PHA Production and PHA Synthases of the Halophilic Bacterium Halomonas sp. SF2003.

Tatiana Thomas,Alexis Bazire,Stéphane Bruzaud,Hui Lim,Kumar Sudesh,Hua Tiang Tan,Anne Elain

doi:10.3390/bioengineering7010029

Abstract

Among the different tools which can be studied and managed to tailor-make polyhydroxyalkanoates (PHAs) and enhance their production, bacterial strain and carbon substrates are essential. The assimilation of carbon sources is dependent on bacterial strain’s metabolism and consequently cannot be dissociated. Both must wisely be studied and well selected to ensure the highest production yield of PHAs. Halomonas sp. SF2003 is a marine bacterium already identified as a PHA-producing strain and especially of poly-3-hydroxybutyrate (P-3HB) and poly-3-hydroxybutyrate-co-3-hydroxyvalerate (P-3HB-co-3HV). Previous studies have identified different genes potentially involved in PHA production by Halomonas sp. SF2003, including two phaC genes with atypical characteristics, phaC1 and phaC2. At the same time, an interesting adaptability of the strain in front of various growth conditions was highlighted, making it a good candidate for biotechnological applications. To continue the characterization of Halomonas sp. SF2003, the screening of carbon substrates exploitable for PHA production was performed as well as production tests. Additionally, the functionality of both PHA synthases PhaC1 and PhaC2 was investigated, with an in silico study and the production of transformant strains, in order to confirm and to understand the role of each one on PHA production. The results of this study confirm the adaptability of the strain and its ability to exploit various carbon substrates, in pure or mixed form, for PHA production. Individual expression of PhaC1 and PhaC2 synthases in a non-PHA-producing strain, Cupriavidus necator H16 PHB¯4 (DSM 541), allows obtaining PHA production, demonstrating at the same time, functionality and differences between both PHA synthases. All the results of this study confirm the biotechnological interest in Halomonas sp. SF2003.

Highlights

Polyhydroxyalkanoates (PHAs) are valuable bio-based and biodegradable polymers produced by numerous bacterial species [1,2]
Several tools can be managed to reduce the final cost of PHA production, including the characterization of selected microorganisms coupled with the optimal selection of carbon substrates [5,6]
There is an important diversity of carbon sources that can be exploited for PHA synthesis, and as a result, a wide range of PHAs which can be synthesized [6]

Summary

Introduction

Polyhydroxyalkanoates (PHAs) are valuable bio-based and biodegradable polymers produced by numerous bacterial species [1,2] Their properties are close to those of conventional petroleum-based plastics; in addition to their biocompatibility, they are considered to be materials with high potential [3]. Research has notably focused on the use of low-value substrates like industrial co-products (from agri-food, waste treatment, or biodiesel industry) [6,8,9] as they can represent up to 50% of the production cost With these carbon substrates, perfect control of PHA’s structure, molecular weight and properties could be difficult. Complete studies of carbon substrates utilization and PHA synthesis are required to soundly select the most adapted carbon sources, whether it is pure carbohydrates or co-products Another way to reduce production costs is to study the strain genome using bioinformatics and genetic engineering. These tools are exploiting for expression of PHA synthesis operon in non-producing strains exposing less restrictive growth and production conditions [5,10]

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