Chemical fertilizers have substantially increased crop yields but have also contributed to significant environmental challenges, including soil and water contamination and the emergence of human health issues. As a more sustainable alternative, biofertilizers-comprising beneficial microorganisms such as bacteria-have been promoted as eco-friendly solutions. However, their use may pose risks to soil microbial communities and biodiversity under certain conditions. For instance, horizontal gene transfer among bacteria can convert non-pathogenic strains into pathogenic ones. Additionally, the introduction of microbial inoculants may outcompete native microbial species, potentially disrupting soil microbial balance and impairing ecosystem functioning. The long-term effects of biofertilizers on nutrient cycling and soil biodiversity remain insufficiently studied. To mitigate these risks, it is crucial to establish rigorous production standards, prioritize native microbial strains, continuously monitor soil microbial dynamics, and implement comprehensive regulatory frameworks. Therefore, the adoption of biofertilizers in agricultural practices should be approached cautiously and guided by evidence-based regulations.
- MeSH
- Bacteria MeSH
- Nitrogen Fixation MeSH
- Glycine max MeSH
- Nitrogen Isotopes MeSH
- Soil MeSH
- Geographicals
- Egypt MeSH
There is an increasing demand for bioinoculants based on plant growth-promoting rhizobacteria (PGPR) for use in agricultural ecosystems. However, there are still concerns and limited data on their reproducibility in different soil types and their effects on endemic rhizosphere communities. Therefore, this study explored the effects of inoculating the PGPR, Pseudomonas fluorescens strain UM270, on maize growth (Zea mays L.) and its associated rhizosphere bacteriome by sequencing the 16S ribosomal genes under greenhouse conditions. The results showed that inoculation with PGPR P. fluorescens UM270 improved shoot and root dry weights, chlorophyll concentration, and total biomass in the three soil types evaluated (clay, sandy-loam, and loam) compared to those of the controls. Bacterial community analysis of the three soil types revealed that maize plants inoculated with the UM270 strain showed a significant increase in Proteobacteria and Acidobacteria populations, whereas Actinobacteria and Bacteroidetes decreased. Shannon, Pielou, and Faith alpha-biodiversity indices did not reveal significant differences between treatments. Beta diversity revealed a bacterial community differential structure in each soil type, with some variation among treatments. Finally, some bacterial groups were found to co-occur and co-exclude with respect to UM270 inoculation. Considered together, these results show that PGPR P. fluorescens UM270 increases maize plant growth and has an important effect on the resident rhizobacterial communities of each soil type, making it a potential agricultural biofertilizer.
- MeSH
- Bacteria classification genetics isolation & purification growth & development MeSH
- Biodiversity MeSH
- Biomass MeSH
- Phylogeny MeSH
- Plant Roots * microbiology growth & development MeSH
- Zea mays * microbiology growth & development MeSH
- Pseudomonas fluorescens * genetics growth & development physiology MeSH
- Soil * chemistry MeSH
- Soil Microbiology * MeSH
- Rhizosphere * MeSH
- RNA, Ribosomal, 16S genetics MeSH
- Publication type
- Journal Article MeSH
Due to insufficient amount of soluble phosphate and poor persistence of traditional chemical phosphate fertilizers in agricultural soils, the eco-friendly and sustainable phosphorus sources for crops are urgently required. The efficient phosphate-releasing fungal strain designated y2 was isolated and identified by the internal transcribed spacer of rDNA as Penicillium oxalicum y2. When lecithin, Ca3(PO4)2, or ground phosphate rock were separately used as sole phosphorus source, different phosphate-releasing modes were observed. The strain y2 was able to release as high as 2090 mg/L soluble phosphate within 12 days of incubation with Ca3(PO4)2 as sole phosphorus source. In the culture solution, high concentration of oxalic, citric, and malic acids and high phosphatase activity were detected. The organic acids contributed to solubilizing inorganic phosphate sources, while phosphatase was in charge of the mineralization of organic phosphorus lecithin. Afterwards, the fungus culture was applied to the soil with rape growing. During 50 days of incubation, the soil's available phosphate concentration increased by three times compared with the control, the dry weight of rape increased by 78.73%, and the root length increased by 38.79%. The results illustrated that P. oxalicum y2 possessed both abilities of solubilizing inorganic phosphorus and mineralizing organic phosphorus, which have great potential application in providing biofertilizer for modern agriculture.
- MeSH
- Biological Availability MeSH
- Brassica napus growth & development MeSH
- Nitrogen metabolism MeSH
- Phosphoric Monoester Hydrolases metabolism MeSH
- Phosphates metabolism pharmacokinetics MeSH
- Phosphorus metabolism MeSH
- Phylogeny MeSH
- Carboxylic Acids metabolism MeSH
- DNA, Ribosomal Spacer genetics MeSH
- Penicillium classification genetics isolation & purification metabolism MeSH
- Soil chemistry MeSH
- Soil Microbiology * MeSH
- Carbon metabolism MeSH
- Publication type
- Journal Article MeSH
Alginate lyases have countless potential for application in industries and medicine particularly as an appealing biocatalyst for the production of biofuels and bioactive oligosaccharides. Solid-state fermentation (SSF) allows improved production of enzymes and consumes less energy compared to submerged fermentation. Seaweeds can serve as the most promising biomass for the production of biochemicals. Alginate present in the seaweed can be used by alginate lyase-producing bacteria to support growth and can secrete alginate lyase. In this perspective, the current study was directed on the bioprocessing of brown seaweeds for the production of alginate lyase using marine bacterial isolate. A novel alginate-degrading marine bacterium Enterobacter tabaci RAU2C which was previously isolated in the laboratory was used for the production of alginate lyase using Sargassum swartzii as a low-cost solid substrate. Process parameters such as inoculum incubation period and moisture content were optimized for alginate lyase production. SSF resulted in 33.56 U/mL of alginate lyase under the static condition maintained with 75% moisture after 4 days. Further, the effect of different buffers, pH, and temperature on alginate lyase activity was also analyzed. An increase in alginate lyase activity was observed with an increase in moisture content from 60 to 75%. Maximum enzyme activity was perceived with phosphate buffer at pH 7 and 37 °C. Further, the residual biomass after SSF could be employed as biofertilizer for plant growth promotion based on the preliminary analysis. To our knowledge, this is the first report stating the usage of seaweed biomass as a substrate for the production of alginate lyase using solid-state fermentation.
- MeSH
- Alginates * metabolism MeSH
- Biomass MeSH
- Enterobacter * metabolism enzymology isolation & purification growth & development MeSH
- Fermentation * MeSH
- Hydrogen-Ion Concentration MeSH
- Glucuronic Acid metabolism MeSH
- Seaweed * microbiology MeSH
- Phaeophyceae microbiology MeSH
- Polysaccharide-Lyases * metabolism MeSH
- Sargassum * microbiology metabolism MeSH
- Temperature MeSH
- Publication type
- Journal Article MeSH
The plant microbiomes consist of a myriad of microorganisms that inhabit and interact with plant tissues and play pivotal roles in improving crop productivity and sustainability. These microbiomes constitute bacteria, fungi, archaea and viruses that have coevolved and supported plants inhabiting the Earth for millions of years. Among these, bacterial members play major functional roles in fostering plant growth and are regarded as plant growth-promoting bacteria (PGPB). One of the major bacterial genera of the plant microbiome that colonizes the entire plant system is the genus Methylobacterium. The genus Methylobacterium is categorized as a member of the class Alphaproteobacteria and is distinguished by its pink pigmentation, which is a result of the synthesis of carotenoids, mainly xanthophiles. Members of the Methylobacterium genus are commonly known as pink-pigmented facultative methylotrophs, which are ubiquitous in nature and have gained significant importance in crop production in various agricultural ecosystems because of their versatile ability to promote plant growth and enhance stress tolerance. They have the unique ability to utilize single-carbon compounds that are released during plant cell metabolism, improve plant growth, siderophore and phytohormone (auxin and cytokinin) production, and nitrogen fixation; phosphorous and zinc solubilization and induced systemic resistance against phytopathogens; protective biofilm formation; and the production of 1-aminocyclopropane-1-carboxylate deaminase to increase stress tolerance and carotenoid production for UV stress tolerance. Owing to its use as a biostimulant, biofertilizer and biocontrol agent, Methylobacterium has potential applications in agriculture for increasing soil health, crop productivity and environmental sustainability. This review provides broad perspectives on the multifaceted role and sustainable application of Methylobacterium in climate-smart agriculture.
Functional diversity covers diverse functional traits of microorganisms in an ecosystem. Thus, we hypothesized that it could play an important role in the isolation of nitrogen-fixing and phosphate-solubilizing bacteria. These bacteria have been considered as biofertilizer for sustainable agriculture development. Soils were collected from different sites of agricultural field and performed several microbiological tests in which we observed considerable differences in heterotrophic microbial abundance and microbial activities among the microcosms. Functional diversity depends on both microbial richness and evenness. Based on the results of metabolic fingerprinting of the carbon sources of BiOLOG-ECO plates, richness and evenness was measured by determining Shannon diversity index and Gini coefficient, respectively. The results showed significant differences in both microbial richness and evenness, suggesting considerable variation of functional diversity among the microcosms. Thereafter, nitrogen-fixing and phosphate-solubilizing bacteria were isolated on Burk's and Pikovskaya media, respectively. The results revealed considerable variation of both types of bacterial abundance among the microcosms. Microcosm (T2) showing the highest functional diversity houses the maximum numbers of nitrogen-fixing and phosphate-solubilizing bacteria. Similarly, the microcosm (T5) exhibiting the lowest functional diversity houses the minimum numbers of nitrogen-fixing and phosphate-solubilizing bacteria. Thus, a strong positive correlation was observed between functional diversity and both types of bacterial abundance among the soil samples. Higher richness and evenness lead to the development of increased functional diversity that facilitates to accommodate substantial numbers of nitrogen-fixing and phosphate-solubilizing bacteria in soil. Taken together, the results demonstrated that functional diversity plays an important role in the isolation of nitrogen-fixing and phosphate-solubilizing bacteria from soil.
Halotolerant bacteria get adapted to a saline environment through modified physiological/structural characteristics and may provide stress tolerance along with enhanced growth to the host plants by different direct and indirect mechanisms. This study reports on multiple halotolerant plant growth-promoting rhizobacteria isolated from the coastal soils in Bangladesh, in fields where the halophytic wild rice Oryza coarctata is endemic. The aim was to find halotolerant bacteria for potential use as biofertilizer under normal/salt-stressed conditions. In this study, eight different strains were selected from a total of 20 rhizobacterial isolates from the saline-prone regions of Debhata and Satkhira based on their higher salt tolerance. 16S rRNA gene sequencing results of the rhizobacterial strains revealed that they belonged to Halobacillus, Bacillus, Acinetobactor, and Enterobactor genera. A total of ten halotolerant rhizobacteria (the other 2 bacteria were previously isolated and already reported as beneficial for rice growth) were used as both single inoculants and in combinations and applied to rice growing in pots. To investigate their capability to improve rice growth, physiological parameters such as shoot and root length and weight, chlorophyll content at the seedling stage as well as survival and yield at the reproductive stage were measured in the absence or presence (in concentration 40 or 80 mmol/L) of NaCl and in the absence or presence of the rhizobacteria. At the reproductive stage, only 50% of the uninoculated plants survived without setting any grains in 80 mmol/L NaCl in contrast to 100% survival of the rice plants inoculated with a combination of the rhizobacteria. The combined halotolerant rhizobacterial inoculations showed significantly higher chlorophyll retention as well as yield under the maximum NaCl concentration applied compared to application of single species. Thus, the use of a combination of halotolerant rhizobacteria as bioinoculants for rice plants under moderate salinity can synergistically alleviate the effects of stress and promote rice growth and yield.
Biofilms represent mixed communities present in a diverse range of environments; however, their utility as inoculants is less investigated. Our investigation was aimed towards in vitro development of biofilms using fungal mycelia (Trichoderma viride) as matrices and nitrogen-fixing and P-solubilizing bacteria as partners, as a prelude to their use as biofertilizers (biofilmed biofertilizers, BBs) and biocontrol agents for different crops. The most suitable media in terms of population counts, fresh mass and dry biomass for Trichoderma and Bacillus subtilis/Pseudomonas fluorescens was found to be Pikovskaya broth ± 1 % CaCO(3), while for Trichoderma and Azotobacter chroococcum, Jensen's medium was most optimal. The respective media were then used for optimization of the inoculation rate of the partners in terms of sequence of addition of partners, fresh/dry mass of biofilms and population counts of partners for efficient film formation. Microscopic observations revealed significant differences in the progress of growth of biofilms and dual cultures. In the biofilms, the bacteria were observed growing intermingled within the fungal mycelia mat. Further, biofilm formation was compared under static and shaking conditions and the fresh mass of biofilms was higher in the former. Such biofilms are being further characterized under in vitro conditions, before using them as inoculants with crops.
- MeSH
- Biofilms * MeSH
- Culture Media chemistry metabolism MeSH
- Mycelium growth & development physiology MeSH
- Agricultural Inoculants genetics growth & development physiology MeSH
- Trichoderma genetics growth & development physiology MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
The growing interest in a healthy lifestyle and in environmental protection is changing habits regarding food consumption and agricultural practices. Good agricultural practice is indispensable, particularly for raw vegetables, and can include the use of plant probiotic bacteria for the purpose of biofertilization. In this work we analysed the probiotic potential of the rhizobial strain PEPV40, identified as Rhizobium laguerreae through the analysis of the recA and atpD genes, on the growth of spinach plants. This strain presents several in vitro plant growth promotion mechanisms, such as phosphate solubilisation and the production of indole acetic acid and siderophores. The strain PEPV40 produces cellulose and forms biofilms on abiotic surfaces. GFP labelling of this strain showed that PEPV40 colonizes the roots of spinach plants, forming microcolonies typical of biofilm initiation. Inoculation with this strain significantly increases several vegetative parameters such as leaf number, size and weight, as well as chlorophyll and nitrogen contents. Therefore, our findings indicate, for the first time, that Rhizobium laguerreae is an excellent plant probiotic, which increases the yield and quality of spinach, a vegetable that is increasingly being consumed raw worldwide.
- MeSH
- Biofilms MeSH
- Cellulose biosynthesis MeSH
- Phenotype MeSH
- Phylogeny MeSH
- Plant Roots microbiology MeSH
- Probiotics * MeSH
- Rhizobium classification physiology MeSH
- Seedlings microbiology MeSH
- Spinacia oleracea growth & development microbiology MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
