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Dynamic interspecies interactions and robustness in a four-species model biofilm

Interspecific interactions within biofilms determine relative species
abundance, growth dynamics, community resilience, and success or failure
of invasion by an extraneous organism. However, deciphering
interspecific interactions and assessing their contribution to biofilm
properties and function remain a challenge. Here, we describe the
constitution of a model biofilm composed of four bacterial species
belonging to four different genera (Rhodocyclus sp., Pseudomonas
fluorescens, Kocuria varians, and Bacillus cereus), derived from a
biofilm isolated from an industrial milk pasteurization unit. We
demonstrate that the growth dynamics and equilibrium composition of this
biofilm are highly reproducible. Based on its equilibrium composition,
we show that the establishment of this 4-species biofilm is highly
robust against initial, transient perturbations but less so towards
continuous perturbations. By comparing biofilms formed from different
numbers and combinations of the constituent species and by fitting a
growth model to the experimental data, we reveal a network of dynamic,
positive, and negative interactions that determine the final composition
of the biofilm. Furthermore, we reveal that the molecular determinant of
one negative interaction is the thiocillin I synthesized by the B.
cereus strain, and demonstrate its importance for species distribution
and its impact on robustness by mutational analysis of the biofilm
ecosystem.