Bacteria strains
Our model synthetic community consists of five bacterial isolates
previously cultured and typed (based on 16S rDNA) from potting compost,
with the 5 isolates chosen because of their consistent persistence over
6 weeks in multiple replicates in diluted tryptic soy broth (TSB), and
ease at which they can be distinguished morphologically on King’s medium
B (KB) agar plates (Hesse et al. 2018). The closest sequence
matches of the 5 isolates are: Pseudomonas corrugata ,Stenotrophomonas rhizophilia , Achromobacter agilis ,Variovorax guangxiensis and Ochrobactrum daejonense .
Competition experiments have shown that the interactions among these
species range from growth-enhancing asymmetric cross-feeding to
competition (Padfield et al. 2020). We have demonstrated stable
coexistence of all species combinations (i.e. 2, 3, 4 and 5 species
communities) through the ability of each species to invade from rare for
at least 28 days without pulse disturbance and for at least 10 weeks
when pulsed weekly (Castledine et al. 2020; Padfield et
al. 2020). Indeed, the species have coexisted whilst retaining
morphological distinctiveness for over the 13 months we have propagated
them to date under weekly pulse disturbance (unpublished). For our
invader, we used the opportunistic human pathogen Pseudomonas
aeruginosa PA01 (O’Brien et al. 2018) which also grows well in
TSB. P. aeruginosa is a fast growing, competitive species capable
of invading and surviving in an array of environments including rivers,
medical equipment and humans (Chatterjee et al. 2017; Rutherfordet al. 2018). This strain was lacZ-marked, which allows it to be
easily identified when plated on agar containing X-gal due to a blue
colour change (O’Brien et al. 2018).