Detalle de: Mixed growth curve data do not suffice to fully characterize the dynamics of mixed cultures

In PNAS, Ram et al. (1) present an approach to decipher competition in mixed cultures of biotechnological interest. The approach—devoted to those cases in which competitive behavior depends on cellular densities—is intended to characterize mixed-culture individual dynamics by fitting the mixed-culture optical density (OD) data to a nonlinear competition Lotka–Volterra (NLV) model (2, 3). Here we show, with experimental data and numerical examples, that the method does not guarantee convergence to the real individual dynamics. From a theoretical point of view, it would be in principle possible to estimate competition parameters ( c i ) from mixed-culture OD data (i.e., parameters are structurally identifiable) (4, 5). However, the method faces other difficulties in practice due to poor practical identifiability (6). We illustrate, with various examples, that the success of the method strongly depends on 1) the actual values of the individual growth and competition parameters, 2) the experiment design, that is, the initial densities, the duration of the experiment, and the number and location of sampling times, and 3) the data uncertainty. First, we considered the individual and mixed growth of 2 yeast species ( Saccharomyces cerevisiae and Saccharomyces kudriavzevii ) following the experimental approach in ref. 7. Fig. 1 shows that the mixed … [↵][1]1To whom correspondence may be addressed. Email: ebalsa{at}iim.csic.es. [1]: #xref-corresp-1-1