Petroleum contamination significantly changes soil microbial communities in three oilfield locations in Delta State, Nigeria.

Soil microbial community structure is altered by petroleum contamination in response to compound toxicity and degradation. Understanding the relation between petroleum contamination and soil microbial community structure is crucial to determine the amenability of contaminated soils to bacterial- and fungal-aided remediation. To understand how petroleum contamination and soil physicochemical properties jointly shaped the microbial structure of soils from different oilfields, high-throughput sequencing of 16S and ITS amplicons were used to evaluate the shifts of microbial communities in the petroleum-contaminated soils in Ughelli East (UE), Utorogu (UT), and Ughelli West (UW) oilfields located in Delta State, Nigeria. The results showed 1515 bacteria and 919 fungal average OTU number, and community richness and diversity, trending as AL > UT > UW > UE and AL > UW > UT > UE for bacteria, and AL > UW > UT > UE and UW > UT > AL > UE for fungi, respectively. The bacterial taxa KCM-B-112, unclassified Saccharibacteria, unclassified Rhizobiales, Desulfurellaceae, and Acidobacteriaceae and fungal Trichocomaceae, unclassified Ascomycota, unclassified Sporidiobolales, and unclassified Fungi were found to be the dominant families in petroleum-contaminated soils. Redundancy analysis (RDA) and Spearman's correlation analysis revealed that total carbon (TC), electric conductivity (EC), pH, and moisture content (MO) were the major drivers of bacterial and fungal communities, respectively. Gas chromatography-mass spectrophotometer (GC-MS) analysis exhibited that the differences in C7-C10, C11-C16, and C12-C29 compounds in the crude oil composition and soil MO content jointly constituted the microbial community variance among the contaminated soils. This study revealed the bacterial and fungal communities responsible for the biodegradation of petroleum contamination from these oilfields, which could serve as biomarkers to monitor oil spill site restoration within these areas. Further studies on these contaminated sites could offer useful insights into other contributing factors such as heavy metals.

The seasonal changes of core bacterial community decide sewage purification in sub-plateau municipal sewage treatment plants.

The decline of sewage purification efficiency in winter is a frequent problem in sub-plateau municipal sewage treatment plants (MSTPs). Understanding the links between activated sludge (AS) bacterial community and sewage purification is crucial for exploring the cause of this problem. In this study, Illumina high-throughput sequencing technology was applied to investigate the seasonal changes of AS bacterial community in sub-plateau MSTPs. The sequencing result indicates that the bacterial community OTU number, diversity, and relative abundance in winter are significantly lower than that in summer samples. The discriminant linear effect size analysis (LEfSe) reveals that Proteobacteria and Chloroflexi members were enriched in summer AS, while Actinobacteria and Firmicutes were enriched in winter AS. The results indicate that different core bacterial community assembly was developed in summer and winter, respectively. The changes in bacterial community may be the reasons for the lower sewage purification efficiency in winter. Furthermore, redundancy analysis (RDA) shows that temperature and dissolved oxygen (DO) are the principal factors that drive the seasonal changes in the core bacterial community diversity, richness and structure in sub-plateau MSTPs. Thus, the sub-plateau AS selects for a unique community assembly pattern and shapes the particular AS ecosystem. These results expand previous understanding and provide insight into the relationship between bacterial community and performance of sub-plateau MSTPs.

Structural and functional responses of bacterial and fungal communities to multiple heavy metal exposure in arid loess.

Concentration gradients of multiple heavy metals (HMs) in the arid loess region near a smelter were determined. In order to understand the response of soil microbes to multiple HM gradients, bacterial and fungal community structures and functions were analyzed using high-throughput RNA gene sequencing and the PICRUSt method. RDA/PCA analyses revealed that soil pH, HMs, and electrical conductivity (EC) jointly affected the bacterial communities in the soils. The soil microbial community structures responded differently to HMs, EC, and pH. High HMs increased the abundances of the bacterial phyla Actinobacteria, Bacteroidetes, Deinococcus-Thermus, and Chloroflexi, and the genera Blastococcus, Rubrobacter, Quadrisphaera, and Tunicatimonas, whereas they decreased the abundances of the phyla Proteobacteria and Acidobacteria and the genera Streptomyces and Nocardioides. High EC and low pH decreased the abundance of most of the dominant bacterial phyla but increased the abundances of Firmicutes, Deinococcus-Thermus, and Nitrospirae. Furthermore, high HMs and EC reduced the numbers of soil-specific bacterial and fungal groups and drove the succession of certain groups that were highly resistant to increased HMs and EC. In addition, many bacterial and fungal groups exhibited different response patterns to each HM, implying that, in multiple HM-contaminated soils, HMs jointly shaped the microbial communities. PICRUSt analysis suggested that high HMs significantly decreased the total gene abundance and most KEGG modules in the soils. High EC and low pH significantly enhanced the abundances of several two-component system-, electron transfer-, and methanogenesis-related modules. We conclude that excessive multiple HMs and EC principally repressed the microbial activity and severely drove the gradient succession of bacterial and fungal communities in the arid loess region.

Indole-3-butyric acid mediates antioxidative defense systems to promote adventitious rooting in mung bean seedlings under cadmium and drought stresses.

In vitro experiments were performed to determine whether auxin can mediate the formation of adventitious roots in response to heavy metal and drought stresses using a model rooting plant, mung bean [Vigna radiata (L.) Wilczek]. The treatments with CdCl2 or mannitol alone significantly inhibited the formation and growth of adventitious roots in mung bean seedlings. In contrast, when CdCl2 or mannitol was applied together with indole-3-butyric acid (IBA), IBA considerably cancelled the inhibition of adventitious rooting by stresses. Treatment with CdCl2 or mannitol alone significantly increased the soluble protein and malondialdehyde (MDA) contents. CdCl2 and mannitol stress each induced differentially significant changes in the activities of antioxidative enzyme and antioxidant levels during adventitious rooting. Notably, both CdCl2 and mannitol stress strongly reduced the peroxidase (POD) and ascorbate peroxidase (APX) activities and glutathione (GSH) and phenols levels. Catalase and superoxide dismutase (SOD) activity were enhanced by CdCl2 but reduced by mannitol. CdCl2 increased the ascorbate acid (ASA) level, which was decreased by mannitol. Furthermore, when CdCl2 or mannitol was applied together with IBA, IBA counteracted the CdCl2- or mannitol-induced increase or decrease in certain antioxidants, MDA, and antioxidative enzymes. These results suggest that Cd and mannitol stress inhibition of adventitious rooting is associated with the regulation of antioxidative enzymes and antioxidants in cells to defense the oxidative stress. Moreover, IBA alleviates the effects of Cd and mannitol stress on the rooting process partially through the regulation of antioxidative defense systems.