Role of commensal relationships on the spatial structure of a surface-attached microbial consortium

A flow cell-grown model consortium consisting of two organisms, Burkholderi a sp. LB400 and Pseudomonas sp, B13(FR1), was studied. These bacteria have the potential to interact metabolically because Pseudomonas sp. B13(FR1) ca n metabolize chlorobenzoate produced by Burkholderia sp. LB400 when grown o n chlorobiphenyl. The expected metabolic interactions in the consortium wer e demonstrated by high performance liquid chromatography (HPLC) analysis. T he spatial structure of the consortium was studied by fluorescent in situ r RNA hybridization and scanning confocal laser microscopy. When the consorti um was fed with medium containing a low concentration of chlorobiphenyl, mi crocolonies consisting of associated Burkholderia sp, LB400 and Pseudomonas sp. B13(FR1) bacteria were formed, and separate Pseudomonas sp. B13(FR1) m icrocolonies were evidently not formed. When the consortium was fed citrate , which can be metabolized by both species, the two species formed separate microcolonies. The structure development in the consortium was studied onl ine using a gfp-tagged Pseudomonas sp. B13(FR1) derivative. After a shift i n carbon source from citrate to a low concentration of chlorobiphenyl, move ment of the Pseudomonas sp, B13(FR1) bacteria led to a change in the spatia l structure of the consortium from the unassociated form towards the associ ated form within a few days. Experiments involving a gfp-based Pseudomonas sp. B13(FR1) growth activity reporter strain indicated that chlorobenzoate supporting growth of Pseudomonas sp. B13(FR1) is located close to the Burkh olderia sp, LB400 microcolonies in chlorobiphenyl-grown consortia.