Screening actinomycetes for extracellular peroxidase activity

A diverse collection of actinomycete strains were screened for production of extracellular peroxidase activity by adapting a chemiluminescence analysis system developed for horseradish peroxidase-based enzyme-linked immunosorbent assay. Extracellular peroxidase activity was found to be common but quantitatively variable, and this rapid and sensitive screening system permitted identification of a small group of high-producing strains. A range of spectrophotometric assays were compared for the measurement of peroxidase activity in concentrated culture supernatants of two selected thermophilic streptomycetes. Of these, the peroxide-dependent oxidation of 2,4-dichlorophenol was identified as the most robust and reproducible assay for quantitative studies.

Oxidative stress in colon tissue induced by vitamin E depletion

Inflammatory disorders of the bowel and colon cancer are associated with elevated indices of oxidative stress. Analogous elevations in markers of oxidative stress and loss of cell-membrane integrity are also observed in the colons of rats deficient in vitamin E (D-α-tocopherol), the major lipid-soluble antioxidant in biological systems. The causal relationship between colon pathologies associated with oxidative stress and dietary deficiency in antioxidant vitamins such as vitamin E is still uncertain. Investigation of potential mechanisms by which lack of dietary vitamin E may lead to clinically relevant pathological changes in colon tissue was conducted using gene expression profiling strategies on vitamin E-sufficient and -deficient rats. Morphological changes and increased indices of lipid peroxidation were linked to vitamin E deficiency. These changes in colon tissue are potentially important in disease pathogenesis of the colon linked with oxidative stress or other direct consequences of inadequate levels of vitamin E.

Novel tetracycline resistance gene, tet(32), in the Clostridium-related human colonic anaerobe K10 and its transmission in vitro to the rumen anaerobe Butyrivibrio fibrisolvens

A novel tetracycline resistance gene, designated tet(32), which confers a high level of tetracycline resistance, was identified in the Clostridium-related human colonic anaerobe K10, which also carries tet(W). tet(32) was transmissible in vitro to the rumen anaerobe Butyrivibrio fibrisolvens 2221(R). The predicted gene product of tet(32) has 76% amino acid identity with Tet(O). PCR amplification indicated that tet(32) is widely distributed in the ovine rumen and in porcine feces.

Transformation of an oral bacterium via chromosomal integration of free DNA in the presence of human saliva

Transformation of Streptococcus gordonii DL1 by free DNA was studied in human saliva. Competent S. gordonii could be transformed in vitro with plasmid DNA that had been taken into the human mouth. Transformation also occurred with a plasmid that cannot replicate in S. gordonii, but that has a region of chromosomal homology, by integration into the bacterial chromosome, although linearised plasmid DNA gave no transformants. Linear chromosomal DNA fragments did however transform S. gordonii/Tn916 efficiently in saliva when regions of homology with the recipient chromosome flanked the marker gene. These findings are discussed in relation to the potential for acquisition of DNA sequences, including genetically modified DNA, by gut and oral bacteria.

Sequence analysis of the plasmid pRRI2 from the rumen bacterium Prevotella ruminicola 223/M2/7 and the use of pRRI2 in Prevotella/Bacteroides Shuttle Vectors

pRRI2 is a small cryptic plasmid from the rumen bacterium Prevotella ruminicola 223/M2/7 which has been used for the construction of shuttle vectors (pRH3 and pRRI207) that replicate in many Bacteroides/Prevotella strains as well as in Escherichia coli. Sequence analysis of pRRI2 reveals that it is a 3240-bp plasmid carrying two clear open reading frames. Rep, encoded by ORF1, shows 48 and 47% amino acid sequence identity with RepA proteins from Bacteroides vulgatus and Bacteroides fragilis, respectively. ORF2, named Pre, shares 34% amino acid sequence identity with a putative plasmid recombination protein from the Flavobacterium spp. plasmid pFL1 and 30% amino acid sequence identity with BmpH from B. fragilis Tn5520. Disruption of ORF1 with HindIII prevents replication and maintenance in Bacteroides spp. hosts, but shuttle vectors carrying pRRI2 interrupted within ORF2, by EcoRI*, are able to replicate. pRRI2 shows no significant similarity with the only other P. ruminicola plasmid to have been studied previously, pRAM4.

Chromosomal integration of the green fluorescent protein gene in lactic acid bacteria and the survival of marked strains in human gut simulations

An integration vector was constructed to allow introduction of the gfp gene into the chromosomes of Gram-positive bacteria. Integration depends on homologous recombination between a short 458-nt sequence of the tet(M) gene in the vector and a copy of Tn916 in the host chromosome. Strains of Lactococcus lactis IL1403, Enterococcus faecalis JH2-SS, and Streptococcus gordonii DL1 stably marked with single chromosomal copies of the gfp were readily visualised by epifluorescence microscopy. The marked L. lactis strain survived poorly in a continuous culture system inoculated with human faecal flora, while the laboratory E. faecalis strain was lost at approximately the dilution rate of the fermenter.

Natural genetic transformation in the rumen bacterium Streptococcus bovis JB1

Natural transformation of Streptococcus bovis JB1 was demonstrated after development of competence in normal culture medium. Transformation efficiencies were not significantly increased when heat-inactivated horse serum was added to the medium before growth. This is the first time that a resident rumen bacterial species has been shown to be naturally transformable. Transformation allowed the acquisition of plasmids or integration of sequences into the chromosome. No transformation was observed in the presence of undiluted autoclaved or filter-sterilised ovine rumen fluid or filter-sterilised ovine saliva, suggesting that transformation in the ruminant digestive tract is a rare event, although transformation was observed in the presence of 1% and 0.5% filter-sterilised rumen fluid. The use of natural transformation of S. bovis should facilitate further molecular biological studies on this species.

Fate of free DNA and transformation of the oral bacterium Streptococcus gordonii DL1 by plasmid DNA in human saliva

Competitive PCR was used to monitor the survival of a 520-bp DNA target sequence from a recombinant plasmid, pVACMC1, after admixture of the plasmid with freshly sampled human saliva. The fraction of the target remaining amplifiable ranged from 40 to 65% after 10 min of exposure to saliva samples from five subjects and from 6 to 25% after 60 min of exposure. pVACMC1 plasmid DNA that had been exposed to degradation by fresh saliva was capable of transforming naturally competent Streptococcus gordonii DL1 to erythromycin resistance, although transforming activity decreased rapidly, with a half-life of approximately 50 s. S. gordonii DL1 transformants were obtained in the presence of filter-sterilized saliva and a 1-microg/ml final concentration of pVACMC1 DNA. Addition of filter-sterilized saliva instead of heat-inactivated horse serum to S. gordonii DL1 cells induced competence, although with slightly lower efficiency. These findings indicate that DNA released from bacteria or food sources within the mouth has the potential to transform naturally competent oral bacteria. However, further investigations are needed to establish whether transformation of oral bacteria can occur at significant frequencies in vivo.

Novel bioactive compounds from actinomycetes

Actinomycetes form an enormous reservoir of secondary metabolites and enzymes. The potential for exploiting rare actinomycetes is highlighted by the discovery of novel compounds from strains of Spirillospora and Nocardioides. Novel compounds of well known classes of antibiotics, such as polyenes, continue to be discovered. For compounds containing a chromophore, the analysis by high-performance liquid chromatography coupled with a diode-array detector enables the elimination of producers of known compounds and facilitates the discovery of novel compounds or derivatives. The complexity of the regulatory mechanisms is illustrated by glutamine synthetase. The characterization of thermostable amylolytic, lignolytic, peroxidase and neuramidase activities, and the isolation of novel cellulolytic actinomycetes clearly demonstrate the potential of Actinomycetes as producers of enzymes.