Impacts of Microbial Inoculants on the Growth and Yield of Maize Plant

Lactic Bacteria with Plant-Growth-Promoting Properties in Potato

This study aimed to evaluate the abilities of three bacteria, Bacillus cereus, Succinovibrio dextrinosolvens, and Lactobacillus acidophilus, to fix nitrogen, solubilize phosphorus, and produce cellulosic and amylolytic enzymes. Then, these bacteria were evaluated in potato plants under field conditions. The bacterium B. cereus showed the ability to synthesize amylase, indole acetic acid (IAA) production of 9.08 μg mL−1, phosphorus solubilization of 14.93 mg P L−1, and nitrogen fixation of 0.7 mg of nitrogen L−1. S. dextrinosolvens showed the ability to synthesize siderophores and amylase, IAA production of 10.25 μg mL−1, phosphorus solubilization of 41.38 mg P L−1, and nitrogen fixation of 0.42 mg N L−1. L. acidophilus showed the ability to synthesize siderophores, IAA production of 7.25 μg mL−1, phosphorus solubilization of 5.58 mg P L−1, and nitrogen fixation of 0.5 mg N L−1. Some plant parameters were increased as shoot dry matter by B. cereus, and the mixture of bacteria increased shoot and root dry matter and increased phosphorus from the root. More studies are needed to deepen the understanding of the potential of these bacteria; however, B. cereus showed great potential to be used as a plant growth promoter in potato crops in the future.

The bacterial world inside the plant

Sustainable agriculture requires the recruitment of bacterial agents to reduce the demand for mineral fertilizers and pesticides such as bacterial endophytes. Bacterial endophytes represent a potential alternative to the widespread use of synthetic fertilizers and pesticides in conventional agriculture practices. Endophytes are formed by complex microbial communities and microorganisms that colonize the plant interior for at least part of their life. Their functions range from mutualism to pathogenicity. Bacterial endophytes colonize plant tissues, and their composition and diversity depend on many factors, including the plant organ, physiological conditions, plant growth stage, and environmental conditions. The presence of endophytes influences several vital activities of the host plant. They can promote plant growth, elicit a defense response against pathogen attack, and lessen abiotic stress. Despite their potential, especially with regard to crop production and environmental sustainability, research remains sparse. This review provides an overview of the current research, including the concept of endophytes, endophytes in plant organs, endophyte colonization, nutrient efficiency use, endophytes and crop nutrition, inoculation with synergistic bacteria, the effect of inoculum concentration on plant root microbiota and synthetic communities. It also examines the practical opportunities and challenges when utilizing endophytes in the field of sustainable agriculture. Finally, it explores the importance of these associations with regard to the future of agriculture and the environment.

Metagenomic Insight into the Community Structure of Maize-Rhizosphere Bacteria as Predicted by Different Environmental Factors and Their Functioning within Plant Proximity

The rhizosphere microbiota contributes immensely to nutrient sequestration, productivity and plant growth. Several studies have suggested that environmental factors and high nutrient composition of plant's rhizosphere influence the structural diversity of proximal microorganisms. To verify this assertion, we compare the functional diversity of bacteria in maize rhizosphere and bulk soils using shotgun metagenomics and assess the influence of measured environmental variables on bacterial diversity. Our study showed that the bacterial community associated with each sampling site was distinct, with high community members shared among the samples. The bacterial community was dominated by Proteobacteria, Actinobacteria, Acidobacteria, Gemmatimonadetes, Bacteroidetes and Verrucomicrobia. In comparison, genera such as Gemmatimonas, Streptomyces, Conexibacter, Burkholderia, Bacillus, Gemmata, Mesorhizobium, Pseudomonas and Micromonospora were significantly (p ≤ 0.05) high in the rhizosphere soils compared to bulk soils. Diversity indices showed that the bacterial composition was significantly different across the sites. The forward selection of environmental factors predicted N-NO₃ (p = 0.019) as the most influential factor controlling the variation in the bacterial community structure, while other factors such as pH (p = 1.00) and sulfate (p = 0.50) contributed insignificantly to the community structure of bacteria. Functional assessment of the sampling sites, considering important pathways viz. nitrogen metabolism, phosphorus metabolism, stress responses, and iron acquisition and metabolism could be represented as Ls > Rs > Rc > Lc. This revealed that functional hits are higher in the rhizosphere soil than their controls. Taken together, inference from this study shows that the sampling sites are hotspots for biotechnologically important microorganisms.

Impact of cropping systems on the functional diversity of rhizosphere microbial communities associated with maize plant: a shotgun approach

Understanding the functions carried out by rhizosphere microbiomes will further explore their importance in biotechnological improvement and agricultural sustainability. This study presents one of the foremost attempts to understand the functional diversity of the rhizosphere microbiome in mono-cropping and crop rotation farming sites using shotgun metagenomic techniques. We hypothesized that the functional diversity would vary in the cropping sites and more abundant in the rotational cropping site. Hence, we carried out complete DNA extraction from the bulk and rhizospheric soils associated with maize plant cultivated on the mono-cropping farm (LT and LTc) and the crop rotation farm (VD and VDc), respectively, and sequenced employing shotgun approach. Using the SEED subsystem, our result revealed that a total of 24 functional categories dominated the rotational cropping site, while four functional categories dominated the mono-cropping sites. Alpha diversity assessment showed that no significant difference (p > 0.05) was observed across the cropping sites, while beta diversity assessment revealed a significant difference. Going by the high abundance of functional groups observed in the samples from the crop rotational site, it is evident that cropping systems influenced the functions of soil microbiomes. Worthy of note is the high abundance of unknown functions associated with these maize rhizosphere microbiomes. This is an indication that there are still some under-investigated functional genes associated with the maize rhizosphere microbiome. It is, therefore, imperative that further studies explore these functional genes for their agricultural and biotechnological potentials.

Metagenomic profiling of the community structure, diversity, and nutrient pathways of bacterial endophytes in maize plant

This study investigated the diversity, structure and nutrient pathways of the root-associated bacterial endophytes of maize plant cultivated using different fertilizers to verify the claim that inorganic fertilizers have some toxic effects on plant microbiome and not are ecofriendly. Whole DNA was extracted from the roots of maize plants cultivated with organic fertilizer, inorganic fertilizer and maize planted without any fertilizer at different planting sites in an experimental field and sequenced using shotgun metagenomics. Our results using the Subsystem database revealed a total of 28 phyla and different nutrient pathways in all the samples. The major phyla observed were Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria, Acidobacteria, Chloroflexi, Verrucomicrobia, Tenericutes, Planctomycetes, Cyanobacteria, and Chlorobi. Bacteroidetes dominated maize from organic fertilizer sites, Firmicutes dominated the no fertilizers site while Proteobacteria dominated Inorganic fertilizer. The diversity analysis showed that the abundance of endophytic bacteria in all the sites is in the order organic fertilizer (FK) > no fertilizer (CK) > inorganic fertilizer (NK). Furthermore, the major nutrient cycling pathways identified are linked with nitrogen and phosphorus metabolism which were higher in FK samples. Going by the results obtained, this study suggests that organic fertilizer could be a boost to sustainable agricultural practices and should be encouraged. Also, a lot of novel endophytic bacteria groups were identified in maize. Mapping out strategies to isolate and purify this novel endophytic bacteria could help in promoting sustainable agriculture alongside biotechnological applications in future.

Metagenomics methods for the study of plant-associated microbial communities: A review

Plant microbiota have different effects on the plant which can be beneficial or pathogenic. In this study, we concentrated on beneficial microbes associated with plants using endophytic microbes as a case study. Detailed knowledge of the microbial diversity, abundance, composition, functional genes patterns, and metabolic pathways at genome level could assist in understanding the contributions of microbial community towards plant growth and health. Recently, the study of microbial community has improved greatly with the discovery of next-generation sequencing and bioinformatics technologies. Analysis of next generation sequencing data and a proper computational method plays a key role in examining microbial metagenome. This review presents the general metagenomics and computational methods used in processing plant associated metagenomes with concentration on endophytes. This includes 1) introduction of plant-associated microbiota and the factors driving their diversity. 2) plant metagenome focusing on DNA extraction, verification and quality control. 3) metagenomics methods used in community analysis of endophytes focusing on maize plant and, 4) computational methods used in the study of endophytic microbiomes. Limitations and future prospects of metagenomics and computational methods for the analysis of plant-associated metagenome (endophytic metagenome) were also discussed with the aim of fostering its development. We conclude that there is need to adopt advanced genomic features such as k-mers of random size, which do not depend on annotation and can represent other sequence alternatives.

Bacterial Consortium for Improved Maize (Zea mays L.) Production

The ever-increasing human population is a major concern for food security. Maize is the third largest most important food crop. The major problems of cultivation arise from urbanization and land pollution. This reduces the amount of land available for agriculture. The use of chemicals in agriculture is not environmentally friendly. Thus, plant growth-promoting bacteria (PGPB) have been proposed as alternatives. This study aims to test the growth-promoting effect of maize inoculated with six indigenous PGPB isolates. These isolates were assayed for various biochemical and plant growth-promoting activities. They were also assayed for biocontrol activities. Based on the results, six isolates viz A1, A18, A29, NWU4, NWU14, and NWU198 were used to inoculate maize seeds. The inoculated seeds were tried out on the field. A randomized block design was used. PGPB used were in single, consortia of two, and three organisms. The length of the leaves, roots, and stem, plant height, numbers of leaves, and weight of 100 seeds were taken at the fourth and eighth weeks after planting. Microbial consortia increased growth parameters compared to single inoculant treatments. Thus, they can be of advantage in the eradication of low yield. They can also serve as reliable alternatives to chemical fertilizers.