The use of psbB for the identification of cyanobacterial lichen symbionts

Abstract

The genus Pseudocyphellaria includes large fast growing foliose species that are able to exploit both high and low light habitats. This project aims to compare photosynthesis across a range of environmental parameters in different isolated cyanobionts and between the free-living and lichenized forms. The initial step has been the isolation of the cyanobionts from lichen thalli. Methanol-extracted pigments were used to identify cyanobacteria that were cultured from lichen tissue and 16S rRNA gene sequences were used to confirm this assignment. The cyanobacterial 16S rDNA sequences of the isolates and lichen samples were also compared to establish whether the cultured isolates were representative of the lichenized cyanobiont. Finally the tRNALeu(UAA) intron sequences of a number of lichen thalli of the same species were compared to elucidate the specificity of the fungal and cyanobacterial association. Two isolated cyanobacteria, one from P. crocata and one from P. neglecta, had 16S rRNA gene sequences identical to the lichen thalli from which they were cultured. These two high light tolerant species were found to have cyanobacteria with similar Nostoc-like 16S rDNA sequences, but distinct tRNALeu(UAA) intron sequences. The cyanobacterial tRNALeu(UAA) intron sequences from P. crocata thalli that had been collected from different sites were found to be similar and had the same predicted RNA secondary structure. Furthermore, tRNALeu(UAA) intron sequences from several P. neglecta thalli were identical. Interestingly, the cyanobacterial tRNALeu(UAA) intron sequence from the thallus of the low light lichen P. maculata was found to be similar to that from P. crocata.