Comparative genomic analysis of Paenibacillus sp. SSG-1 and its closely related strains reveals the effect of glycometabolism on environmental adaptation

Genome mining, antimicrobial and plant growth-promoting potentials of halotolerant Bacillus paralicheniformis ES-1 isolated from salt mine

Salinity severely affects crop yield by hindering nitrogen uptake and reducing plant growth. Plant growth-promoting bacteria (PGPB) are capable of providing cross-protection against biotic/abiotic stresses and facilitating plant growth. Genome-level knowledge of PGPB is necessary to translate the knowledge into a product as efficient biofertilizers and biocontrol agents. The current study aimed to isolate and characterize indigenous plant growth-promoting strains with the potential to promote plant growth under various stress conditions. In this regard, 72 bacterial strains were isolated from various saline-sodic soil/lakes; 19 exhibited multiple in vitro plant growth-promoting traits, including indole 3 acetic acid production, phosphate solubilization, siderophore synthesis, lytic enzymes production, biofilm formation, and antibacterial activities. To get an in-depth insight into genome composition and diversity, whole-genome sequence and genome mining of one promising Bacillus paralicheniformis strain ES-1 were performed. The strain ES-1 genome carries 12 biosynthetic gene clusters, at least six genomic islands, and four prophage regions. Genome mining identified plant growth-promoting conferring genes such as phosphate solubilization, nitrogen fixation, tryptophan production, siderophore, acetoin, butanediol, chitinase, hydrogen sulfate synthesis, chemotaxis, and motility. Comparative genome analysis indicates the region of genome plasticity which shapes the structure and function of B. paralicheniformis and plays a crucial role in habitat adaptation. The strain ES-1 has a relatively large accessory genome of 649 genes (~ 19%) and 180 unique genes. Overall, these results provide valuable insight into the bioactivity and genomic insight into B. paralicheniformis strain ES-1 with its potential use in sustainable agriculture.

Paenibacillus sp. Strain UY79, Isolated from a Root Nodule of Arachis villosa, Displays a Broad Spectrum of Antifungal Activity

A nodule-inhabiting Paenibacillus sp. strain (UY79) isolated from wild peanut (Arachis villosa) was screened for its antagonistic activity against diverse fungi and oomycetes (Botrytis cinerea, Fusarium verticillioides, Fusarium oxysporum, Fusarium graminearum, Fusarium semitectum, Macrophomina phaseolina, Phomopsis longicolla, Pythium ultimum, Phytophthora sojae, Rhizoctonia solani, Sclerotium rolfsii, and Trichoderma atroviride). The results obtained show that Paenibacillus sp. UY79 was able to antagonize these fungi/oomycetes and that agar-diffusible compounds and volatile compounds (different from HCN) participate in the antagonism exerted. Acetoin, 2,3-butanediol, and 2-methyl-1-butanol were identified among the volatile compounds produced by strain UY79 with possible antagonistic activity against fungi/oomycetes. Paenibacillus sp. strain UY79 did not affect symbiotic association or growth promotion of alfalfa plants when coinoculated with rhizobia. By whole-genome sequence analysis, we determined that strain UY79 is a new species of Paenibacillus within the Paenibacillus polymyxa complex. Diverse genes putatively involved in biocontrol activity were identified in the UY79 genome. Furthermore, according to genome mining and antibiosis assays, strain UY79 would have the capability to modulate the growth of bacteria commonly found in soil/plant communities. IMPORTANCE Phytopathogenic fungi and oomycetes are responsible for causing devastating losses in agricultural crops. Therefore, there is enormous interest in the development of effective and complementary strategies that allow the control of the phytopathogens, reducing the input of agrochemicals in croplands. The discovery of new strains with expanded antifungal activities and with a broad spectrum of action is challenging and of great future impact. Diverse strains belonging to the P. polymyxa complex have been reported to be effective biocontrol agents. Results presented here show that the novel discovered strain of Paenibacillus sp. presents diverse traits involved in antagonistic activity against a broad spectrum of pathogens and is a potential and valuable strain to be further assessed for the development of biofungicides.

Comprehensive Genomic Analysis of the Endophytic Bacillus altitudinis Strain GLB197, a Potential Biocontrol Agent of Grape Downy Mildew

Bacillus has been extensively studied for agricultural application as a biocontrol agent. B. altitudinis GLB197, an endophytic bacterium isolated from grape leaves, exhibits distinctive inhibition to grape downy mildew based on unknown mechanisms. To determine the genetic traits involved in the mechanism of biocontrol and host-interaction traits, the genome sequence of GLB197 was obtained and further analyzed. The genome of B. altitudinis GLB197 consisted of one plasmid and a 3,733,835-bp circular chromosome with 41.56% G + C content, containing 3,770 protein-coding genes. Phylogenetic analysis of 17 Bacillus strains using the concatenated 1,226 single-copy core genes divided into different clusters was conducted. In addition, average nucleotide identity (ANI) values indicate that the current taxonomy of some B. pumilus group strains is incorrect. Comparative analysis of B. altitudinis GLB197 proteins with other B. altitudinis strains identified 3,157 core genes. Furthermore, we found that the pan-genome of B. altitudinis is open. The genome of B. altitudinis GLB197 contains one nonribosomal peptide synthetase (NRPS) gene cluster which was annotated as lichenysin. Interestingly, the cluster in B. altitudinis has two more genes than other Bacillus strains (lgrD and lgrB). The two genes were probably obtained via horizontal gene transfer (HGT) during the evolutionary process from Brevibacillus. Taken together, these observations enable the future application of B. altitudinis GLB197 as a biocontrol agent for control of grape downy mildew and promote our understanding of the beneficial interactions between B. altitudinis GLB197 and plants.

Comparative genomic analysis reveals metabolic diversity of different Paenibacillus groups

The genus Paenibacillus was originally recognized based on the 16S rRNA gene phylogeny. Recently, a standardized bacterial taxonomy approach based on a genome phylogeny has substantially revised the classification of Paenibacillus, dividing it into 23 genera. However, the metabolic differences among these groups remain undescribed. Here, genomes of 41 Paenibacillus strains comprising 25 species were sequenced, and a comparative genomic analysis was performed considering these and 187 publicly available Paenibacillus genomes to understand their phylogeny and metabolic differences. Phylogenetic analysis indicated that Paenibacillus clustered into 10 subgroups. Core genome and pan-genome analyses revealed similar functional categories among the different Paenibacillus subgroups; however, each group tended to harbor specific gene families. A large proportion of genes in the subgroups A, E, and G are related to carbohydrate metabolism. Among them, genes related to the glycoside hydrolase family were most abundant. Metabolic reconstruction of the newly sequenced genomes showed that the Embden-Meyerhof-Parnas pathway, pentose phosphate pathway, and citric acid cycle are central pathways of carbohydrate metabolism in Paenibacillus. Further, the genomes of the subgroups A and G lack genes involved in glyoxylate cycle and D-galacturonate degradation, respectively. The current study revealed the metabolic diversity of Paenibacillus subgroups assigned based on a genomic phylogeny and could inform the taxonomy of Paenibacillus. KEY POINTS: • Paenibacillus clustered into 10 subgroups. • Genomic content variation and metabolic diversity in the subgroup A, E, and G were described. • Carbohydrate transport and metabolism is important for Paenibacillus survival.

Bacteria From the Multi-Contaminated Tinto River Estuary (SW, Spain) Show High Multi-Resistance to Antibiotics and Point to Paenibacillus spp. as Antibiotic-Resistance-Dissemination Players

Bacterial resistance to antibiotics is an ever-increasing phenomenon that, besides clinical settings, is generally assumed to be prevalent in environmental soils and waters. The analysis of bacteria resistant to each one of 11 antibiotics in waters and sediments of the Huelva’s estuary, a multi-contaminated environment, showed high levels of bacteria resistant mainly to Tm, among others. To further gain knowledge on the fate of multi-drug resistance (MDR) in environmental bacteria, 579 ampicillin-resistant bacteria were isolated tested for resistance to 10 antibiotics. 92.7% of the isolates were resistant to four or more antibiotic classes, indicating a high level of multi-resistance. 143 resistance profiles were found. The isolates with different MDR profiles and/or colony morphologies were phylogenetically ascribed based on 16S rDNA to phyla Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes, including 48 genera. Putative intrinsic resistance was detected in different phylogenetic groups including genera Altererythrobacter, Bacillus, Brevundimonas, Erythrobacter, Mesonia, Ochrobactrum, and Ponticaulis. Correlation of the presence of pairs of the non-intrinsic-resistances in phylogenetic groups based on the kappa index (κ) highlighted the co-habitation of some of the tested pairs at different phylogenetic levels. Maximum correlation (κ = 1.000) was found for pairs Cz^R/Tc^R in Betaproteobacteria, and Cc^R/Tc^R and Em^R/Sm^R in Sphingobacteriia at the class level, while at the genus level, was found for Cc^R/Tc^R and Nx^R/Tm^R in Mesonia, Cz^R/Tm^R and Em^R/Km^R in Paenibacillus, and Cc^R/Em^R and Rp^R/Tc^R in Pseudomonas. These results could suggest the existence of intra-class and intra-genus-transmissible genetic elements containing determinants for both members of each pair. Network analysis based on κ values higher than 0.4 indicated the sharing of paired resistances among several genera, many of them centered on the Paenibacillus node and raising the hypothesis of inter-genera transmission of resistances interconnected through members of this genus. This is the first time that a possible hotspot of resistance interchange in a particular environment may have been detected, opening up the possibility that one, or a few, bacterial members of the community could be important promoters of antibiotic resistance (AR) dissemination in this environment’s bacterial population. Further studies using the available isolates will likely give insights of the possible mechanisms and genetic elements involved.

Genome analysis of Paenibacillus polymyxa A18 gives insights into the features associated with its adaptation to the termite gut environment

Paenibacillus polymyxa A18 was isolated from termite gut and was identified as a potential cellulase and hemicellulase producer in our previous study. Considering that members belonging to genus Paenibacillus are mostly free-living in soil, we investigated here the essential genetic features that helped P. polymyxa A18 to survive in gut environment. Genome sequencing and analysis identified 4608 coding sequences along with several elements of horizontal gene transfer, insertion sequences, transposases and integrated phages, which add to its genetic diversity. Many genes coding for carbohydrate-active enzymes, including the enzymes responsible for woody biomass hydrolysis in termite gut, were identified in P. polymyxa A18 genome. Further, a series of proteins conferring resistance to 11 antibiotics and responsible for production of 4 antibiotics were also found to be encoded, indicating selective advantage for growth and colonization in the gut environment. To further identify genomic regions unique to this strain, a BLAST-based comparative analysis with the sequenced genomes of 47 members belonging to genus Paenibacillus was carried out. Unique regions coding for nucleic acid modifying enzymes like CRISPR/Cas and Type I Restriction-Modification enzymes were identified in P. polymyxa A18 genome suggesting the presence of defense mechanism to combat viral infections in the gut. In addition, genes responsible for the formation of biofilms, such as Type IV pili and adhesins, which might be assisting P. polymyxa A18 in colonizing the gut were also identified in its genome. In situ colonization experiment further confirmed the ability of P. polymyxa A18 to colonize the gut of termite.

Green Technology: Bacteria-Based Approach Could Lead to Unsuspected Microbe⁻Plant⁻Animal Interactions

The recent and massive revival of green strategies to control plant diseases, mainly as a consequence of the Integrated Pest Management (IPM) rules issued in 2009 by the European Community and the increased consumer awareness of organic products, poses new challenges for human health and food security that need to be addressed in the near future. One of the most important green technologies is biocontrol. This approach is based on living organisms and how these biocontrol agents (BCAs) directly or indirectly interact as a community to control plant pathogens and pest. Although most BCAs have been isolated from plant microbiomes, they share some genomic features, virulence factors, and trans-kingdom infection abilities with human pathogenic microorganisms, thus, their potential impact on human health should be addressed. This evidence, in combination with the outbreaks of human infections associated with consumption of raw fruits and vegetables, opens new questions regarding the role of plants in the human pathogen infection cycle. Moreover, whether BCAs could alter the endophytic bacterial community, thereby leading to the development of new potential human pathogens, is still unclear. In this review, all these issues are debated, highlighting that the research on BCAs and their formulation should include these possible long-lasting consequences of their massive spread in the environment.

Comparative genomic and functional analyses of four sequenced Bacillus cereus genomes reveal conservation of genes relevant to plant-growth-promoting traits

Some Bacillus strains function as predominant plant-growth-promoting rhizobacteria. Bacillus cereus 905 is a rod-shaped Gram-positive bacterium isolated from wheat rhizosphere and is a rhizobacterium that exhibits significant plant-growth-promoting effects. Species belonging to the genus Bacillus are observed in numerous different habitats. Several papers on B. cereus are related to pathogens that causes food-borne illness and industrial applications. However, genomic analysis of plant-associated B. cereus has yet to be reported. Here, we conducted a genomic analysis comparing strain 905 with three other B. cereus strains and investigate the genomic characteristics and evolution traits of the species in different niches. The genome sizes of four B. cereus strains range from 5.38 M to 6.40 M, and the number of protein-coding genes varies in the four strains. Comparisons of the four B. cereus strains reveal 3,998 core genes. The function of strain-specific genes are related to carbohydrate, amino acid and coenzyme metabolism and transcription. Analysis of single nucleotide polymorphisms (SNPs) indicates local diversification of the four strains. SNPs are unevenly distributed throughout the four genomes, and function interpretation of regions with high SNP density coincides with the function of strain-specific genes. Detailed analysis indicates that certain SNPs contribute to the formation of strain-specific genes. By contrast, genes related to plant-growth-promoting traits are highly conserved. This study shows the genomic differences between four strains from different niches and provides an in-depth understanding of the genome architecture of these species, thus facilitating genetic engineering and agricultural applications in the future.