Phylogeny and characterization of phytoplasmal nusA and use of the nusA gene in detection of group 16SrI strains

Abstract

Phytoplasmas are cell wall-less prokaryotes that exist as obligate parasites and pathogens of insect vectors and plants. In their descent from walled ancestors in the Bacillus/Clostridium group, phytoplasmas evolved some of the smallest known bacterial genomes. In this study, we cloned and sequenced nusA transcription factor gene sequences from clover phyllody (CPh) and other phytoplasmas and from Acholeplasma palmae, a nonphytopathogenic wall-less bacterium. The CPh nusA gene was flanked at its 5'-end by a hypothetical protein gene and smpB (small protein B), and at its 3'-end by a hypothetical protein gene that may be coordinately regulated with nusA and infB (translation initiation factor). The predicted 357-aa NusA protein of CPh phytoplasma was significantly smaller than those of Mycoplasma spp. and similar in size to NusA of Clostridium spp., Bacillus spp., and A. palmae. A phylogenetic tree based on NusA proteins indicated that phytoplasmal and acholeplasmal nusA genes diverged from a common ancestor. Amplification and RFLP analysis of nusA gene sequences, and phylogenetic analysis of NusA proteins indicated that use of nusA may assist in detection and differentiation of distinct lineages within group 16SrI, ‘Candidatus Phytoplasma asteris’-related strains.