Abstract
BackgroundThe terminal organelle is a complex structure involved in many aspects of the biology of mycoplasmas such as cell adherence, motility or cell division. Mycoplasma genitalium cells display a single terminal organelle and duplicate this structure prior to cytokinesis in a coordinated manner with the cell division process. Despite the significance of the terminal organelle in mycoplasma virulence, little is known about the mechanisms governing its duplication.Methodology/Principal FindingsIn this study we describe the isolation of a mutant, named T192, with a transposon insertion close to the 3′ end of the mg192 gene encoding for P110 adhesin. This mutant shows a truncated P110, low levels of P140 and P110 adhesins, a large number of non-motile cells and a high frequency of new terminal organelle formation. Further analyses revealed that the high rates of new terminal organelle formation in T192 cells are a direct consequence of the reduced levels of P110 and P140 rather than to the expression of a truncated P110. Consistently, the phenotype of the T192 mutant was successfully complemented by the reintroduction of the mg192 WT allele which restored the levels of P110 and P140 to those of the WT strain. Quantification of DAPI-stained DNA also showed that the increase in the number of terminal organelles in T192 cells is not accompanied by a higher DNA content, indicating that terminal organelle duplication does not trigger DNA replication in mycoplasmas.Conclusions/SignificanceOur results demonstrate the existence of a mechanism regulating terminal organelle duplication in M. genitalium and strongly suggest the implication of P110 and P140 adhesins in this mechanism.
Highlights
Mycoplasmas are parasites or commensals of humans and other animals, characterized by the lack of a cell wall and fastidious nutritional requirements
We described a method to obtain M. genitalium mutants with an altered locomotion [13,17]. By means of this procedure, a mutant with a minitransposon inserted in position 228984 of the M. genitalium genome and exhibiting a compact colony morphology (Fig. 1A–C) was isolated. In this mutant, designated T192, the transposon insertion was found in antisense near the 39 end of the mg192 gene that encodes for P110, a cytadherence-associated protein required for the stability of P140, the major cytadhesin of M. genitalium [24,26]
Despite the important functions carried out by this structure, most of them involved in mycoplasma virulence, little is known about the mechanisms regulating its duplication and how these mechanisms are interlaced with those regulating the cell cycle of mycoplasmas
Summary
Mycoplasmas are parasites or commensals of humans and other animals, characterized by the lack of a cell wall and fastidious nutritional requirements. These microorganisms with streamlined genomes are considered the smallest self-replicating cells known able to be grown in axenic culture. Consistent with this idea, the number of genes encoding proteins involved in cellular processes such as cell division, stress responses, and protein secretion, is certainly smaller in mycoplasmas as compared to other eubacteria. The terminal organelle is a complex structure involved in many aspects of the biology of mycoplasmas such as cell adherence, motility or cell division. Despite the significance of the terminal organelle in mycoplasma virulence, little is known about the mechanisms governing its duplication
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