Abstract
Biopolymers like polyhydroxyalkanoates (PHA) are a class of metabolites with promising applications in the fields of environmental, agricultural, and biomedical sciences. Commercial production of polyhydroxyalkanoates is a high-cost process generally carried out using heterotrophic species of bacteria. Using algae for intracellular PHA accumulation is an alternative method for bioplastic production. In the present study, cyanobacterium Synechococcus elongates was identified as a potential PHA-producing organism. A range of experimental conditions that include different growth parameters of nitrogen and phosphate starvation with the addition of external carbon sources under photoautotrophic and chemoheterotrophic growth conditions were examined. Our observations revealed that the algal cells cultured in nitrogen-starved medium under phototrophic conditions yield the highest quantity of PHA (17.15%) when 1% sucrose is used as a carbon source. Similarly, under chemotrophic conditions, the highest PHA synthesis (12.98%) was observed in medium containing 1% sucrose. In case of phosphate-starved medium, the highest PHA production was recorded as 7.02% under phototrophic conditions when 1% fructose was used as a carbon source. Similarly, 5.40% PHA synthesis occurred when media was supplemented with 1% glucose under chemotrophic conditions. The present study shows that nitrogen-deficiency stress induced higher PHA yield compared to phosphate-deficiency stress in S. elongates under photoautotrophic conditions when sucrose was present as an external carbon source. Our findings indicated that 17.15% cell dry-weight of PHA was the highest yield obtained from algal forms under nutrient-deficient stress conditions. This yield is lower than the bacterial PHA-producing system. Therefore, more studies are needed to enhance the yield of PHA in algae.
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