​​Polyphasic characterisation of a member of the ecologically important epipelic cyanobacterial Pseudanabaena (Pseudanabaenaceae) isolated from Dian Pu River, Shanghai, China

An epipelic strain of the cyanobacterium Pseudanabaena (USMAC20) obtained from the sediment of Dian Pu River, Shanghai, China, was characterized using combined phenotypic and genetic approaches. The morphological plasticity of this strain under different temperature and photoperiod treatments was assessed to examine the stability of the morphological features in response to environmental changes. Cell dimensions, thylakoid arrangement and apical cell shape without aerotopes of the strain were consistent with the description of P. catenata Lauterborn. 16S rRNA gene analysis showed that the strain shared high sequence identity with characterised strains of P. catenata from Svalbard, Germany and Japan (> 98%). The strain also showed identical 16S-23S ITS configuration with other strains of Pseudanabaena currently represented in the GenBank database. Cultures of the strain were exposed to a range of temperature and photoperiod treatments, and harvested at the exponential phase to examine phenotypic plasticity, and confirm significant relationships between environmental conditions and morphological characteristics (cell dimensions and shape). The greatest cell length (5.79 ± 0.3 μm) and width (2.06 ± 0.1 μm) were observed at 15 °C under a 12 : 12 h L : D photoperiod. The strain showed high plasticity in cell dimension and shape under different temperature and photoperiod treatments, with 15 °C 12 : 12 photoperiod providing the optimal conditions for its growth. These environmental factors induced variations in cell structure, and other morphological traits, reflecting the adaptability and plasticity of this cyanobacterial strain. The consistent presence of a rounded apical cell under various culture conditions is a reliable criterion for the identification of these strains.