Axenic culture of plant pathogenic phytoplasmas

Abstract

Phytoplasmas are microorganisms associated with severe plant diseases affecting diverse agrarian activites worldwide. Since their discovery, conclusive proof of their pathogenicity is lacking due to failure to culture these organisms. This has also hindered studies on their biology, biochemistry and physiology, although significant taxonomic progress has been achieved from study of the 16S ribosomal gene and full genomic sequencing of four phytoplasma strains. The inability to fulfil Koch’s postulates severely restricts the understanding of the roles of these organisms in plant diseases and in plant/insect/phytoplasma interactions. Here we show that specific commercial media support axenic growth of phytoplasmas under defined conditions; the identity of the organisms was confirmed by PCR/RFLP analyses and sequencing of phytoplasma-specific genes. We have demonstrated for the first time that phytoplasmas, similarly to mycoplasmas, can grow independently from their host(s). This should assist reduction of the socio-economic impact of phytoplasma diseases worldwide through improved pathogen detection and consequently better management of the diseases they cause. Knowledge of mechanisms underlying the autonomous life of phytoplasmas, that are among the smallest living organisms, should also provide important information about basic mechanisms of life.