Characterization of PAS domains in Frankia and selected Actinobacteria and their possible interaction with other co-domains for environmental adaptation

A novel phylogenetic tree based on the presence of protein domains in selected actinobacteria

Protein functional domains are semi-autonomous parts of proteins capable of functioning independently. One protein may contain several domains and one domain may be present in different protein sequences. Thus, protein domains represent the niche specific adaptive nature of an organism. We hypothesized that the presence and absence of protein domains in an organism could be used to make a phylogenetic tree, which may better depict the biotope (niche). Here, we selected 100 actinobacteria and built a phylogenetic tree depending upon the presence and absence of protein domains. Strains of different genera from the same niche were found to cluster together suggesting niche specific domain acquisition among selected strains. Thus, the domain based phylogeny clustered the selected actinobacteria mainly according to their niche rather than their taxonomic classification.

Host Plant Compatibility Shapes the Proteogenome of Frankia coriariae

Molecular signaling networks in the actinorhizal rhizosphere select host-compatible Frankia strains, trigger the infection process and eventually the genesis of nitrogen-fixing nodules. The molecular triggers involved remain difficult to ascertain. Root exudates (RE) are highly dynamic substrates that play key roles in establishing the rhizosphere microbiome. RE are known to induce the secretion by rhizobia of Nod factors, polysaccharides, and other proteins in the case of legume symbiosis. Next-generation proteomic approach was here used to decipher the key bacterial signals matching the first-step recognition of host plant stimuli upon treatment of Frankia coriariae strain BMG5.1 with RE derived from compatible (Coriaria myrtifolia), incompatible (Alnus glutinosa), and non-actinorhizal (Cucumis melo) host plants. The Frankia proteome dynamics were mainly driven by host compatibility. Both metabolism and signal transduction were the dominant activities for BMG5.1 under the different RE conditions tested. A second set of proteins that were solely induced by C. myrtifolia RE and were mainly linked to cell wall remodeling, signal transduction and host signal processing activities. These proteins may footprint early steps in receptive recognition of host stimuli before subsequent events of symbiotic recruitment.