Prospecting for Marine Bacteria for Polyhydroxyalkanoate Production on Low-Cost Substrates

Abstract

Polyhydroxyalkanoates (PHAs) are a class of biopolymers with numerous applications, but the high cost of production has prevented their use. To reduce this cost, there is a prospect for strains with a high PHA production and the ability to grow in low-cost by-products. In this context, the objective of this work was to evaluate marine bacteria capable of producing PHA. Using Nile red, 30 organisms among 155 were identified as PHA producers in the medium containing starch, and 27, 33, 22 and 10 strains were found to be positive in media supplemented with carboxymethyl cellulose, glycerol, glucose and Tween 80, respectively. Among the organisms studied, two isolates, LAMA 677 and LAMA 685, showed strong potential to produce PHA with the use of glycerol as the carbon source, and were selected for further studies. In the experiment used to characterize the growth kinetics, LAMA 677 presented a higher maximum specific growth rate (µmax = 0.087 h−1) than LAMA 685 (µmax = 0.049 h−1). LAMA 677 also reached a D-3-hydroxybutyrate (P(3HB)) content of 78.63% (dry biomass), which was 3.5 times higher than that of LAMA 685. In the assay of the production of P(3HB) from low-cost substrates (seawater and biodiesel waste glycerol), LAMA 677 reached a polymer content of 31.7%, while LAMA 685 reached 53.6%. Therefore, it is possible to conclude that the selected marine strains have the potential to produce PHA, and seawater and waste glycerol may be alternative substrates for the production of this polymer.

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

“…PHA, polyoxoesters of hydroxyalkanoates, are typical prokaryotic reserve materials; they are produced as intracellular products of the secondary metabolism of various Gram-negative or Gram-positive bacteria and several extremophilic Archaea. Here, a currently emerging trend is the isolation of novel halophilic microbial species of marine origin, which often display powerful PHA producers based on the conversion of inexpensive substrates [3][4][5][6]. Stored in the cell's cytoplasm, spherical in shape and light-refractive, PHA granules consist of an hydrophobic core of coiled PHA chains and water acting as plasticizer; this core is covered by more hydrophilic enzymes and structural proteins, which, as not yet definitively clarified, may form a protein membrane.…”

Production of Polyhydroxyalkanoates (PHAs) by Vibrio alginolyticus Strains Isolated from Salt Fields

“…Glycerol is the major byproduct of the biodiesel industry and may be employed as a cost-effective substrate for PHA production. V. alginolyticus showed favorable cell growth and PHB accumulation in the media containing 50 g/L NaCl, which could be a suitable concentration to inhibit the growth of common bacteria that lack salt resistance [ 38 ]. Currently, the PHB titer obtained from V. alginolyticus was lower than those produced by other halophiles such as the haloarchaeon Haloferax mediterranei and Halomonas [ 11 ].…”

Advances in Polyhydroxyalkanoate (PHA) Production

“…Takahashi and colleagues screened marine bacteria in order to assess their potential to thrive and accumulate PHA on the inexpensive substrate combination crude glycerol from the biodiesel industry and seawater. Out of 150 isolates, the authors report the identification of two auspicious new marine strains with high potential of PHA production on this substrate combination, which, in the future, should be subjected to detailed investigation and optimization in order to assess their applicability for industrial-scale PHA production [ 16 ].…”

“…First, six articles deal with the assessment of inexpensive [ 16 , 17 , 18 , 19 , 20 ] or exotic [ 21 ] feedstocks to be used as carbon sources for PHA production. Importantly, these feedstocks constitute carbonaceous (agro)industrial waste streams, such as waste glycerol from biofuel production [ 16 , 17 ], lignocellulose waste from the food industry [ 18 , 20 ] and forestry [ 19 ], and even petrochemical plastic waste [ 21 ]. These works aim to find alternatives to commonly used feedstocks of value for human nutrition, in order to avoid the current “plate vs. plastic” dispute.…”