Heavy metals reshaping the structure and function of phylloplane bacterial community of native plant Tamarix ramosissima from Pb/Cd/Cu/Zn smelting regions

Phyllosphere bacterial community and metabolomic analysis revealed the mechanism of Cd tolerance in the bryophyte Tortella tortuosa (Hedw.) Limpr

Introduction

Phytoremediation is a safe and green technology for the remediation of heavy metal pollution, a global environmental problem. Bryophytes are well known for their special physiological properties, but there is little research on the use of bryophytes for phytoremediation.

Methods

In this indoor experiment, the impacts of 40 days of Cd pollution (1 (T1), 5 (T2), 10 (T3) mg·L-1) on Cd absorption, growth and physiological characteristics, and phyllosphere bacterial diversity of Tortella tortuosa were explored.

Results

The results showed that the maximum Cd absorption capacity of T. tortuosa was 5.0135 mg·kg-1. The contents of leaf chlorophyll a (Chl a) and chlorophyll b (Chl b) in T. tortuosa decreased (p < 0.05) with the increase of Cd concentration. Especially, the Chl a and Chl b contents of the T3 treatment reduced by 88% and 91%, respectively compared with those of the CK (Cd: 0 mg·L-1). The catalase (CAT) and peroxidase (POD) activities of the T3 treatment reduced by 55% and 85%, respectively (p < 0.05), and the malondialdehyde (MDA) content increased by 167%, compared with those of the CK. Under Cd exposure, Cyanobacteria (63.49%) and Proteobacteria (26.62%) were the dominant bacterial phyla. The highly abundant phyllosphere bacteria were negatively correlated with the Cd concentration, antioxidant enzyme activity, and chlorophyll content in T. tortuosa, and positively correlated with the relative abundances of Neomycin and N-Acetyl-L-Glutamic acid.

Discussion

Although the severe Cd pollution could affect the physiological and metabolic characteristics of T. tortuosa, T. tortuosa had a strong absorption capacity for Cd. Therefore, it could be used for phytoremediation of heavy metal pollution. This study will provide a reference for the remediation of soil heavy metal pollution.

Impact of Anthropogenic Factors on the Diversity of Microbial Communities of PM10 Air and PM100 of Tilia L. Phylloplane in an Urban Ecosystem

Identifying the relationship between the microbiomes of urban dust particles from different biotopes is important because the state of microorganisms can be used to assess the quality of the environment. The aim of this work was to determine the distribution and interaction patterns of microorganisms of dust particles in the air and on leaf surfaces. Metabarcoding of bacterial and fungal communities, PAH, and metal content analyses and electron microscopy were used in this work. The results obtained allowed us to characterise the biological and chemical components of the dust particles. Some bacterial and fungal genera were correlated with benzanthracene, fluoranthene, and Cu, Ni, Co, Zn, and Mn contents. Bacterial communities were found to be more sensitive to all the pollutants studied. PM10 microbial communities circulated between biotopes and study areas due to air flows, as evidenced by the presence of similar ASVs in fungi and bacteria. The results could help to understand the effects of climate change and anthropogenic activities.

Toxicity factors to assess the ecological risk for soil microbial communities

The toxicity factor (TF), a critical parameter within the potential ecological risk index (RI), is determined without accounting for microbial factors. It is considerable uncertainty exists concerning its validity for quantitatively assessing the influence of metal(loid)s on microorganisms. To evaluate the suitability of TF, we constructed microcosm experiments with varying RI levels (RI = 100, 200, 300, 500, and 700) by externally adding zinc (Zn), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), cadmium (Cd), and mercury (Hg) to uncontaminated soil (CK). Quantitative real-time PCR (qPCR) and high-throughput sequencing techniques were employed to measure the abundance and community of bacteria and fungi, and high-throughput qPCR was utilised to quantify functional genes associated with CNPS cycles. The results demonstrated that microbial diversity and function exhibited significant alterations (p < 0.05) in response to increasing RI levels, and the influences on microbial community structure, enzyme activity, and functional gene abundances were different due to the types of metal(loid)s treatments. At the same RI level, significant differences (p < 0.05) were discerned in microbial diversity and function across metal(loid) treatments, and these differences became more pronounced (p < 0.001) at higher levels. These findings suggest that TF may not be suitable for the quantitative assessment of microbial ecological risk. Therefore, we adjusted the TF by following three steps (1) determining the adjustment criteria, (2) deriving the initial TF, and (3) adjusting and optimizing the TF. Ultimately, the optimal adjusted TF was established as Zn = 1.5, Cr = 4.5, Cu = 6, Pb = 4.5, Ni = 5, Cd = 22, and Hg = 34. Our results provide a new reference for quantitatively assessing the ecological risks caused by metal(loid)s to microorganisms.