TOWARDS A FORMAL DESCRIPTION OF A NEW SPECIES OF SYNECHOCOCCUS (CYANOBACTERIA CYANOPHYCEAE) FROM THE FRESH-WATER PICOPLANKTON

The paper explores the specific identity of a small rod-like organism first recorded in Loch Leven (Scotland) in 1967 and orginally thought to be a colourless bacterium. Its taxonomic affinity is established by considering relevant problems in cyano-bacterial (blue-green algal) taxonomy in relation to information gathered in 1968, when the organism was first suspected to be an undescribed species of Synechococcus. It achieved dense population maxima (10(5)-10(7) cells per ml) during each year 1968 to 1971, but apart from a brief appearance in 1973 it has not been noticed since then. The coincidence of its "disappearance" with the appearance of filter-feeding Daphnia (Crustacea, Cladocera) is noted. While water temperature and the concentrations of nutrients, for example, varied considerably during the period of Synechococcus prominence, cells in the loch and those kept in clonal culture (CHU 10 and ASM 1 media) maintained the features of the genus, e.g. the solitary habit; elongated, isopolar nature of the cells; division by transverse binary fission and the absence of abundant mucilage. Contrastingly, natural material enriched with nutrients and kept in the laboratory, quickly changed into "Anacystis nidulans" type cells. The loch Synechococcus contrasts with all other described species of the genus, in the high (and variable) ratio of cell length (5.5-27.3-mu-m) to breadth (0.7-0.9-mu-m). Moreover, it appears to have only 1 peripheral thylakoid and has simple microtubuli near the cell apex. Together with its special "capitate" morphology, these features substantiate the erection of a new species and the name S. capitatus is proposed.