Potential cyanobacterial inoculants for rice described from a polyphasic approach

Ten heterocyst cyanobacteria isolated from a temperate ricefield in Uruguay were characterized using a polyphasic approach. Based on major phenotypic features, the isolates were divided into two different morphotypes within the Order Nostocales, filamentous without true branching. The isolates were also phylogenetically evaluated by their 16S rRNA and hetR gene sequences. Although the morphological classification of cyanobacteria has not always been supported by the analysis of the 16S rRNA gene, in this case the morphological identification agreed with the 16S rRNA gene phylogenetic analysis and the ten isolates were ascribed at the genus level to Nostoc or Calothrix. Four isolates were identified at species level. As these cyanobacteria were intended to be used as biofertilizer for rice, several physiological parameters were studied. Growth rates, nitrogenase, nitrate reductase and glutamate synthase activities were evaluated. This information will be valuable to select strains to be used as inoculant for ricefields.