Journal of ISSN: 2469 - 2786 JBMOA

Bacteriology & Mycology: Open Access
Mini Review
Volume 2 Issue 6 - 2016
Phytoremediation Enhanced with Concurrent Microbial Plant Growth Promotion and Hexavalent Chromium Bioreduction
Vineet Kumar, Rishabh Omar and Shilpa Deshpande Kaistha*
Department of Microbiology, CSJM University, India
Received: September 01, 2016 | Published: November 03, 2016
*Corresponding author: Shilpa Deshpande Kaistha, Assistant Professor, Department of Microbiology, Institute of Biosciences & Biotechnology, CSJM University, Kanpur 208024, UP, India, Tel: +91 9839765491; Email:
Citation: Kumar V, Omar R, Kaistha SD (2016) Phytoremediation Enhanced with Concurrent Microbial Plant Growth Promotion and Hexavalent Chromium Bioreduction. J Bacteriol Mycol Open Access 2(6): 00045. DOI: 10.15406/jbmoa.2016.02.00045

Abstract

Hexavalent chromium (Cr(VI)) is a toxic and carcinogenic heavy metal accumulating in agricultural soils following effluent releases from chromate releasing industries such as tanneries, electroplating, paper and dye manufacturing etc. Cr(VI) is readily taken up by plants and then passed on through the food cycle. Toxic effects of Cr(VI) affect both prokaryotes and eukaryotes primarily by its ability to generate reactive oxygen radicals causing DNA and protein damage. Cr(VI) bioremediation using multifaceted micro-organisms capable of reduction of toxic Cr(VI) to nontoxicderivatives as well as augmented plant growth capable of phytoremediation by production of growth promoting products is currently being exploited.

Keywords: Plant growth promoting organisms; Chromium reduction; Bioremediation; Phytoremediation

Abbreviations

Cr(VI): Chromium VI; PGP: Plant Growth Promoting; Hg: Mercury; Cd: Cadmium; Pb: Lead; Zn: Zinc

Introduction

Contamination of agriculturally arable land with industry derived pollutants including heavy metals such as chromium has affected soil fertility as well plant, animal and human health by indirectly entering the food chain. Hexavalent chromium is a byproduct of tanning, electroplating, wood, dye, paper, glass, ceramic etc. industries and is usually discharged as industrial effluent. Cr (VI) is a toxic, water insoluble form and Cr (III)/Cr(IV) state is water soluble and less toxic form usually required in the form of micronutrients. Chromium and its derivatives have shown to decrease biomass, affect physiological activity, histological alterations leading to mutagenic and carcinogenic effects for plant and animal cells [1-3]. Chromium bioremediation has long being recognized as an economical and ecofriendly solution to the problem [4]. Recent field and in situ studies now provide concrete evidence to the effectiveness of novel bio augmentation strategies that integrate desirable properties to achieve the end goal. One such strategy is to use multifaceted micro-organisms that can concurrently reduce toxic Cr(VI), produce plant growth promoting products that enhance plant growth of species which exhibit phytoremediation properties [5,6].

Discussion

Rhizospheric soil serves as a high concentration root exuded nutrition which attracts large diversity of microbial life depending on physicochemical conditions as well as plant species. Many of these root residents have been shown to serve mutualistic association by enhancing plant growth directly or indirectly via plant growth promoting products (PGP) [7]. These PGP include biocontrol agents such as anti phytopathogenic compounds such as hydrogen cyanide, growth inducing phytohormones such as indole acetic acids, nitrogen fixation, organic acids for phosphate and potassium solubilization, iron chelating siderophores as well as stress relieving compounds such as ACC deaminase, superoxide dismutase [8]. Many of this PGP producing rhizospheric micro-organisms form association known as biofilms on root surfaces [9]. Biofilms are communities of organisms adhering onto a substrate encased in an exopolymeric substance. The biofilm existence confers on its residents high levels of resistance to environmental stressors including chromate [10].

Cr(VI) reducing ability of micro-organisms is attributed to several factors including their ability to form biofilms, presence of extracellular and intracellular chromate reductases and chromate efflux pump [11-13]. Microorganisms catalyze redox reactions by combination of non-enzymatic reduction by bacterial surfaces, exopolymeric substances of the biofilm, and enzymatic extracellular/ intracellular reduction of Cr(VI) to non-toxic Cr(III)/Cr(IV) oxidative state [13].

Plants are also capable of phytoaccumulation, which consists of uptake of Cr(VI) from soil through plant roots, ultimately to shoots where it complexes with organic acids to reduced Cr states [6]. Phytostabilization involves the conversion of toxic Cr to Cr(III) by plant tissues. Based on their strategies of growing in heavy metal contaminated soils, plants are classified as extruders, accumulators and indicators. Use of Cr tolerant plants whose remediation activity can be enhanced by use of PGP rhizospheric organisms has integrated several approaches for finding optimal solutions to the problem of Cr contamination of agricultural soils.

Micro-organisms selected for their Cr reducing ability as well as PGP production enhanced phytoremediation of plants can be developed as effective bioinoculants. The effective use of a PGP producing Cr(VI) reducing Staphylococcus arlette strain in enhancing Triticum aestivum seed germination and in vivo plant growthin upto 500 µg/kg soil Cr (VI) was reported [14].

Application of Cr- resistant bacteria from rhizosphere and endosphere of Prosopisjuliflora were used to enhance the phytoremediation of ryegrass. The inoculation of three isolates to ryegrass (Lolium multiflorum L.) improved plant growth and heavy metal removal from the tannery effluent contaminated soil [15]. Rhodococcus erythropolis MTCC 7905 reduced substantial amounts of Cr(VI) at 10 ËšC and showed plant growth promotion. This isolate offers promise as a bioinoculant to promote plant growth of pea (Pisum sativum) in the presence of toxic Cr(VI) concentration at low temperature [16].

Inoculation of four chromate tolerate rhizobacteria RZB-03 increased Scirpus lacustris biomass by 59 and 104%, while total chlorophyll content by 1.76 and 15.3% and protein content increased by 23 and 138% under 2 µg/ml and 5 µg/ml concentrations of Cr(VI), respectively after 14 days as compared to non-inoculated plant. Similarly, Cr accumulation also increased by 97 and 75% in shoot and 114 and 68% in root of inoculated plants as compared to non-inoculated plants at 2 and 5 µg/ml Cr(VI) concentrations, respectively after 14 days [17].

Microbacterium sp strain SUCR 140 was studied with arbuscularmycorrhizal fungi (AMF-Glomus mosseae, G. aggregatum, G. fasciculatum, and G. intraradices) alone or in combination, on Zea mays in artificially Cr(VI)-amended soil (Soni, Singh, Awasthi, & Kalra, 2014). Presence of Microbacterium sp. SUCR140 reduced the chromate toxicity resulting in improved growth and yields of plants compared to control by lowering bioavailability and mycorrhiza restricting chromate translocation to aerial plant parts [18]. The effects of pretreatment of chromate reducing Microbacterium sp. strain SUCR 140 on P. sativum plant growth, chromate uptake, bioaccumulation, nodulation, and population of Rhizobium was studied. 15 days pretreatment before sowing showed maximum increase in growth and biomass in terms of root length (93%), plant height (94%), dry root biomass (99%), and dry shoot biomass (99 %). Coinoculation of Rhizobium with SUCR140 showed further 117, 116, 136, and 128 % increase, respectively, in root length, plant height, dry root biomass, and dry shoot biomass. The bioavailability of Cr(VI) decreased significantly in soil (61%) and in uptake (36%) in SUCR140-treated plants; the effects of Rhizobium, however, either alone or in the presence of SUCR140, were not significant [19].

Chromium reducing and plant growth promoting Mesorhizobium strain RC3 and Bacillus species PSB10 significantly improved growth, nodulation, chlorophyll, leghemoglobin, seed yield and grain protein of chickpea crop grown in the presence of different concentrations of chromium compared to the plants grown in the absence of bio-inoculant [20,21].

Bioremediation studies with other heavy metals such as mercury (Hg), cadmium (Cd), lead (Pb), zinc (Zn) have also been well studied and reviewed [9]. Many Cr(VI) reducing bacteria are cross tolerant to other heavy metals such as mercury (Hg), lead (Pb), cadmium (Cd), zinc (Zn), nickel (Ni), cobalt (Co) and arsenic (As). Chromate remediation has a higher success rate in comparison to many other heavy metals in that micro-organisms are capable of reducing a toxic Cr(VI) to non toxic Cr(III) and Cr(IV) oxidation states in addition to separation of Cr(VI) from environment by bioadsortion and bioaccumulation [11]. Commercial production and application of biofertilizers or PGP bio formulationsfor sustainable agriculture are already available [7]. Many of the in situ plant bioassay and field experiments with PGP producing Cr(VI) remediating micro-organisms enhanced phytoremediation case studies cited in this review provide promising pilot studies. Development of heavy metal bioremediationbio formulations for commercial applications and marketing of such products to agriculturists as well as industries would be enhanced with academia-user collaborations. Augmenting the scale of phytoremediation methods such that it can be adopted by the chromate pollution causing industries as part of its effluent treatment protocols would be enormous value.

Conclusion

The chromate tolerant rhizobacteria which play an important role in chromium uptake and growth promotion in plant may be useful in development of microbes assisted phytoremediation systems for decontamination of chromium polluted sites. Intensive research is essential in understanding compatibility parameters affecting rhizosphericcolonization as well as factors affecting chromium availability for PGP organisms in plants growing in Cr(VI) polluted soils. Role of genetic engineering in creating custom made bioinoculant consortia to increase efficacy of remediation process as well as allowing effective monitoring of biological activity are currently being explored. Effective bioformulations and carriers for increased life shelf of boinoculants are also areas requiring further investigations. An in depth understanding of the underlying mechanisms wherein PGP producing organisms facilitate chromate uptake and evasion by plants can provide a strong basis for using PGP organism assisted phytoremediation of chromate.

Acknowledgement

Authors are grateful for research facilities provided at IBSBT, CSJM University, Kanpur. VK acknowledges financial support from University Grants Commission, Government of India.

References

  1. Cervantes C, Campos García J, Devars S, Gutiérrez Corona F, Loza Tavera H, et al. (2001) Interactions of chromium with microorganisms and plants. FEMS Microbiol Rev 25(3): 335-347.
  2. Cohen MD, Kargacin B, Klein CB, Costa M (1993) Mechanisms of chromium carcinogenicity and toxicity. Critical Reviews in Toxicology 23(3): 255-281.
  3. Wise SS, Wise JP (2012) Chromium and genomic stability. Mutat Res 733(1-2): 78-82.
  4. Zayed AM, Terry N (2003) Chromium in the environment: factors affecting biological remediation. Plant and Soil 249(1): 139-156.
  5. Ahemad M (2015) Enhancing phytoremediation of chromium-stressed soils through plant-growth-promoting bacteria. Journal of Genetic Engineering and Biotechnology 13(1): 51-58.
  6. Tak HI, Ahmad F, Babalola OO (2013) Advances in the application of plant growth-promoting rhizobacteria in phytoremediation of heavy metals. Reviews of Environmental Contamination and Toxicology 223: 33-52.
  7. Glick BR (2012) Plant growth-promoting bacteria: mechanisms and applications. Scientifica 2012: 1-15.
  8. Zhuang X, Chen J, Shim H, Bai Z (2007) New advances in plant growth-promoting rhizobacteria for bioremediation. Environment International 33(3): 406-413.
  9. Pastorella G (2012) Biofilms: Applications in Bioremediation. In: Lear G & Lewis G (Eds.), Microbial Biofilms: Current Research and Applications. Caister Academic Press, UK, pp. 73-98.
  10. Coleman RN, Paran JH (2008) Biofilm concentration of chromium. Environmental Technology 12(12): 1079-1093.
  11. Joutey NT, Sayel H, Bahafid W, El Ghachtouli N (2015) Mechanisms of hexavalent chromium resistance and removal by microorganisms. Rev Environ Contam Toxicol 233: 45-69.
  12. Ramírez Díaz MI, Díaz Pérez C, Vargas E, Riveros Rosas H, Campos García J, et al. (2008) Mechanisms of bacterial resistance to chromium compounds. Biometals 21(3): 321-332.
  13. Viti C, Marchi E, Decorosi F, Giovannetti L (2014) Molecular mechanisms of Cr(VI) resistance in bacteria and fungi. FEMS Microbiol Rev 38(4): 633-659.
  14. Sagar S, Dwivedi A, Yadav S, Tripathi M, Kaistha SD (2012) Hexavalent chromium reduction and plant growth promotion by Staphylococcus arlettae strain Cr11. Chemosphere 86(8): 847-852.
  15. Khan MU, Sessitsch A, Harris M, Fatima K, Imran A, et al. (2014) Cr-resistant rhizo- and endophytic bacteria associated with Prosopis juliflora and their potential as phytoremediation enhancing agents in metal-degraded soils. Front Plant Sci 5: 755.
  16. Trivedi P, Pandey A, Sa T (2007) Chromate reducing and plant growth promoting activities of psychrotrophic Rhodococcus erythropolis MtCC 7,905. J Basic Microbiol 47(6): 513-517.
  17. Singh NK, Rai UN, Singh M, Tripathi RD (2010) Impact of rhizobacteria on growth and chromium accumulation in Scirpus lacustris L. grown under chromium supplementation. J Environ Biol 31(5): 709-714.
  18. Soni SK, Singh R, Singh M, Awasthi A, Wasnik K, et al. (2014) Pretreatment of Cr(VI)-amended soil with chromate-reducing rhizobacteria decreases plant toxicity and increases the yield of Pisum sativum. Archives Arch Environ Contam Toxicol 66(4): 616-627.
  19. Soni SK, Singh R, Singh M, Awasthi A, Wasnik K, et al. (2014) A Cr(VI)-reducing Microbacterium sp. strain SUCR140 enhances growth and yield of Zea mays in Cr(VI) amended soil through reduced chromium toxicity and improves colonization of arbuscular mycorrhizal fungi. Arch Environ Contam Toxicol 21(3): 1971-1979.
  20. Wani PA, Khan MS, Zaidi A (2008) Chromium-reducing and plant growth-promoting Mesorhizobium improves chickpea growth in chromium-amended soil. Biotechnol Lett 30(1): 159-163.
  21. Wani PA, Khan MS (2010) Bacillus species enhance growth parameters of chickpea (Cicer arietinum L.) in chromium stressed soils. Food Chem Toxicol 48(11): 3262-3267.
© 2014-2016 MedCrave Group, All rights reserved. No part of this content may be reproduced or transmitted in any form or by any means as per the standard guidelines of fair use.
Creative Commons License Open Access by MedCrave Group is licensed under a Creative Commons Attribution 4.0 International License.
Based on a work at http://medcraveonline.com
Best viewed in Mozilla Firefox | Google Chrome | Above IE 7.0 version | Opera |Privacy Policy