Changes in Bacterial Diversity and Composition in Response to Co-inoculation of Arbuscular Mycorrhizae and Zinc-Solubilizing Bacteria in Turmeric Rhizosphere

The Ectomycorrhizal Fungi and Soil Bacterial Communities of the Five Typical Tree Species in the Junzifeng National Nature Reserve, Southeast China

To explore the contribution of microorganisms to forest ecosystem function, we studied the ectomycorrhizal (ECM) fungal and soil bacterial community of the five typical tree species (Pinus massoniana, PM; Castanopsis carlesii, CC; Castanopsis eyrei, CE; Castanopsis fargesii, CF; and Keteleeria cyclolepis, KC) at the Junzifeng National Nature Reserve. The results indicated that the ECM fungal and soil bacterial diversity of CC and CF was similar, and the diversity rates of CC and CF were higher than those of PM, CE, and KC. Cenococcum geophilum and unclassified_Cortinariaceae II were the most prevalent occurring ECM fungi species in the five typical tree species, followed by unclassified_Cortinariaceae I and Lactarius atrofuscus. In bacteria, the dominant bacterial genera were Acidothermus, Bradyrhizobium, Acidibacter, Candidatus_Solibacter, Candidatus_Koribacter, Roseiarcus, and Bryobacter. EMF fungi and soil bacteria were correlated with edaphic factors, especially the soil pH, TP, and TK, caused by stand development. The results show that the community characteristics of ECM fungi and bacteria in the typical tree species of the Junzifeng National Nature Reserve reflect the critical role of soil microorganisms in stabilizing forest ecosystems.

Biofortification revisited: Addressing the role of beneficial soil microbes for enhancing trace elements concentration in staple crops

Trace element deficiency is a pervasive issue contributing to malnutrition on a global scale. The primary cause of this hidden hunger is related to low dietary intake of essential trace elements, which is highly prevalent in numerous regions across the world. To address deficiency diseases in humans, fortification of staple crops with vital trace elements has emerged as a viable solution. Current methods for fortifying crops encompass chemical amendments, genetic breeding, and transgenic approaches, yet these approaches possess certain limitations, constraining their agricultural application. In contrast, fortifying staple crops through the utilization of soil-beneficial microbes has emerged as a promising and economically feasible approach to enhance trace element content in crops. A specific subset of these beneficial soil microbes, referred to as plant growth-promoting microbes, have demonstrated their ability to influence the interactions between plants, soil, and minerals. These microbes facilitate the transport of essential soil minerals, such as zinc, iron, and selenium, into plants, offering the potential for the development of tailored bioinoculants that can enhance the nutritional quality of cereals, pulses, and vegetable crops. Nevertheless, further research efforts are necessary to comprehensively understand the molecular mechanisms underlying the uptake, transport, and augmentation of trace element concentrations in staple crops. By delving deeper into these mechanisms, customized bioinoculants of soil-beneficial microbes can be developed to serve as highly effective strategies in combating trace element deficiency and promoting global nutritional well-being.

Co-inoculation of antagonistic Bacillus velezensis FH-1 and Brevundimonas diminuta NYM3 promotes rice growth by regulating the structure and nitrification function of rhizosphere microbiome

Microbial inoculation with plant growth-promoting microorganisms (PGPMs) is one of the most promising technologies to solve the current global challenges. Co-inoculants is more efficient and stable than mono-inoculants. However, the growth promoting mechanism of co-inoculants in complex soil system is still poorly understood. In this study, the effects on rice, soil and the microbiome of the mono-inoculant Bacillus velezensis FH-1 (F) and Brevundimonas diminuta NYM3 (N) and the co-inoculant FN obtained in previous works were compared. Correlation analysis and PLS-PM were used to explore the primary mechanism of different inoculants promoting rice growth. We hypothesized that inoculants promoted plant growth (i) by themselves, (ii) by improving soil nutrient availability or (iii) by regulating the rhizosphere microbiome in complex soil system. We also assumed that different inoculants had different ways of promoting plant growth. The results showed that FN significantly promoted rice growth and nitrogen absorption and slightly increased soil total nitrogen and microbial network complexity compared with F, N and the control (CK). B. velezensis FH-1 and B. diminuta NYM3 interfered with each other's colonization in FN. FN increased the complexity of the microbial network compared to F and N. The bacterial community of FN was quite different from CK and N, while the fungal community was not significantly different from other treatments. The species and functions enriched or inhibited by FN are part of F. The correlation analysis and PLS-PM results showed that inoculants (F/N/FN) promoted the growth of rice mainly by regulating the rhizosphere microbiome rather than by themselves or by improving soil nutrient availability. Co-inoculant FN promotes rice growth specifically by enhancing microbial nitrification function through enriching related species compared with F or N. This may provide theoretical guidance for the construction and application of co-inoculants in the future.

Effects of Bradyrhizobium Co-Inoculated with Bacillus and Paenibacillus on the Structure and Functional Genes of Soybean Rhizobacteria Community

Plant growth-promoting rhizobacteria (PGPR) are widely used to improve soil nutrients and promote plant growth and health. However, the growth-promoting effect of a single PGPR on plants is limited. Here, we evaluated the effect of applying rhizobium Bradyrhizobium japonicum 5038 (R5038) and two PGPR strains, Bacillus aryabhattai MB35-5 (BA) and Paenibacillus mucilaginosus 3016 (PM), alone or in different combinations on the soil properties and rhizosphere bacterial community composition of soybean (Glycine max). Additionally, metagenomic sequencing was performed to elucidate the profile of functional genes. Inoculation with compound microbial inoculant containing R5038 and BA (RB) significantly improved nodule nitrogenase activity and increased soil nitrogen content, and urease activity increased the abundance of the nitrogen cycle genes and Betaproteobacteria and Chitinophagia in the rhizosphere. In the treatment of inoculant-containing R5038 and PM (RP), significant changes were found for the abundance of Deltaproteobacteria and Gemmatimonadetes and the phosphorus cycle genes, and soil available phosphorus and phosphatase activity were increased. The RBP inoculants composed of three strains (R5038, BA and PM) significantly affected soybean biomass and the N and P contents of the rhizosphere. Compared with RB and RP, RBP consistently increased soybean nitrogen content, and dry weight. Overall, these results showed that several PGPR with different functions could be combined into composite bacterial inoculants, which coordinately modulate the rhizosphere microbial community structure and improve soybean growth.

Characterization of an Endophytic Antagonistic Bacterial Strain Bacillus halotolerans LBG-1-13 with Multiple Plant Growth-Promoting Traits, Stress Tolerance, and Its Effects on Lily Growth

Microbial inoculants are an important tool for increasing arable land productivity and decreasing mineral fertilizer application. This study was aimed at isolating and identifying endophytic antagonistic bacteria from lily (Lilium davidii var. unicolor) roots grown in Northwestern China and at evaluating their antifungal activity and plant growth-promoting characteristics. For this purpose, endophytic bacteria were isolated from plant roots, and plant growth-promoting strains were identified. One bacterial strain, isolated from the root part, was identified as Bacillus halotolerans based on 16S rRNA gene sequence analysis and was designated as LBG-1-13. The strain showed antagonistic activities against important plant pathogens of lily including Botrytis cinerea, Botryosphaeria dothidea, and Fusarium oxysporum. The highest percentage of growth inhibition, i.e., 71.65 ± 2.39%, was observed for LBG-1-13 against Botryosphaeria dothidea followed by 68.33 ± 4.70% and 48.22 ± 4.11% against Botrytis cinerea and Fusarium oxysporum, respectively. Meanwhile, the isolated strain also showed plant growth-promoting traits such as the production of indole-3-acetic acid (IAA), siderophore, ACC deaminase, and phosphate solubilization activity. The strain showed ACC deaminase activity and was able to cleave 58.41 ± 2.62 nmol α-ketobutyrate (mg protein)⁻¹ min⁻¹. The strain exhibited tolerance to salt and drought stress in an in vitro experiment. The strain LBG-1-13 was able to grow in the presence of 10% NaCl and 20% polyethylene glycol (PEG) in the growth medium. Inoculation of Lilium varieties, Tresor and Bright Diamond, with LBG-1-13 enhanced plant growth under greenhouse and field conditions, respectively. All these results demonstrated that Bacillus halotolerans LBG-1-13 could be utilized as a good candidate in the biocontrol of lily disease and plant growth promotion in sustainable agriculture.