Diversity and growth conditions for Polyhydroxyalkanoate (PHA) production in phytoplankton community from freshwater habitats at Visakhapatnam, Andhra Pradesh, India

Abstract

Polyhydroxyalkanoates (PHA) are biopolymers synthesized by a wide range of microbes and they have been considered as substitutes for the petroleum-based plastics. The only way to select microalgae for PHA synthesis is to assess their diversity, occurrence, and environmental factors in various environments. Occurrence, habitat diversity, and environmental tolerance are assessed for selecting the microalgae for PHA production. In this study, microalgal and cyanobacterial diversity is analyzed along with its physicochemical parameters of water samples from 10 freshwater habitats of Visakhapatnam, Andhra Pradesh, India. The whole 132 species from 55 microalgal genera have been identified. The diversity index revealed the dominancy of Chlorophyceae (Green algae) members preceding the Cyanophyceae (Cyanobacteria) and Bacillariophyceae (Diatoms). Physicochemical parameter of water indicated the presence of calcium and chloride in increased concentration. Nitrite and sulphate significantly influence the microalgal population dynamics with distinct pond, stream, lake, waterfalls and stagnant water habitats. Furthermore, the influence of nitrogen and phosphorous availability in protein, lipid and accumulation of PHA during the cultivation of axenic cyanobacterial isolates of Visakhapatnam including Oscillatoria acuta, Nostoc calcicola and Spirulina fusiformis, are visualized using nile red dye and estimated. Modification of cyanobacterial growth media composition leads to the degradation of proteins, and accumulation of lipids and PHAs. Oscillatoria acuta and Nostoc calcicola unable accumulate PHA granules in a culture medium formulated with limited nitrogen, phosphorous and combination of both. Remarkably, Spirulina fusiformis as a unique species accumulates 8.2 % PHA in nitrogen limited zarrouk media. Nevertheless, no traces of PHA granules are observed in other nutrient limited and standard culture media (BG-11⁺, BG-11⁻ and Zarrouk). Therefore, S. fusiformis possess the tendency for the production of higher concentration of PHA.