Analysis of the integration functions of phi304L: an integrase module among corynephages

Complete nucleotide sequence and annotation of the temperate corynephage ϕ16 genome

The complete genome of ϕ16, a temperate corynephage from Corynebacterium glutamicum ATCC 21792, was sequenced and annotated (GenBank: KY250482). The electron microscopy study of ϕ16 virion confirmed that it belongs to the family Siphoviridae. The ϕ16 genome consists of a linear double-stranded DNA molecule of 58,200 bp (G+C = 52.2%) with protruding cohesive 3’-ends of 14 nt. Four major structural proteins were separated by SDS-PAGE and identified by peptide mass fingerprinting technique. Using bioinformatics analysis, 101 putative ORFs and 5 tRNA genes were predicted. Only 27 putative gene products could be assigned to known biological functions. The ϕ16 genome was divided into functional modules. Seven putative promoters and eight putative unidirectional intrinsic terminators were predicted. One site of putative «-1» programmed ribosomal frameshifting was proposed in the phage tail assembly genome region. C. glutamicum genetic tools could be broadened by exploiting the known integrase gene (gp33) and the newly identified excisionase gene (gp47), participating in site-specific recombination between ϕ16-attP/attB.

Bacteriophage-based vectors for site-specific insertion of DNA in the chromosome of Corynebacteria

In Corynebacterium diphtheriae, diphtheria toxin is encoded by the tox gene of some temperate corynephages such as beta. beta-like corynephages are capable of inserting into the C. diphtheriae chromosome at two specific sites, attB1 and attB2. Transcription of the phage-encoded tox gene, and many chromosomally encoded genes, is regulated by the DtxR protein in response to Fe(2+) levels. Characterizing DtxR-dependent gene regulation is pivotal in understanding diphtheria pathogenesis and mechanisms of iron-dependent gene expression; although this has been hampered by a lack of molecular genetic tools in C. diphtheriae and related Coryneform species. To expand the systems for genetic manipulation of C. diphtheriae, we constructed plasmid vectors capable of integrating into the chromosome. These plasmids contain the beta-encoded attP site and the DIP0182 integrase gene of C. diphtheriae NCTC13129. When these vectors were delivered to the cytoplasm of non-lysogenic C. diphtheriae, they integrated into either the attB1 or attB2 sites with comparable frequency. Lysogens were also transformed with these vectors, by virtue of the second attB site. An integrated vector carrying an intact dtxR gene complemented the mutant phenotypes of a C. diphtheriae DeltadtxR strain. Additionally, strains of beta-susceptible C. ulcerans, and C. glutamicum, a species non-permissive for beta, were each transformed with these vectors. This work significantly extends the tools available for targeted transformation of both pathogenic and non-pathogenic Corynebacterium species.

Large-scale engineering of the Corynebacterium glutamicum genome

The engineering of Corynebacterium glutamicum is important for enhanced production of biochemicals. To construct an improved C. glutamicum genome, we developed a precise genome excision method based on the Cre/loxP recombination system and successfully deleted 11 distinct genomic regions identified by comparative analysis of C. glutamicum genomes. Despite the loss of several predicted open reading frames, the mutant cells exhibited normal growth under standard laboratory conditions. With a total of 250 kb (7.5% of the genome), the 11 genomic regions were loaded with cryptic prophages, transposons, and genes of unknown function which were dispensable for cell growth, indicating recent horizontal acquisitions to the genome. This provides an interesting background for functional genomic studies and can be used in the improvement of cell traits.

Resistance of corynebacterial strains to infection and lysis by corynephage BFK 20

AIMS

Defence mechanisms of the corynebacterial strains against corynephage BFK 20, which causes lysis of Brevibacterium flavum CCM 251.

METHODS AND RESULTS

We tested adsorption of the phage BFK 20 to the corynebacterial cell surface. We observed strong adsorption ranging from ca 79 to 93% on the cells of B. flavum ATCC strains, but only ca 76% for B. flavum CCM 251. Minor adsorption for Brevibacterium lactofermentum BLOB (ca 13%) and no adsorption for Corynebacterium glutamicum RM3 were determined. BFK 20 infection had no significant effect on growth and viability of C. glutamicum and B. lactofermentum, but significantly influenced growth and viability of B. flavum ATCC 21127, 21128 and 21474. Cell growth stopped in short time after infection but with no lysis. Brevibacterium flavum CCM 251 cell growth was arrested too and lysis occurred. The Southern hybridization confirmed the presence of significant amount of BFK 20 DNA in samples from B. flavum CCM 251 and B. flavum ATCC strains after BFK 20 infection. Only weak hybridization signal was detected for DNA from infected cells of B. lactofermentum BLOB and no signal for C. glutamicum RM3.

CONCLUSIONS

Based on the above results we suggest presence of a mechanism leading to abortive infection in B. flavum ATCC 21127, 21128 and 21474. In B. lactofermentum BLOB and C. glutamicum RM3 the adsorption barrier is more likely.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study increases the knowledge on defence mechanisms of corynebacteria against bacteriophages.

Tools for genetic engineering in the amino acid-producing bacterium Corynebacterium glutamicum

During the last decades, the gram-positive soil bacterium Corynebacterium glutamicum has been shown to be a very versatile microorganism for the large-scale fermentative production of L-amino acids. Up to now, a vast amount of techniques and tools for genetic engineering and amplification of relevant structural genes have been developed. The objectives of this study are to summarize the published literature on tools for genetic engineering in C. glutamicum and to focus on new sophisticated and highly efficient methods in the fields of DNA transfer techniques, cloning vectors, integrative genetic tools, and antibiotic-free self-cloning. This repertoire of C. glutamicum methodology provides an experimental basis for efficient genetic analyses of the recently completed genome sequence.