20.500.12556/RUL-113418 Produkcija, izolacija in karakterizacija poli-y-glutaminske kisline z mutanto bakterije Bacillus subtilis PS216. Production, isolation and characterisation of poly-γ-glutamic acid by Bacillus subilis PS-216 mutant V produkcijskem gojišču poli-γ-glutaminske kisline (γ-PGA), ki ne vsebuje glutamata, je bila mutanta Bacillus subtilis PS-216 srf-cfp pri šaržnem načinu gojenja s koncentracijo (4,1 ± 0,5) g/L γ-PGA najboljši producent med vsemi testiranimi »od glutaminske kisline neodvisnimi« sevi. Z rotacijskim reološkim testom smo pokazali, da je bila tudi viskoznost rabljenega produkcijskega gojišča γ-PGA najvišja pri mutanti Bacillus subtilis PS-216 srf-cfp. Najbolj, 2-krat, se je v časovnem optimumu produkcije, povečala viskoznost produkcijskega gojišča, ki smo mu dodali glutamat v primerjavi z viskoznostjo produkcijskega gojišča brez glutamata. Z združitvijo rezultatov izbranih sevov smo pokazali, da koncentracija γ-PGA v produkcijskem gojišču močno pozitivno korelira z njegovo viskoznostjo izmerjeno pri visokih strižnih hitrostih. Z meritvami viskoznosti rabljenega gojišča lahko torej hitro napovemo koncentracijo γ-PGA v produkcijskem gojišču. Pokazali smo, da kljub relativno veliki biomasi (⡈ 2 x 109 celic/mL) k viskoznosti rabljenega gojišča večinsko prispeva γ-PGA, celice pa lahko pomembno povišajo viskoznost gojišča pri nizkih strižnih hitrostih, ko so vpete v mrežo prepletenih molekul γ-PGA. Skladno s tem smo z amplitudnim oscilacijskim testom pokazali, da ima rabljeno gojišče lastnosti viskoelastične trdnine, gela. Ko smo odstranili celice, se je rabljeno gojišče obnašalo kot viskoelastična tekočina. S frekvenčnim testom smo pokazali, da z višanjem frekvence rabljeno gojišče najhitreje pridobiva lastnosti viskoelastične trdnine, medtem ko v območju testiranih frekvenc ločena γ-PGA ali celice ohranjajo lastnosti viskoelatične tekočine, kar kaže na vpetost celic v mrežo γ-PGA. In a batch culture with poly-γ-glutamic acid (γ-PGA) production growth medium without glutamic acid a mutant Bacillus subtilis PS-216 srf-cfp strain produced the most γ-PGA, (4,1 ± 0,5) g/L, among all »glutamic acid independent strains«. Rotational rheology demonstrated that the viscosity of the mutant Bacillus subtilis PS-216 srf-cfp was also the highest. At the time of the highest γ-PGA production viscosity of production medium with addition of glutamic acid doubled compared to the unsupplemented production medium. By analyzing the results of the selected strains we showed that γ-PGA concentration in the spent production medium strongly positively correlates with its viscosity measured at high shear rates. It is thus possible to predict the concentration of γ-PGA by measuring the viscosity of its production medium. We showed that despite relatively high biomass concentration (⡈ 2 x 109 cells/mL) the main factor increasing the viscosity of the production medium is γ-PGA. Cells, however, can significantly increase viscosity of the production medium at low shear rates by forming a network with entangled molecules of γ-PGA. Accordingly, oscillatory rheology, the amplitude sweep test, showed that spent medium has properties of a gel-like viscoelastic solid. When the cells were removed, the spent medium had properties of a viscoelastic liquid. By applying a frequency sweep test we demonstrated that spent medium gains properties of a viscoelastic solid, different than in the case of samples with separated γ-PGA or cells that retained properties of a viscoelastic liquid in the entire range of tested frequencies. This indicates that cells are embedded in a network of entangled molecules of γ-PGA. Bacillus subtilis γ-PGA reologija viskoznost viskoelastičnost Bacillus subtilis γ-PGA rheology viscosity viscoelasticity true false false [T. Šendlinger Krajnc] Slovenski jezik Angleški jezik Magistrsko delo/naloga 2020-01-02 07:45:35 2020-01-02 07:45:38 2022-08-25 03:56:16 0000-00-00 00:00:00 2020 0 0 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 602.3:579.852.11:604.2:577.112.5:532.135(043.2) 175347 18178563 8830.pdf 8830.pdf 1 3A8C9D8CB85A157BD8ECEB5FB41C3B7D 437c229a8ce551a621ef4a2a8d6e68142393d6abe72a5f43b19dedc99f2dc4d3 1959f771-a1b8-11eb-a523-00155dcfd717 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=125493 Biotehniška fakulteta 0 0 0