LIPOPOLYSACCHARIDE DEPENDENCE OF CYANOPHAGE SENSITIVITY AND AEROBIC NITROGEN-FIXATION IN ANABAENA SP STRAIN PCC-7120

Citation
Xd. Xu et al., LIPOPOLYSACCHARIDE DEPENDENCE OF CYANOPHAGE SENSITIVITY AND AEROBIC NITROGEN-FIXATION IN ANABAENA SP STRAIN PCC-7120, Journal of bacteriology, 179(9), 1997, pp. 2884-2891
Citations number
56
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Microbiology
Journal title
ISSN journal
0021-9193
Volume
179
Issue
9
Year of publication
1997
Pages
2884 - 2891
Database
ISI
SICI code
0021-9193(1997)179:9<2884:LDOCSA>2.0.ZU;2-Q
Abstract
Fox(-) mutants of Anabaena sp, strain PCC 7120 are unable to fu; dinit rogen in the presence of oxygen. A fragment of the DNA of Anabaena sp, was cloned by complementation of a spontaneous Fox(-), cyanophage-res istant mutant, R56, and characterized. Random insertion of transposon Tn5 delimited the complementing DNA to a 0.6-kb, portion of the cloned fragment. Sequencing of this region and flanking DNA showed one compl ete open reading frame (ORI) similar to the gene rfbD (undecaprenyl-ph osphate galactose phosphotransferase) and two partial ORFs similar to genes rfbD (GDP-D-mannose dehydratase) and rfbZ (first mannosyl transf erase), all of which are active in the synthesis of the O antigen unit of the lipopolysaccharide (LP8) component of the outer membrane of gr am-negative bacteria. In a transposon (Tn5-1087b)-induced, Fox(-), cya nophage-resistant mutant, B14, the transposon was found within the sam e rfbP-like ORF, The three ORFs were insertionally inactivated with th e omega cassette (P, Prentki and H, M. Krisch, Gene 29:303-313, 1954) or with Tn5::omega, Only the insertions in the rfbZ- and rfbP-like ORF s led to resistance to cyanophages A-I(L) and A-4(L) and to a Fox(-) p henotype, Electrophoretic analysis showed that interruption of the rfb Z- and rfbP-like ORFs resulted in a change ill or loss of the characte ristic pattern of the lengths of the LPS, whereas interruption of the rfbD-like ORF merely changed the distribution of the lengths of the LP S to one with a greater prevalence of low molecular weights, According to electron microscopy, interruption of the rfbP-like ORF may have le d to aberrant deposition of the layers of the heterocyst envelope, res ulting in increased leakage of oxygen into the heterocyst. The results suggest that modified LPS may prevent cyanophage infection of Anabaen a sp. vegetative cells and the formation of a functional heterocyst en velope.