Reduction in Hg phytoavailability in soil using Hg‐volatilizing bacteria and biochar and the response of the native bacterial community

Abstract

Summary Biological approaches are considered promising and eco‐friendly strategies to remediate Hg contamination in soil. This study investigated the potential of two ‘green’ additives, Hg‐volatilizing bacteria (Pseudomonas sp. DC‐B1 and Bacillus sp. DC‐B2) and sawdust biochar, and their combination to reduce Hg(II) phytoavailability in soil and the effect of the additives on the soil bacterial community. The results showed that the Hg(II) contents in soils and lettuce shoots and roots were all reduced with these additives, achieving more declines of 12.3–27.4%, 24.8–57.8% and 2.0–48.6%, respectively, within 56 days of incubation compared to the control with no additive. The combination of DC‐B2 and 4% biochar performed best in reducing Hg(II) contents in lettuce shoots, achieving a decrease of 57.8% compared with the control. Pyrosequencing analysis showed that the overall bacterial community compositions in the soil samples were similar under different treatments, despite the fact that the relative abundance of dominant genera altered with the additives, suggesting a relatively weak impact of the additives on the soil microbial ecosystem. The low relative abundances of Pseudomonas and Bacillus, close to the background levels, at the end of the experiment indicated a small biological disturbance of the local microbial niche by the exogenous bacteria.

A critical review of the interactions between rhizosphere and biochar during the remediation of metal(loid) contaminated soils

“…Moreover, heavy metal(loid)s are harmful to microorganisms due to their long biological half-life, toxicity, and non-biodegradability (Abdu et al 2016). The microbial abundance and community diversity of metal(loid) contaminated soils are significantly lower than those of clean soils due to heavy metal(loid) stress (Chang et al 2019;Wan et al 2022). The addition of biochar amendments to soil facilitates the stabilization of heavy metal(loid)s, reducing their bioavailability and mitigating stress to microorganisms, ultimately contributing to the growth and metabolism of microorganisms, and improving both their abundance and activity.…”

“…In general, the relative abundance changes in dominant groups Acidobacteria, Actinobacteria, Bacteroidetes, Firmicutes, Gemmatimonadetes, and Proteobacteria at the phylum level are found in Pb, As, Cd, and Hg contaminated soils after the biochar amendments addition. Besides these dominant groups, the relative abundance changes in Chloroflexi and Patescibacteria are easily detected in Pb contaminated soils (Liu et al 2022a;Wan et al 2022), the relative abundance changes in Chloroflexi and Planctomycetes are easily monitored in As contaminated soils (Irshad et al 2022;Liu et al 2017b;Zhang et al 2020a), the relative abundance changes in Chloroflexi, Planctomycetes, and Patescibacteria are easily observed in Cd contaminated soils (Liu et al 2020b(Liu et al , 2022aZhou et al 2022), and the relative abundance changes in Planctomycetes are easily measured in Hg contaminated soils after the biochar amendments addition (Chang et al 2019). At the genus level, the relative abundance changes in Bacillus, Flavisolibacter, Sphingomonas, Clostridium, Nitrospira, and Nocardioides are generally observed in Pb-contaminated soils after biochar addition (Liu et al 2022a;Wei et al 2022;Zhang et al 2020a), while the relative abundance changes in Bacillus, Flavisolibacter, Clostridium, Nitrospira, Nocardioides, and Gemmatimonas are generally observed in As contaminated soils (Irshad et al 2022;Liu et al 2017b;Zhang et al 2020a), and the relative abundance changes in Bacillus, Flavisolibacter, Sphingomonas, Clostridium, Nitrospira, Nocardioides, Massilia, and Lysobacter are generally detected in Cd contaminated soils (Liu et al 2022a;Qi et al 2022;Wu et al 2019a;Zhou et al 2022), while the relative abundance changes in Sphingomonas, Clostridium, Nitrospira, Nocardioides, Massilia, and Gemmatimonas are generally detected in Hg contaminated soils (Chang et al 2019).…”

“…The addition of biochar amendments immobilizes heavy metal(loid)s, thereby reducing toxicity and stress on metal-sensitive microorganisms, resulting in an increase in the abundance and activity of microbial communities (Zhou et al 2022). Liu et al (2020b) found that nanoscale zero-valent iron-loaded biochar reduced leachability of Cd toxicity characteristic leaching procedure by 42% compared to the control and converted the labile Cd into the stable fraction, which increased the relative abundance of Firmicutes and Bacteroidetes by 33-90% and 9-88% at the phylum level, respectively, As and Hg; F: Cd) after remediation with biochar amendments (Chang et al 2019;Igalavithana et al 2017;Irshad et al 2022;Liu et al 2020bLiu et al , 2017bLiu et al , 2022aMa et al 2020;Qi et al 2022;Tu et al 2020;Wan et al 2022;Wei et al 2022;Wu et al 2019a;Zhang et al 2020aZhang et al , 2021Zhou et al 2022) through reduced heavy metal(loid)s toxicity. In addition, many studies have found that applying biochar amendments to reduce heavy metal(loid) toxicity increases the relative abundance of genus-level Bacillus, which can survive in adverse soil conditions and are tolerant to heavy metal(loid)s (Irshad et al 2022;Ma et al 2020;Qi et al 2022;Zhou et al 2022).…”

Recent advances in biochar engineering for soil contaminated with complex chemical mixtures: Remediation strategies and future perspectives

“…Generally, Gram-positive bacteria are recognised as most effective in the removal of HMs due to presence of glycoproteins compared to Gram-negative bacteria comprising phospholipids and lipopolysaccharides (Das et al, 2008;Gourdon et al, 1990). Chang et al, (2019) had shown that augmenting biochar with Pseudomonas sp. DC-B1 and Bacillus sp.…”

Bioengineered biochar as smart candidate for resource recovery toward circular bio-economy: a review

“…The relative abundance of Bacteroides and Firmicutes was increased as compared to the Proteobacteria members in biochar applied soils. In a different study, biochar application increased the abundance of a particular genus of bacteria such as Haliangium [ 195 ] and Asticcacaulis [ 196 ].…”