Prevalence of CTGCAG Recognizing Restriction and Modification Systemsin Ruminal Selenomonades

GATC-specific restriction and modification systems in treponemes

AIMS

To investigate the presence of GATC-specific modification and restriction activities in rumen isolates of Treponema sp.

METHODS

The presence of N6-methyladenine within GATC (Dam) sequences was analysed using isoschizomeric restriction endonucleases having different sensitivities to the methylation of the target sequence. A fast screening method was used for testing of site-specific endonuclease activities directly in crude cell extracts. Three out of six rumen isolates of Treponema sp. showed restriction activities. Restriction endonucleases were further purified by Heparin-Sepharose chromatography. Using PCR and specific primers, no sequence homologous to the T. pallidum dam gene was found.

CONCLUSIONS

Three rumen treponemal strains were documented to possess MboI isoschizomeric restriction-modification systems.

SIGNIFICANCE

This is the first report on restriction activity in rumen treponemes.

GATC-specific restriction-modification systems in ruminal bacteria

The GATC-specific restriction and modification activities were analyzed in 11 major bacterial representatives of ruminal microflora. Modification phenotype was observed in 13 out of 40 ruminal strains. MboI isoschizomeric restriction endonucleases were detected in 10 bacterial strains tested; three strains lacked any detectable corresponding endonuclease activity. The only examined strain of Mitsuokella multi-acida was found to possess a different type of endonuclease activity. This is the first report on restriction activity in ruminal treponemes M. multiacida and Megasphaera elsdenii.

Characterization of a complex restriction-modification system detected in Staphylococcus aureus and Streptococcus agalactiae strains isolated from infections of domestic animals

Characterization of classic type II restriction-modification systems (RMS) (restriction endonucleases and modification methyltransferases) was carried out in isolates of Staphylococcus aureus and Streptococcus agalactiae obtained from clinical material. Among the 100 isolates of S. aureus two different RMS type II were detected. The first was expressed in isolates 32 and 33 (Sau32 I and Sau33 I); the targeting sequence was determined as 5'-GGN CC-3' (Sau96 I isoschizomer). The second was found in isolates no. 90, 93, 96*, and 98 (Sau90 I, Sau93 I, Sau96* I, Sau98 I) and enzymes recognized sequence 5'-CTY RAG-3' (SmlI isoschizomer). Analysis of 40 isolates of S. agalactiae revealed only one RMS; it was detected in two isolates (no. 16 and 23; Sag16 I and Sag23 I). Restriction endonuclease expressed by these isolates cleaved DNA in sequence 5'-CTG CA/G-3' (PstI isoschizomer). In RMS-positive S. aureus and S. agalactiae isolates plasmid DNA capable of replication in Escherichia coli and Bacillus subtilis was also detected and isolated.

Non-specific DNAases from the rumen bacterium Prevotella bryantii

Extracellular non-specific nucleases were observed in some strains belonging to the ruminal species of the genus Prevotella, mostly P. brevis and P. bryantii. The nuclease from P. bryantii appeared to be extracellular; it mediates the degradation of the supercoiled plasmid DNA via an open circle intermediate. The cleavage is not site specific although a preference for certain cleavage sites does seem to exist. Our attempts to clone the wild-type P. bryantii B(1)4 nuclease in E. coli strain ER1992 that reports on the DNA damage sustained, were unsuccessful probably due to excessive intracellular nuclease activity that killed the cells bearing the gene for the nuclease. On the other hand, the nuclease from a related strain TCl-1, which has a less active enzyme of the same type, was successfully cloned.

Restriction and modification systems of ruminal bacteria

A high frequency of type II restriction endonuclease activities was detected in Selenomonas ruminantium but not in other rumen bacteria tested. Eight different restriction endonucleases were characterized in 17 strains coming from genetically homogeneous local population. Chromosomal DNA isolated from S. ruminantium strains was found to be refractory to cleavage by various restriction enzymes, implying the presence of methylase activities additional to those required for protection against the cellular endonucleases. The presence of Dam methylation was detected in S. ruminantium strains as well as in several other species belonging to the Sporomusa subbranch of low G + C Gram-positive bacteria (Megasphaera elsdenii, Mitsuokella multiacidus).