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.
Highlights
Lignin is one of the most plentiful biopolymers on Earth
The bacterial colonies grown in these experiments were subsequently isolated by restreaking until obtaining pure cultures
The isolates found on guaiacol and softwood stream plates were tested for growth on ferulate, p-coumarate, benzoate, syringate and guaiacol in liquid shake flask cultures, no growth was found (Additional file 1)
Summary
Lignin is one of the most plentiful biopolymers on Earth. It is a complex alkyl–aromatic heteropolymer found in the plant cell wall, which provides strength and protection to terrestrial plants. There are several bacterial species capable of catabolizing lignin or lignin-related aromatic compounds (Brown and Chang 2014; Bugg et al 2011b). Our initial aim was to isolate and identify culturable bacterial species from sediments in the Baltic Sea, close to the wastewater stream of a sulfite pulp production plant in northern Sweden (Kramfors). In this environment, lignin-rich residuals were deposited and accumulated between 1907 and 1977 (Apler et al 2014). Further experiments were conducted with the excreted intermediates and the conversion rates of various upper funneling branches leading to β-ketoadipate pathway were assessed
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