Endophytic Bacterial Diversity Research Articles

Analysis of endophytic bacterial diversity in seeds of different genotypes of cotton and the suppression of Verticillium wilt pathogen infection by a synthetic microbial community

BackgroundIn agricultural production, fungal diseases significantly impact the yield and quality of cotton (Gossypium spp.) with Verticillium wilt posing a particularly severe threat.ResultsThis study is focused on investigating the effectiveness of endophytic microbial communities present in the seeds of disease-resistant cotton genotypes in the control of cotton Verticillium wilt. The technique of 16S ribosomal RNA (16S rRNA) amplicon sequencing identified a significant enrichment of the Bacillus genus in the resistant genotype Xinluzao 78, which differed from the endophytic bacterial community structure in the susceptible genotype Xinluzao 63. Specific enriched strains were isolated and screened from the seeds of Xinluzao 78 to further explore the biological functions of seed endophytes. A synthetic microbial community (SynCom) was constructed using the broken-rod model, and seeds of the susceptible genotype Xinluzao 63 in this community that had been soaked with the SynCom were found to significantly control the occurrence of Verticillium wilt and regulate the growth of cotton plants. Antibiotic screening techniques were used to preliminarily identify the colonization of strains in the community. These techniques revealed that the strains can colonize plant tissues and occupy ecological niches in cotton tissues through a priority effect, which prevents infection by pathogens.ConclusionThis study highlights the key role of seed endophytes in driving plant disease defense and provides a theoretical basis for the future application of SynComs in agriculture.

Selection of the Dominant Endophytes Based on Illumina Sequencing Analysis for Controlling Bacterial Wilt of Patchouli Caused by Ralstonia solanacearum.

Bacterial wilt caused by Ralstonia solanacearum (RS) is one of the most devastating diseases in patchouli (Pogostemon cablin [Blanco] Benth.), which results in low yield and quality of patchouli. However, no stable and effective control methods have been developed yet. To evaluate the potential of dominant bacterial endophytes in biocontrol, the endophytic bacterial diversity of patchouli was investigated based on Illumina sequencing analysis, and the ability of isolates belonging to the dominant bacterial genera to control RS wilt of patchouli was explored in pot experiments. A total of 245 bacterial genera were detected in patchouli plants, with the highest relative abundance of operational taxonomic units belonging to the genus Pseudomonas detected in roots, leaves, and stems. The Pseudomonas isolates S02, S09, and S26 showed antagonistic activity against RS in vitro and displayed many plant growth-promoting characteristics, including production of indole-3-acetic acid, siderophores, and 1-aminocyclopropane-1-carboxylic acid deaminase and phosphate- and potassium-solubilizing capability. Inoculation of patchouli plants with the isolates S02, S09, and S26 significantly improved shoot growth and decreased the incidence of bacterial wilt caused by RS. The results suggest that screening of dominant bacterial endophytes for effective biocontrol agents based on Illumina sequencing analysis is more efficient than random isolation and screening procedures.

Unraveling the functional characteristics of endophytic bacterial diversity for plant growth promotion and enhanced secondary metabolite production in Pelargonium graveolens

The rich diversity of microbial endophytic communities associated with plants, often referred to as the second genome, serves as a compelling illustration of efficient co-evolution. This noteworthy partnership plays a pivotal role in sustaining plant well-being and enhancing plant adaptability across diverse habitats. Therefore, examining the diversity of endophytic microbes associated with their particular host plant is valuable for gaining insights into the vast spectrum of plant-microbe interactions. The present experiments aimed at investigating the bacterial endophytic diversity in both root and shoot tissues of Pelargonium graveolens, employing culture dependent and culture independent high-throughput metagenomics approach. A total of 614 and 620 operational taxonomic units (OTUs), encompassing 291 and 229 genera, were identified in the shoot and root tissues of P. graveolens, respectively. Furthermore, the subsequent classification of OTUs revealed 15 highly abundant phyla, with Proteobacteria dominating both root and shoot tissues. Notably, an exceptionally high abundance of Firmicutes phyla was observed in the shoot compared to the root. Additionally, 30 bacterial endophytes from the root, stem, petiole, and leaves were isolated and molecularly characterized, unveiling a consistent pattern of diversity distribution between the root and shoot of P. graveolens. Upon screening all isolates for plant growth promoting traits, Pseudomonas oryzihabitans was found to be positive for major biochemical test like nitrogen fixation, phosphate solubilization etc. and on inoculation resulted in about two-fold increase in content of essential oil accompanied by a significant rise in the geraniol and citronellol content. Diving deep into the genetic constitution of P. oryzihabitans unveiled a substantial number of genes directly and indirectly contributing to the endophyte’s capability in colonizing host plants effectively. In summary, data obtained from metagenomics and culture dependent approaches including glass house trials suggest potential bacterial endophytes suitable for field applications for yield enhancement and in planta secondary metabolite enhancement investigations.

Structure and Functions of Endophytic Bacterial Communities Associated with Sphagnum Mosses and Their Drivers in Two Different Nutrient Types of Peatlands

Sphagnum mosses are keystone plant species in the peatland ecosystems that play a crucial role in the formation of peat, which shelters a broad diversity of endophytic bacteria with important ecological functions. In particular, methanotrophic and nitrogen-fixing endophytic bacteria benefit Sphagnum moss hosts by providing both carbon and nitrogen. However, the composition and abundance of endophytic bacteria from different species of Sphagnum moss in peatlands of different nutrient statuses and their drivers remain unclear. This study used 16S rRNA gene amplicon sequencing to examine endophytic bacterial communities in Sphagnum mosses and measured the activity of methanotrophic microbial by the 13C-CH4 oxidation rate. According to the results, the endophytic bacterial community structure varied among Sphagnum moss species and Sphagnum capillifolium had the highest endophytic bacterial alpha diversity. Moreover, chlorophyll, phenol oxidase, carbon contents, and water retention capacity strongly shaped the communities of endophytic bacteria. Finally, Sphagnum palustre in Hani (SP) had a higher methane oxidation rate than S. palustre in Taishanmiao. This result is associated with the higher average relative abundance of Methyloferula an obligate methanotroph in SP. In summary, this work highlights the effects of Sphagnum moss characteristics on the endophytic bacteriome. The endophytic bacteriome is important for Sphagnum moss productivity, as well as for carbon and nitrogen cycles in Sphagnum moss peatlands.

Endophytic bacterial community structure and diversity of the medicinal plant Mirabilis himalaica from different locations

Endophytic bacteria play important roles in medicinal plant growth, abiotic stress, and metabolism. Mirabilis himalaica (Edgew.) Heimerl is known for its medicinal value as Tibetan traditional plant; however, little is known about the endophytic bacteria associated with this plant in different geographic conditions and vegetal tissues. To compare the endophytic bacterial community associated with this plant in different geographic conditions and vegetal tissues, we collected the leaves, stems, and roots of M. himalaica from five locations, Nongmu college (NM), Gongbujiangda (GB), Zhanang County (ZL), Lang County (LX), and Sangri County (SR), and sequenced the 16S rRNA V5-V7 region with the Illumina sequencing method. A total of 522,450 high-quality sequences and 4970 operational taxonomic units (OTUs) were obtained. The different tissues from different locations harbored unique bacterial assemblages. Proteobacteria and Actinobacteria were the dominant phyla in all the samples, while the dominant genera changed based on the different tissues. The endophytic bacterial structures in the leaf and stem tissues were different compared to root tissues. Redundancy analysis (RDA) showed that the endophytic bacterial community was significantly correlated with pH, available phosphorus (AP), total phosphorus (TP), total nitrogen (TN), and soil organic matter (SOM). These findings suggested that the geographic conditions, climate type, ecosystem type, and tissues determined the endophytic bacterial composition and relative abundances. This conclusion could facilitate an understanding of the relationship and ecological function of the endophytic bacteria associated with M. himalaica and provide valuable information for artificial planting of M. himalaica and identifying and applying functional endophytic bacteria.

Proteobacterial dominance in endophytic bacterial diversity in switchgrass growing under nitrogen range and effect on plant growth

Switchgrass (Panicum virgatum L.) is native to North America and cultivated as a forage and bioenergy crop. Inorganic fertilizers enhance biomass production, increase production costs, and pollute the environment. Switchgrass cultivation using an eco-friendly approach might be achieved by inoculation with beneficial microbes. Therefore, the diversity of cultivable endophytic bacteria from roots and shoots of switchgrass growing under a nitrogen regime was studied. The potential of bacteria for plant growth promotion (PGP) was tested under in vitro conditions. A total of 216 bacterial isolates obtained belonged to four phyla and 33 genera, and most isolates were obtained from plants growing under no (0 kg/ha) or low nitrogen (90 kg/ha) input, rather than higher N (180 kg/ha). Higher numbers of isolates belonged to the phylum Proteobacteria, and genus-wise representation showed the dominance of Pseudomonas, Enterobacter, and rhizobia. Bacterial isolates were tested for PGP properties, e.g. phosphate solubilization, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, Indole Acetic Acid (IAA) production, and nitrogen fixation. Many isolates were positive for one or more PGP properties. In in vitro analysis, selected bacterial isolates were inoculated in two commercial switchgrass cultivars and a showed cultivar-specific response. PGP isolates can be used for pot or field trials and eventually for the sustainable cultivation of switchgrass.

Endophytic bacterial community diversity in genetically related hybrid rice seeds.

The Food and Agriculture Organization of the United Nations (FAO) has identified hybrid rice as ideal for addressing food scarcity in poor nations. A comprehensive investigation of the endophytic bacteria in hybrid rice seeds is essential from a microecological perspective to illuminate the mechanisms underlying its high yield, high quality, and multi-resistance. The endophytic bacterial diversity and community structures of 11 genetically correlated hybrid rice seeds with different rice blast resistance levels were studied using high-throughput sequencing (HTS) on the Illumina MiSeq platform to reveal their "core microbiota" and explore the effect of genotypes, genetic relationships, and resistance. Proteobacteria (78.15-99.15%) represented the most abundant group in the 11 hybrid rice cultivars, while Pantoea, Pseudomonas, and Microbacterium comprised the "core microbiota." Hybrid rice seeds with different genotypes, genetic correlations, and rice blast resistance displayed endophytic bacterial community structure and diversity variation. In addition, the network relationships between the rice seed endophytic bacteria of "the same female parent but different male parents" were more complex than those from "the same male parent but different female parents." Matrilineal inheritance may be the primary method of passing on endophytic bacteria in rice from generation to generation. The endophytic bacterial interaction network in rice blast-resistant hybrid rice seed varieties was more complicated than in susceptible varieties. In summary, this study demonstrated that the genotype, genetic relationship, and rice blast resistance were important factors affecting the community structures and diversity of endophytic bacteria in hybrid rice seeds, which was vital for revealing the interaction between endophytic bacteria and the host. KEY POINTS: • Pantoea, Pseudomonas, and Microbacterium represent the main endophytic bacteria in hybrid rice seeds. • Genotype is the primary factor affecting endophytic bacterial diversity in hybrid rice seeds. • The diversity of the endophytic bacterial community in hybrid rice seeds is related to their genotypes, genetic relationships, and rice blast resistance.

Isolation and Identification of Endophytic Bacteria Bacillus sp. ME9 That Exhibits Biocontrol Activity against Xanthomonas phaseoli pv. manihotis.

In recent years, the bacterial blight of cassava has caused substantial economic losses to the Chinese cassava industry. Chemical control methods have become the primary approach to control this disease; however, their widespread usage and harmful residues have raised concerns about environmental pollution. In order to avoid this, it is urgent to seek a green ecological method to prevent and control it. Biological control through the utilization of microorganisms not only effectively inhibits the disease, but also gives consideration to environmental friendliness. Therefore, investigating an endophytic biological control method for cassava bacterial blight is of great importance. In this study, cassava leaf tissues were used as test specimens in order to isolate endophytic bacteria by using dilution and separation methods. Bacillus ME9, derived from cassava endophytic bacteria, exhibits good antagonism against a diverse range of pathogens, including Xpm11. Its genome consists of a series of genes encoding antibacterial lipopeptides, which may be directly related to its antibacterial capabilities. Furthermore, inoculation resulted in a substantial change in the diversity of the endophytic bacterial community, characterized by improved diversity, and displayed an obvious inhibition of pathogenic bacterial growth, demonstrating successful colonization within plants. The results laid a foundation and provided theoretical support for the development and utilization of cassava endophytic bacterial diversity and endogenous disease control strategies.

Isolation and Characterization of Bacterial Endophytes from Maize Genotypes Varying in Resistance against Macrophomina phaseolina

The present work aims to isolate and characterize the bacterial endophytes associated with different maize genotypes varying in resistance to disease reaction against Macrophomina phaseolina. A total of 50 endophytic bacteria were isolated from root and stem of healthy maize plants at 30 DAS, 60 DAS by using two different media like TSA, NA medium and maximum number of endophytic bacterial population were recovered from root followed by stem in all the genotypes and TSA medium was found to be the most suitable medium for deciphering maximum endophytic bacterial diversity. The isolated bacterial endophytes were characterized on the basis of morphological parameters viz., size, shape, colour, margin and texture, elevation, gram staining reaction and it was observed that Gram positive bacteria (68.0 %) formed the dominant group. The colony characterization revealed that circular forms (38.0 %) were dominated. Among the colony features the colonies with entire margins (66.0 %) and convex elevation (44.0 %) were found to be dominating.

Cadmium alters the rhizosphere bacterial community structure in blueberry roots and increases the content of lipids in the soil

Vaccinium spp. Is a small berry that grows in acidic environments. Relying on the exchange of nutrients and defense against adverse environments through the root system microbiota, bacteria play an important role. As a widely distributed pollutant, the mobility and bioavailability of Cd are enhanced in acidic environments, which can affect the community composition of blueberry root microbiota and alter the composition of soil metabolites. Therefore, studying the changes in the bacterial microbiota of blueberry roots and soil metabolomics under Cd stress can provide a foundation for the development of blueberry microbial fertilizers and the management of soil Cd pollution. In this study, 16 S rDNA sequencing and untargeted metabolomics were used to analyze the rhizosphere, root surface and root endophytic bacterial diversity as well as soil metabolites of Vaccinium spp. Under cadmium (Cd) contamination. The results indicate that the addition of cadmium (Cd) significantly reduces the α-diversity of the rhizosphere, rhizoplane, and endophytic bacteria in blueberries and has a significant impact on the dominant bacterial species. With the application of Cd, the relative abundance of the dominant taxa such as Diplorickettsiaceae_unclassified, Legionella, Streptomyces and Rhodanobacter decreased significantly at the genus level and turned into general or rare bacterial taxa. Meanwhile, the relative abundance of LWQ8_unclassified, WPS-2_unclassified, Acetobacteraceae_unclassified, Acidibacter, Acidiphilium and Granulicella with extreme tolerances increased significantly and gradually became the dominant taxa. Of the 364 metabolites in the soil, 31 varied significantly as the structure of the rhizosphere bacterial community changed. Among them, the lipids and lipid-like molecules clade showed the greatest variation in species and a significant increase in content. It was also associated with changes in bacterial taxa such as Tundrisphaera, Spirochaetaceae_unclassified, Dyella and CHAB_XI_27_unclassified.

Analysis of Endophytic Bacterial Diversity in Rice Seeds with Regional Characteristics in Yunnan Province, China, Based on High-Throughput Sequencing Technology.

Examining the endophytic bacteria in rice seeds from Yunnan Province displaying regional characteristics is vital for exploring strain resources, improving rice production, and conducting subsequent research. This study investigated nine characteristic rice varieties from Yunnan Province using high-throughput sequencing technology based on the Illumina Novaseq platform to reveal their dominant bacterial communities and discussed their endophytic bacterial community differences. A total of 829 shared OTUs, and 233 unique OTUs were identified in the nine samples, while the bacteria included Proteobacteria, Actinobacteriota, and Firmicutes, of which Proteobacteria was the most dominant. Pantoea and Methylorubrum were the most abundant at the genus level, with Curtobacterium, Brevundimonas, and Luteibacter representing the specific genera in the rice seed samples. This study revealed the endophytic structure and diversity in the seeds of nine rice varieties displaying regional characteristics and provided a foundation for further research into rice containing endophytic bacteria.

Endophytic bacterial taxonomic and functional diversity in the seeds of wheat genotypes from different agroecologies

ABSTRACT Plant genotype and agroecology influence the composition and functionality of seed endophytic bacterial communities. Taxonomic analysis of 123 wheat seeds endophytic bacteria classified these into 23 genera predominantly under Firmicutes followed by Actinobacteria and Proteobacteria. Genus Bacillus was most abundant (30.7%) followed by Streptomyces (18.4%) with other representative genera such as Stenotrophomonas, Paenibacillus, Mixta, Enterobacter, Micrococcus, Pantoea, Alkalihalobacillus, Cortiobacterium, and more. Across agroecologies, the core microbiota of seeds consists of Bacillus, Streptomyces, Paenibacillus, and Stenotrophomonas, with maximum diversity and abundance observed in seeds of the North Western Plain Zone of India. Seed endophytic bacteria had PGP traits; nitrogen fixation (n = 101), production of IAA (n = 65), siderophores (n = 43), ammonia (n = 82) and solubilization of phosphate (n = 47), potassium (n = 37), and zinc (n = 8). The isolates produced HCN and hydrolytic enzymes and displayed antagonism against fungal pathogens. Overall, the information generated on wheat seeds’ endophytic bacterial taxonomy and beneficial traits may pave the path for the development of novel bioinoculants. Key message Wheat seeds from various agro-ecologies of India harbor diverse endophytic bacteria. Firmicutes were dominant followed by Actinobacteria and Proteobacteria. Genus Bacillus, Stenotrophomonas, Streptomyces, and Paenibacillus were core endophytic bacteria in different agro-ecologies. The endophytic bacterial strains were displaying diverse functional traits.

A reduced but stable core microbiome found in seeds of hyperaccumulators

The seed microbiota is currently of great interest in the scientific community since seed germination is a critical stage in plant life cycle. Some seed endophytic bacteria could be commonly found in seeds of hyperaccumulating plants and may confer them an evolutionary advantage over non-hyperaccumulating plants when confronted to biotic or abiotic stress. This study focuses on the endophytic bacterial diversity of a wide diversity of metal hyperaccumulating and non-hyperaccumulating plants (93 seed samples from Mediterranean regions, Oceania, South-East Asia) to reveal the core endophyte communities specific of hyperaccumulating plants. The rather low richness of the seed bacterial communities found in all seeds suggest that a sub-population of specialized endophytic strains is able to colonize seeds and survive. The factor that shapes the diversity of those bacterial communities was first the botanical family and secondly the hyperaccumulation trait of the host plants. Based on the taxonomic affiliation, we revealed that the Brassicales had 1349 OTUs that were specific to them and the Asterales 204 OTUs, independently of their metal accumulation strategy. Nonetheless, a set of 12 OTUs were shared by the seeds of all the hyperaccumulators independently of the taxonomic order of the plants (among Asterales and Brassicales) and could be considered as a ‘stable’ core microbiome. Those OTUs identified as Luteibacter, Alphaproteobacteria unclassified, Sphingopyxis, Alishewanella, bacteria unclassified, Heliimonas, Aeromicrobium, Proteobacteria unclassified, Xanthomonadales unclassified and Micromonosporaceae unclassified may constitute an endophytic bacterial core with PGP traits. Further studies are needed to extend our knowledge of the possible role played by those bacteria.

Different assembly mechanisms of leaf epiphytic and endophytic bacterial communities underlie their higher diversity in more diverse forests

Abstract Plant microbiomes are known to influence host fitness and ecosystem functioning, but mechanisms regulating their structure are poorly understood. Here, we explored the assembly mechanisms of leaf epiphytic and endophytic bacterial communities using a subtropical forest biodiversity experiment. Both epiphytic and endophytic bacterial diversity increased as host tree diversity increased. However, the increased epiphytic diversity in more diverse forests was driven by greater epiphytic diversity (i.e. greater α‐diversity) on individual trees, whereas the increased endophytic diversity in more diverse forests was driven by greater dissimilarity in endophytic composition (i.e. greater β‐diversity) among trees. Mechanistically, responses of epiphytes to changes in host diversity were consistent with mass effects, whereas responses of endophytes were consistent with species sorting. Synthesis. These results provided novel experimental evidence that biodiversity declines of plant species will lead to biodiversity declines of plant‐associated microbiomes, but the underlying mechanism may differ between habitats on the plant host.

Differential modulation of the bacterial endophytic microbiota of Festuca arundinaceae (tall fescue) cultivars by the plant-growth promoting strain Streptomyces albidoflavus UYFA156

AimsThe bacterial endophyte Streptomyces albidoflavus UYFA156 was isolated from seeds of tall fescue, Festuca arundinaceae cultivar SFRO Don Tomás, promoting growth specifically in its host cultivar. Under the hypothesis that along with the growth promotion effect by UYFA156, a shift of the endophytic bacterial community occurs, we aimed to explore the effect of inoculation of this strain on the endophytic bacterial microbiota in F. arundinaceae cultivars SFRO Don Tomás and in cultivar Tacuabé, in which no growth promotion has been observed.MethodsInitially, growth inhibition of fourteen bacterial endophytes from both cultivars was tested in vitro, and then endophytic microbiota of plants and seeds were explored through high throughput sequencing of 16S rRNA.ResultsDiversity and composition in the seeds, along plant development, and in response to inoculation were examined in both cultivars, finding significant differences between them. In 7 days old uninoculated plants, endophytic bacterial diversity was lower in cultivar SFRO Don Tomás than in cv. Tacuabé. However, upon inoculation, Simpson's diversity index in the cultivar in which growth promotion was observed increased significantly, approximately two-fold in inoculated plants with respect to uninoculated plants. However, no differences were observed in cultivar Tacuabé. In addition, microbiota composition was significantly altered in plants of the cultivar SFRO Don Tomás, whereas in Tacuabé plants, changes by inoculation did not reach statistical significance.ConclusionOur results show that growth promotion by UYFA156 is accompanied by an early effect in endophytic diversity and composition and encourage further explorations in the relationship between the observed community modulation and plant growth promotion.

Both Adaptability and Endophytic Bacteria Are Linked to the Functional Traits in the Invasive Clonal Plant Wedelia trilobata

The role of the interactions between endophytes and host plants is unclear in invasive plants from different geographical latitudes. In this study, we aimed to explore the relationship between endophytic microbes and the functional traits of the invasive plant Wedelia trilobata. We explored the relationship between endophytes and the clonal growth traits of the invasive clonal plant Wedelia trilobata from different geographical latitudes using high-throughput sequencing technology and a common garden-planting experiment. We found that: (1) Different W. trilobata populations had similar endophytic fungi but different endophytic bacteria. However, no latitudinal variation pattern of the overall microbial community was found; (2) plant clonal growth performance (i.e., spacer length) was significantly correlated with endophytic bacterial diversity but not fungal diversity; and (3) the latitudinal variation pattern of the plant clonal growth performance of W. trilobata populations was found in pre-cultivated (i.e., wild) individuals but disappeared in post-cultivated W. trilobata. Our results suggest both environmental adaptability and the endophytic bacterial community are linked to the functional traits of the invasive clonal plant W. trilobata, and these functional traits tend to increase its invasiveness, which may enhance its invasion success.

Diversity of root endophytic bacteria from maize seedling involved in biocontrol and plant growth promotion

BackgroundNative endophytes from maize could play a vital role in plant protection and growth promotion. The present study was undertaken to elucidate the effect of soil types and different maize varieties on culturable endophytic bacterial diversity and to use potential endophytes as biocontrol agents and plant growth promoters.ResultsBased on rpoB and 16S rRNA genes, one hundred seventy-four (174) endophytes distributed into twenty-five (25) genera were identified, in which the greatest number of isolates were classified into Bacillus (52.30%), followed by Streptomyces (13.22%), Paenibacillus (6.32%), and Pseudomonas (4.60%). Out of the total isolated strains, endophytic strains with total number thirteen (13), eighty-four (84), one hundred and five (105), and nine (9) were able to fix nitrogen, and solubilize calcium phosphate, calcium phytate, and potassium, respectively. Moreover, out of total endophytes; twenty-four (24), thirty-three (33) and twenty-one (21) endophytic strains displayed marked antagonistic effects against important fungal pathogens such as Fusarium graminearum, Rhizoctonia solani and Exserohilum turcicum, respectively.ConclusionsSoil types play a functional role in culturable endophyte diversity and provide an isolation reference for endophytic reserves with multiple functions such as growth promoters and biocontrol agents.

Insight into the Taxonomic and Functional Diversity of Bacterial Communities Inhabiting Blueberries in Portugal.

Vaccinium myrtillus is a dwarf shrub of the Ericaceae family with a Palearctic distribution, associated with temperate and cold humid climates. It is widespread on the European continent; on the Iberian Peninsula it is located on Atlantic climate mountains and glacial relicts. In Portugal, we find scattered and interesting populations; however, the majority of them are threatened by climate change and wildfires. Given that, the objective of this study is to determine the rhizospheric and root bacterial communities of this plant in the southernmost regions, and, consequently, its potential range and ability to be used as a biofertilizer. In this work, metabarcoding of 16S rRNA gene showed that the endophytic bacterial diversity is dependent on the plant and selected by it according to the observed alpha and beta diversity. Moreover, a culturomic approach allowed 142 different strains to be isolated, some of them being putative new species. Additionally, some strains belonging to the genera Bacillus, Paenibacillus, Pseudomonas, Paraburkholderia, and Caballeronia showed significant potential to be applied as multifunctional biofertilizers since they present good plant growth-promoting (PGP) mechanisms, high colonization capacities, and an increase in vegetative parameters in blueberry and tomato plants.

First Report of the Endophytic Bacteria Associated with Phormidium sp.

Recent molecular studies on endophytic bacterial diversity have revealed a large richness of species. Associations between endobiotic bacterial-algae interactions have been studied for more than 40 years but were, up to now, never molecularly analyzed within the filamentous Cyanobacteria Phormidium. Therefore, the endophytic bacteria associated with fresh microalgae Phormidium, a group of ubiquitous photosynthetic organisms that play an important role in aquatic ecosystems, has been investigated. To study this partnership, Phormidium sp. was cultured in BG-11 medium using optimal conditions, and after the incubation period, cell biomass was obtained. Total genomic DNA from biomass was extracted and used for endophytic bacteria determination by using the 16S rRNA gene. Sequencing results revealed that a total of seven endophytic bacteria living within the cytoplasm of the host Phormidium sp. have been identified, including six bacteria belonging to three genera, namely Sphingomonas, Sphingopyxis, and Stenotrophobacter and while one bacteria remained unidentified due to low sequence homology in the GenBank database. The results highlighted the importance of endophytic bacteria associated with Phormidium sp. for the first time by using sequence-based identification.

Spread and driving factors of antibiotic resistance genes in soil-plant system in long-term manured greenhouse under lead (Pb) stress

Livestock manure is often used as fertilizer in greenhouses, resulting in simultaneous enrichment of heavy metals and antibiotic resistance genes (ARGs) in soils. The soil-plant system is a non-negligible way to spread ARGs; however, the effects of lead (Pb) on the spread of ARGs and their driving factors in the greenhouse soil-plant system remain unclear. In this present study, the occurrence of ARGs in greenhouse soils and their spread into plants under Pb stress were studied. Overall, Pb promoted the accumulation of ARGs in root endophytes at 10, 50, and 100 mg/kg as well as in soils at 10 and 200 mg/kg, but reduced the total relative abundance of ARGs in leaf endophytes. Particularly, Pb increased the mobile genetic elements (MGEs) relative abundance and endophytic bacterial community diversity in roots, consistent with the change in the total relative abundance of ARGs. Network analysis revealed that bacterial community and MGEs may jointly affect the migration of ARGs in the soil-plant system of greenhouses. Overall, this study extended our knowledge of how Pb can promote the transmission of ARGs to plant roots from greenhouse soils receiving long-term manure applications, which must be considered when assessing the risk of ARGs to public health.