Microorganisms are integral to the soil phosphorus (P) cycle and as such play an important role in mediating the availability of phosphorus to plants. The concept of microbial enhancement of phosphorus availability to plants is not new. (Gerretsen, 1948) showed that pure cultures of soilbacteria could increase the phosphorus nutrition of plants under controlled conditions through solubilization of precipitated forms of calcium (Ca) phosphates. Phosphorus (P) is one of the major essential macronutrients for plant and is applied to soil in the form of phosphatic fertilizers. In soil inorganic and organic forms of phosphorus is present. The inorganic forms of the element in soil are compound of calcium, iron, aluminum and fluorine. The organic forms are compounds of phytins, phospholipids and nucleic acid which come mainly by way of decaying undergrowth. Therefore, soils containing high organic matter are also rich in organic forms of phosphorus . Soil microorganisms enhance plant nutrient acquisition. They are involved in a wide range of biological processes including the transformation of insoluble soil nutrients .
The rhizosphere zone has been defined as the volume of soildirectly influenced by the presence of living plant roots or soil compartment influenced by the root. Rhizosphere supports large and active microbial population capable of exerting beneficial, neutraland detrimental effects on the plants. Rhizobacteria (root colonizing bacteria) that exert the beneficial effects on the growth of the host plant via direct or indirect mechanisms are termed as plantgrowth promoting rhizobacteria (PGPR). The plant-microbe interactions in the rhizosphere are responsible for increasing plant health and soil fertility.
Abstract- This paper deals with the concept of rhizosphere, its divisions and the rhizobacteria which are assumed to be very useful in promoting the plantgrowth. The narrow zone of soil directly surrounding the root system is referred to as rhizosphere, also known as unique region, while the term ‘rhizobacteria’ implies a group of rhizosphere bacteria competent in colonizing the root environment. Rhizosphere has an enormous pool of soil microorganisms and is considered as the ‘hot spot’ for microbial colonization and activity. Researchers have revealed that diverse forms of microorganisms found in the rhizosphere influence the host plant in a variety of ways. Bacteria that colonize plant roots and promote plantgrowth are referred to as plantgrowth- promoting rhizobacteria (PGPR). This is the reason that rhizosphere is considered as a unique region distinct from the bulk soil and a region which has so many beneficial effects for crops. It plays significant roles in ecosystem functioning through controlling nutrient cycling reactions essential for maintaining soil fertility and reducing the demand of chemical fertilizers.
Environmental microbiology promoted the soil microorganisms that are able to decompose the organic matter and improve soil fertility. Similar studies described microbial strains with complex role as plants growth promoters. Those two types of beneficial microorganisms are much easier implemented in contrast with the biocontrol strains. The legislation is less permissive with plant protection microorganisms, compared to the microbial biofertilizers. Since biological control means are included in the plant protection products, for their authorization being required, not only efficacy studies but also toxicological, residues, ecotoxicological and environmental studies, according to the same legislation as for chemical pesticides. Despite the obvious benefits for environmental protection, this aspect is a drawback for biopesticide diversification and expansion on the market. Since the governmental context is very restrictive in authorizing biological pesticides, finding competitive and highly efficient biocontrol strains is still a challenge.
Phosphorus is an essential element for plantgrowth and development. Because of its sparingly soluble nature it is present in very less proportion in the soil for plant uptake. Major proportions of soil-P remains interlocked in various insoluble forms and not available for plant use. To circumvent the P-deficiency, large amount of chemical P fertilizers are applied to attain reasonable crop yields. Indiscriminate use of P-fertilizers deteriorates the soil quality as well as cause negative impact in respect to both environment and economy. Consequently, it is important to search for sustainable strategies to alleviate the detrimental effects of chemical fertilizer on soil. Some bacterial species have a natural potential to solublize the phosphorus. The use of phosphorus solubilizing bacteria (PSBs) as an inoculant simultaneously enhances P availability to plants and crop yield. Present review emphasizes availability and dynamics of soil-phosphorus and the occurrence, mechanism and role of Phosphate solubilizing bacteria in sustainable management of soil by solubilization of fixed-phosphorus in relation to crop responses. This review exhaustively explores the potential of PSB to solublize phosphate by highlighting the current practices and future prospects of their utility in soil management.
With the introduction of high yielding crop varieties and the progressive intensification of agriculture, the soils are getting exhausted in K stock at a faster rate. Many bacteria such as Acidothiobacillus ferrooxidans, Paenibacillus spp., Bacillus mucilaginosus, B. edaphicus, and B. circulans dissolve silicate minerals (e.g., biotite, feldspar, illite, muscovite, orthoclase, and mica) and release K through the production of organic and inorganic acids, acidolysis, polysaccharides, complexolysis, chelation, and exchange reactions (Etesami et al., 2017). Inoculation of seeds and seedlings of different plants with KSB showed significant enhancement of germination percentage, seedling vigor, plantgrowth, yield, and K uptake by plants under greenhouse and field conditions (Anjanadevi et al., 2016; Awasthi et al., 2011; 2013; Meena et al., 2015a and Meena et al., 2014). Inoculation with KSB exerted beneficial effects on growth of pepper and cucumber (Sangeeth et al., 2012), maize (Singh et al., 2010), wheat (Sheng and He, 2006), Sudan grass (Basak and Biswas, 2012; Basak and Biswas, 2010) and Okra (Prajapati et al., 2013). Use of KSB as bio-fertilizers for agriculture improvement can reduce the use of agrochemicals and support ecofriendly crop production (Archana et al., 2013; Archana et al., 2012; Prajapati et al., 2013).
Intense use of agrochemicals, including inorganic fertilizers and pesticides, since “green revolution” of 1960s boosted crop productivity but at the expense of environment and health. This led to the exploration of alternatives to chemical fertilizers and pesticides among scientific communities. Several researches on potential of earthworms to degrade solid organic matter and analysis of worm cast have demonstrated the use of earthworm cast (vermicompost) in sustainable agriculture. Vermicompost is a nutritive organic fertilizer enriched with plant available forms of macro (Nitrogen, Phosphorus and Potassium) and micro (Iron, Copper, Zinc, etc.) nutrients, beneficialsoil microbes; nitrogen-fixing and phosphate solubilizing bacteria, actinomycetes and plantgrowth regulators like auxins, cytokinins and gibberellins. In addition, composition of vermicompost show antagonistic ability against soil-borne pathogens thereby improving plant health. This article presents the importance and use of vermicompost in plantgrowth and protection and provides the insight on vermicomposting research in Nepal.
input and high-yield agricultural practices that do not harm natural ecosystems (Tilman, Cassman, Matson, Naylor, & Polasky, 2002). Application of beneficial microbes that promote plantgrowth is thought to hold potential for reducing the extensive use of chemical fertilizers and pesticides in modern agriculture (Vessey, 2003). Plantgrowth-promoting microbial communities can provide various services to the plant such as protection from pathogen invasion (Hu et al., 2016; Wei et al., 2015), production of plantgrowth hormones (Muhammad Arshad 1991) and mobilization of soil nutrients that would be otherwise inaccessible for plants (Lugtenberg & Kamilova, 2009). Unfortunately, current intensive agricultural practices that depend on high inputs of chemical fertilizers and pesticides are often detrimental to the plant-associated beneficial rhizosphere bacteria and microbial ecosystem functioning (Tsiafouli et al., 2015). While the loss of functionality can be restored by inoculating beneficial microbes into the microbe-poor rhizosphere (Wubs, van der Putten, Bosch, & Bezemer, 2016), this approach is often limited by poor survival of microbial inoculants. In particular, direct antagonism and competition for space and resources with the indigenous microbes can severely limit inoculant establishment and functioning in the rhizosphere (Kadam & Chuan, 2016). In this study, we applied the biodiversity-ecosystem functioning (BEF) framework to test how the richness of a probiotic bacterial community affects its survival and plantgrowth-promotion activity in the tomato rhizosphere in vivo.
hair to curl. Rhizobia then invade the root through the hair tip where they induce the formation of an infection thread as shown in Figure 3. This thread is constructed by the root cells and not the bacteria and is formed only in response to infection. The infection thread develops from the inner primary cell wall, which grows inwards in the form of invagination enclosing bacterial cells. The infection thread further grows inwards and invades the cortex and finally it finds its way into pericyclic region where the end of the infection thread bursts open releasing bacterial cells. As the infection grows inwards bacterial cells multiply by cell division and the process of multiplication continues even after they are released into the host cells. Bacterial cells assume various shapes and also they aggregate into groups. Such bacterial clusters surrounded by a thin membrane are called bacteroids.
Phytohormone, especially indole-3-acetic acid plays an important role in the plantgrowth regulation like cell enlargement, cell division, cell elongation and root initiation by tryptophan dependent and independent pathways . Rhizospheric colonization of cereal crop plants and plantgrowth promoting activity involving indole-3-acetic acid (IAA) production by Klebsiella sp. and Bacillus sp. has been well documented [4, 6, 7]. Klebsiella species have been isolated and studied for IAA production from rhizosphere of sugarcane , soya bean , rice , pearl millet  and Kentucky blue grass . Iodole acetic acid (IAA), a phytohormone, is produced in young leaves and stems from transamination and decarboxylation reactions of tryptophan . Effect of IAA on plants are significant and some of them are promotes cambial activity, delays in abscission of leaves and induces flowering and fruits production . Therefore, IAA has much importance in plantgrowthpromotion as well as soil fertility and here the present study is conducted to isolate the potential IAA producing bacterial strain from forest soil samples around different places of Paderu Mandal, Visakhapatnam District, India. The potent IAA producing bacteria is further characterized by 16S rRNA sequence. 2. MATERIALS AND METHODS
Mansoureh Sadat et al (2012)  also reported that Pseudomonas fluorescens forms a major constituent of Rhizobacteria that encourage the plantgrowth through their diverse mechanisms. In this investigation, 20 strains of Pseudomonads isolated from the rhizosphere soils of paddy areas in Malaysia and were screened for their plantgrowth promoting activity. All the 20 tested isolates of Pseudomonads were positive for the production of siderophores and HCN, while of the 20 antagonist bacteria strains, 15 strains (75%) showed positive for the production of plantgrowth-promoting hormone, IAA. All the twenty bacterial isolates (except DL21) inhibited the pathogen in the dual culture assay. Following API 20NE biochemical identification kit, of the 20 isolates, 15 strains were identified as Pseudomonas fluorescens, 3 isolates belong to the species of P.luteola, one isolates to the P.aeruginosa.
for plants (Upadhyay et al., 2017). Thus, it is the need of the hour to restore soil properties as well as plantgrowth using microbes.As toxic metal tolerance is one of the vital factors for utilization of native micro-flora in bioremediation. Thus, estimation of Cr(VI) tolerance of 14 bacterial isolates has been carried out in previous study of Pattnaik et al., (2017). In present study, these bacterial isolates were subjected to IAA production using both qualitative and semi-qualitative methods. Among all, bacterial isolates such as Bacillus sp. CTSI-07, Enterobacter sp. CTWI-06 and Acinetobacter sp. CTWI-07 produced approximately 24 µg/ml, 114 µg/ml and 106 µg/ml of IAA respectively (Figure 1; Table 1). In contrast to findings of present study, Upadhaya et al., (2017) reported production of IAA (56.95 µg/ml) by the chromium resistant bacteria Bacillus sp. MNU16 isolated from contaminated coal mining soil. Similar IAA producing metal tolerant bacteria such as Pantoea stewartii strain ASI11, Microbacterium arborescens strain HU33 and Enterobacter sp. strain HU38 were also isolated from rhizospheric soil of P. juliflora (Khan et al., 2015). Thus, utilization of these metal resistant
biological control agents such as predatory fish, bacteria, protozoa, fungus and nematodes had shown promising results to control mosquito populations (Murugesan et al., 2009). The development of new strategies, including naturally occurring larvicides to control mosquitoes, is important in order to counter the evolution of resistance in target populations and the possible effects on non target organisms (Cetin and Yanikoglu, 2006). Vector control is a necessary and effective means for scheming transmission of vector-borne diseases, especially in areas where resistance in parasite to drugs is growing. Unlike insecticides, bio-control agents are host specific, safer to the environment, find easy application in the field, are cost-effective in production, lack infectivity and pathogenicity in mammals including man and has little evidence of resistance development in target mosquito species.
Biological control of bacterial wilt is still in its research stage, with few studies reported by Messiha (2007). Biological control not only increases yield and decreases disease severity, but also avoids environmental pollution by chemicals. Among plant pathogens, soil borne pathogens are considered to be more limiting than seed borne or air borne pathogens in the production of numerous crops and reported for 10–20% of yield losses yearly (Yuliar et al. 2015). Management of bacterial wilt in tomato has been difficult and it still threatens commercial tomato production (Coll and Valls 2013).The environmental pollution caused by extreme usage of agrochemicals (Fertilizers
The miscellaneous microorganisms are associated with plants which play a momentous role in plant defense responses. Endophytes spend the whole or at least a part of their life cycle colonizing in the healthy living tissue of the host plant, typically causing no obvious symptoms of disease. The Abelmoschus esculentus plant part (leaves) was utilized to isolate bacterial endophytes. 20 bacterial colonies with different colony morphology were selected from different plates for differential staining and biochemical tests (MR-VP, starch, oxidase, catalase, citrate, motility, cetrimide test etc.) Around 3 colonies were selected based on their plantgrowth promoting Activity (PGPA) which includes phosphate solubilization, Ammonia production, IAA production, Siderophore production, HCN production. From the results obtained through PGPA, a single endophyte was molecular characterized using 16srRNA sequencing. The bacterial endophyte was identified as Pseudomonas sp. The selected endophyte was mixed with carrier sugarcane bagasse, applied to plants and the growth parameters were observed high in endophyte applied plants.
3. Role in Industry and Medicine: Bacteria play very important roles in various industrial products. The products obtained as a result of bacterial activities cannot be chemically prepared [26, 29]. For example, ethyl alcohol and butyl alcohol are manufactured by the bacterial activities in the sugar solution, e.g., clostridium acetobutylicum. Vinegar is prepared by the activities of Acetobacter aceti in the sugarcane juice. The preparation of butter, cheese etc. is also done by bacteria. The Lactobacillus lactis is responsible for souring of milk resulting in curd preparation. Bacterial activities also impart the typical flavors. Typical types of bacteria are cultured for this purpose, e.g., micrococcus. Fibers from the hemp are isolated after rotting the stems by activity of bacteria (e.g., clostridium butyricum). The hairs and fats are removed from the skin by the action of bacteria in the leather industry. According to Sir Alexander Fleming, the growth of harmful staphylococcits is checked by penicillium natatum. This has led to the production of various types of antibiotics being used in treatment.
Cover crops are defined as the crops which are used to cover the ground surface. These crops are precisely grown to protect the soil from erosion and prevent loss of nutrients in deep layers through leaching and surface runoff  . Cover crops are planted between main crops to improve agriculture production and productivity. Basically, cover crops revolve around legumes which are cultivated to cover the surface of the soil and helpful in improving physical, chemical and biological soil properties. Ideal cover crops should germinate and emerge quick- ly, be tolerant to adverse climatic conditions, be able to fix atmospheric nitrogen from the air, absorb nutrients from soil by developing deep roots, produce high- er amount of biomass in shorter period, be easy to work and cultivate, not com- pete with main crop, be tolerant to insect-pest and diseases, have ability to sup- press weeds, and be cost-effective for cultivation . Cover crops have been well known for decades defining the benefits for the environment and farming community   . No tillage system (NTS)  is a soil management tech- nique that increases soil organic matter  accumulation, reduces soil distur- bance and can increase crop yield . The SOM can be increased by growing cover crops under an NTS . Approximately half of the agriculture area in Bra- zil has practiced no tillage system . Interest is growing in using cover crops to improve crop production and soil quality in worldwide including Brazil .
The bacterium promoted initial root system effect, perhaps due to greater endophytic colonization initially in the roots, as this just bacterium infects roots, stalks and leaves of grasses, not being found in leaves of sugar cane . However, the mechanisms of these beneficial associations between plants and the bacterium Herbaspirillum frisingense are still little known. Working with different diazotrophic bacteria, , stated that the positive interaction of the bacteria with the root growth of Brachiaria brizantha plants that can contribute to the improvement of the global acquisition of nutrients and water to the plant and the production of biomass.
Phosphorus in soil is important for plant development, and the lack of P limits plantgrowth. Although chemical fertilizers are added to the soils, plants can only utilize low amounts of phosphatic fertilizers. In this case, the selection of highly efficient PSB will practically increase phosphorus in plant rhizosphere. Various PSB have been isolated from different plant roots (Sundara-Rao and Sinha, 1963; Yu et al., 2011). In the present study Out of 128 samples analyzed, total 34 isolates were isolated from salinity affected soils in Amravati district (Daryapur, Bhatkuli, and Anjangaon tahshil). Out of 34 isolates 21 PSB and 13 fungi were found, but only 3 fungi species showed significant zone of P solubilization. Among 21, only 8 PSB bacterial culture showed variation and others were repeated. A clear halo zone was formed around the colonies after 2 days of incubation on solidified Pikovaskaya`s agar plates and all phosphate solubilizing bacteria and fungi were selected and sub cultured on Pikovaskaya`s agar plates for further studies.. That is Bacillus cereus, Bacillus megaterium, Bacillus subtilis, Bacillus polymyxa, two pseudomonas spp., Micrococcus spp., Enterobacter spp., fungi (Aspergillus spp., Penicillium spp. and tricoderma spp.) Out of this isolate fungi (Aspergillus spp., Penicillium spp. and tricoderma spp.) having
Studies have shown that probiotic bacteria or so-called human-friendly bacteria are a group of organisms which have certain requirements and specifications to stay alive during their journey in the gut of man until they reach the last part of the small intestine, and studies have shown that this group has a significant impact on improving human and public health as well as help the body to resist many diseases and some of the most important strains of these bacteria are Lactobacillus and Bifid bacterium which were used to produce many dairy products raised on Worldwide for their important benefits. So the study focused on probiotic bacteria. The study was divided into two main parts. First: the definition of probiotic bacteria isolated from fermented milk products. Second: the preparation of some probiotic extracts from certain herbs and nutrients from the local environment to improve and increase the productivity of probiotic bacteria and comparison between these sources to identify the best materials and which have the capacity to improve the dynamic growth of these friendly bacteria through study. There was first: Isolation and identification of each of the bacteria Streptococcus. saccharolyticus, Bifidobacterium.sp, and Lactobacillus acidophilus. As well as the yeast Saccaromycess .sp was isolated by definition tests such as dye test gram – movement of bacteria tests –oxidize catalase test or the analytical profile index (API). Second: water extracts were prepared from sources which are Green tea – turmeric – naekhh – cloves – sage-Mint-Ginger-carobs (spectrophotometer) and it was found that the three best extracts in improving growth of bacteria probiotics were cloves then green tea followed by carob compared to the control sample grown on the liquid environment of the growth of probiotic bacteria MRS.