Intergeneric protoplast fusion between Fusobacterium varium and Enterococcus faecium for enhancing dehydrodivanillin degradation

Abstract

Intergeneric protoplast fusion between Fusobacterium varium (Pcs Glu+) and Enterococcus faecium (Pcr Glu-) was performed under strictly anaerobic conditions to improve dehydrodivanillin (DDV) degradation. The fusion frequency obtained from the selective medium (Pc+ Glu-) was about 0.9 X 10(-5) to 1.3 X 10(-5). The seven fusants isolated were all gram-negative anaerobes with rod shapes like that of F. varium and with main phenotypical properties of cocci like those of E. faecium such as esculin and starch hydrolysis, milk clotting, and lactate production. Five fusants showed enhanced DDV degradation activities that were 2 to 4 times higher than those of parental strains. Genetic relatedness between a fusant (FE7) and the parents was estimated by DNA-DNA Southern blot hybridization with 32P-labeled chromosomal DNA fragments of F. varium and E. faecium as respective probes. The fusant FE7 presented a very high cross-hybridization with both probes, indicating a high DNA homology between the fusant and both parental strains. Almost all the fusants obtained here have stably kept the properties described above for about 2 years. These results suggest that intergeneric gene transfer takes place through protoplast fusion and that the fusants that were obtained are stable recombinants.