Potential of hexavalent chromium-resistant rhizosphere bacteria in promoting plant growth and hexavalent chromium reduction

Abstract

This research aimed to evaluate three Cr(VI)-resistant rhizosphere bacteria (Bacillus cereus, Bacillus aerius and Exiguobacterium profundum) for their ability to produce plant growth-promoting (PGP) substances and to remove Cr(VI). Three rhizosphere bacteria were characterized for their ability to produce several PGP substances, including ammonia and indole-3-acetic acid (IAA) and solubilized phosphate. The Cr(VI)-1 reduction ability of the rhizosphere bacteria was determined by diphenylcarbazide method with 60 mg l Cr(VI). Bioreduction of Cr(VI) in the reduction media by B. cereus was 13.7%, which was higher compared with those of B. aerius (4.4%) and E. profundum (3.6%). B. aerius adsorbed high Cr(VI)-1 concentration of 56.1 mg g. The best condition for these rhizobacteria to remove or adsorb Cr(VI) was at-1 acidic pH (5.36-5.97). All rhizobacteria could not stand the toxic effect of Cr(VI) at 60 mg l , which decreased almost 100% of rhizobacteria growth. B. cereus and B. aerius produced PGP substances, including ammonia and IAA and solubilized phosphate. B. cereus and B. aerius with high PGP activities can be considered promising agents in microbe-assisted phytoremediation. All rhizosphere bacteria tolerated Cr(VI) and protected plants against the inhibitory effect of Cr(VI) by reducing Cr(VI) to Cr(III) and assisting the plant uptake of Cr(III). Bioreduction, Hexavalent chromium, Plant growth-promoting rhizobacteria, Rhizobacteria, Scirpus grossus Potential of hexavalent chromium-resistant rhizosphere bacteria in promoting plant growth and hexavalent chromium reduction

Practical limitations of bioaugmentation in treating heavy metal contaminated soil and role of plant growth promoting bacteria in phytoremediation as a promising alternative approach

“…He et al., 2020 ; Manoj et al., 2020 ). These combination actions are a mutual symbiosis, in which plants receive benefits from the ability of bacteria to provide suitable growth condition for plants while bacteria benefit from available nutrients from plant's exudates for its enzymatic reaction and suitable living environment leading it to exhibit phytostimulation mechanism ( Jin et al., 2019a , Jin et al., 2019b ; Kamaruzzaman et al., 2019 ; Purwanti et al., 2020 ).

Figure 3 General properties of plant growth promoting bacteria (PGPB).

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“…Performance of PGPB that is reproduced gradually by time in new environment also depends on its resistivity to environmental changes including competition between native microbial community ( Kong et al., 2019 ). Different species of bacteria involve and react differently in plant–microbe symbiosis as not every single species of bacteria can perform simultaneously as toxicity reducer and growth promoter ( Kamaruzzaman et al., 2019 ; Mello et al., 2020 ).…”

“…Indirect PGPB mechanism is not involved directly in plant growth, but it helps by providing better growing condition and reducing stresses caused by biotic and abiotic factors such as temperature, metal toxicity, and organic pollutants ( Manoj et al., 2020 ; Novo et al., 2018 ). PGPB produces biocompounds such as antibiotic, lytic enzymes, and siderophores to suppress phytopathogen, thus proving better growth environment ( Novo et al., 2018 ; Kamaruzzaman et al., 2019 ).…”

Role of Salvinia molesta in biodecolorization of methyl orange dye from water

“…In comparison, phytoremediation is a promising approach to protect the aquatic environment, based on a plant's ability to degrade, absorb, transform, and remove organic pollutants in water 8,9 . This technology has been widely used to degrade or remove different types of pollutants, including heavy metals [10][11][12][13] , hydrocarbons [14][15][16][17] and nutrients [18][19][20][21] . Phytoremediation of textile dyes has been an alternative treatment due to its inexpensive and eco-friendly approach and the lower amount of sludge produced 22,23 .…”

Biosorption of Heavy Metals from Synthetic Wastewater by Using Macro Algae Collected from Iraqi Marshlands

“…The heavy metal pollution has been recognized as a serious problem because these metals are non-biodegradable elements and they have a great danger to human, animals and plants (He and Chen, 2014;Huang et al, 2016;Gong et al, 2019). Biosorption could be defined as the ability of biological materials such as bacteria (Titah et al, 2019, Titah et al, 2018Purwanti et al, 2019), plants (Ismail et al 2019; Kamaruzzaman et al 2019) and algae (Deng et al, 2007) to adsorb heavy metal ions from aqueous solutions by the physico-chemical pathways of uptake. The conventional treatments used for metals removal, such as chemical precipitation, membrane separation, evaporation, electro winning or resin ionic exchange, could be very expensive, and sometimes not effective enough (Aydın and Bulut, 2008).…”