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

Author

Summary, in English

Microorganisms are important sources of diverse intracellular and extracellular biopolymers having
different functions such as serving as carbon and energy reserves, or as protective layers around the cells in the
form 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 extremophilic
microorganisms has revealed that exposure to unfavorable environmental conditions often triggers the synthesis
of 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 a
variety of residual feedstocks, some of which being prevalent in Bolivia. Integrated production of the two
biopolymers or one biopolymer with another co-product is also investigated as a means of resource efficiency and
value addition.
EPS are carbohydrate polymers present on the surface of several bacteria, and have found applications as food
additives to provide structural and sensory properties to the product. PHAs are biodegradable polyesters, produced
as storage granules inside the bacterial cells, and are regarded as promising alternatives to fossil based polyolefins
like polyethylene and polypropylene. A bacterial isolate BU-4, identified as Bacillus sp. from the hypersaline region
of Bolivia, Salar de Uyuni, was used for the production of EPS from readily available agriculture and forestry
residues in the country – quinoa stalks and Curupaú sawdust. The bacteria grown on the pretreated quinoa stalk
hydrolysate 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 (a
polysaccharide) as products, both at high concentrations of 16.97 and 2.33 g/L, respectively. Analysis of process
variables including aeration and agitation rates, and statistical optimization of the process were performed to
maximize 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 was
studied. Growth on sucrose gave the highest EPS yield of 288 mg/L, while fructose gave 259.6 g/L EPS and the
highest 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 for
production of hydrogen and PHA was designed comprising two microbial steps, the first involving Caldicellulosiruptor
species for anaerobic fermentation of wheat straw hydrolysate to hydrogen, and the second utilizing the liquid
effluent with acetate and unconsumed glucose to produce PHA under aerobic conditions using Ralstonia eutropha
at a biopolymer yield of 9.4 g/L and 83.4% w/w.

Department/s

Publishing year

2021-10-06

Language

English

Volume

1

Document type

Dissertation

Publisher

Biotechnology, Lund University

Topic

  • Industrial Biotechnology

Keywords

  • Microbial polymers, Exopolysaccharides, Polyhydroxybutyrates, residual biomass, agrowaste, pretreatment, hydrolysates, optimisation

Status

Published

ISBN/ISSN/Other

  • ISBN: 978-91-7422-836-6
  • ISBN: 978-91-7422-837-3

Defence date

28 October 2021

Defence time

14:15

Defence place

Lecture hall E:A, building E, Ole Römers väg 3, Faculty of Engineering LTH, Lund University, Lund. For online link, contact Emma Poaches: emma.poaches@biotek.lu.se

Opponent

  • Stanislav Obruca (Dr.)