Microbial polymers produced from residual biomass: exploring the potential of different microbes

Sammanfattning: Microorganisms are important sources of diverse intracellular and extracellular biopolymers havingdifferent functions such as serving as carbon and energy reserves, or as protective layers around the cells in theform of capsules and/or biofilms. They have also found use in foods, medicine and other industrial applications.Research on understanding the synthesis of several biopolymers as well as the field of extremophilicmicroorganisms has revealed that exposure to unfavorable environmental conditions often triggers the synthesisof the biopolymers as a way of protection and survival. This thesis focuses on two types of biopolymers –exopolysaccharides (EPS) and polyhydroxyalkanaotes (PHAs) produced by different microorganisms grown on avariety of residual feedstocks, some of which being prevalent in Bolivia. Integrated production of the twobiopolymers or one biopolymer with another co-product is also investigated as a means of resource efficiency andvalue addition.EPS are carbohydrate polymers present on the surface of several bacteria, and have found applications as foodadditives to provide structural and sensory properties to the product. PHAs are biodegradable polyesters, producedas storage granules inside the bacterial cells, and are regarded as promising alternatives to fossil based polyolefinslike polyethylene and polypropylene. A bacterial isolate BU-4, identified as Bacillus sp. from the hypersaline regionof Bolivia, Salar de Uyuni, was used for the production of EPS from readily available agriculture and forestryresidues in the country – quinoa stalks and Curupaú sawdust. The bacteria grown on the pretreated quinoa stalkhydrolysate gave the highest EPS yield of 2.73 g/L. Yet another abundantly available residual stream from a brewery,was used as a raw material for the yeast Candida maltosa SM4 to produce microbial biomass and a biopolymer (apolysaccharide) as products, both at high concentrations of 16.97 and 2.33 g/L, respectively. Analysis of processvariables including aeration and agitation rates, and statistical optimization of the process were performed tomaximize the amount of the target products. Characterization of the polysaccharides from Bacillus sp. and C.maltosa revealed high thermal stability and water retention ability. Ability of another moderate halophile Yangia sp.ND199 to coproduce PHAs and EPS from different carbon sources and under varying cultivation parameters wasstudied. Growth on sucrose gave the highest EPS yield of 288 mg/L, while fructose gave 259.6 g/L EPS and thehighest PHA yield of 3.3 g/L and 84.7% w/w cell dry weight in a medium with 5% w/v NaCl. Finally, a bioprocess forproduction of hydrogen and PHA was designed comprising two microbial steps, the first involving Caldicellulosiruptorspecies for anaerobic fermentation of wheat straw hydrolysate to hydrogen, and the second utilizing the liquideffluent with acetate and unconsumed glucose to produce PHA under aerobic conditions using Ralstonia eutrophaat a biopolymer yield of 9.4 g/L and 83.4% w/w.