Complex ecosystems harbor multiple predators and prey species whose direct and indirect interactions are under study. In particular, the combined effects of predator diversity and resource preference on prey removal are not known. To understand the effect of interspecies interactions, combinations of micro-predators—i.e., protists (generalists), predatory bacteria (semi-specialists), and phages (specialists)—and bacterial prey were tracked over a 72-h period in miniature membrane bioreactors. While specialist predators alone drove their preferred prey to extinction, the inclusion of a generalist resulted in uniform losses among prey species. Most importantly, presence of a generalist predator enabled coexistence of all predators and prey. As the generalist predator also negatively affected the other predators, we suggest that resource partitioning between predators and the constant availability of resources for bacterial growth due to protist predation stabilizes the system and keeps its diversity high. The appearance of resistant prey strains and subsequent evolution of specialist predators unable to infect the ancestral prey implies that multitrophic communities are able to persist and stabilize themselves. Interestingly, the appearance of BALOs and phages unable to infect their prey was only observed for the BALO or phage in the absence of additional predators or prey species indicating that competition between predators might influence coevolutionary dynamics.

Bacteriophages (phages), viruses that infect bacteria, are considered to be highly host-specific. To add to the knowledge about the evolution and development of bacteriophage speciation toward its host, we conducted a 21-day experiment with the broad host-range bacteriophage Aquamicrobium phage P14. We incubated the phage, which was previously isolated and enriched with the Alphaproteobacteria Aquamicrobium H14, with the Betaproteobacteria Alcaligenaceae H5. During the experiment, we observed an increase in the phage’s predation efficacy towards Alcaligenaceae H5. Furthermore, genome analysis and the comparison of the bacteriophage’s whole genome indicated that rather than being scattered evenly along the genome, mutations occur in specific regions. In total, 67% of the mutations with a frequency higher than 30% were located in genes that encode tail proteins, which are essential for host recognition and attachment. As control, we incubated the phage with the Alphaproteobacteria Aquamicrobium H8. In both experiments, most of the mutations appeared in the gene encoding the tail fiber protein. However, mutations in the gene encoding the tail tubular protein B were only observed when the phage was incubated with Alcaligenaceae H5. This highlights the phage’s tail as a key player in its adaptation to different hosts. We conclude that mutations in the phage’s genome were mainly located in tail-related regions. Further investigation is needed to fully characterize the adaptation mechanisms of the Aquamicrobium phage P14.

We consider a recently suggested “equation of state” for natively folded proteins, and verify its validity for a set of about 5800 proteins. The equation is based on a fractal viewpoint of proteins, on a generalization of the Landau-Peierls instability, and on a marginal stability criterion. The latter allows for coexistence of stability and flexibility of proteins, which is required for their proper function. The equation of state relates the protein fractal dimension , its spectral dimension , and the number of amino acids N. Using structural data from the protein data bank (PDB) and the Gaussian network model (GNM), we compute and for the entire set and demonstrate that the equation of state is well obeyed. Addressing the fractal properties and making use of the equation of state may help to engineer biologically inspired catalysts.