Potential and Prospects of Continuous Polyhydroxyalkanoate (PHA) Production

Koller, Martin; Braunegg, Gerhart

doi:10.3390/bioengineering2020094

Cited by 60 publications

(40 citation statements)

References 96 publications

(124 reference statements)

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“…Further, novel processes to recover PHA from microbial biomass are currently in status of development, predominately aiming at the reduction of the input of chemicals and solvents, and at the conservation of the native polymer properties, hence, the PHA´s molecular mass and its quasi-amorphous state [22][23][24]. In addition, new process engineering strategies to increase productivity and to optimize the polyester composition on the monomeric level are currently in status of development; here, one-, two, and multistage continuous process-engineering concepts, optimally matching the kinetic characteristics of PHA biosynthesis (microbial growth phase followed by PHA-accumulation phase, the latter provoked by nutritionally unbalanced conditions together with excess feeding of exogenous carbon source), were designed in the recent years [25,26].…”

Section: Introductionmentioning

confidence: 99%

Production of Polyhydroxyalkanoate (PHA) Biopolyesters by Extremophiles?

Koller¹

2017

MOJPS

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The article reviews the current state of knowledge of the production of polyhydroxyalkanoate (PHA) biopolyesters under extreme environmental conditions.Although PHA production by extremophiles is not realized yet at industrial scale, significant PHA accumulation under high salinity or extreme pH-or temperature conditions was reported for diverse representatives of the microbial domains of both Archaea and Bacteria. Several mechanisms were proposed to explain the mechanistic role of PHA and their monomers as microbial cell-and enzyme protective chaperons and the factors boosting PHA biosynthesis under environmental stress conditions. The potential of selected extremophile strains, isolated from extreme environments like glaciers, hot springs, saline brines, or from habitats highly polluted with heavy metals or solvents, for efficient future PHA production on an industrially relevant scale is assessed based on the basic data available in the scientific literature. The article reveals that, beside the needed optimization of other cost-decisive factors like inexpensive raw materials or efficient downstream processing, the application of extremophile production strains can drastically safe energy costs, are easily accessible towards long-term cultivation in chemostat processes, and therefore might pave the way towards cost-efficient PHA production, even combined with safe disposal of industrial waste streams. However, further challenges have still to be overcome in terms of strain improvement and process engineering aspects.

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Section: Introductionmentioning

confidence: 99%

Production of Polyhydroxyalkanoate (PHA) Biopolyesters by Extremophiles?

Koller¹

2017

MOJPS

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“…This implies PHB accumulation due to the deviation of the carbon flux from biomass production. In this second phase, PHB accumulation is much higher than biomass formation [81]. A potential reactor configuration could be the serial arrangement of two sequential reactors: (i) reactor I for biomass production under optimal growth conditions; (ii) reactor II for PHB accumulation under nitrate-starvation conditions.…”

Section: Continuous Phb Productionmentioning

confidence: 99%

Industrial Production of Poly-β-hydroxybutyrate from CO2: Can Cyanobacteria Meet this Challenge?

et al. 2020

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The increasing impact of plastic materials on the environment is a growing global concern. In regards to this circumstance, it is a major challenge to find new sources for the production of bioplastics. Poly-β-hydroxybutyrate (PHB) is characterized by interesting features that draw attention for research and commercial ventures. Indeed, PHB is eco-friendly, biodegradable, and biocompatible. Bacterial fermentation processes are a known route to produce PHB. However, the production of PHB through the chemoheterotrophic bacterial system is very expensive due to the high costs of the carbon source for the growth of the organism. On the contrary, the production of PHB through the photoautotrophic cyanobacterium system is considered an attractive alternative for a low-cost PHB production because of the inexpensive feedstock (CO2 and light). This paper regards the evaluation of four independent strategies to improve the PHB production by cyanobacteria: (i) the design of the medium; (ii) the genetic engineering to improve the PHB accumulation; (iii) the development of robust models as a tool to identify the bottleneck(s) of the PHB production to maximize the production; and (iv) the continuous operation mode in a photobioreactor for PHB production. The synergic effect of these strategies could address the design of the optimal PHB production process by cyanobacteria. A further limitation for the commercial production of PHB via the biotechnological route are the high costs related to the recovery of PHB granules. Therefore, a further challenge is to select a low-cost and environmentally friendly process to recover PHB from cyanobacteria.

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“…The inverse value of D, the so called retention time τ, determines the time provided to the cells to convert substrate and accumulate PHA as intracellular product. Often, "continuous processes" are used in the same meaning as "chemostat" processes; merging these terminations is not correct in senso stricto, because "continuous" process regimes encompass, in addition to chemostats ("chemical environment remaining static"), also pH-stat, mass-stat, redox-stat, or volume-stat processes [115,116]. In order to address the current trend in the literature, the expression "continuous PHA-production" in the subsequent paragraphs refers to chemostat studies for PHA production.…”

Section: Generalmentioning

confidence: 99%

“…Continuous cultivation processes, especially those that run for extended periods, always carry the risk of microbial infection, which endangers the entire cultivation process. As a way out of this dilemma, extremophilic organisms can be used for PHA production under restricted sterility precautions, or even under non-sterile cultivation conditions in open reaction vessels; such processes can also be operated in continuous mode (reviewed by [115,116,129]).…”

Section: Non-sterile Single-stage Chemostat Processesmentioning

confidence: 99%

A Review on Established and Emerging Fermentation Schemes for Microbial Production of Polyhydroxyalkanoate (PHA) Biopolyesters

Koller¹

2018

Preprint

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Polyhydroxyalkanoates (PHA) are microbial biopolyesters utilized as “green plastics”. Their production under controlled conditions resorts to bioreactors operated in different modes. Because PHA biosynthesis constitutes a multiphase process, both feeding strategy and bioreactor operation mode need smart adaptation. Traditional PHA production setups based on batch, repeated batch, fed-batch or cyclic fed-batch processes are often limited in productivity, or display insufficient controllability of polyester composition. For highly diluted substrate streams like it is the case for (agro)industrial waste streams, fed-batch enhanced by cell recycling were recently reported as a viable tool to increase volumetric productivity. As emerging trend, continuous fermentation processes in single-, two-, and multi-stage setups are reported, which bring the kinetics of both microbial growth and PHA accumulation into agreement with process engineering, and allow tailoring PHA´s molecular structure. Moreover, we currently witness an increasing number of CO2-based PHA production processes using cyanobacteria; these light-driven processes resort to photobioreactors similar to those used for microalgae cultivation, and can be operated both discontinuously and continuously. This development goes in parallel to the emerging use of methane and syngas as an abundantly available gaseous substrates, which also calls for bioreactor systems with optimized gas transfer. The review sheds light on the challenges of diverse PHA production processes in different bioreactor types and operational regimes using miscellaneous microbial production strains such as extremophilic Archaea, chemoheterotrophic eubacteria and phototrophic cyanobacteria. Particular emphasize is dedicated to the limitations and promises of different bioreactor-strain combinations, and to efforts devoted to upscaling these processes to industrially relevant scales.

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Potential and Prospects of Continuous Polyhydroxyalkanoate (PHA) Production

Cited by 60 publications

References 96 publications

Production of Polyhydroxyalkanoate (PHA) Biopolyesters by Extremophiles?

Production of Polyhydroxyalkanoate (PHA) Biopolyesters by Extremophiles?

Industrial Production of Poly-β-hydroxybutyrate from CO2: Can Cyanobacteria Meet this Challenge?

A Review on Established and Emerging Fermentation Schemes for Microbial Production of Polyhydroxyalkanoate (PHA) Biopolyesters

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