Biodiversity Profile of Cyanobacterial genus Calothrix

Abstract

The present investigation was undertaken in thirty cyanobacterial strains of Calothrix (family Rivulariaceae) to analyse their morpho-physiological and molecular relatedness. These strains including reference strain (UTEX 379) were procured from culture collection of Centre for Conservation and Utilisation of Blue Green Algae, IARI, New Delhi - 110012. Most of the forms were planktonic or free floating while some exhibited benthic growth behaviour. Variation in colour of thallus was expressed distinctly and the colour ranged from brown, blackish green to dark green. Large number of strains grew as floccose masses while some grew as spreading and few formed evenly distributed suspension. Microscopic examination revealed that the trichomes grew as densely entangled/distinctly or slightly constricted except in few where trichomes were irregularly straight or bent. The number of cells in a filament ranged from 2-300. Trichomes of genus Calothrix comprised heteropolarity and showed clear distinction from the base and the apex. Heterocysts were easily distinguishable and the colour of these cells was yellow, green or hyaline. Terminal heterocysts occured at the broad basal end of the trichomes in most of the strains studied. Akinetes were observed after the exponential phase and the length of the akinetes was 2-3.5 folds higher as compared to the vegetative cells. Hormogones were formed in almost all the strains from the terminal portion of trichome after fragmentation. A firm and distinct sheath was always noted amongst the strains and the sheath was lamellate() or unlamellated and lamellation was parallel or divergent. .Colour of the sheath varied from yellowish. bluish, brownish or reddish but in most of the cases, it was hyaline. Loop formation and false branching was also seen as a very common feature amongst the strains analysed. Mean dry weight varied from 61.20 mg/mL to 137.47 mg/mL. Mean chlorophyll content ranged between 3.51 pg/mL to 11.16 pg/mL and carotenoids ranged from 6.46 pg/mL to 25.74 pg/mL.