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Two Distinct Cardiolipin Synthases Operate in Agrobacterium tumefaciens.

ABSTRACT: Cardiolipin (CL) is a universal component of energy generating membranes. In most bacteria, it is synthesized via the condensation of two molecules phosphatidylglycerol (PG) by phospholipase D-type cardiolipin synthases (PLD-type Cls). In the plant pathogen and natural genetic engineer Agrobacterium tumefaciens CL comprises up to 15% of all phospholipids in late stationary growth phase. A. tumefaciens harbors two genes, atu1630 (cls1) and atu2486 (cls2), coding for PLD-type Cls. Heterologous expression of either cls1 or cls2 in Escherichia coli resulted in accumulation of CL supporting involvement of their products in CL synthesis. Expression of cls1 and cls2 in A. tumefaciens is constitutive and irrespective of the growth phase. Membrane lipid profiling of A. tumefaciens mutants suggested that Cls2 is required for CL synthesis at early exponential growth whereas both Cls equally contribute to CL production at later growth stages. Contrary to many bacteria, which suffer from CL depletion, A. tumefaciens tolerates large changes in CL content since the CL-deficient cls1/cls2 double mutant showed no apparent defects in growth, stress tolerance, motility, biofilm formation, UV-stress and tumor formation on plants.

SUBMITTER: Czolkoss S

PROVIDER: S-EPMC4966929 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Rotary flagella propel bacteria through liquid and across semisolid environments. Flagella are composed of the basal body that constitutes the motor for rotation, the curved hook that connects to the basal body, and the flagellar filament that propels the cell. Flagellar filaments can be composed of a single flagellin protein, such as in Escherichia coli, or made up of multiple flagellins, such as in Agrobacterium tumefaciens The four distinct flagellins FlaA, FlaB, FlaC, and FlaD produced by wild-type A. tumefaciens are not redundant in function but have specific properties. FlaA and FlaB are much more abundant than FlaC and FlaD and are readily observable in mature flagellar filaments, when either FlaA or FlaB is fluorescently labeled. Cells producing FlaA with any one of the other three flagellins can generate functional filaments and thus are motile, but FlaA alone cannot constitute a functional filament. In flaA mutants that manifest swimming deficiencies, there are multiple ways by which these mutations can be phenotypically suppressed. These suppressor mutations primarily occur within or upstream of the flaB flagellin gene or in the transcription factor sciP regulating flagellin expression. The helical conformation of the flagellar filament appears to require a key asparagine residue present in FlaA and absent in other flagellins. However, FlaB can be spontaneously mutated to render helical flagella in the absence of FlaA, reflecting their overall similarity and perhaps the subtle differences in the specific functions they have evolved to fulfill.IMPORTANCE Flagellins are abundant bacterial proteins comprising the flagellar filaments that propel bacterial movement. Several members of the alphaproteobacterial group express multiple flagellins, in contrast to model systems, such as with Escherichia coli, which has one type of flagellin. The plant pathogen Agrobacterium tumefaciens has four flagellins, the abundant and readily detected FlaA and FlaB, and lower levels of FlaC and FlaD. Mutational analysis reveals that FlaA requires at least one of the other flagellins to function, as flaA mutants produce nonhelical flagella and cannot swim efficiently. Suppressor mutations can rescue this swimming defect through mutations in the remaining flagellins, including structural changes imparting helical shape to the flagella, and putative regulators. Our findings shed light on how multiple flagellins contribute to motility.

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Two Distinct Cardiolipin Synthases Operate in Agrobacterium tumefaciens.

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