Enhanced bioproduction of poly-3-hydroxybutyrate from wheat straw lignocellulosic hydrolysates

Abstract

13Polyhydroxyalkanoates (PHAs) are bioplastics that can replace conventional 14 petroleum derived products in various applications. One of the major barriers for 15 their widespread introduction in the market is the higher production costs when 16 compared with their petrochemical counterparts. In this work, a process was 17 successfully implemented with high productivity based on wheat straw, a cheap 18 and readily available agricultural residue, as raw material. The strain 19Burkholderia sacchari DSM 17165 which is able to metabolize glucose, xylose 20 and arabinose, the main sugars present in wheat straw hydrolysates (WSH), 21 was used. Results in shake flask showed that B. sacchari cells accumulated ca 22 * Corresponding author. Tel.: +351 21 8419137; fax: +351 21 8419062.e-mail address: teresa.cesario@ist.utl.pt 2 70 % g P(3HB)/g cell-dry-weight with a yield of polymer on sugars (Y P/S ) of 0.18 23 g/g when grown on a mixture of commercial C6 and C5 sugars (control), while 24 these values reached ca 60 % g P(3HB)/g cell-dry-weight and 0.19 g/g, 25 respectively, when WSHs were used as carbon source. In fed-batch cultures 26 carried out in 2L stirred tank reactors on WSH, a maximum polymer 27 concentration of 105 g/L was reached after 61 h of cultivation corresponding to 28 an accumulation of 72% of CDW. Polymer yield and productivity were 0.22 g 29 P(3HB)/g total sugar consumed and 1.6 g/L . h, respectively. The selected 30 feeding strategy successfully overcame the carbon catabolite repression 31 phenomenon observed in sugar mixtures containing hexoses and pentoses. 32 This is the first work describing fed-batch cultivations aiming at PHA production 33 using real lignocellulosic hydrolysates. Additionally, the P(3HB) volumetric 34 productivities attained are, by far, the highest achieved ever on agricultural 35 wastes hydrolysates. 36 Keywords 37Wheat straw hydrolysates ; poly 3-hydroxybutyrate; Burkholderia sacchari; carbon

Production of Polyhydroxyalkanoate (PHA) Biopolyesters by Extremophiles?

“…This becomes important in the case of cultivating cells on highly saline waste streams. Thirdly, HCl-catalyzed hydrolysis of inexpensive raw materials to generate feedstocks for PHA production, as demonstrated in the past for bagasse [18], whey [42], straw [19,20], spent coffee ground [21], or "liquefied wood" [43] requires neutralization of the cocktail of hydrolysis products. This neutralization, typically accomplished by addition of NaOH, generates considerable amounts of NaCl which contributes to the salinity of the fermentation medium when added as substrate.…”

“…Efforts in this direction are to an increasing extent devoted to the selection of inexpensive carbon feedstocks, which can replace costly raw materials typically used for biotechnological purposes, such as sugars or edible oils [11]. Among such inexpensive feedstocks, a number of [agro]industrial surplus materials was already investigated for PHA production, such as waste streams from dairy and cheese making industry [12,13], residues of the biodiesel and animal processing industry [14][15][16], or various abundant lignocellulosics [17], e.g., hydrolyzed bagasse and fruit peels [18], straw [19,20] or even spent coffee ground [21]. 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].…”

Strategies for Large-scale Production of Polyhydroxyalkanoates

“…In yet another interesting approach, feeding was controlled by a decrease in the stirring speed, which resulted from exhaustion of the carbon source in the medium. 66 This strategy made it possible to reduce catabolite repression, thus allowing the utilization of sugars other than glucose in the medium by the microorganism. It resulted in achieving a polymer concentration as high as 105 g L -1 , which translated into high polymer productivity of 1.6 g L -1 h -1…”

Efficient P(3HB) extraction from Burkholderia sacchari cells using non-chlorinated solvents

“…The accumulation of P(3HB) was triggered upon phosphate exhaustion in the cultivation medium. All the details on P(3HB) production have been described in a previous paper [26]. The lyophilized cells used contained 57.7% (w/w) of P(3HB).…”