Straight-Chain Fatty Acids Are Dispensable in the Myxobacterium Myxococcus xanthus for Vegetative Growth and Fruiting Body Formation

Abstract

Inactivation of the MXAN_0853 gene blocked the production in Myxococcus xanthus of straight-chain fatty acids which otherwise represent 30% of total fatty acids. Despite this drastic change in the fatty acid profile, no change in phenotype could be observed, which contrasts with previous interpretations of the role of straight-chain fatty acids in the organism's development.Myxobacteria have very complex fatty acid (FA) profiles, with up to 40 different compounds belonging to all known classes of FAs (2, 27). The most dominant fatty acid usually belongs to the iso-branched fatty acids (iso-FAs), which contribute up to 80% of total FAs in some species. All other fatty acids are straight-chain fatty acids (scFAs), whereas anteisoFAs are found only as trace compounds in myxobacteria. Interestingly, mono-and diunsaturated species as well as 2-OH and 3-OH derivatives of these FAs are common in myxobacteria, and iso-2-OH FAs especially have been proposed as chemotaxonomic markers to identify myxobacteria and other gliding bacteria (7). The resulting abundance of different fatty acids is unexpected because several bacteria from different environments, like Escherichia coli, bacilli, and actinomycetes, live with much simpler fatty acid profiles. One might argue that this mixture allows myxobacteria to maintain their membrane fluidity over a broad temperature range, but except for some thermophilic species (8), almost all myxobacteria described are mesophiles, most of which grow only in a narrow temperature range. Additionally, myxobacteria possess members of different FA families thought to fulfill the same functions (e.g., isoand unsaturated FAs) (13). Even FAs with more than one functional group can be observed in substantial amounts.It was postulated previously that some of these FAs play a role in the complex life cycle of myxobacteria which culminates in the formation of fruiting bodies containing heat-and desiccation-resistant myxospores (11,22). The model organism for studying the development of and sporulation in myxobacteria is Myxococcus xanthus, for which different extracellular signals and regulators have already been described. These are required for M. xanthus to proceed through the developmental program (12). However, the underlying biochemistry is barely understood. It was shown previously by Toal et al. that disruption of the branched-chain keto acid dehydrogenase (Bkd) complex results in a developmental phenotype with almost no aggregates or spores formed under starvation conditions (25). The Bkd complex is involved in the degradation of the branched-chain amino acids leucine, valine, and isoleucine to isovaleryl-coenzyme A (isovaleryl-CoA), isobutyryl-CoA, and 2-methylbutyryl-CoA, respectively. These thioesters are the starting units for iso-and anteiso-fatty acids and for several secondary metabolites from different bacteria (e.g., avermectin from Streptomyces avermitilis [6] and myxothiazol [24], myxalamides [23], and aurafuron [16] from Stigmatella aurantiaca).In all myxobacteria analyzed so far, ...

Fatty Acid-Related Phylogeny of Myxobacteria as an Approach to Discover Polyunsaturated Omega-3/6 Fatty Acids

“…Thirty-two were identified in Nannocystineae and 44 in Cystobacterineae. In Myxococcaceae alone, from the latter suborder, 34 were identified, approximately the same number as reported earlier (1,2,6). Most surprising was the discovery of 49 FAs in Sorangiineae.…”

“…Certain species of Corallococcus and Myxococcus have been used as the preferred models in most FA biosynthesis (1,4,42) and developmental studies (2,13,26,41). In Pyxidicoccus, the FA composition was evaluated here for the first time.…”

Novel Iso-branched Ether Lipids as Specific Markers of Developmental Sporulation in the Myxobacterium Myxococcus xanthus

“…The bkd mutant showed a high excess of this and other SCFAs, which would result in an excess of the required signal and therefore in a loss of the chemotaxis. However, recent analysis of a mutant that produces only trace amounts of SCFAs revealed that this FA or the corresponding PE is not required for fruiting body formation or sporulation as both occurred indistinguishable to the wild type (25). Interestingly, inactivation of the bkd locus does not lead to a complete loss of iso-FA production, which is due to the presence of a novel alternative pathway to isovaleryl-CoA ( Fig.…”

Edonamides, the first secondary metabolites from the recently described myxobacterium Aggregicoccus edonensis

“…25 Furthermore, myxobacteria produce a variety of different fatty acids with unknown biological function. However, Bode et al 26 have shown iso-branched fatty acids play a role in the myxobacterial life cycle. A decrease in iso-branched fatty acid production resulted in a strongly delayed and reduced aggregation and sporulation.…”