The gas vesicle gene cluster from Microcystis aeruginosa and DNA rearrangements that lead to loss of cell buoyancy.
Microcystis aeruginosa is a planktonic unicellular cyanobacterium often responsible for seasonal mass occurrences at the surface of freshwater environments. An abundant production of intracellular structures, the gas vesicles, provides cells with buoyancy. A 8.7-kb gene cluster that comprises twelve genes involved in gas vesicle synthesis was identified. Ten of these are organized in two operons, gvpA(I)A(II)A(III)CNJX and gvpKFG, and two, gvpV and gvpW, are individually expressed. In an attempt to elucidate the basis for the frequent occurrence of nonbuoyant mutants in laboratory cultures, four gas vesicle-deficient mutants from two strains of M. aeruginosa, PCC 7806 and PCC 9354, were isolated and characterized. Their molecular analysis unveiled DNA rearrangements due to four different insertion elements that interrupted gvpN, gvpV, or gvpW or led to the deletion of the gvpA(I)-A(III) region. While gvpA, encoding the major gas vesicle structural protein, was expressed in the gvpN, gvpV, and gvpW mutants, immunodetection revealed no corresponding GvpA protein. Moreover, the absence of a gas vesicle structure was confirmed by electron microscopy. This study brings out clues concerning the process driving loss of buoyancy in M. aeruginosa and reveals the requirement for gas vesicle synthesis of two newly described genes, gvpV and gvpW.
Mlouka
Alyssa
A
Unité des Cyanobactéries (URA-CNRS 2172), Département de Microbiologie fondamentale et médicale, Institut Pasteur, 75724 Paris Cedex 15, France.
Comte
Katia
K
Castets
Anne-Marie
AM
Bouchier
Christiane
C
Tandeau de Marsac
Nicole
N
D004269:DNA, Bacterial / Q000032:analysis; D015321:Gene Rearrangement; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D046931:Microcystis / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D005810:Multigene Family; D009876:Operon; D011506:Proteins / Q000235:genetics*; D014617:Vacuoles
D004269:DNA, Bacterial; D011506:Proteins; C038524:gas vesicle protein