Exploring nutrient limitation for polyhydroxyalkanoates synthesis by newly isolated strains ofAeromonassp. using biodiesel-derived glycerol as a substrate

Justyna Możejko-Ciesielska,Tomasz Pokoj

doi:10.7717/peerj.5838

Abstract

Aeromonas spp. strains isolated from activated sludge in a municipal wastewater treatment plant were found to be able to synthesize polyhydroxyalkanoates (PHA) utilizing pure and crude glycerol. The 16S rRNA gene sequence of the isolates exhibited similarity to Aeromonas hydrophila, A. aquatica, and A. salmonicida. Our results confirmed that the adequate supply of nitrogen and phosphorus during culture in 250-ml shake flasks did not stimulate the synthesis of PHAs. The results indicate that the PHA content of cells was higher under a phosphorus-limiting environment compared to nitrogen starvation. In the two-stage cultivation using glucose (in the first step) and crude glycerol from biodiesel industry (in the second step) as a component of the growth medium, the analyzed strains grew to 3.06 g/l of cell dry weight containing up to 22% of PHAs. Furthermore, during the same culture strategy up to 42% of PHAs were extracted, when in the second step of the process, Aeromonas sp. AC_03 was grown on pure glycerol under phosphorus limitation. The purified biopolymer was confirmed to be polyhydroxybutyrate. Aeromonas sp. AC_02 was also capable to accumulate the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer when pure glycerol was added as a substrate under nitrogen-deficiency one-step bioprocess. Our results confirm that due to the biopolymer productivity, newly isolated strains could be exploited for obtaining valuable biopolymers using wastes generated from biodiesel industry.

Highlights

With the exhaustion of fossil fuels and increasing environmental issues, an alternative to conventional petrochemical plastics has attracted much attention in recent years
Phylogenetic analysis The phylogenetic tree demonstrated that the bacterial isolates could be assigned into the Aeromonas genus (Fig. 1)
The results showed that all strains were able to utilize the pure and crude glycerol (Fig. 2)

Summary

Introduction

With the exhaustion of fossil fuels and increasing environmental issues, an alternative to conventional petrochemical plastics has attracted much attention in recent years. There is growing interest in the group of biopolymers known as polyhydroxyalkanoates (PHAs). They are biopolyesters accumulated intracellularly by a variety of bacteria as a storage. How to cite this article Możejko-Ciesielska and Pokoj (2018), Exploring nutrient limitation for polyhydroxyalkanoates synthesis by newly isolated strains of Aeromonas sp. Due to their biodegradability, thermoplasticity, or biocompatibility, PHAs have potential in agricultural, industrial, and biomedical applications

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