Insight on green-biopolymer production via photosynthetic microbes

Abstract

Since the use of synthetic plastics has raised exponentially in the past few decades, there is an utmost importance of to find for an alternative. As a result, we have bioplastics, also termed as green polymers in the line, possessing similar characters to synthetic plastics as well as being environment friendly/biodegradable and non-toxic in nature as an additional boon. In this work, polyhydroxyalkanoates (PHAs), a type of bioplastics have been focussed, extracting from E. texensis (a microalgae) and a purple bacterial strain isolate. The two groups pof photosynthesizing microbes, i.e., microalga and the purple bacteria were first screened (based on their growth curves) from 7 available microalgae and 4 available purple bacterial strains in our lab. Once finalizing the species, these two candidate species were provided with different conditions like; presence of volatile fatty acids in the surrounding (source of external carbon), nitrate-phosphate variations, salinity, etc. to determine their impact on PHA accumulation in these groups of microbes. Based on the previous studies carried out in this lab, all of these factors were checked in the presence of external carbon source (galactose) in the surrounding of the microalgae, that was found to be best uptaken by them switching on to mixotrophic mode of nutrition and respond better. Also, harvesting time duration was optimized at which best results in terms of PHA accumulation was found both in microalga and purple bacteria. This study was done keeping in mind with the future prospect of scaling up the study with wastewater, determing the techno-economic analysis of the overall process and thereby finding the economic feasibility involved. As majority of these conditions are naturally available in wastewater, the study provides a novel and significant contribution in this field. As a result of which, better growth and PHA accumulation was found in absence of nitrates and phosphates than in control. VFAs had no significant effect on PHA accumulation, though they promoted photosynthetic pigment synthesis. Salts negatively regulated bioplastics accumulation. And 72 hours was found to be the best harvesting time duration they maximum accumulated PHA. For purple bacteria, as they were grown for 15 days, two types of conditions were provided to them i.e., a stirring and a still condition. For the growth profile study of the 4 purple bacterial strains (PBYB, EB, EA and 4C), majority of them attained their decline phase after 10th day and grew better in still condition (since are anoxygenic). Also, PBYB was found to be highest PHA accumulating bacteria among the 4. And on both 10th and 15th day of their growth, PHB was the major PHA (as compared to PHV) being accumulated by all the 4 strains in still condition. Also, in the presence of acetate (a VFA), PBYB accumulated highest PHA on 48th hour. Future studies of growing these species at larger scale in raceway ponds with wastewater to determine the economic efficiency of the process is to be carried out further, that acclamitization of the species in that condition first, followed by their growth profile study and then determining PHA accumulation potential by these candidate species at larger scale.