title: Precursor and temperature modulation of fatty acid composition and growth of Listeria monocytogenes cold-sensitive mutants with transposon-interrupted branched-chain alpha-keto acid dehydrogenase.
abstract: Branched-chain fatty acids (BCFAs) typically constitute more than 90 % of the fatty acids of Listeria monocytogenes. The authors have previously described two Tn917-induced, cold-sensitive, BCFA-deficient (<40 %) L. monocytogenes mutants (cld-1 and cld-2) with lowered membrane fluidity. Sequence analyses revealed that Tn917 was inserted into different genes of the branched-chain alpha-keto acid dehydrogenase cluster (bkd) in these two mutants. The cold-sensitivity and BCFA deficiency of cld-1, in which Tn917 was inserted into bkdB, were complemented in trans by cloned bkdB. The growth and corresponding BCFA content of the mutants at 37 degrees C were stimulated by fatty acid precursors bypassing Bkd, 2-methylbutyrate (precursor for odd-numbered anteiso-fatty acids), isobutyrate (precursor for even-numbered iso-fatty acids) and isovalerate (precursor for odd-numbered iso-fatty acids). In contrast, the corresponding Bkd substrates, alpha-ketomethylvalerate, alpha-ketoisovalerate and alpha-ketoisocaproate, exhibited much poorer activity. At 26 degrees C, 2-methylbutyrate and isovalerate stimulated the growth of the mutants, and at 10 degrees C, only 2-methylbutyrate stimulated growth. Pyruvate depressed the BCFA content of cld-2 from 33 % to 27 %, which may be close to the minimum BCFA requirement for L. monocytogenes. The transcription of bkd was enhanced by Bkd substrates, but not by low temperature. When provided with the BCFA precursors, cld-2 was able to increase its anteiso-C15 : 0 fatty acid content at 10 degrees C compared to 37 degrees C, which is the characteristic response of L. monocytogenes to low temperature. This implies that Bkd is not the major cold-regulation point of BCFA synthesis.
authors.affiliation: Microbiology Group, Department of Biological Sciences, Illinois State University, Normal, IL 61790-4120, USA.
authors.forename: Kun
authors.initials: K
authors.lastname: Zhu
authors.affiliation: Microbial Food Safety Research Unit, Eastern Regional Research Center (ERRC), Agricultural Research Service, US Department of Agriculture, Wyndmoor, PA 19038, USA.
authors.forename: Darrell O
authors.initials: DO
authors.lastname: Bayles
authors.affiliation: Microbiology Group, Department of Biological Sciences, Illinois State University, Normal, IL 61790-4120, USA.
authors.forename: Anming
authors.initials: A
authors.lastname: Xiong
authors.affiliation: Microbiology Group, Department of Biological Sciences, Illinois State University, Normal, IL 61790-4120, USA.
authors.forename: R K
authors.initials: RK
authors.lastname: Jayaswal
authors.affiliation: Microbiology Group, Department of Biological Sciences, Illinois State University, Normal, IL 61790-4120, USA.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Wilkinson
mesh_terms: D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) / Q000235:genetics / Q000378:metabolism*; D003080:Cold Temperature; D003470:Culture Media; D004251:DNA Transposable Elements; D005227:Fatty Acids / Q000032:analysis / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D007651:Keto Acids / Q000378:metabolism*; D008089:Listeria monocytogenes / Q000737:chemistry / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D013379:Substrate Specificity
chemical_list: D003470:Culture Media; D004251:DNA Transposable Elements; D005227:Fatty Acids; D007651:Keto Acids; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)