To analyze the effects of interactions between abiotic environmental parameters and antibiotics, three isolated bacterial species (E. coli, A. cryaerophilus, and S. suis) were exposed to cross-factor combinations of salinity, temperature, and either azithromycin or ciprofloxacin. The population density was measured by photospectrometry, and the resulting data were used to parameterize a generalized tolerance curve, mapping growth proxies (r and K) onto a multidimensional space defined by these environmental parameters.
This multidimensional tolerance curve was then projected onto temperature and conductivity measurements sampled in two Barcelona sewer to predict the population dynamics of these three species under realistic conditions, with or without the presence of environmental concentrations of antibiotics.
We subsequently quantified how environmental abiotic parameters influenced interspecies interactions and how these interactions, in turn, affected tolerance to abiotic conditions. This was achieved by monitoring the same species within synthetic communities of up to three species. Their frequency and density were tracked via flow cytometry, using two markers to differentiate them by genome size and GRAM status.
To dissect the interactions between temperature, salinity, and antibiotics, RNA from E. coli was extracted and sequenced following exposure to cross-factor conditions involving these three variables. Bioinformatic and statistical analyses were then conducted to relate environmental parameter values to gene expression plasticity and fitness in these complex environments.
