Combined effects of Bacillus sp. M6 strain and Sedum alfredii on rhizosphere community and bioremediation of cadmium polluted soils

Abbas Ali Abid; Gengmiao Zhang; Dan He; Huanhe Wang; Itrat Batool; Hongjie Di; Qichun Zhang

doi:10.3389/fpls.2022.913787

Combined effects of Bacillus sp. M6 strain and Sedum alfredii on rhizosphere community and bioremediation of cadmium polluted soils

Front Plant Sci. 2022 Sep 21:13:913787. doi: 10.3389/fpls.2022.913787. eCollection 2022.

Authors

Abbas Ali Abid¹, Gengmiao Zhang², Dan He¹, Huanhe Wang³, Itrat Batool⁴, Hongjie Di¹, Qichun Zhang¹

Affiliations

¹ Zhejiang Provincial Key Laboratory of Agricultural Resources and Environment, Key Laboratory of Environment Remediation and Ecological Health, Ministry of Education, Zhejiang University, Hangzhou, China.
² Zhuji Agricultural Technology Extension Center, Zhuji, China.
³ Zhuji Economic Speciality Station, Zhuji, China.
⁴ Institute of Food Science, Chinese Academy of Agricultural Sciences, Beijing, China.

Abstract

Concerns regarding inevitable soil translocation and bioaccumulation of cadmium (Cd) in plants have been escalating in concomitance with the posed phytotoxicity and threat to human health. Exhibiting a Cd tolerance, Bacillus sp. M6 strain has been reported as a soil amendment owing to its capability of reducing metal bioavailability in soils. The present study investigated the rhizospheric bacterial community of the Cd hyperaccumulator Sedum alfredii using 16S rRNA gene sequencing. Additionally, the Cd removal efficiency of strain Bacillus sp. M6 was enhanced by supplementing with biochar (C), glutamic acid (G), and rhamnolipid (R) to promote the phytoremediation effect of hyperaccumulator S. alfredii. To the best of our knowledge, this is the first time the amendments such as C, G, and R together with the plant-microbe system S. alfredii-Bacillus sp. M6 has been used for Cd bioremediation. The results showed that soil CaCl₂ and DTPA (Diethylenetriamine penta-acetic acid) extractable Cd increased by 52.77 and 95.08%, respectively, in all M6 treatments compared to unamended control (CK). Sedum alfredii with Bacillus sp. M6 supplemented with biochar and rhamnolipid displayed a higher phytoremediation effect, and the removal capability of soil Cd (II) reached up to 16.47%. Moreover, remediation of Cd polluted soil by Bacillus sp. M6 also had an impact on the soil microbiome, including ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and cadmium transporting ATPase (cadA) genes. Quantitative PCR analysis confirmed the Bacillus sp. M6 strain increased the abundance of AOB and cadA in both low Cd (LC) and high Cd (HC) soils compared to AOA gene abundance. Besides, the abundance of Proteobacteria and Actinobacteria was found to be highest in both soils representing high tolerance capacity against Cd. While Firmicutes ranked third, indicating that the additionof strain could not make it the most dominant species. The results suggested the presence of the hyperaccumulator S. alfredii and Cd tolerant strain Bacillus sp. M6 supplemented with biochar, and rhamnolipid, play a unique and essential role in the remediation process and reducing the bioavailability of Cd.

Keywords: Bacillus sp. M6; Sedum alfredii; biochar (BC); bioremediation; cadmium; rhamnolipid; soil microbial community.