Resident populations
Ancestral Pseudomonas fluorescens SBW25 was grown overnight to
carrying capacity in shaken glass vials (microcosms) containing 6mL of
King’s medium B (KB) at 28°C. Sixty microliters of this culture was then
transferred into static microcosms containing KB of varying
concentrations (100% KB, 10% or 1%) to create different resource
abundances; KB was diluted with M9 salt solution (3g
KH2PO4, 6g
Na2HPO4, 5g NaCl L-1).
Microcosms were disturbed every 1, 2, 4, 8 or 16 days (Fig. 1) by
transferring 1% of homogenised broth into fresh media (99% mortality)
for a total of 16 days. Invaders were inoculated at days 4, 8 and 12
(Fig. 1 and see Invasions below). In between transfers and
invasions, all microcosms were kept static at 28°C with loose lids to
allow oxygen transfer. We used 12 replicates of each resource abundance
(3) and disturbance frequency (5) combination, for a total of 180
microcosms. Additional microcosms (n=3 per resource abundance x
disturbance combination) were set up to quantify resident density on day
4 – the first invasion time point. This was necessary as the sampling
microcosms required homogenisation of treatments that would otherwise
not be disturbed.