Identification of a strain Prototheca zopfii var. hydrocarbonea by analyzing the sequence of ribosome RNA gene / 中国人兽共患病学报

ABSTRACT

A strain of Prototheca species isolated from a case of meningitis was identified by routine morphologic and biochemical methods as well as amplification of the related genes, in which the 28S large-subunit (LSU) region of ribosomal RNA (rRNA) gene and intergenic space (ITS) were amplified with universal fungal primers. The small-subunit (SSU) rRNA gene was amplified with eukaryote-specific primers and Prototheca genus-specific primers. Then, compared the sequences with the ones posted on BLAST (www. ncbi. nlm. nih. gov/BLAST). The organism choice giving the closest match, up to 99%, was considered the most likely correct identification. It was found that this strain of fungus grew well at 25 ℃ or 37 ℃. Smooth,moist colonies with white color were observed on Sabouraud Dextrose Agar (SDA) and Potato Dextrose Agar (PDA). Microscopically, globular or ovoid cells, a number of round, ovoid shaped endospores could be observed. No hypha, ascus or blastic conidia was found upon cultivation on SDA. Based on the morphological characteristics, this isolate could be identified as Prototheca species. The identity with Prototheca wickerhamii was 2.9 % as demonstrated by the API 20C AUX system. Sequence analysis showed that the ITS gene was proved to be a complex structural region which was not suitable for the identification of Prototheca species, but the LSU and SSU rDNA regions showed 94% and 99.9% sequence identities with Prototheca zopfii var. hydrocarbonea (P. zopfii var. hydrocarbonea) respectively, indicating that the SSU rRNA gene sequence might be more reliable on than the LSU rRNA gene sequence for identification of Prototheca species.