[DNA mapping in the capsid of giant bacteriophage phiEL (Caudovirales: Myoviridae: Elvirus) by analytical electron microscopy].

INTRODUCTION: Giant phiKZ-like bacteriophages have a unique protein formation inside the capsid, an inner body (IB) with supercoiled DNA molecule wrapped around it. Standard cryo-electron microscopy (cryo-EM) approaches do not allow to distinguish this structure from the surrounding nucleic acid of the phage. We previously developed an analytical approach to visualize protein-DNA complexes on Escherichia coli bacterial cell slices using the chemical element phosphorus as a marker. In the study presented, we adapted this technique for much smaller objects, namely the capsids of phiKZ-like bacteriophages. MATERIAL AND METHODS: Following electron microscopy techniques were used in the study: analytical (AEM) (electron energy loss spectroscopy, EELS), and cryo-EM (images of samples subjected to low and high dose of electron irradiation were compared). RESULTS: We studied DNA packaging inside the capsids of giant bacteriophages phiEL from the Myoviridae family that infect Pseudomonas aeruginosa. Phosphorus distribution maps were obtained, showing an asymmetrical arrangement of DNA inside the capsid. DISCUSSION: We developed and applied an IB imaging technique using a high angle dark-field detector (HAADF) and the STEM-EELS analytical approach. Phosphorus mapping by EELS and cryo-electron microscopy revealed a protein formation as IB within the phage phiEL capsid. The size of IB was estimated using theoretical calculations. CONCLUSION: The developed technique can be applied to study the distribution of phosphorus in other DNA- or RNA-containing viruses at relatively low concentrations of the element sought.

Diversity of limestone bacteriophages infecting Dickeya solani isolated in the Czech Republic.

Seven novel tailed lytic viruses (Ds3CZ, Ds5CZ, Ds9CZ, Ds16CZ, Ds20CZ, Ds23CZ, Ds25CZ) infecting the bacterium Dickeya solani were isolated in the Czech Republic. Genomes of these viruses are dsDNA, 149,364 to 155,285 bp in length, and the genome arrangement is very similar to that of the type virus Dickeya virus LIMEstone 1. All but the Ds25CZ virus should be regarded as strains of a single species. Most of the sequence differences are due to the presence or absence of homing endonuclease (HE) genes, with 23 HEs found in Ds3CZ, Ds5CZ, and Ds20CZ, 22 in Ds9CZ, 19 in Ds16CZ, 18 in Ds25CZ, and 15 in Ds23CZ.