Microbes as Bio-fertilizers

Microbes as Bio-fertilizers

Bio-fertilizers are an optional source to meet the nutrient requirements of crops. The emergence of this concept is to domesticate the microbes in our agriculture production systems to obtain additional yield by improving crop productivity with these bioinuculants.

Microbes as Bio-fertilizers

Abstract

With the purpose of enhancing the productivity of crops within shorter time lapse, bio-fertilizer technology is introduced in recent era that demands the utilization of various strains of micro-organisms to enhance the nutritional content of soil and to overcome the growth-retarding factors like environmental stresses. By speed up various biochemical cycles, for example; Nitrogen cycle, Phosphorus cycle, Potassium solubilisation (mineralization), microbes ensure the satisfactory uptake of plant growth-regulatory components. A strain of Rhizobium, Cyanobacteria and other microbes often degrades several soil- borne plant pathogens by releasing various chemicals during the competition against antagonistic pathogens. Bio-fertilizers prove better than chemical fertilizers as it don’t effect directly and trim down the side effects. We can attain a lot of colonies of microbes to work within no time at low cost, hence proves a major outbreak for future in Agriculture Department.

Introduction

Microbial bio-fertilizers are a biological preparation of sufficient densities of microbial strains that cast beneficial effects in rhizospheres for plant growth (Far-four et al., 2015). A bio-fertilizer of selected effective living microbial cultures, when applied to pant surfaces, seed or soil, can colonize the rhizospheres or the interior of the host plant and then uphold plant growth by increasing the availability, supply, or uptake of primary nutrients to the host. Moreover, contrary to chemical fertilizers, bio-fertilizers are more manageable to marginal and small farmers. The most important groups of microbes used in the preparation of microbial bio-fertilizer are bacteria, fungi, and Cyanobacteria, majority of which have symbiotic association with plants. The imperative types of microbial fertilizers, based on their nature and function, are those which supply nitrogen and phosphorus. Major sources of bio-fertilizers are living organisms, decomposed dead organism and decomposed organic waste (Thomas and Singh 2019). In-vitro cultures of specific microbes are selected for the preparation of bio-fertilizers to fulfill the specific nutrient requirements of different plants (Dahm et al., 2010).

Major groups of microbial fertilizers includes: nitrogen fixing, phosphate solubilizing, phosphate mobilizing, potassium solubilizing, silicate and zinc solubilizing and plant growth-promoting rhizobacteria.

Nitrogen-Fixing Microbes

Nitrogen is most abundant and ubiquitous in the air, yet becomes a limiting nutrient due to difficulty of its fixation and uptake by the plants. However, certain microorganisms, some of which can form various associations with plants as well, are capable of considerable nitrogen fixation. This property allows for the efficient plant uptake of the fixed nitrogen and reduces loses by de-nitrification, leaching, and volatilization. These microbes can be:

Free-living in the soil

• The assessment of nitrogen fixation by free- living bacteria is difficult, but in some plants like Medicago sativa, it has been  estimated to range from 3 kg N/ha to 10 kg N/ha (Roper et al. 1995). Azotobacter chroococcum in arable soils can fix 2–15 mg N/g of carbon source in culture media, and it further produces copious slime which aggregates soil. However, free-living cultures of nodulating bacterial symbionts (e.g., Frankia) fix atmospheric nitrogen in the rhizosphere of their host and even non-host plants (Smolander and Sarsa 1990). Free-living Cyanobacteria (blue green algae) provide up to 20–30 kg N ha_1 under ideal conditions when harnessed in rice cultivation in India (Kannaiyan 2002).

Examples: Anabaena, Azotobacter, Beijerinkia, Derxia, Aulosira, Tolypothrix, Cylindrospermum, Stigonema, Clostridium, Klebsiella, Nostoc, Rhodopseudomonas, Rhodospirillum, Desulfovibrio, Chromatium, and Bacillus polymyxa.

Symbiotic or endophytic associations

• An important group of bio-fertilizers are Rhizobial bacteria that can vary till 450 kg N/ha among different strains e.g. Rhizobium, Bradyrhizobium, Sinorhizobium, Azorhizobium, Mesorhizobium, and Allorhizobium, and other host legume species where there is the formation of root nodules. (Stamford et al. 1997; Unkovich et al. 1997; Spaink et al. 1998; Vance 1998; Graham and Vance 2000; Unkovich and Pate 2000). These rhizobial bio-fertilizers available in different formulations say, powder, liquid or granular having different sterilized carriers like mineral soil and charcoal (Stephens and Rask 2000). Frankia, the mycelia bacterium, a nitrogen-fixing actinomycete, show symbiotic association with the roots of non-legume plants like Rubus etc. These actinorhizal plants are now used in mixed plantations and land reclamation. (Diagne et al. 2013; Schwencke and Carù 2001). Cyanobacteria, also known as blue-green algae is another vital group in ecosystem including Nostoc and Anabaena that contributes in increasing rice-field fertility for rice cultivation, and contributes to about 36% of global nitrogen fixation. Aquatic cyanobacteria can provide proteins, minerals and different natural growth hormone to the soil. (Kundu and Ladha 1995; Gallon 2001; Irisarri et al. 2001).

Examples: Rhizobia (Rhizobium, Bradyrhizobium, Sinorhizobium, Azorhizobium Mesorhizobium Allorhizobium), Frankia, Anabaena azollae, and Trichodesmium

Associative symbiotic relation

• The microbes falls in this category has less association with roots. E.g. Azospirillum that has high host specificity and due to nitrogen fixation it increase the crop yield of sunflower, carrot, tomato, pepper etc. The inoculums of this strain can be produced and applied by a simple peat formulation. (Vande Broek et al. 2000). The biofertilizer of Acetobacter diazotrophicus was found to fix and contribute about 70% of sugarcane crop nitrogen requirement, of about 150 kg N/ha annually (Boddey et al. 1995).

Examples: Azospirillum spp. (A. brasilense, A. lipoferum, A. amazonense, A. halopraeferens, and A. irakense), Acetobacter diazotrophicus, Herbaspirillum spp., Azoarcus spp., Alcaligenes, Bacillus, Enterobacter, Klebsiella, and Pseudomonas.

Phosphorus-Solubilizing Microbes

After Nitrogen, Phosphorus is second most limiting plant nutrient. As it is present abundantly in soil but cannot take up by plants due to its presence in others forms which plants cannot use directly (Schachtman et al.1998). Some species of bacteria like Bacillus and pseudomonas, also called as phosphorus-solubilzing bacteria (PSB) aid the plants for the uptake of soil phosphorus by converting it into desirable forms which the plants can use (Richardson 2001). Different soil fungi like Penicillium and Aspergillus along with PSB secretes organic acids having low PH in order to dissolute the bound phosphate in soil for plant uptake (Sundara et al. 2002).

Phosphorus-Mobilizing bio-fertilizers

These are phosphate-absorbers or Mycorrhizal Biofertilizers. These Mycorrhizal fungi with their mycelium extends from host roots to the soil to cover larger surface areas for absorbance of nutrients like insoluble phosphorus sources and others like zinc, copper, calcium, etc. (Singh and Giri 2017). Ectomycorrhiza of various Basidiomycetes penetrate into the root region mainly cortical region to obtain plant secreted sugar and other nutrition and in return increase surface area of absorbance, soil humus organic matter to absorb and release inorganic nutrients and by secreting various anti-microbial substance to protect plant from different pathogens (White 1941; Wilde 1944; Mikola 1970; Smith and Read 1997).

Cross inoculation group concept:

The term ‘Cross inoculation groups’ refers to a classification scheme used to designate which groups of forage legumes are successfully inoculated by which species or biovars of rhizobia. Inoculation may be defined as the process of adding effective bacteria to the host plant seed before planting.

Plant growth-promoting microbes

Bacteria that colonize plant roots and promote plant growth are called plant growth-promoting rhizobacteria (PGPR), and are highly diverse. Their effects can occur via local antagonism to soil-borne pathogens or by induction of SAR against pathogens throughout the entire plant. Several substances produced by antagonistic rhizobacteria have been related to pathogen control and indirect promotion of growth in many plants, such as antibiotics.

Rhizobacteria belonging to the genera Pseudomonas and Bacillus are well known for their antagonistic effects and their ability to trigger ISR. Resistance-inducing and antagonistic rhizobacteria might be useful in formulating new inoculants with combinations of different mechanisms of action, leading to a more efficient use for bio-control strategies to improve cropping systems (Beneduzi et al. 2012).

Compost Biofertilizers

Compost is produced from a wide variety of materials like leaves, straw cattle-shed bedding, fruit and vegetable wastes, biogas plant slurry, industrial wastes, city garbage, sewage sludge, factory waste, etc. The compost is formed from these materials by different decomposing microorganisms like Trichoderma viridae, Aspergillus niger, A. terreus, Bacillus spp., several Gram-negative bacteria (Pseudomonas, Serratia, Klebsiella, and Enterobacter), etc. having plant cell wall-degrading cellulolytic or lignolytic and other activities, besides having proteolytic activity and antibiosis  (by production of antibiotics) that suppresses other parasitic or pathogenic micro- organisms (Boulter et al. 2002). It acts as a bio-fertilizer and enhances microbial diversity and keep the soil moist and enrich in nutrients.

Bio-fertilizers application methods

Seed treatment

Seed treatment is an extremely efficient, financially experienced and updated technique for a wide range of inoculants (Sethi et al. 2014). The seeds are mixed and constantly covered in a thick suspension and then dried, before being planted within 24 hours. The coating should be possible in a plastic bag (if the quantity is small) or in a container (if the quantity is huge) for the liquid fertilizer, depending on the quantity of seeds. Seed treatment should be possible with at least two microscopic organisms (e.g. nitrogen-fixing microorganisms, e.g. Rhizobium, Azospirillum and Azotobacter, can be introduced with phosphorus-dissolving organisms), without the opposite impact, and provide the maximum extreme amount. of each singular seed bacterium necessary for better results (Chen 2006).

Seedling Root Dipping

This is the usual application in which the seedlings that underlie different yields such as oats, vegetables, natural products, trees, sugar cane, cotton, grapes and tobacco are immersed in the suspension of water of the biofertilizer (Azotobacter or Azospirillum fixer of nitrogen and microbial biofertilizer solubilizing phosphorus) for explicit terms. The time varies according to the variety of the yields, for example the vegetable yields are treated for 20-30 minutes and the rice for 8-12 hours (Barea and Brown 1974).

Soil Application

This technique varies from performance to editing depending on the length. Steers compost is mixed with bio-manure and then this mixture is dusted with water and then communicated to the soil at the time of sowing or at the time of the water system with constant yield. Some examples of biofertilizers in which the application of the soil is used are Rhizobium (for legumes or trees) and Azotobacter (for tea, espresso, elastic, coconuts, all organic / agroturgent service plants for firewood, cereals , natural products, chewing gum, aroma, leaves, flowers, nuts and seeds) (Zahran 1999; Hayat et al. 2010).

Mode of action of various fertilizers

The genome sequencing of two EM (ectomycorrhizae) parasites, L. bicolor 13 and T. melanosporum (black truffle) 14, helps to distinguish the evidence from the elements that guide the improvement of mycorrhizae and their capacity in the plant cell. Fifteen qualities that were directed upward during the beneficial interaction were recognized as transporters of putative hexose in L. bicolor. Its genome needed qualities that encode invertases, so it’s attached to plants for glucose. In any case, melanosporum has an inverted quality and is not at all similar to L. bicolor, it can legitimately use the guest’s sucrose (Bonfante, 2010). Among the PGPR species, Azospirillum has been proposed to emit gibberellins, ethylene and auxins (Perrig et al, 2007). Some plant-related microscopic microorganisms may also cause the combination of phytohormones, e.g. lodgepol pine when vaccinated with Paenibacillus polymyxa had increased IAA levels in the roots (Bent et al, 2001). Rhizobium and Bacillus have been found to combine IAA in various social conditions, e.g. pH, temperature and in view of the waste of agro as a substrate (Sudha et al, 2012). Ethylene, unlike different phytohormones, is responsible for limiting the development of dicotyledon plants. PGPR could improve plant development by stifling ethylene runoff. Interestingly, a model has been proposed in which it has been shown that the fusion of ethylene from 1-aminocyclopropane-1-carboxylate (ACC), an immediate antecedent of ethylene, which is hydrolyzed by the bacterial catalyst ACC-deaminase that needs nitrogen and carbon source. also one of the components of enlisting appropriate conditions for development. ACC-deaminase movement has also been found in microorganisms, e.g. Alcaligenes sp., Bacillus pumilus, Pseudomonas sp. moreover, Variovorax paradoxus (Ansari et al, 2013). The contribution of ACC deaminase to the indirect impact on plant development was demonstrated in Canola, where transformations in the quality of ACC deaminase caused the loss of impact on development as Pseudomonas putida advanced (Bhattacharyya and Jha, 2012). Interestingly, the capacity of the PGPRs has been further enhanced by exhibiting qualities associated with the immediate oxidation pathway (DO) and the solubilization of the mineral phosphate (MPS) in some useful PGPR strains. The quality that codes for glucose dehydrogenase (mcd) compromised with the DO pathway has been cloned and represented by Acinetobacter calcoaceticus and E. coli and Enterobacter asburiae (Tripura et al, 2007)

Hypothetical mechanism of action of biofertilizers in the root cell.

Bioactive ligands called Myc factors and Nod factors secreted by mycorrhiza and Rhizobium were perceived by host roots to trigger the signal transduction pathway which initiates further signal transduction pathway through unknown receptors (SYMRK and NORK) which trigger release of Ca2+ in the cytosol The whole pathway involves receptor like kinases or other kinase related proteins like DMI and SYM71 to phosphorylate their substrates Nuclear pore complex (NPC) and some of its proteins (NUP) play role in calcium spiking. DM1 proteins play role in maintaining periodic oscillation of calcium ions inside and outside the nucleus. Several channels proteins (Ca2+channel proteins) also facilitate this process with the help of various transporters .CCaMK is a calcium calmodulin-dependent protein kinase, which phosphorylate the product of CYCLOPS protein thus initiating activation of various genes involving formation of structures like nodule and (PPA) pre-penetration apparatus.

Constraints of bio-fertilizers in agriculture

Though the bio-fertilizer technology is a low cost, eco-friendly technology, several constraints limit the application or implementation of technology, the limitation may be environmental, technological, infrastructural, financial, human resources, unawareness, quality marketing etc.

Technological Constraints                                   Financial constraints

a. Use of less effective strains                                             a.  Non-availability of sufficient funds

b. Absence of competent technical staff                              b. Problems in getting bank loans

c. Synthesis of poor-quality inoculants                                c. less return by sale of products in

d. Short shelf life of inoculants                                                smaller production units.

Infrastructural Constraints                                Conservational Constraints

a. Deficiency of appropriate production facilities               a. cyclic demands for bio-fertilizers

b. Absence of crucial production equipments                     b. instantaneous harvesting

c. Availability of space for production or storage, etc.       c. short duration of sowing/planting

d. Lack of cold storage facility for inoculants                     d. soil characteristics

Conclusion

Green loads are becoming a serious problem and efficiency is decreasing at a remarkable rate. Our dependence on fertilizers for substances and pesticides has fueled the prosperity of companies that are supplying dangerous synthetic compounds that are dangerous for human use, as well as disrupting environmental equalization. Bio-fertilizers can help tackle the problem of caring for an expanding world population when agriculture faces multiple ecological burdens. It is essential to understand the valuable parts of biofertilizers and update their application to current agricultural practices. The new innovation created using the useful resource of atomic biotechnology can improve the natural pathways for the creation of phytohormones. As long as valuable PGPRs are recognized and transferred, these innovations can help ease ecological burdens. In any case, the lack of awareness about improving the conventions of biofertilizer applications in the field is one of the few reasons why many useful PGPRs have still transmitted information about biologists and farmers. In any case, the continuous progress in the progress identified with microbial science, the collaborations between plants and pathogens and genomics will help improve the necessary conventions. The achievement of the science identified with biofertilizers is based on the creation of imaginary systems identified with the elements of the PGPR and their legitimate application in the field of horticulture. The significant evidence of the research here lies in the way in which, together with the identification of different PGPR strains and their properties, it is essential to dismember the real component of PGPR’s functioning from its suitability for abuse in a reasonable agricultural sector.