Biology subjects

Cangioli, L.

Publications and source records attributed to Cangioli, L..

3 recordsLinked to original sources

bioRxiv2021

DNA methylation patterns in bacteria of the genus Ensifer during free living growth and during nitrogen-fixing symbiosis with Medicago spp.

Methylation of specific DNA sequences is ubiquitous in bacteria and has known roles in immunity and regulation of cellular processes, such as the cell cycle. Using single-molecule real-time sequencing, six genome-wide methylated motifs were identified across four Ensifer strains, five of which were strain-specific. Only the GANTC motif, recognized by the cell cycle-regulated CcrM methyltransferase, was methylated in all strains. In actively dividing cells, methylation of GANTC motifs increased progressively from the ori to ter regions in each replicon, in agreement with a cell cycle-dependent regulation of CcrM. In contrast, there was near full genome-wide GANTC methylation in the early stage of symbiotic differentiation. This was followed by a moderate decrease in the overall extent methylation and a progressive decrease in chromosomal GANTC methylation from the ori to ter regions in later stages of differentiation. We interpret these observations as evidence of dysregulated and constitutive CcrM activity during terminal differentiation, and we hypothesize that it is a driving factor for endoreduplication of terminally differentiated bacteroids.

microbiology↗

bioRxiv2020

Dissecting transcriptomic signatures of genotype x genotype interactions during the initiation of plant-rhizobium symbiosis

Rhizobia are ecologically important, facultative plant symbiotic microbes. In nature there exists large variability in the association of rhizobial strains and host plant of the same species. Here, we evaluated whether plant and rhizobial genotypes influence the initial transcriptional response of rhizobium following perception of host plant. RNA-sequencing of the model rhizobium Sinorhizobium meliloti exposed to root exudates or luteolin was performed in a combination of three S. meliloti strains and three Medicago sativa varieties. The response to root exudates involved hundreds of changes in the rhizobium transcriptome. Of the differentially expressed genes, expression of 35% were influenced by strain genotype, 16% by the plant genotype, and 29% by strain x host plant genotype interactions. We also examined the response of a hybrid S. meliloti strain, in which the symbiotic megaplasmid (~ 20% of the genome) was mobilized between two of the above-mentioned strains. Dozens of genes resulted up-regulated in the hybrid strain, indicative of nonadditive variation in the transcriptome. In conclusion, this study demonstrated that transcriptional responses of rhizobia upon perception of legumes is influenced by the genotypes of both symbiotic partners, and their interaction, suggesting a wide genetic spectrum of partner choice selection in plant-rhizobium symbiosis.

microbiology↗

bioRxiv2020

Symbiotic and non-symbiotic members of the genus Ensifer (syn. Sinorhizobium) are separated into two clades based on comparative genomics and high-throughput phenotyping

Rhizobium - legume symbioses serve as a paradigmatic example for the study of mutualism evolution. The genus Ensifer (syn. Sinorhizobium) contains diverse plant-associated bacteria, a subset of which can fix nitrogen in symbiosis with legumes. To gain insights into the evolution of symbiotic nitrogen fixation (SNF), and inter-kingdom mutualisms more generally, we performed extensive phenotypic, genomic, and phylogenetic analyses of the genus Ensifer. The data suggest that SNF emerged several times within the genus Ensifer, likely through independent horizontal gene transfer events. Yet, the majority (105 of 106) of the Ensifer strains with the nodABC and nifHDK nodulation and nitrogen fixation genes were found within a single, monophyletic clade. Comparative genomics highlighted several differences between the "symbiotic" and "non-symbiotic" clades, including divergences in their pangenome content. Additionally, strains of the symbiotic clade carried 325 fewer genes, on average, and appeared to have fewer rRNA operons than strains of the non-symbiotic clade. Characterizing a subset of ten Ensifer strains identified several phenotypic differences between the clades. Strains of the non-symbiotic clade could catabolize 25% more carbon sources, on average, than strains of the symbiotic clade, and they were better able to grow in LB medium and tolerate alkaline conditions. On the other hand, strains of the symbiotic clade were better able to tolerate heat stress and acidic conditions. We suggest that these data support the division of the genus Ensifer into two main subgroups, as well as the hypothesis that pre-existing genetic features are required to facilitate the evolution of SNF in bacteria.

microbiology↗