title: Identification and functional analysis of the cyclopropane fatty acid synthase of Brucella abortus.
abstract: The brucellae are facultative intracellular pathogens of mammals that are transmitted by contact with infected animals or contaminated materials. Several major lipidic components of the brucella cell envelope are imperfectly recognized by innate immunity, thus contributing to virulence. These components carry large proportions of acyl chains of lactobacillic acid, a long chain cyclopropane fatty acid (CFA). CFAs result from addition of a methylene group to unsaturated acyl chains and contribute to resistance to acidity, dryness and high osmolarity in many bacteria and to virulence in mycobacteria. We examined the role of lactobacillic acid in Brucella abortus virulence by creating a mutant in ORF BAB1_0476, the putative CFA synthase gene. The mutant did not incorporate [(14)C]methyl groups into lipids, lacked CFAs and synthesized the unsaturated precursors, proving that BAB1_0476 actually encodes a CFA synthase. BAB1_0476 promoter-luxAB fusion studies showed that CFA synthase expression was promoted by acid pH and high osmolarity. The mutant was not attenuated in macrophages or mice, strongly suggesting that CFAs are not essential for B. abortus intracellular life. However, when the mutant was tested under high osmolarity on agar and acid pH, two conditions likely to occur on contaminated materials and fomites, they showed reduced ability to grow or survive. Since CFA synthesis entails high ATP expenses and brucellae produce large proportions of lactobacillic acyl chains, we speculate that the CFA synthase has been conserved because it is useful for survival extracellularly, thus facilitating persistence in contaminated materials and transmission to new hosts.
authors.affiliation: Instituto de Salud Tropical y Departamento de Microbiología y Parasitología, Universidad de Navarra, Pamplona, Spain.
authors.forename: Leyre
authors.initials: L
authors.lastname: Palacios-Chaves
authors.affiliation: Instituto de Salud Tropical y Departamento de Microbiología y Parasitología, Universidad de Navarra, Pamplona, Spain.
authors.forename: Amaia
authors.initials: A
authors.lastname: Zúñiga-Ripa
authors.affiliation: Instituto de Recursos Naturales y Agrobiología de Sevilla, Consejo Superior de Investigaciones Científicas, Seville, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Gutiérrez
authors.affiliation: Instituto de Salud Tropical y Departamento de Microbiología y Parasitología, Universidad de Navarra, Pamplona, Spain.
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Gil-Ramírez
authors.affiliation: Instituto de Salud Tropical y Departamento de Microbiología y Parasitología, Universidad de Navarra, Pamplona, Spain.
authors.forename: Raquel
authors.initials: R
authors.lastname: Conde-Álvarez
authors.affiliation: Instituto de Salud Tropical y Departamento de Microbiología y Parasitología, Universidad de Navarra, Pamplona, Spain.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Moriyón
authors.affiliation: Instituto de Salud Tropical y Departamento de Microbiología y Parasitología, Universidad de Navarra, Pamplona, Spain.
authors.forename: Maite
authors.initials: M
authors.lastname: Iriarte
mesh_terms: D000143:Acids / Q000378:metabolism; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002003:Brucella abortus / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity; D002460:Cell Line; D003521:Cyclopropanes / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism*; D005260:Female; D015964:Gene Expression Regulation, Bacterial; D006863:Hydrogen-Ion Concentration; D008264:Macrophages / Q000382:microbiology; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D016297:Mutagenesis, Site-Directed; D016366:Open Reading Frames; D014774:Virulence
chemical_list: D000143:Acids; D001426:Bacterial Proteins; D003521:Cyclopropanes; D005227:Fatty Acids; C028775:cyclopropane fatty acids; D008780:Methyltransferases; C019964:cyclopropane synthetase