| 1. |
- Abdelaziz, Omar Y., et al.
(författare)
-
Membrane filtration of alkali-depolymerised kraft lignin for biological conversion
- 2019
-
Ingår i: Bioresource Technology Reports. - : Elsevier BV. - 2589-014X. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we have investigated the possibility of membrane filtration as a means for obtaining a fraction containing mainly low-molecular-weight (LMW) compounds from depolymerised lignin (DL) for subsequent microbial conversion. A DL stream from continuous-mode alkali depolymerisation of a softwood kraft lignin produced at a temperature of 220 °C and a residence time of 2 min, using a NaOH/lignin weight ratio of 1 with 5 wt% lignin loading was fractionated using a polymeric membrane with a molecular weight cut-off of 500–700 Da. The permeate (DLP) volume recovery of LMW phenolics (250–450 Da) was 70% after filtration for 3.7 h. The DLP was used as a carbon source for growth of three bacterial strains; Pseudomonas fluorescens, P. putida EM42 and Rhodococcus opacus, and good growth was obtained by the first two microorganisms. This proof-of-concept study demonstrates a novel strategy for technical lignin valorisation by combining depolymerisation, nanofiltration and bioconversion.
|
|
| 2. |
- Ravi, Krithika, et al.
(författare)
-
Bacterial conversion of depolymerized Kraft lignin
- 2019
-
Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- BackgroundLignin is a potential feedstock for microbial conversion into various chemicals. However, the microbial degradation rate of native or technical lignin is low, and chemical depolymerization is needed to obtain reasonable conversion rates. In the current study, nine bacterial strains belonging to the Pseudomonas and Rhodococcus genera were evaluated for their ability to grow on alkaline-treated softwood lignin as a sole carbon source.ResultsPseudomonas fluorescens DSM 50090 and Rhodococcus opacus DSM1069 showed the best growth of the tested species on plates with lignin. Further evaluation of P. fluorescens and R. opacus was made in liquid cultivations with depolymerized softwood Kraft lignin (DL) at a concentration of 1 g/L. Size-exclusion chromatography (SEC) showed that R. opacus consumed most of the available lower-molecular weight compounds (approximately 0.1–0.4 kDa) in the DL, but the weight distribution of larger fractions was almost unaffected. Importantly, the consumed compounds included guaiacol—one of the main monomers in the DL. SEC analysis of P. fluorescens culture broth, in contrast, did not show a large conversion of low-molecular weight compounds, and guaiacol remained unconsumed. However, a significant shift in molecular weight distribution towards lower average weights was seen after cultivation with P. fluorescens.ConclusionsRhodococcus opacus and P. fluorescens were identified as two potential microbial candidates for the conversion/consumption of base-catalyzed depolymerized lignin, acting on low- and high-molecular weight lignin fragments, respectively. These findings will be of relevance for designing bioconversion of softwood Kraft lignin.
|
|
| 3. |
- Ravi, Krithika, et al.
(författare)
-
Biological conversion of aromatic monolignol compounds by a Pseudomonas isolate from sediments of the Baltic Sea
- 2018
-
Ingår i: AMB Express. - : Springer Science and Business Media LLC. - 2191-0855. ; 8:1
-
Tidskriftsartikel (refereegranskat)abstract
- Bacterial strains were isolated from the sediments of the Baltic Sea using ferulic acid, guaiacol or a lignin-rich softwood waste stream as substrate. In total nine isolates were obtained, five on ferulic acid, two on guaiacol and two on a lignin-rich softwood stream as a carbon source. Three of the isolates were found to be Pseudomonas sp. based on 16S rRNA sequencing. Among them, isolate 9.1, which showed the fastest growth in defined M9 medium, was tentatively identified as a Pseudomonas deceptionensis strain based on the gyrB sequencing. The growth of isolate 9.1 was further examined on six selected lignin model compounds (ferulate, p-coumarate, benzoate, syringate, vanillin and guaiacol) from different upper funneling aromatic pathways and was found able to grow on four out of these six compounds. No growth was detected on syringate and guaiacol. The highest specific growth and uptake rates were observed for benzoate (0.3 h−1 and 4.2 mmol gCDW −1 h−1) whereas the lowest were for the compounds from the coniferyl branch. Interestingly, several pathway intermediates were excreted during batch growth. Vanillyl alcohol was found to be excreted during growth on vanillin. Several other intermediates like cis,cis-muconate, catechol, vanillate and 4-hydroxybenzoate from the known bacterial catabolic pathways were excreted during growth on the model compounds.
|
|
