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International Journal of Research and Review Vol.7; Issue: 3; March 2020 Website: www.ijrrjournal.com Review Article E-ISSN: 2349-9788; P-ISSN: 2454-2237

Mycorrhiza Helper : Future Prospects

Subash Kumar Gupta1, Arka Pratim Chakraborty2

1Assistant Professor, Department, Gyan Jyoti College, Siliguri-734003 West Bengal (India) 2Assistant Professor, Botany Department, Raiganj University, Uttar Dinajpur-733134 West Bengal (India)

Corresponding Author: Subash Kumar Gupta

ABSTRACT rhizobacteria (PGPR), such as sp. Another factor that complicates the helper bacteria (MHB) are a group distinction of the two terms (PGPR and of organism that selectively promotes the MHB) is that studies with PGPR generally establishment of mycorrhizal . The exclude the evaluation of mycorrhization. establishment of mycorrhizal symbioses can be However, it is interesting to note that some positively influenced by certain bacterial isolates, an effect exhibited by mycorrhiza fungal signaling pathways are mutually helper bacteria. Nowadays MHB are considered regulated by different rhizobacteria, while as growth promoting rhizobacteria others are specific to some MHB. (PGPR). There are potential practical According to Garbaye, the MHB are not application of mycorrhiza helper bacteria in plant specific, but are clearly selective about agriculture and forestry. On the basis of the fungal , and the term - scientific and practical interests, supported by specific can be used. Among the development of genomics, may represent a ectomycorrhizal fungi, only basidiomycetes unique opportunity to place MHB at the have been described to be interacting with forefront of future mycorrhiza research and to MHB. boost the more general field of fungal-bacterial MHB are the best studied inhabitants interactions in and for the benefit of mankind. of the . Although most studies of MHB have been conducted in Keywords: Mycorrhiza, symbioses, genomics, ectomycorrhizal systems, MHB have also ecosystems, fungal. been shown to occur in arbuscular symbioses. In ectomycorrhizal systems, INTRODUCTION MHB have been isolated from the 'Mycorrhiza helper bacteria' (MHB) mycorrhizospheres of many -fungus was first coined to refer only to bacteria that symbioses in nursery, plantation and semi promote the establishment of the - natural situations. Garbaye (1994) proposed fungus symbiosis, or bacteria associated five main mechanisms by which MHB with and mycorrhizal fungi that could promote mycorrhiza formation, selectively promote the establishment of although to date there has been little robust mycorrhizal symbiosis. The establishment evidence for the relative importance of any of mycorrhizal symbioses can be positively of them. Most evidence for MHB influenced by certain bacterial isolates, an mechanisms has been gathered from in vitro effect exhibited by mycorrhiza helper studies of the interactions between bacteria. The MHB include a variety of mycorrhizal fungi and bacteria or their Gram-negative and Gram-positive species metabolites in the absence of the plant, usually associated with mycorrhizal although there is evidence that some MHB symbiosis. Many MHB are considered require close proximity or contact with the nowadays as plant growth promoting plant to exert MHB effects. [1]

International Journal of Research and Review (ijrrjournal.com) 387 Vol.7; Issue: 3; March 2020 Subash Kumar Gupta et.al. Mycorrhiza helper bacteria: future prospects

Occurrence of mycorrhiza helper symbioses are formed by a large number of bacteria fungal species, mainly Basidiomycetes, but There are different types of mycorrhizal also Ascomycetes. The fungus forms a symbiosis, the arbuscular mycorrhizal one mantle which encloses the root. Some being the most common and the most hyphae extend to the surrounding ; frequent all over the world. The arbuscular others pass between the epidermal and mycorrhizal symbiosis is formed by cortical cells and form the so-called Hartig obligately symbiotic fungi from the net, the site for nutritional exchange . Colonization of plant roots between the fungal and plant cells. Many by arbuscular mycorrhizal fungi is achieved bacterial strains have been reported to be via and mycelia originating from able to promote either arbuscular or infected roots. The hyphae enter the root ectomycorrhizal. [2,3] Many plant models tissues and develop inter- and have been used to study the MHB effect intracellularly, forming running hyphae, (Table 1). coils and arbuscules. Ectomycorrhizal

Table 1: The list of mycorrhiza helper bacteria found in ectomycorhiza Mycorrhizal Identity of the Host plant Ecological origin of Effect of MHB References fungi MHB isolates MHB isolates Amanita Streptomyces Picea abies, A. muscaria- containing 1.2-1.7-fold increase in the muscaria, Pinus sylvestris spruce stand second- order root mycorrhizal [4] bovines rate Pseudomonas Pseudostuga L. laccata sporocarps 1.2-1.4- fold increase in the [3] bicolor/ fluorescens, menziesii and ectomycorrhizal infection laccata Pseudomonas sp., Bacillus sp. Laccaria Bacillus sp., Eucalyptus Sporocarps and 1.8-3.9 fold increase in the [5] fraterna, Pseudomonas diversicolor ectomycorrhizae of L. ectomycorrhizal infection Laccaria sp. fraternal laccata Lactarius rufus sp., Pinus sylvestris L. rufus 1.9-2.4- fold increase in the [6] Burkholderia sp. ectomycorrhizal infection Pisolithus alba Pseudomonas Acacia 2.2- fold increase in the monteilii, holosericea ectomycorrhizal infection [7] Pseudomonas resinovorans Pisolithus sp. Fluorescent Acacia Rhizosphere, 1.7-2.3- fold increase in the pseudomonads holosericea mycorrhizosphere, galls ectomycorrhizal infection [8] Rhizopogon Unidentified bacterial Pinus radiate Rhizopogon luteolus 1.2-2.3- fold increase in the luteolus isolates ectomycorrhizas ectomycorrhizal infection [9] Different Pseudomonas monteilii Different Rhizosphere, 1.4-2.8-fold increase in the species of Acacia species ectomycorrhizal infection [10] Scleroderma and Pisolithus Bacillus Pinus sylvestris S. luteus 2.1 fold increase in the ectomycorrhizas percentage of arbascular [11] mycorrhizal infection of the root

Multiple mechanisms exhibited by germination by eroding walls by mycorrhiza helper bacteria producing stimulatory compounds such as The of mycorrhization both CO2 and other volatiles, or by influencing ecto and endo are dependent upon helper AMF acquisition. Root bacteria. Bacteria associated with AMF exudation could enhance spore germination spores colonize mainly the outer wall layer by stimulating the growth of bacteria and rarely penetrate into the inner layers. beneficial for AMF. Lehr et al. [12] found Nevertheless, some bacteria have been that Streptomyces sp. AcH505 acting as found in the of AMF spores. The MHB suppressed the plant defence role of AMF spore associated bacteria is not response. Streptomyces sp. AcH505 acts as clear. They could stimulate spore an MHB by expressing a combination of

International Journal of Research and Review (ijrrjournal.com) 388 Vol.7; Issue: 3; March 2020 Subash Kumar Gupta et.al. Mycorrhiza helper bacteria: future prospects mechanisms which add to existing symbiosis. It twas reported a relationship signalling mechanisms operating between between the mycorrhizal formation on the mycorrhizal fungus and plant symbionts. Pseudotsuga menziesii (Douglas fir) and The metabolite, auxofuran, appears to Pseudomonas fluorescens BBc6, where stimulate presymbiotic growth of the there was a decrease in mycorrhizal fungus, adding to the action of root-derived colonization with increasing bacterial doses. metabolites which direct growth of [15] mycorrhizal hyphae towards the root. MHB Paenibacillus spp. has been shown promote the establishment of symbiosis by to be capable of degrading complex stimulating mycelial extension; increasing . For instance, the production root-fungus contacts and colonization; and of cellulolytic , such as xylanases reducing the impact of advers and cellulases that degrade insoluble environmental conditions on the polysaccharides (cellulose and xylan) by of the mycorrhizal fungi. Using established Paenibacillus curdlanolyticus. microbiological techniques, the screening process showed the presence of bacteria species from Firmicutes, Actinobacteria, Alphaproteobacteria and gammaproteo- bacteria represented by six genera namely - Bacillus, Paenibacillus, Curtobacterium, Rhizobium, Enterobacter and Strenotrophomonas. Among the isolates, Bacillus and Rhizobium have been previously reported as potential MHBs. [13,14] The major hypotheses by Garbaye Fig.1: Simplified representation of the rhizosphere (1994) provide evidence for a multitude of pointing out five possible ways by which a bacterium can MHB mechanisms (Fig. 1). A direct effect promote mycorrhizal establishment: (1) effect on the root receptivity to mycorrhizal fungi; (2) effect on the root- of the helper bacteria on the root receptivity fungus recognition and attachment; (3) effect on the fungus to mycorrhizal fungi has been frequently survival and growth; (4) effect on the physico-chemical evoked in the different papers that deal with properties of the soil; and (5) effect on the germination of fungal propagules. [16] the mechanisms of the mycorrhiza helper effect. However, the main mechanism Close associations of Rhizobium favoured so far in all these studies is the with mycorrhizal have previously direct effect of helper bacteria on the been described (Garbaye, 1994) to indirectly presymbiotic survival and growth of the influence mycorrhizal formation. The mycorrhizal fungi in the soil (Founoune et isolation of a close relative of Rhizobium al. 2002). At the molecular level, this from the ascocarp harvested could have mechanism likely relies on the modification originated from leguminous such as of the fungal use efficiency and on Acacia erioloba at the site of ascocarp the regulation of the fungal cycle by the collection. The isolation of Rhizobium from helper bacteria. Little is known about the T. borchii ascocarps was previously signal molecules produced by the helper reported. Similarly, fixation was bacteria, the fungal factors that recognize confirmed by in Tuber magnatum. [17] The the bacterial signal molecules as well as the significant stimulatory effect of Rhizobium fungal networks underlying the tropici on the growth of K. pfeilii mycelium fungal–bacterial interactions. It was could be attributed to their capability to demonstrated the involvement of bacterial supply the nitrogen requirement of the Nod factors in the helper effect of fungus. Some fungal regulated were japonicum on the discovered in Pseudomonas aeruginosa mosseae–soybean endomycorrhizal during their investigation of the

International Journal of Research and Review (ijrrjournal.com) 389 Vol.7; Issue: 3; March 2020 Subash Kumar Gupta et.al. Mycorrhiza helper bacteria: future prospects pathogenicity of the bacterium on the undoubtedly benefit the other research areas Candida albicans fungus. [18] reported that where fungal–bacterial interactions play a Bacillus megaterium EG24 and other major practical and economical role. More isolates of Bacillus, identified on the basis work on mycorrhiza helper bacteria should of 16S rDNA sequencing showed cellulase, be dedicated to model mycorrhizal fungi pectinase and activities. These that are of obvious commercial interest as bacteria associated with spores of well as being of use as research laboratory Gigaspora margarita showed their models. In addition, growing concern about potentiality for stimulating root mycorrhizal the pollution of , and the resulting trend stimulation and seedling growth of neem towards reducing the input of chemicals in plant plant production, should foster more Applied prospects of mycorrhiza helper environmentally friendly practices such as bacteria in future controlled mycorrhization or microbial As it proven that the potential bioremediation, for instance by using practical application of mycorrhiza helper mycorrhizal fungi as carriers of depolluting bacteria in agriculture and forestry, there is bacteria. [20] MHB helps mycorrhiza a need for the identification of new establish symbiotic associations in stressful screening criteria allowing a quick and environments such as those high in toxic efficient selection of performing bacterial metals. In harsh environments, the bacteria isolates. The screening strategies used so far assist in acquiring more such as are too time‐consuming. Therefore, any nitrogen and phosphorus. MHB helps to molecular approach leading to identify prevent the uptake of toxic metals including fungal marker genes, such as master lead, , and cadmium. The bacteria regulators specific for the mycorrhiza helper decrease the amount of metals taken up by effect, will have crucial practical outputs, the plant and also promote detoxifying soil. especially for the improvement of tree This converging of scientific and practical yields in poor forest soils [19] can interests, supported by the development of undisputably be considered as pioneers in genomics, may represent a unique the analysis of the molecular mechanisms opportunity to place MHB at the forefront underlying the interactions between helper of future mycorrhiza research and to boost bacteria and mycorrhizal fungi. However, the more general field of fungal-bacterial many complementary studies on different interactions in ecosystems. mycorrhizal fungi are still required in order to identify and validate the preliminary REFERENCES marker genes that have been identified so 1. Garbaye J. Helper bacteria: a new far. In parallel to these studies, one should dimension to the mycorrhizal symbiosis pay attention to the research on fungal– (Tansley Review, 76). New Phytologist 1994; 128: 197-210. bacterial interactions presently developing 2. Johansson JF, Paul LR, Finlay RD. in other fields, such as plant protection and Microbial interactions in the medicine. Comparing the mycorrhizal mycorrhizosphere and their significance for fungus genes differentially expressed in the . FEMS presence of helper bacteria to the ones Ecology 2004; 48: 1-13. identified in these other model systems 3. Duponnois R, Garbaye J. Mycorrhization would allow us to overcome, more helper bacteria associated with the Douglas efficiently, the bottlenecks in studying the fir-Laccarial accata symbiosis: effects in mechanisms of the mycorrhiza helper effect. aseptic and in glasshouse conditions. Conversely, any breakthrough in the Annalesdes Sciences Forestitres 1991; 48: understanding of the mechanisms 239-251. 4. Schrey SD, Schellhammer M, Ecke M, underlying the interactions between helper Hampp R, Tarkka MT. Mycorrhiza helper bacteria and mycorrhizal fungi will bacterium Streptomyces AcH 505 induces

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International Journal of Research and Review (ijrrjournal.com) 391 Vol.7; Issue: 3; March 2020