CULTURAL AND MOLECULAR CHARACTERIZATION OF PHOTOBIONTS OF PELTIGERA-MEMBRANACEA

A molecular study was undertaken to clarify the identity of the photob iont in colourmorphs of the lichen, Peltigera membranacea. Two strains of cyanobacteria, identified as Nostoc sp. by morphology, were cultiv ated from each of two lichen specimens. Prokaryotic (16S) ribosomal RN A gene fragments were amplified by the polymerase chain reaction (PCR) from DNA extracted from the isolated strains and the lichens, and seq uenced directly. Sequences were 98.1% identical between lichen specime ns, TDI#AR94 and TDI#AR95, and highly similar to sequences published, or generated in this study from a type culture, for Nostoc. The 16S ri bosomal RNA gene sequences ('16S rDNA') of all four lichen-derived cya nobacteria appeared the same, even though the lichen specimens from wh ich they originated had different sequences. The 16S rDNA from strains 9A and 9B were different from that of specimen TDI#AR94, the thallus from which they were isolated, and instead were the same as that of st rains 10A and 10B, and their source, specimen TDI#AR95. When primers s elective for the strain 9A sequence were used, however, a small amount of PCR product corresponding to the 16S rDNA of strain 9A was obtaine d from lichen TDI#AR94. The results confirm that the photobionts of P. membranacea belong to Nostoc, and suggest that genetic differences in the photobiont may be a factor in the occurrence of colourmorphs amon g cyanolichens. (C) 1997 The British Lichen Society.