Characterisation of a novel bacteriophage, 0BHG1, and its interactions with its host Rhodopseudomonas blastica

• Main Author: Gorham, Hazel Claire
• Published: University of Warwick 1987
• Subjects: 591.35; QR Microbiology
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329300

0BHG1, a lytic phage specific for Rhodopseudomonas blastica has an icosahedral head of 62 ran diameter and a short, 39 nm long, non- contractile tail with a collar, base plate and short spikes. Caesium chloride density centrifugation of phage normally gave a single phage band corresponding to a density of 1.3850 g cm, but occasionally a second band was observed (1.3838 g cm. No apparent differences were observed between the two phage bands. The nucleic acid of 0BHG1 is double stranded DNA, with a G+C content of 50.6 mol %, and a molecular weight of 48 kb. The capsid proteins are observed ranging in molecular weight from 18,000 to 98,000 and corresponding to approximately 26% of the coding capacity of the genome. 0BHG1 adsorbed to both photo- synthetically and chemohetero-trophically grown Rp. blastica at an identical rate of 1.39 ml'1 min". The phage has no specific cation requirement for adsorption. One-step growth curve studies of 0BHG1 with phage antisera gave a lag period of 80-100 min, a rise period of 100 min and a final burst size of 25 ± 2.5 and 30 + 2.1 for chemohetero-trophically and photoheterotrophically grown cells respectively. Synchronisation of cells for one-step growth curves with potassium cyanide altered the burst size with photosynthetically grown cells. Adsorption of 0BHG1 was specific to the 'old' pole of Rp. blastica. Lysis of Rp. blastica by French pressing gave three distinct bands after differential sucrose density centrifugation corresponding to the cytoplasmic membrane and two cell wall fractions B1 and B2. Both cell wall fractions contained a dominant heat modifiable protein of molecular weight 35,000, and in addition cell wall fraction B1 contained two dominant proteins of Mr 14,500 and 15,000. Amino acid analysis suggests a difference in the amount of cross-linkage of the peptidoglycan between the two cell wall fractions. Comparisons of Rp. blastica with a spontaneous phage resistant mutant Rp. blastica to which 0BHG1 fails to adsorb showed only trace amounts of the Mr 14,500 and 15,000 proteins in the resistant strain. Analysis of lipopolysaccharide from the two strains showed the loss of the neutral sugar 2-0-methyl-6-deoxyhexgse and a reduction in the concentration of galactose in Rp. blastica Evidence suggests that an LPS/protein complex may function as the bacterial phage receptor and is required to inactivate 0BHG1 in vitro.