Table 4.

Summary of studies on rhizobacterial mechanisms involved in the bioremediation of heavy metal-contaminated soils.

Heavy Metals	Microbes	Host Plant(s)	Proposed Mechanism(s)	References
As	Penicillium aculeatum PDR-4	Sunflower	Phosphatase, siderophore	[267]
Cd	Bacillus sp., Endophytic sp., Rahnella sp., Enterobacter sp., Klebsiella spp., Pseudomonas sp., Arthrobacter sp. TISTR 2220, Agromyces AR33, Brevundimonas Kro13, Ralstonia sp. TISTR 2219, Streptomyces AR17, Variovorax paradoxus L.	Wheat, Mustard, Soybean, Mung bean, Willow, Amaranthus, Sunflower, Basil, Goat willow	Exopolysaccharide production, siderophores	[231,268,269,270,271,272,273,274]
Cd	Bacillus badius L., Cronobacter muytjensii L., Drepanomonas revolute L., Euplotes sp., Pseudomonas azotoformans L., Uronema nigricans L.	–	Biosorption	[275,276,277,278]
Cd	Alcaligenes sp., Bacillus sp., Pseudomonas sp., Rhodococcus sp., and Variovorax sp.	Canola, Sunflower	ACC deaminase activity and reduction in ethylene levels	[68,279]
Co	Enterobacter ludwigii L.	Sunflower	Exopolysaccharide production	[280]
Cr	Aerococcus sp., Bacillus sp., Endophytic sp., Rhizobacteria sp., Staphylococcus sp., Ochrobactrum intermedium L., Pseudomonas aeruginosa L., Pseudomonas pseudoalcaligenes L.	Chickpea, Mesquite, Prosopis, Maize, Sorghum, Wheat, Mung bean, Soybean, Sunflower	Exopolysaccharide production	[271,281,282,283,284,285]
Cr	Bacillus circulans L., Bacillus megaterium L., Cronobacter muytjensii L., Saccharomyces cerevisiae L.	–	Biosorption	[276,286,287]
Cu	Pseudomonas sp., Rhizobacteria sp., Bacillus subtilis L., Brevibacterium halotolerans L., Bacillus pumilus L., Brevibacterium casei MH8a, Paenibacillus polymyxa L., Pseudomonas pseudoalcaligenes L.	Maize, Sunflower, Sorghum, Mustard, Trailing daisy	Exopolysaccharide production, siderophores	[282,288,289,290,291,292]
Cu	Aspergillus flavus L., Cronobacter muytjensii L., Pseudomonas azotoformans L., Drepanomonas revolute L., Euplotes sp., Uronema nigricans L., Pichia guilliermondii L.	Maize, Wheat, Sorghum	Biosorption	[275,276,277,293,294]
Fe	Pseudomonas sp., Psychrobacter sp.	Castor bean	Exopolysaccharide production, siderophores	[295]
Ni	Micrococcus sp., Pseudomonas sp., Psychrobacter sp., Bacillus subtilis SJ-101, Bacillus pumilus L., Rhodococcus erythropolis X79289, Rhodococcus globerulus X80619	Mustard, Alyssum sp., Alpine pennycress, Castor bean, Mung bean, Wheat, Soybean	Exopolysaccharide production, siderophores	[271,295,296,297,298,299]
Ni	Kluyvera ascorbate L. (SUD165), Pseudomonas putida L. (UW4)	Tomato, Canola, Tobacco	ACC deaminase activity and reduction in ethylene levels	[288,300]
Pb	Enterobacter sp., Klebsiella sp., Enterobacter ludwigii L., AgromycesAR33, Bacillus subtilis L., Brevibacterium halotolerans L., Bacillus megaterium HKP-1, Bacillus pumilus L., Penicillium aculeatum PDR-4, Pseudomonas pseudoalcaligenes L., Streptomyces AR17	Sunflower, Mustard, Maize, Sorghum, Goat willow	Exopolysaccharide production, siderophores	[91,231,272,274, 279,280,282,301]
Pb	Aspergillus niger L., Bacillus xiamenensis L., Pseudomonas azotoformans L.	–	Biosorption	[277,293,302]
Zn	Enterobacter sp., Klebsiella sp., Pseudomonas sp., Rahnella sp., Rhizobacteria sp., Psychrobacter sp. Agromyces AR33, Bacillus megaterium HKP-1, Bacillus subtilis L., Brevibacterium halotolerans L., BrevibacteriumcaseiMH8a, Bacilluspumilus L., Enterobacter ludwigii L., Streptomyces AR17	Mustard, Sunflower, Castor bean, Maize, Sorghum, Goat willow,	Exopolysaccharide production, siderophores	[272,279,280,282,291,295,303]
Zn	Cronobacter muytjensii L., Drepanomonas revolute L., Euplotes sp., Uronema nigricans L.	–	Biosorption	[275,276]