Replicative oriC plasmids were recently developed for several mollicutes, including three Mycoplasma species belonging to the mycoides cluster that are responsible for bovine and caprine diseases: Mycoplasma mycoides subsp. mycoides small-colony type, Mycoplasma mycoides subsp. mycoides large-colony type, and Mycoplasma capricolum subsp. capricolum. In this study, oriC plasmids were evaluated in M. capricolum subsp. capricolum as genetic tools for (i) expression of heterologous proteins and (ii) gene inactivation by homologous recombination. The reporter gene lacZ, encoding beta-galactosidase, and the gene encoding spiralin, an abundant surface lipoprotein of the related mollicute Spiroplasma citri, were successfully expressed. Functional Escherichia coli beta-galactosidase was detected in transformed Mycoplasma capricolum subsp. capricolum cells despite noticeable codon usage differences. The expression of spiralin in M. capricolum subsp. capricolum was assessed by colony and Western blotting. Accessibility of this protein at the cell surface and its partition into the Triton X-114 detergent phase suggest a correct maturation of the spiralin precursor. The expression of a heterologous lipoprotein in a mycoplasma raises potentially interesting applications, e.g., the use of these bacteria as live vaccines. Targeted inactivation of gene lppA encoding lipoprotein A was achieved in M. capricolum subsp. capricolum with plasmids harboring a replication origin derived from S. citri. Our results suggest that the selection of the infrequent events of homologous recombination could be enhanced by the use of oriC plasmids derived from related mollicute species. Mycoplasma gene inactivation opens the way to functional genomics in a group of bacteria for which a large wealth of genome data are already available and steadily growing.