Photoautotrophic and Mixotrophic Cultivation of Polyhydroxyalkanoate-Accumulating Microalgae Consortia Selected under Nitrogen and Phosphate Limitation.

Parichat Phalanisong,Pensri Plangklang,Alissara Reungsang

doi:10.3390/molecules26247613

Abstract

Microalgae consortia were photoautotrophically cultivated in sequencing batch photobioreactors (SBPRs) with an alteration of the normal growth and starvation (nutrient limitation) phases to select consortia capable of polyhydroxyalkanoate (PHA) accumulation. At the steady state of SBPR operation, the obtained microalgae consortia, selected under nitrogen and phosphate limitation, accumulated up to 11.38% and 10.24% of PHA in their biomass, which was identified as poly(3-hydroxybutyrate) (P3HB). Photoautotrophic and mixotrophic batch cultivation of the selected microalgae consortia was conducted to investigate the potential of biomass and PHA production. Sugar source supplementation enhanced the biomass and PHA production, with the highest PHA contents of 10.94 and 6.2%, and cumulative PHA productions of 100 and 130 mg/L, with this being achieved with sugarcane juice under nitrogen and phosphate limitation, respectively. The analysis of other macromolecules during batch cultivation indicated a high content of carbohydrates and lipids under nitrogen limitation, while higher protein contents were detected under phosphate limitation. These results recommended the selected microalgae consortia as potential tools for PHA and bioresource production. The mixed-culture non-sterile cultivation system developed in this study provides valuable information for large-scale microalgal PHA production process development following the biorefinery concept.

Highlights

The potential of fossil fuel depletion and environmental problems caused by the use of plastics originating from petroleum hydrocarbons has driven the exploration of biodegradable plastics as environmentally friendly substitutes
The microalgae consortia obtained after 26 cycles of sequencing batch photobioreactors (SBPRs) operation were observed under a light microscope and scanning electron microscope (SEM) (Figure 1)
The transmission electron microscopic (TEM) images indicated the presence of insoluble inclusions in the cytoplasm of the dominant microalgae species (Figure 2)

Summary

Introduction

The potential of fossil fuel depletion and environmental problems caused by the use of plastics originating from petroleum hydrocarbons has driven the exploration of biodegradable plastics as environmentally friendly substitutes. They have attracted attention from many researchers as alternatives to solve the problems associated with petroleum-based bioplastics As they are biocompatible, PHAs have recently been applied in the biomedical field as drug delivery carriers, bone and tissue replacement materials, surgical noodles, etc. Autotrophic microalgae and cyanobacteria have been proposed to have advantages over heterotrophic bacteria They represent an exceptionally diverse group of microorganisms that can thrive in freshwater, seawater, and wastewater and are highly tolerant to environmental stress. Pure culture cultivation requires the supplementation of sterile carbon sources under aseptic conditions to prevent microbial contamination, which makes the large-scale PHA production process economically unfeasible. Batch accumulation tests were further performed with photoautotrophic and mixotrophic cultivation modes under phosphate and nitrogen limitation to investigate the potential of biomass and PHA production using the selected microalgae consortia. The variation in macromolecules, including proteins, lipids, and carbohydrates, was examined during PHA production by the selected microalgae consortia

Enrichment and Selection of PHA-Accumulating Microalgae Consortia

Media Preparation

Batch Accumulation Test with Photoautotrophic and Mixotrophic Cultivation