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Bioprospecting of Microbial Diversity for Sustainable Agriculture and Environment
Published in Vineet Kumar, Vinod Kumar Garg, Sunil Kumar, Jayanta Kumar Biswas, Omics for Environmental Engineering and Microbiology Systems, 2023
Hiren K. Patel, Nensi K. Thumar, Priyank D. Patel, Azaruddin V. Gohil
Biological nitrogen is an essential component for agricultural crops and is required for the biosynthesis of proteins, enzymes, growth factors, nucleic acids, hormones, cell components, and different pigments. Nitrogen is also a compulsory component of fertilizers. From the environment, nitrogen is lost due to the leaching mechanism. Atmospheric nitrogen (N2) is made available to plants in reduced form (NH3) by microbial actions, as plants cannot utilize molecular nitrogen directly. Microbes carrying out nitrogen fixation are known as diazotrophs. Nitrogen fixation is a part of the nitrogen cycle that involves the steps of fixation, ammonification, nitrification, denitrification, and assimilation. Nodule formation surrounding root is characteristic of symbiotic microbes for nitrogen fixation in legumes (Zahran 1999) (Figure 14.3). Microbes fix atmospheric nitrogen into soil through enzyme nitrogenase, which requires molybdenum and iron as cofactors. Nitrogenases are very sensitive towards the presence of oxygen. Due to this reason, nitrogen fixation is mostly carried out in anaerobic environmental conditions. Leghemoglobin is a protein that helps in the maintenance of anaerobic conditions (Robson and Postgate 1980). Nitrogenase enzyme complex is encoded by a complex of genes known as nif (Gaby and Buckley 2011). Overall, the microbial nitrogen fixation can be represented as follows (Postgate 1998).
Role of Endophytes in Crop Improvement
Published in Jyoti Ranjan Rout, Rout George Kerry, Abinash Dutta, Biotechnological Advances for Microbiology, Molecular Biology, and Nanotechnology, 2022
Bicky Jerin Joseph, A. R. Nayana, E. K. Radhakrishnan
From several studies related to N fertilizer usage, it is estimated that out of 100 Tg N only 17 Tg N is available for agriculture (Kandel et al., 2017). Thus the nitrogen-fixing bacteria have got a significant role in reducing the nitrogen fertilizer load of the soil. The diazotrophs associated with root nodules are known to help the plant to fix atmospheric nitrogen (Ke et al., 2019). Several genera of endophytic diazotrophs such as Burkholderia (Govindarajan et al., 2007), Klebsiella (Lin et al., 2019), and Pseudomonas (Ke et al., 2019) located at various plant parts are considered to promote the growth of crops under harsh conditions. This indicates the nitrogen-fixing organisms to have a remarkable influence on the plant system.
Endophytic Microorganisms from Synanthropic Plants
Published in Amitava Rakshit, Manoj Parihar, Binoy Sarkar, Harikesh B. Singh, Leonardo Fernandes Fraceto, Bioremediation Science From Theory to Practice, 2021
Olga Marchut-Mikolajczyk, Piotr Drozdzynski
For plants, nitrogen deficiency is most adversely affected. It causes poor tillering, yellowing of leaves, weakness or stiffness of tissues (Chodari et al. 1980). However, this state can be easily resolved by the presence of endophytic microorganisms which have nitrogenase activity, namely, diazotrophs Thanks to nitrogenase activity, microorganisms may fix the atmospheric nitrogen, due to its reduction to NH3, thus significantly increasing nitrogen uptake by plants. Endophytes that have nitrogenase activity belong to genus Azospirillum, Acetobacter, Herbaspirillum, Azoarcus or Azotobacter (Pisarska and Pietr 2014). Rodrigues et al. (2008) in their research inoculated the Oryza sativa L. (seed rice) plants with diazotrophic endophytic bacteria Azospirillum amazonense. They noticed that the presence of diazotrophic bacteria increases the uptake of nitrogen by the plant from 3.5 up to 18.5%; also, it increased the biomass of tested plants (Rodrigues et al. 2008). Worth mentioning is the fact that sugar cane grows in some areas of Brazil without any nitrogen fertilization. A great amount, namely 50-80% of this element, is taken from the atmosphere, and this is possible due to endosymbiosis with the diazotrophic bacterium Gluconacetobacter diazotrophicus (Blaszczyk 2010, Chawla et al. 2014). The nitrogen-fixation by endophytic bacteria has been reported by Elbeltagy et al. (2001) for Enterobacter cloacae, Alcaligenes, A. diazotrophicus, Azospirillum, Azoarcus, Herbaspirillum seropedicae and Ideonella dechloratans (Elbeltagy et al. 2001, Gunjal et al. 2018).
Mercury resistance and plant growth promoting traits of endophytic bacteria isolated from mercury-contaminated soil
Published in Bioremediation Journal, 2022
Reni Ustiatik, Yulia Nuraini, Suharjono Suharjono, Paramsothy Jeyakumar, Christopher W. N. Anderson, Eko Handayanto
Usually, contaminated soil from mining activities has low soil fertility, and only a few plants can survive. The presence of diazotrophic bacteria can reduce stress due to limited nutrients. The potential for diazotrophic bacteria to produce plant-available ammonium (NH4+) from N2 in the air is an important component of biological nitrogen fixation (BNF) and this can supply N for host plants (Li et al. 2019). In the current study, incubation time and the type of isolate significantly affected ammonium production (P < 0.05) (Figure 6). Ammonium production was low at the initial incubation time (0 and 1 day) for all isolates, but increased from day 3 for isolates EI5 and EI6 and peaked at day 5 for these two isolates. The highest ammonium concentration was produced by isolate EI6 at 5 days incubation (2.58 mg/L). This concentration was low compared to ammonium production by rhizosphere bacteria isolated from Syzygium aromaticum in Tidore Island, Indonesia (11.3 mg/L) (Ishak, Ardyati, and Aini 2018), but higher than for endophytic bacteria isolated from Camellia sinensis in India (approximately 0.0019 mg/L) (Borah et al. 2019). Bacteria that can produce ammonium, even at low concentrations, are beneficial for Hg phytoremediation due to the low soil fertility of Hg-contaminated soil such as the ASGM study site we describe (total-N = 0.034%). Innoculated bacteria could provide N for plants, and thus support plant growth and subsequently Hg extraction from soil.
Biochar application on heavy metal immobilization in unsaturated soil with vegetation: a review
Published in International Journal of Geotechnical Engineering, 2023
Bacteria also share available nutrients for plant growth. Diazotrophs, a specialized group of bacteria, have the ability to transform atmospheric N2 into NH3, which could be nitrified (NO3−) before plant uptake due to the possession of enzyme nitrogenase. Plant growth-promoting rhizobacteria (PGPR) regulate the balance of hormone and nutrition, solubilize the nutrients to promote the plant uptake and induce resistance against pathogens of plant. Besides, PGPR show the interactions of synergy and antagonism with microorganisms in the rhizosphere and bulk soil, leading to the indirect boost of plant growth rate (Vejan et al. 2016).