of the phospholipase operon, inhibits the phospholipase activity of PhlA. Formation of this enzymatically inactive PhlA/PhlB complex is required for maintenance of cell viability.
Title: Expression of extracellular phospholipase from Serratia liquefaciens is growth-phase-dependent, catabolite-repressed and regulated by anaerobiosis Givskov M, Molin S Ref: Molecular Microbiology, 6:1363, 1992 : PubMed
Many members of the genus Serratia synthesize and excrete a number of extracellular hydrolytic enzymes. One of these is the phospholipase A1 from Serratia liquefaciens, the expression of which is growth-phase-dependent. Through the use of gene fusions and primer extension analysis we show that the expression of phospholipase is subject to positive transcriptional regulation of a dual promoter system; one promoter positioned approximately 600bp upstream from the phlA gene is responsible for the induction of phospholipase expression under anaerobic conditions, and the other promoter positioned 50bp upstream from the phlA gene is subject to catabolite repression and induced during the transition from exponential to late log-phase of bacterial growth. On the basis of sequence homology and behaviour in the relevant Escherichia coli mutants, we suggest that distant promoter to be Fnr-controlled and the proximal phlA promoter to be a member of the FIbB-controlled flagellar-chemotaxis regulon.
Title: Cloning and expression in Escherichia coli of the gene for extracellular phospholipase A1 from Serratia liquefaciens Givskov M, Olsen L, Molin S Ref: Journal of Bacteriology, 170:5855, 1988 : PubMed
From a genomic library of Serratia liquefaciens, a cloned DNA fragment comprising a two-gene operon was isolated and expressed in Escherichia coli. One of the gene products was identified as a phospholipase A1, and the enzyme was found to be excreted to the outer environment from S. liquefaciens as well as from E. coli. Both genes were sequenced, and the relationship between open reading frames in the DNA sequence and in vitro-expressed polypeptides was established. The length of the phospholipase polypeptide was found to be 319 amino acids. In the amino-terminal end of the coding sequence was a stretch of about 20 hydrophobic amino acids, but, in contrast to consensus signal peptides, no basic residues were present. The length of the second polypeptide was 227 amino acids. It was found that expression of the phospholipase gene in both E. coli and S. liquefaciens was growth phase regulated (late expression).
