Bioaccumulation of Chromium by Autochthonous Bacteria Associated With The Heavy Metal- Resistant Halophyte  Arthrocnemum macrostachyum

Youghly, Nesma; Taher, Heba S.; Youssef, Hanan H.; Fayez, Mohammed; EL-Bana, Magdy I.; ELbous, Mona M.; Hegazi, N.A.

doi:10.21608/ejm.2020.19136.1125

Bioaccumulation of Chromium by Autochthonous Bacteria Associated With The Heavy Metal- Resistant Halophyte Arthrocnemum macrostachyum

Document Type : Original Article

Authors

¹ Department of Botany, Faculty of Science, Port Said University, Port Said, Egypt

² Department of Botany, Faculty of Science, Suez Canal University, Ismailia, Egypt

³ Environmental Studies and Research Unit (ESRU), Department of Microbiology, Faculty of Agriculture, Cairo University, Giza, Egypt

10.21608/ejm.2020.19136.1125

Abstract

ARTHROCNEMUM macrostachyum is a halophyte naturally growing on Manzala Lake shoreline of Egypt and able to tolerate and accumulate heavy metals. The use of metal-resistant rhizobacteria is an important technology to improve the tolerance capability of the halophytes in metal-polluted environments. A total of 33 bacterial isolates were obtained from the root system of A. macrostachyum and screened for resistance to 1.25 and 12.5mM of Cr(VI) in plant-based culture medium prepared from the halophyte shoot juice. The six most tolerant isolates were identified based on cell morphology and API microtube profiles. Those isolates were found closely related to Bacillus lentus, Burkholderia cepacia, Raoultella ornithinolytica and Providencia retgeri indicated on the online database. Among the strains tested for their ability to accumulate chromium, Bacillus lentus was the most effective with an average accumulation percentage of 17.8, Providencia retgeri ranked thereafter (15.1%). Bacillus circulance was the least with a negligible accumulation level of 0.5%. The biosorption rate of the heavy metal was contact time- and bacterial strain-dependent. Again, Bacillus lentus showed the highest uptake capacity of 32.8mg g-1, a parameter that positively correlated with contact time (r= 0.865), this was not the case with Burkholderia cepacia where the correlation was negative (r= – 0.811). When introduced into an aqueous solution of 25mg L^-1 Cr(VI), Burkholderia cepacia was the superior in Cr(VI) reduction (86.7%), while Bacillus circulance failed to reduce the heavy metal. The pH 5.5 was the most favorable for bacterial Cr accumulation which proportionally decreased as the acidity of the solution increased. This study provides more understanding of the significant contribution of the heavy metal-tolerant microbiome to improve the metal remediation efficiency of halophytic plant covers of stressed environments.

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