Phage-host interactions in Lactobacillus delbrueckii: host recognition and transcription of early phage genes
1University of Oulu, Faculty of Science, Department of Biology
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|Academic dissertation to be presented, with the assent of the Faculty of Science of the University of Oulu, for public defence in Kuusamonsali (Auditorium YB210), Linnanmaa, on May 4th, 2007, at 12 noon
Professor Jaana Bamford
Professor Per Saris
The scope of this study includes aspects of phage evolution and antagonistic/mutualistic coevolution between a phage and its host. As a basic study it may provide tools for developing phage resistant starters and offer regulatory elements and factors for biotechnological applications.
The LL-H anti-receptor was characterized by isolation of spontaneous LL-H host range mutants and subsequent sequencing of candidate genes. All LL-H host range mutants carried a single point mutation at the 3' end of a minor tail protein encoding gene g71. The genomic location of g71 is congruent with the other verified anti-receptor genes found in the λ supergroup. The C-terminus of Gp71 determines the adsorption specificity of phage LL-H similarly for the number of phages infecting Gram-positive and Gram-negative bacteria. A Gp71 homolog of phage JCL1032 showed 62% identity to LL-H Gp71 within the last 300 amino acids at the C-terminus.
Lactobacillus delbrueckii phage receptors were investigated by the purification of different cell surface structures. Certain Lb. delbrueckii phages from homology groups a and c including LL-H, LL-H host range mutants and JCL1032, were specifically inactivated by the LTAs. In structural analyses LTAs showed differences in the degree of α-glucosyl and ᴅ-alanyl substitution. α-glucose is necessary for LL-H adsorption. A high level of ᴅ-alanine esters in LTA backbones inhibited Lb. delbrueckii phage inactivation in general. Lysogenization of strain ATCC 15808 with the temperate phage JCL1032 revealed a rarely described coexistence of phage adsorption resistance and phage immunity, which could not be explained by lysogenic conversion. In this case the role of spontaneously induced JCL1032 may be significant.
The LL-H early gene region was localized between the dysfunctional lysogeny module and the terminase encoding genes. The function of five ORFs could be connected to phage DNA replication and/or homologous recombination. Transcription of LL-H genes could be divided into two, possibly three, phases in which large gene clusters were sequentially transcribed. The intensity of the late transcripts exceeded the intensity of the early transcripts by several times. Two candidate genes for transcription regulators were found. One of the two candidates is the first ORF in the LL-H early gene region.
Acta Universitatis Ouluensis. A, Scientiae rerum naturalium
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