A first cytomorphological and molecular characterisation of a new Stigonomatalean cyanobacterial morphotype isolated from Maltese catacombs

Two heterocytous filamentous cyanobacterial strains were isolated from biofilms growing in separate palaeo-Christian catacombs dedicated to St Agatha and St Paul at Rabat in Malta. The strains are characterised by a heterotrichous habit, intercalary hetero-cytes, true T-type branches and the presence of hormogonia. The ultrastructure was studied. Phylogenetic trees constructed using both distance and parsimony methods on 16S rRNA gene sequences showed that the isolates cluster with the heterocytous cyanobateria, but there is no apparent close similarity with any Stigonematalean genera described so far. The taxonomic and phylogenetic position of the isolates is discussed.