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Title: EFFECTS OF THE NICKEL HYPERACCUMULATOR ALYSSUM MURALE ON RHIZOSHERE MICROBIAL POPULATIONS

Author
item ABOU-SHANAB, R - GENETIC ENG INST, EGYPT
item DELORME, T - DEP NATURAL RES, UMD
item ANGLE, J - DEP NATURAL RES, UMD
item Chaney, Rufus
item GHANEM, K - U OF ALEXANDRIA, EGYPT
item MOAWAD, H - NAT RES CNTR, EGYPT
item GHOZLAN, H - U OF ALEXANDRIA, EGYPT

Submitted to: International Journal of Phytoremediation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2003
Publication Date: 11/15/2003
Citation: Abou-Shanab, R.I., Delorme, T.E., Angle, J.S., Chaney, R.L., Ghanem, K., Moawad, H., Ghozlan, H.A. 2003. Effects of the nickel hyperaccumulator alyssum murale on rhizoshere microbial populations. International Journal of Phytoremediation. 5(4):367-379.

Interpretive Summary: Phytoextracting of soil metals using metal hyperaccumulator plants is becoming a commercial technology both for soil remediation and for phytomining. Because soil microorganisms play a role in plant absorption of several nutrient elements from soils, we examined the effect of soil microbes on growth and metal accumulation of Ni and nutrients by the Ni-hyperaccumulator plant Alyssum murale. Our CRADA team developed use of this and related Ni hyperaccumulators for phytoextraction of soil Ni, including all aspects of plant production and soil management, and the improved cultivars we generated are being used commercially both in the US and in Canada. To examine the possible role of soil microbes, we grew A. murale in sterilized and non-sterilized serpentine soil from Oregon. Interestingly, plants attained higher yields and higher metal concentrations when grown in non-sterile soils. In a separate paper we selected three strains which could induce higher Ni hyperaccumulation/yield even when they were used to inoculate non-sterilized soil. In the present study the characteristics of microbes which improved plant growth or Ni hyperaccumulation were evaluated. Significantly higher numbers of cultureable actinomycetes, bacteria and fungi were found in the rhizosphere soil compared to bulk soil. A higher percent of Ni-resistant bacteria were also found in the rhizosphere soil compared to bulk soil. Percentage of acid producing bacteria was higher among the rhizosphere soil isolates compared to isolates from bulk soil. However, proportions of siderophore producing, and phosphate solubilizing bacteria were not affected by the presence of the plant. We hypothesize that A. murale selected microbes in the rhizosphere that were capable of reducing soil pH leading to an increase in metal uptake by this hyperaccumulator.

Technical Abstract: Metal hyperaccumulator plants like Alyssum murale are used for phytoremediation of Ni contaminated soils. Soil microorganisms are known to play an important role in nutrient acquisition for plants, however, little is known about the rhizosphere microorganisms of hyperaccumulators. Fresh and dry weight, and Ni and Fe concentrations in the plant shoots were higher when A. murale was grown in non-sterilized compared to sterilized soils. The analysis of microbial populations in the rhizosphere of A. murale and in bulk soils demonstrated that microbial numbers were affected by the presence of the plant. Significantly higher numbers of culturable actinomycetes, bacteria and fungi were found in the rhizosphere compared to bulk soil. A higher percent of Ni-resistant bacteria were also found in the rhizosphere compared to bulk soil. Percentage of acid producing bacteria was higher among the rhizosphere isolates compared to isolates from bulk soil. However, proportions of siderophore producing, and phosphate solubilizing bacteria were not affected by the presence of the plant. We hypothesize that A. murale selected microbes in the rhizosphere that were capable of reducing soil pH leading to an increase in metal uptake by this hyperaccumulator.