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 four-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.

Potential osmoprotectants for the lactic acid bacteria Pediococcus pentosaceus and Tetragenococcus halophila.

The physiological responses of the lactic acid bacteria Pediococcus pentosaceus and Tetragenococcus halophila (formely known as P. halophila), subjected to osmotic stress in the presence of molecules known to act as osmoprotectants for other bacteria were studied. In a defined medium, glycine betaine, dimethylsulfonioacetate, choline, proline and L-carnitine were able to relieve inhibition of growth at 0.8 M NaCl. The five compounds were shown to efficiently compete with glycine betaine transport, suggesting the existence of common transporter(s) for these molecules. T. halophila, the most tolerant strain, exhibited a larger spectrum of compatible solutes including dimethylsulfonioacetate, dimethylsulfoniopropionate and ectoine. Preliminary data suggest that restoration of growth by ectoine under osmotic constraint seems specific to the genus Tetragenococcus.

Isolation and characterization of ButA, a secondary glycine betaine transport system operating in Tetragenococcus halophila.

Through functional complementation of an Escherichia coli mutant defective in glycine betaine uptake, we identified a single-component glycine betaine transporter from Tetragenococcus halophila, a moderate halophilic lactic acid bacterium. DNA sequence analysis characterized the ButA protein as a member of the betaine choline carnitine transporter (BCCT) family, that includes a variety of previously characterized compatible solute transporters such as OpuD from Bacillus subtilis, EctP and BetP from Corynebacterium glutamicum, and BetL from Listeria monocytogenes. When expressed in the heterologous host E. coli, the permease is specific for glycine betaine and does not transport the other osmoprotectants previously described for T. halophila (i.e. carnitine, choline, dimethylsulfonioacetate, dimethylsulfoniopropionate, and ectoine). In E. coli, statement of ButA is mainly constitutive and maximal uptake activity may result from a weak osmotic induction. This is the first study demonstrating a role for a permease in osmoregulation, and GB uptake, of a lactic acid bacterium.