Characterisation of inhibitory substances produced by two Pseudoalteromonas species and the cyanobacterial strain Flo1

In the present study the inhibitory substances of P. aurantia NCIMB 2052T and P. citrea NCIMB 1889T were investigated with respect to their substantial and functional nature, their inhibitory potential, their stability against various treatments as well as the growth phases and incubation conditions when the substances are produced. In addition, an inhibitory substance produced by strain Flo1 was examined regarding its structure, function, and inhibitory potential. Furthermore, its taxonomic position amongst closely related cyanobacteria was investigated by re-constructing phylogenetic trees, showing that strain Flo1 is most closely related to the genus Geitlerinema. The results clearly indicate that the inhibitory substances produced by both Pseudoalteromonas species as well as by Geitlerinema strain Flo1 are L-amino acid oxidases (L-AAOs) with broad respectively very specific substrate spectra. Furthermore, it could be shown that the Pseudoalteromonas L-AAOs are active against methicillin-resistant Staphylococcus aureus (MRSA).