Endophytic bacteria and their potential to enhance heavy metal phytoextraction

Plant endophytic bacteria have received special attention in recent decades for their ability to improve plant response to multiple stresses. A positive effect of endophytes on plant’s ability to cope with drought, salinity, nitrogen deficiency, and pathogens have already been demonstrated in numerous studies, and recently this evidence was consolidated in a meta-analysis of published data. Endophytic bacteria have also been implicated in increasing resistance to heavy metals in plants; despite the important biotechnological applications of such effect in heavy metal bioremediation and agriculture, efforts to systematically analyze studies in this field have been limited. In this study, we address this task with the objective of establishing whether the findings made for other types of stresses extend to the response to heavy metals. Specifically, we seek to establish if plant inoculation with plant-growth promoting endophytic bacteria have an impact on their tolerance to heavy metal stress? We carried out a meta-analysis of the effect size of inoculation with endophytic bacteria on the host plant biomass in response to heavy metal stress (aluminum, arsenic, cadmium, copper, chromium, manganese, nickel, lead, and zinc), which included 27 (from 76 published in the last 10 years) studies under controlled conditions that evaluated 19 host plants and 20 bacterial genera. Our results suggest that endophytic bacteria increase the biomass production of host plants subjected to different heavy metals, indicating their effectiveness in protecting plants from a wide range of metal toxicities. Stress mitigation by the bacteria was similar among the different plant groups with the exception of non-accumulating plants that benefit most from the symbiotic association. Host identity and heavy metal concentration seem to influence the effect of the bacteria. Our analysis revealed that bacterial consortia provide the greatest benefit although the most common biotechnological applications are not directed towards them, and support the value of endophytic bacteria as an alternative to mitigate heavy metal stress in a wide variety of hosts.

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Heavy Metal Resistance by Endophytic Bacteria Isolated from Guava (Psidium Guajava) and Mango (Mangifera Indica) Leaves

International Annals of Science ◽

10.21467/ias.9.1.16-23 ◽

2019 ◽

Vol 9 (1) ◽

pp. 16-23

Author(s):

Maryam Lami Riskuwa-Shehu ◽

Haruna Yahaya Ismail ◽

Udem Joshua Josiah Ijah

Keyword(s):

Heavy Metals ◽

Heavy Metal ◽

Endophytic Bacteria ◽

Mangifera Indica ◽

Bacterial Species ◽

Heavy Metal Resistance ◽

Psidium Guajava ◽

Metal Resistance ◽

Resistant Bacteria ◽

Mango Leaves

Heavy metal resistant bacteria are widespread in nature and their application in decontamination of polluted ecosystems is promising. In this study, ability of endophytic bacteria isolated from Psidium guajava (Guava) and Mangifera indica (Mango) for heavy metal resistance was assessed. Leaves samples form the two plants were collected and processed according to the standard laboratory practices. Heavy metals were analyzed using Atomic absorption spectrophotometer. Endophytic bacteria were isolated and identified using morphological and biochemical characteristics; heavy metal resistance was determined by plate dilution method. Heavy metal analysis revealed that the leaves samples contained considerable quantities of Manganese (Mn), Lead (Pb) and Cadmium (Cd) ranging from 1.21±1.6 mg/Kg (for Cd in Guava leaves) to 116.58±1.3 mg/Kg (for Mn in Mango leaves). A total of six bacterial species were isolated from both of the plants leaves (3 each). Guava endophytes were identified as Streptococcus sp, Staphylococcus albus and Staphylococcus seiuri whereas Staphylococcus aureus, Staphylococcus xylulose and Staphylococcus intermedius were from Mango leaves. The identified isolates were tested for ability to resist heavy metals in-vitro and were capable of showing different patterns of resistance to MnCl2, PbCl2 and CdCl2. All the endophytes were highly resistant to PbCl2 followed by MnCl2 but susceptible to CdCl2. The ability of plants and bacterial endophytes understudy to tolerate or resist heavy metals is a good indication of their phytoremediation potentials and thus, should be harnessed.

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Metal Resistant Endophytic Bacteria Reduces Cadmium, Nickel Toxicity, and Enhances Expression of Metal Stress Related Genes with Improved Growth of Oryza Sativa, via Regulating Its Antioxidant Machinery and Endogenous Hormones

Plants ◽

10.3390/plants8100363 ◽

2019 ◽

Vol 8 (10) ◽

pp. 363 ◽

Cited By ~ 14

Author(s):

Rahmatullah Jan ◽

Muhammad Aaqil Khan ◽

Sajjad Asaf ◽

Lubna ◽

In-Jung Lee ◽

...

Keyword(s):

Heavy Metal ◽

Endophytic Bacteria ◽

Synergistic Effects ◽

Heavy Metal Concentration ◽

Heavy Metal Stress ◽

Metal Stress ◽

Metal Hyperaccumulation ◽

Bacterial Strains ◽

Fresh Weight ◽

Ni Accumulation

The tolerance of plant growth-promoting endophytes (PGPEs) against various concentrations of cadmium (Cd) and nickel (Ni) was investigated. Two glutathione-producing bacterial strains (Enterobacter ludwigii SAK5 and Exiguobacterium indicum SA22) were screened for Cd and Ni accumulation and tolerance in contaminated media, which showed resistance up to 1.0 mM. Both strains were further evaluated by inoculating specific plants with the bacteria for five days prior to heavy metal treatment (0.5 and 1.0 mM). The enhancement of biomass and growth attributes such as the root length, shoot length, root fresh weight, shoot fresh weight, and chlorophyll content were compared between treated inoculated plants and treated non-inoculated plants. Both strains significantly increased the accumulation of Cd and Ni in inoculated plants. The accumulation of both heavy metals was higher in the roots than in the shoots, however; Ni accumulation was greater than Cd. Heavy metal stress-responsive genes such as OsGST, OsMTP1, and OsPCS1 were significantly upregulated in treated non-inoculated plants compared with treated inoculated plants, suggesting that both strains reduced heavy metal stress. Similarly, abscisic acid (ABA) was increased with increased heavy metal concentration; however, it was reduced in inoculated plants compared with non-inoculated plants. Salicylic acid (SA) was found to exert synergistic effects with ABA. The application of suitable endophytic bacteria can protect against heavy metal hyperaccumulation by enhancing detoxification mechanisms.

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