Chromium Hyper-Tolerant Bacillus sp. MH778713 Assists Phytoremediation of Heavy Metals by Mesquite Trees (Prosopis laevigata)

Abstract

Heavy metal accumulation in mesquite trees ( Prosopis laevigata ) growing in aluminum, titanium, chromium and zirconium-polluted soils of a semi-arid region in Mexico was investigated using wavelength dispersive X-ray fluorescence analysis. The results showed that P. laevigata trees can hyper accumulate up to 4100 mg/kg of Al, 14000 mg/kg of Fe, 1600 mg/kg of Ti, 2500 mg/kg of Zn, but not chromium, regarding high chromium concentrations found in soils (435 mg/kg). Since plant-associated microorganism can modulate phytoremediation efficiency, the biodiversity of P. laevigata associated bacteria was studied. Eighty-eight isolates from P. laevigata nodules were obtained; all isolates tolerated high concentrations of Al, Fe, Zn and Cr in vitro . The top-six chromium tolerant strains were identified by 16S rRNA sequence analysis as belonging to genus Bacillus . Bacillus sp. MH778713, close to Bacillus cereus group, showed to be the most resistant strain, tolerating up to 15000 mg/L Cr (VI) and 10000 mg/L of Al. Regarding the bioaccumulation traits, Bacillus sp. MH778713 accumulated up to 100 mg Cr(VI)/g of cells when it was exposed to 1474 mg/L of Cr VI. To assess Bacillus sp. MH778713 ability to assist Prosopis laevigata phytoremediation; twenty plants were inoculated or non-inoculated with Bacillus sp. MH778713 and grown in nitrogen-free Jensen’s medium added with 0, 10 and 25 mg/L of Cr(VI). Only plants inoculated with Bacillus sp. grew in the presence of chromium showing the ability of this strain to assist chromium phytoremediation. P. laevigata and Bacillus spp. may be considered as good candidates for soil restoration of arid and semiarid sites contaminated with heavy metals.

Long-Chain Hydrocarbons (C21, C24, and C31) Released by Bacillus sp. MH778713 Break Dormancy of Mesquite Seeds Subjected to Chromium Stress

“…MH778713 is also highly tolerant to aluminum (up to 10000 mg L −1 ), it could be expected that the system P. laevigata-Bacillus sp. MH778713 could also work in aluminum polluted sites (Ramírez et al, 2019). The deleterious and signaling role of ROS in plants is well documented, thus ROS fine-tuning plays a key role in seed physiology (Bailly et al, 2008).…”

“…Bacillus sp. MH778713, an isolate from P. laevigata nodules (Ramírez et al, 2019), and Escherichia coli BL21(DE3) were streaked onto yeast-extract mannitol agar (YMA) plates and incubated for 24 h in darkness at 28 • C. For long-term storage, bacterial strains were kept at −80 • C in yeast-extract mannitol broth with 20%(v/v) glycerol. Prosopis laevigata seeds were surface-sterilized by rinsing with distilled water and then soaking in concentrated sulfuric acid (98%) for 20 min, followed by rinsing 3-4 times in sterile distilled water.…”

“…Chromium(VI) at concentrations ranged 50-100 mg kg −1 soil are toxic for most plants affecting germination rate, chlorophyll content, and most of the growth parameters (Akinci and Akinci, 2010;Jain et al, 2016;Amin et al, 2019). For plants growing in a nutrient solution, 10-25 mg L −1 Cr VI is detrimental for plant development (Dube et al, 2003;Ramírez et al, 2019). Nonetheless, Prosopis plants can tolerate, translocate, and hyper accumulate heavy metals, including Pb, As and Cr 6+ (Aldrich et al, 2003(Aldrich et al, , 2007Jayaram and Prasad, 2009).…”

“…We reported that Prosopis trees grown in polluted wildlife habitats are highly tolerant of Cr (VI), in part, by their interaction with the endophytic chromium hyper-tolerant Bacillus sp. MH778713 (Ramírez et al, 2019). Bacillus sp.…”

Treatment of Solid Waste Containing Metals by Biological Methods

“…The fast-developing of industries, such as mining, smelting operations, farming, energy stations, processing in refineries, coal burning in power plants, petroleum combustion, nuclear power stations and high tension lines, plastics, textiles, microelectronics, wood preservation, paper processing plants, and agricultural and anthropogenic activities, generally use metal-containing compounds and, due to the inappropriate waste disposal practices, has contributed to the contamination of soil and water with organic compounds and heavy metals with permanent toxic effects on ecosystems and humans [1,2]. To counteract the effects of such contaminants, several methods and techniques have been implemented, each having its advantages and disadvantages.…”