Climate change has reshaped global weather patterns and intensified extreme events, with drought and soil salinity negatively impacting the yield and quality of crop production. To mitigate the detrimental effects of drought stress, the introduction of beneficial plant growth-promoting rhizobacteria (PGPR) has proven to be a promising approach. In this study, we evaluated a synthetic microbial community (SynCom) comprising bacterial strains belonging to the species Bacillus velezensis, Pseudomonas simiae, P. salmasensis, Glutamicibacter halophytocola, and Leclercia sp., which have been demonstrated to promote tomato growth both individually and collectively. The SynCom and most of its individual bacterial strains were shown to mitigate the detrimental effects of polyethylene glycol (PEG)-induced drought stress in vitro in Arabidopsis thaliana seedlings, either by reducing alterations in xylem elements or promoting the formation of new xylem strands. In a greenhouse trial, soil drenching with the SynCom and two individual strains, B. velezensis PSE31B and P. salmasensis POE54, improved the water stress response in soilless-grown tomato plants under a 40% reduced irrigation regime. Additionally, bacterial treatments positively influenced the diversity of rhizosphere bacterial communities, with distinct changes in bacterial composition, which suggest a treatment-specific interplay between the introduced strains and the native microbiome. These findings highlight the potential of microbial consortia and individual PGPR strains as sustainable tools to improve plant resilience to abiotic stresses.

Mal secco is a vascular disease of citrus caused by the mitosporic fungus Plenodomus tracheiphilus. Soil containing infected plant material constitutes an inoculum source for root infections. In this study, the soil bacterial and fungal communities of five lemon orchards located in Syracuse Province (Sicily, Italy) affected by mal secco were analyzed. Soil samples were collected under lemon tree canopies and subjected to total genomic DNA extraction. The fungal DNA was detected through qPCR in all orchards, with variable concentrations. Bacterial and fungal communities were profiled using 16S and ITS amplicon-based high-throughput sequencing, respectively. According to our results, the relative abundances of the most represented bacterial phyla (e.g., Proteobacteria, Actinobacteriota, Acidobacteriota) changed across the orchards, while in the fungal community, the phylum Ascomycota was dominant, with Basidiomycota and Mortierellomycota abundances fluctuating. On the whole, β diversity analysis showed significant variation in the composition of the soil microbial communities across the orchards. This result was confirmed by the analysis of the core community (taxa present at ≥ 75% of total samples), where putative beneficial bacteria resulted in significantly enriched fungus-infected soil samples, suggesting complex microbial interactions. Our findings shed light on the composition and diversity of the soil microbiome in lemon orchards with the occurrence of mal secco infections.

The management of Meloidogyne incognita often depends on chemical nematicides, which pose environmental and health risks. This study investigated the potential of bacterial strains isolated from uncultivated native soil as biocontrol agents and plant growth-promoting rhizobacteria (PGPR) in tomato plants artificially infected with this nematode. Fifteen strains were screened in vitro for nematicidal and ovicidal activity, and four promising strains (307, GB16, GB24, and GB29) were selected for greenhouse trials. All strains reduced the nematode reproduction factor and the number of nematodes/g of root. Strains 307 and GB24 showed the highest reductions, 61.39 and 57.24%, respectively. Despite some positive physiological trends, Bacillus spp. did not promote a significant increase in plant growth. Metabolomic analysis revealed that the strains produced a wide range of primary metabolites with potential nematicidal activity. All strains also secreted proteases and chitinases, enzymes linked to nematode cuticle degradation. Preliminary identification based on the 16S rRNA gene and phylogenetic analysis grouped the four strains into the Bacillus subtilis group (strains GB16, GB29 and 307) or Bacillus cereus group (strain GB24); however, genome sequencing will be required in future studies. Overall, strains 307 and GB24 demonstrated strong biocontrol potential, supporting their use as sustainable and complementary alternatives to chemical nematicides.

Here, we report the draft genome sequence of Xanthomonas arboricola pv. pruni strain PVCT 262.1, isolated from almond ( Prunus dulcis ) leaves affected by bacterial spots in Italy in 2020. Genome size is 5,076,418 bp and G+C content is 65.44%. A total of 4,096 protein-coding genes and 92 RNAs are predicted.

In sustainable agriculture, the application of microorganisms to soil is a widely adopted strategy aimed at enhancing soil microbiome functionality, restoring fertility, and recovering biodiversity diminished by intensive farming. While introducing individual beneficial microbes often encounters issues with establishment and persistence, multispecies microbial consortia offer a more robust alternative, providing complementary functions that enhance both their resilience and effectiveness. To test this approach, we designed three synthetic bacterial communities (SynComs), each composed of varying combinations of ten bacterial endophytes previously shown to promote plant growth and exert biocontrol effects. The SynComs were designed with ascending levels of richness (4, 6, and 10 members) and diversity (ranging from 3 to 6 bacterial genera). In growth chamber trials with tomatoes, the SynComs not only promoted plant growth but also induced significant shifts in the rhizosphere bacterial communities, primarily affecting less abundant taxa. The SynComs MIX2 and MIX3, which included Pseudomonas species, exhibited the greatest impact on both plant growth enhancement and shifts within the resident microbial community. Monitoring of the introduced strains over time demonstrated that most bioinoculants successfully established although at very low concentration in the rhizosphere.

Plasmids are key in the evolution and adaptation of plant pathogenic Gammaproteobacteria (PPG), yet their diversity and functional contributions remain underexplored. Here, comparative genomics revealed extensive variation in plasmid size, replicon types, mobility, and genetic content across PPG. Most plasmids are small (< 200 kb), except in Pantoea, exhibiting high coding densities (76% to 78%). Five ancestral replicon types were identified across multiple orders, indicating vertical descent yet efficient horizontal transfer across taxa, although with limited genetic conservation. Virulence plasmids are widespread (56% to 68%) but differ in virulence gene content across orders: type III effector (T3E) genes are common in Pseudomonas and Xanthomonas, but rare in Enterobacterales and Xylella, aligning with their smaller effector repertoires. Plasmids frequently carry regulatory genes, highlighting their role in bacterial phenotype modulation. Distinct patterns were observed among orders: Enterobacterales plasmids often harbor thiamin biosynthesis operons and transcriptional regulators but lack post-transcriptional regulators, while most Pseudomonas and Xanthomonas plasmids are mobile, enriched in T3E genes, and exhibit high insertion sequence densities, fostering DNA mobility. Resistance to ultraviolet light is common, but not to antimicrobial compounds. These findings highlight the dynamic role of plasmids in spreading adaptive traits, shaping virulence, and driving the evolution of plant pathogenic bacteria.