Isolation and identification of Ammodendron bifolium endophytic bacteria and the action mechanism of selected isolates-induced seed germination and their effects on host osmotic-stress tolerance

Distinct Bacterial Communities Within the Nonrhizosphere, Rhizosphere, and Endosphere of Ammodendron bifolium Under Winter Condition in the Takeermohuer Desert

Due to human activities and severe climatic conditions, the population of Ammodendron bifolium, an excellent sand-fixing plant, has gradually decreased in the Takeermohuer Desert. The plant-associated bacteria community can enhance its survival in harsh environments. However, the understanding of A. bifolium-associated bacterial community is still unclear during the harsh winter. We investigated the bacterial community structure from the A. bifolium rhizosphere and nonrhizosphere at different depths (i.e., 0-40 cm, 40-80 cm, 80-120 cm) and from endosphere (i.e., root endosphere and stem endosphere) in winter. At the same time, we analyzed the impact of different compartments and soil factors on the bacterial community structure. Studies have shown that the A. bifolium rhizosphere exhibits higher levels of SOM (soil organic matter), SOC (soil organic carbon), SAN (soil alkaline nitrogen), and SAK (soil available potassium) compared with the nonrhizosphere. The dominant bacterial phyla were Proteobacteria (19.6%), Cyanobacteria (15.9%), Actinobacteria (13.6%), Acidobacteria (9.0%), and Planctomycetota (5.7%) in the desert. Proteobacteria (24.0-30.2%) had the highest relative abundance in rhizosphere, Actinobacteria (18.3-22.6%) had the highest relative abundance in nonrhizosphere, and Cyanobacteria had the highest relative abundance in endosphere. At the genus level, the relative abundance of Pseudomonas (1.2%) in the root endosphere was the highest and the other genera were mostly unclassified. The Chao1 and PD_whole_tree indices showed that the diversity of the bacterial communities decreased from nonrhizosphere, rhizosphere, root endosphere to stem endosphere. Co-occurrence network analyses identified Proteobacteria and Actinobacteria as key species across the three compartments. Additionally, unique keystone species like Cyanobacteria, Verrucomicrobiota, and Desulfobacterota were found only in the endosphere. The bacterial community in the rhizosphere was influenced by factors such as EC (electrical conductivity), STC (soil total carbon), SOM, SOC, STN (soil total nitrogen), SAN, STP (soil total phosphorus), and SAK, while that of the nonrhizosphere was mainly influenced by pH, C/N (STC/STN), SAP, and distance. The study highlighted differences in bacterial community composition, diversity, and influencing factors across the three compartments, which can provide a better understanding of the association/interactions between A. bifolium and bacterial communities and lay a foundation for revealing its adaptability in winter.

Invisible Inhabitants of Plants and a Sustainable Planet: Diversity of Bacterial Endophytes and their Potential in Sustainable Agriculture

Uncontrolled usage of chemical fertilizers, climate change due to global warming, and the ever-increasing demand for food have necessitated sustainable agricultural practices. Removal of ever-increasing environmental pollutants, treatment of life-threatening diseases, and control of drug-resistant pathogens are also the need of the present time to maintain the health and hygiene of nature, as well as human beings. Research on plant-microbe interactions is paving the way to ameliorate all these sustainably. Diverse bacterial endophytes inhabiting the internal tissues of different parts of the plants promote the growth and development of their hosts by different mechanisms, such as through nutrient acquisition, phytohormone production and modulation, protection from biotic or abiotic challenges, assisting in flowering and root development, etc. Notwithstanding, efficient exploitation of endophytes in human welfare is hindered due to scarce knowledge of the molecular aspects of their interactions, community dynamics, in-planta activities, and their actual functional potential. Modern "-omics-based" technologies and genetic manipulation tools have empowered scientists to explore the diversity, dynamics, roles, and functional potential of endophytes, ultimately empowering humans to better use them in sustainable agricultural practices, especially in future harsh environmental conditions. In this review, we have discussed the diversity of bacterial endophytes, factors (biotic as well as abiotic) affecting their diversity, and their various plant growth-promoting activities. Recent developments and technological advancements for future research, such as "-omics-based" technologies, genetic engineering, genome editing, and genome engineering tools, targeting optimal utilization of the endophytes in sustainable agricultural practices, or other purposes, have also been discussed.

The Composition and Diversity of the Rhizosphere Bacterial Community of Ammodendron bifolium Growing in the Takeermohuer Desert Are Different from Those in the Nonrhizosphere

Soil microorganisms play important roles in vegetation establishment and soil biogeochemical cycling. Ammodendron bifolium is a dominant sand-fixing (i.e., stabilizing sand dunes) and endangered plant in the Takeermohuer Desert, and the bacterial community associated with this plant rhizosphere is still unclear. In this study, we investigated the composition and diversity of the bacterial community from the A. bifolium rhizosphere and bulk soil at different soil depths (i.e., 0-40 cm, 40-80 cm, 80-120 cm) using culture and high-throughput sequencing methods. We preliminarily analyzed the edaphic factors influencing the structure of bacterial communities. The results showed that the high-salinity Takeermohuer Desert has an oligotrophic environment, while the A. bifolium rhizosphere exhibited a relatively nutrient-rich environment due to higher contents of soil organic matter (SOM) and soil alkaline nitrogen (SAN) than bulk soil. The dominant bacterial groups in the desert were Actinobacteria (39.8%), Proteobacteria (17.4%), Acidobacteria (10.2%), Bacteroidetes (6.3%), Firmicutes (6.3%), Chloroflexi (5.6%), and Planctomycetes (5.0%) at the phylum level. However, the relative abundances of Proteobacteria (20.2%) and Planctomycetes (6.1%) were higher in the rhizosphere, and those of Firmicutes (9.8%) and Chloroflexi (6.9%) were relatively higher in barren bulk soil. A large number of Actinobacteria were detected in all soil samples, of which the most abundant genera were Streptomyces (5.4%) and Actinomadura (8.2%) in the bulk soil and rhizosphere, respectively. The Chao1 and PD_whole_tree indices in the rhizosphere soil were significantly higher than those in the bulk soil at the same soil depth and tended to decrease with increasing soil depth. Co-occurrence network analyses showed that the keystone species in the Takeermohuer Desert were the phyla Actinobacteria, Acidobacteria, Proteobacteria, and Chloroflexi. Furthermore, the major edaphic factors affecting the rhizosphere bacterial community were electrical conductivity (EC), SOM, soil total nitrogen (STN), SAN, and soil available potassium (SAK), while the major edaphic factors affecting the bacterial community in bulk soil were distance and ratio of carbon to nitrogen (C/N). We concluded that the A. bifolium rhizosphere bacterial community is different from that of the nonrhizosphere in composition, structure, diversity, and driving factors, which may improve our understanding of the relationship between plant and bacterial communities and lay a theoretical foundation for A. bifolium species conservation in desert ecosystems.

Composition and Distribution Characteristics of Rhizosphere Bacterial Community of Ammodendron bifolium Growing in Takeermohuer Desert Are Different from Those in Non-rhizosphere

Soil microorganisms play important roles in vegetation establishment and soil biogeochemical cycling. Ammodendron bifolium is a dominant sand-fixing and endangered plant in Takeermohuer Desert, and bacterial community associated with this plant rhizosphere is still unclear. In this study, we studied the composition and diversity of bacterial community from A. bifolium rhizosphere and bulk soil at different soil depths (i.e., 0-40 cm, 40-80 cm, 80-120 cm) using traditional bacterial isolation and high-throughput sequencing approaches, and preliminarily analyzed the edaphic factors influencing the structure of bacterial communities. Results showed that Takeermohuer Desert with high salinity has been an oligotrophic environment, while the rhizosphere exhibited eutrophication resulting from high content SOM (soil organic matter) and SAN (soil alkaline nitrogen) compared with bulk soil. The dominant bacterial groups in the desert were Actinobacteria (39.8%), Proteobacteria (17.4%), Acidobacteria (10.2%), Bacteroidetes (6.3%), Firmicutes (6.3%), Chloroflexi (5.6%), and Planctomycetes (5.0%) at the phyla level. However, the relative abundances of Proteobacteria (20.2%) and Planctomycetes (6.1%) were higher in eutrophic rhizosphere, and Firmicutes (9.8%) and Chloroflexi (6.9%) relatively higher in barren bulk soil. A large number of Actinobacteria were detected in all soil samples, of which the most abundant genus was Streptomyces (5.4%) and Actinomadura (8.2%) in the bulk soil and rhizosphere, respectively. The Chao1 and PD indexes in rhizosphere were significantly higher than those in bulk soil at the same soil depth, and tended to decrease with increasing soil depth. Co-occurrence network analyses showed that the keystone species in Takeermohuer Desert were Actinobacteria, Acidobacteria, Proteobacteria, and Chlorofexi. Furthermore, the major environmental factors affecting rhizosphere bacterial community were EC (electrical conductivity), SOM, STN (soil total nitrogen), SAN, and SAK (soil available potassium), while bulk soil were distance and C/N (STC/STN). We concluded that A. bifolium rhizosphere bacterial community is different from non-rhizosphere in composition, distribution, and environmental influencing factors, which will have important significances for understanding their ecological functions and maintaining biodiversity.

Effects of time-space conversion on microflora structure, secondary metabolites composition and antioxidant capacity of Codonopsis pilosula root

In order to study the relationship between medicinal plant Codonopsis pilosula phenotype, secondary metabolites, antioxidant capacity and its rhizosphere soil nutrients, root-related microorganisms under seasonal and geographical changes, high-throughput sequencing technology was used to explore the bacterial community structure and variation in rhizosphere soil and root endosphere from six regions of Dingxi City, Gansu Province during four seasons. Secondary metabolites composition and antioxidant capacities of C. pilosula root collected successively from four seasons were determined. The chemical properties, nutrient content and enzyme activities of rhizosphere of C. pilosula were significantly different under different temporal and spatial conditions. All soil samples were alkaline (pH 7.64-8.42), with water content ranging from 9.53% to 19.95%, and electrical conductivity varied widely, showing obvious time-scale effects. Different time scales were the main reasons for the diversity and structure of rhizosphere bacterial community of C. pilosula. The diversity and richness of rhizosphere bacterial community in autumn and winter were higher than those in spring and summer, and bacterial community structure in spring and summer was more similar to that in autumn and winter. The root length and diameter of C. pilosula showed significant time gradient difference under different spatiotemporal conditions. Nutrition and niche competition lead to significant synergistic or antagonistic interactions between rhizosphere bacteria and endophytic bacteria, which invisibly affect soil properties, abundance of functional bacteria and even yield and quality of C. pilosula. Soil properties, rhizosphere bacteria and endophytic bacteria directly promoted root phenotype, stress resistance and polysaccharide accumulation of C. pilosula.

Diversity and distribution of culturable fouling bacteria in typical mariculture zones in Daya Bay, South China

The diversity and distribution of culturable fouling bacteria in shellfish, fish and non-mariculture zones in Daya Bay were investigated by using a traditional culture-dependent approach combined with an analysis of bacterial 16S rRNA gene sequences. A total of 129 isolates of fouling bacteria belonging to 37 species in 25 genera were collected and identified, which indicated that the three different mariculture zones harbored abundant and diverse fouling bacterial community. At the genus level, Pseudomonas, Arcobacter and Curtobacterium dominated the fouling bacterial community. Moreover, approximately 46% of the 37 representative isolates could form biofilms. After comparing the diversity and distribution of the biofilm-forming bacteria in three different mariculture zones, it was concluded that the ratios of biofilm-forming bacteria in shellfish (68.4%) and fish (63.4%) in mariculture zones were much greater than those in non-mariculture (42.0%) zone. These results provide important information, for the first time, regarding the fouling bacterial community in typical mariculture zones in South China, which will establish a foundation to develop strategies for biofilm control and disease defense.

Beneficial Relationships Between Endophytic Bacteria and Medicinal Plants

Plants benefit extensively from endophytic bacteria, which live in host plant tissues exerting no harmful effects. Bacterial endophytes promote the growth of host plants and enhance their resistance toward various pathogens and environmental stresses. They can also regulate the synthesis of secondary metabolites with significant medicinal properties and produce various biological effects. This review summarizes recent studies on the relationships between bacterial endophytes and medicinal plants. Endophytic bacteria have numerous applications in agriculture, medicine, and other industries: improving plant growth, promoting resistance toward both biotic and abiotic stresses, and producing metabolites with medicinal potential. Their distribution and population structure are affected by their host plant's genetic characteristics and health and by the ecology of the surrounding environment. Understanding bacterial endophytes can help us use them more effectively and apply them to medicinal plants to improve yield and quality.

Comprehensive assessment of growth parameters for screening endophytic bacterial strains in Solanum lycopersicum (Tomato)

Conventional agricultural practices demand application of pesticides for better yield, yet their uncontrolled use for longer duration exhibit deleterious effects on the soil health and subsequent plant productivity. These circumstances have displayed alarming effects on food security in the modern world. Therefore, biological solutions to the crisis can be practiced in consideration to their environmental benefits. Bacterial endophytes are ubiquitous in the phytosystem and beneficial for the plant growth and productivity. The present study aimed to obtain endophytic bacterial strains that can be developed as effective plant growth promoters. For this purpose twelve strains of bacterial endophytes were isolated from different plant sources and their putative plant growth promoting attributes were analyzed by morphological and biochemical studies. Subsequently these isolates were inoculated in the Solanum lycopersicum (Tomato) and the factors like germination percentage, seedling length, biomass production, and leaf variables were analyzed. However, the vigour index was considered as the prime parameter for determining plant growth. In essence, RR2 and RR4 strains were observed as effective growth promoter, hence in future they can be utilized as effective biofertilizers.