Partial characterization ofPseudomonas fluorescens subsp.cellulosa endoglucanase activity produced inEscherichia coli

Low temperature growth, freezing survival, and production of antifreeze protein by the plant growth promoting rhizobacterium Pseudomonas putida GR12-2

The plant growth promoting rhizobacterium Pseudomonas putida GR12-2 was originally isolated from the rhizosphere of plants growing in the Canadian High Arctic. Here we report that this bacterium was able to grow and promote root elongation of both spring and winter canola at 5 degrees C, a temperature at which only a relatively small number of bacteria are able to proliferate and function. In addition, the bacterium survived exposure to freezing temperatures, i.e., -20 and -50 degrees C. In an effort to determine the mechanistic basis for this behaviour, it was discovered that following growth at 5 degrees C, P. putida GR12-2 synthesized and secreted to the growth medium a protein with antifreeze activity. Analysis of the spent growth medium, following concentration by ultrafiltration, by SDS-polyacrylamide gel electrophoresis revealed the presence of one major protein with a molecular mass of approximately 32-34 kDa and a number of minor proteins. However, at this point it is not known which of these proteins contains the antifreeze activity.

DNA sequence analysis of endoglucanase genes from Pseudomonas fluorescens subsp. cellulosa and Pseudomonas sp. NCIB 8634

The DNA of two previously isolated recombinant clones, one from Pseudomonas sp. NCIB 8634 (= Cellvibrio mixtus) (pPC71) and another from Pseudomonas fluorescens subsp. cellulosa (pPFC4) that express endoglucanase activity in E. coli was sequenced. Plasmid pPC71 had three open reading frames, two of which include portions of plasmid pBR322. The third open reading frame occurs entirely within the Pseudomonas DNA insert and encodes a protein with a molecular mass of 5845 Da. The DNA insert in pPFC4 was found to contain an open reading frame (PFC-ORF) that encodes a protein of 32189 Da. The major endoglucanase produced in E. coli cells carrying pPFC4 is about 30,000 Da. It is concluded that PFC-ORF encodes this endoglucanase. Both ribosome and catabolite gene activator protein binding sites lie upstream from the initiating codon of PFC-ORF. An interesting feature of the PFC-ORF protein is the presence of amino acid motifs Val-Ser-Ser-Ser-Ser and Val-Val-Ser-Ser-Ser-Ser-Ser that occur within a 25 amino acid span.