Occurrence of restriction-modification systems in ruminal butyrate-producing bacteria.

Thirty-five strains of ruminal bacteria belonging to the former Butyrivibrio fibrisolvens species were screened for the presence of site-specific restriction endonuclease and modification methyltransferase activities. Seven strains possessed endonuclease activities detectable in crude cell extracts. The recognition sequences and optimal reaction conditions for seven of them were determined. Five enzymes were found to be isoschizomers of type II endonucleases (EcoRV, NsiI, AseI (2x) and SauI), one was type IIS (FokI) and two remained unknown. The optimal reaction buffer was found to be a low ionic strength buffer and all enzymes possessed sufficient activity at 39 degrees C. The presence of DNA modification among all strains was also determined. Most of the methylation activities correlated with restriction activities, yet some strains possessed unaccompanied modification methyltransferases.