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UBC Theses and Dissertations

Bacterial siderophore production on lignin-derived aromatic compounds Newman, Brianne


Lignin is a highly branched, recalcitrant polymer found in plant cell walls and is a major waste product of the pulp and paper industry. There is interest in lignin valorization through microbial transformation using bacteria capable of growing on lignin-derived aromatic compounds (LDACs). Bacteria in aerobic and neutral environments, such as in association with plant material, often find iron is a limiting nutrient. Microorganisms secrete siderophores to solubilize ferric iron for uptake into the cell. Siderophores are used for applications such as preservatives in the cosmetic industry. Identifying bacteria that produce siderophores while grown on LDACs as a carbon source may serve as a method for valorizing or upgrading lignin waste products. A method was developed to screen bacteria for their ability to produce siderophores when cultured on different carbon substrates. Bacteria were cultured in a minimal media supplemented with LDACs or alternative carbon substrate and siderophore production was determined by colorimetric assay. Suspected siderophores were subsequently purified and identified using HPLC and LCMS/MS. Rhodococcus jostii RHA1 was shown previously to produce the siderophore rhodochelin when grown on glucose under low-iron conditions. Screening for siderophore production by R. jostii RHA1 showed that growth on 4-hydroxybenzoate (4HBA) also led to production of rhodochelin. In contrast, siderophore production was not detected when cultured on other LDACs and the downstream products of LDAC catabolism. This finding indicates that siderophore production is dependent on the identity of the carbon substrate. Rhodococcus. rhodochrous GD02 and Sphingobium spp. SYK-6 were also screened for siderophore production. R. rhodochrous GD02 showed evidence of siderophore production when cultured on 4HBA. Genome mining of the R. rhodochrous GD02 genome revealed a putative siderophore biosynthetic gene cluster however, more work is needed to validate these findings and identify the structure of the siderophore produced. Screening of Sphingobium spp. SYK-6 showed weak siderophore production but the levels produced were not sufficient to purify or identify a siderophore. More work is needed to understand why siderophore production is dependent on the carbon substrate in the growth media and to optimize culture and purification methods for identification of siderophores produced by other bacteria.

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