Although fertilization plays an important role in determining the contents of soil dissolved organic matters or water-extractable organic matter (DOM, WEOM), knowledge regarding the dynamics, biodegradability, and microbial community shifts of WEOM in response to different fertilization treatments is very limited, particularly in rice–wheat cropping soil. Thus, in the present study, we performed biodegradation experiments using WEOM extracted from samples of soil that had been subjected to four different fertilization treatments: unfertilized control (CK), chemical fertilizer (CF), 50% chemical fertilizer plus pig manure (PMCF), and 100% chemical fertilizer plus rice straw (SRCF). UV spectrum and fluorescence 3D excitation–emission matrix analyses applied to investigate the chemical composition of WEOM revealed that all examined WEOMs were derived from microbial activity and the dominant portion comprised humic acid-like compounds. After the incubation, 31.17, 31.63, 43.47, and 33.01% of soil WEOM from CK, CF, PMCF, and SRCF treatments, respectively, were biodegraded. PMCF- derived WEOM had the highest biodegradation rate. High-throughput sequencing analyses performed to determine the microbial community before and after the incubation indicated that Sphingomonas, Bacillus, and Flavisolibacter were the predominant bacterial genera in the original inoculum derived from the four fertilization treatments. Following biodegradation, we observed that the dominant bacteria differed according to fertilization treatments: Curvibacter (43.25%) and Sphingobium (10.47%) for CK, Curvibacter (29.68%) and Caulobacter (20.00%) for CF, Azospirillum (23.68%) and Caulobacter (13.29%) for PMCF, and Ralstonia (51.75%) for SRCF. Canonical correspondence analysis revealed that, shifts in the microbial community were closely correlated with pH and specific UV absorbance at 254 nm. We speculated that the inherent traits of different WEOM and the properties of soil solutions under different fertilization treatments shaped the soil microbial community structure, thereby influencing the biodegradation of WEOM.

Triphenyl phosphate (TPHP) is one of the major organophosphate esters (OPEs) with increasing consumption. Considering its largely distribution and high toxicity in aquatic environment, it is important to explore an efficient treatment for TPHP. This study aimed to investigate the accelerated degradation of TPHP in a three-electrode single chamber bioelectrochemical system (BES). Significant increase of degradation efficiency of TPHP in the BES was observed compared with open circuit and abiotic controls. The one-order degradation rates of TPHP (1.5 mg L⁻¹) were increased with elevating sodium acetate concentrations and showed the highest value (0.054 ± 0.010 h⁻¹) in 1.0 g L⁻¹ of sodium acetate. This result indicated bacterial metabolism of TPHP was enhanced by the application of micro-electrical field and addition acetate as co-substrates. TPHP could be degraded into diphenyl phosphate (DPHP), hydroxyl triphenyl phosphate (OH-TPHP) and three byproducts. DPHP was the most accumulated degradation product in BES, which accounted more than 35.5% of the initial TPHP. The composition of bacterial community in BES electrode was affected by the acclimation by TPHP, with the most dominant bacteria of Azospirillum, Petrimonas, Pseudomonas and Geobacter at the genera level. Moreover, it was found that the acute toxic effect of TPHP to Vibrio fischeri was largely removed after the treatment, which revealed that BES is a promising technology to remove TPHP threaten in aquatic environment.

The bioremediation of historic industrial contaminated sites is a complex process. Co-contamination, often with lead which was commonly added to gasoline until 16 years ago is one of the biggest challenges affecting the clean-up of these sites. In this study, the effect of heavy metals, as co-contaminant, together with total petroleum hydrocarbons (TPH) is reported, in terms of remaining soil toxicity and the structure of the microbial communities. Contaminated soil samples from a relatively hot and dry climate in Western Australia were collected (n = 27). Analysis of soils showed the presence of both contaminants, TPHs and heavy metals. The Microtox test confirmed that their co-presence elevated the remaining ecotoxicity. Toxicity was correlated with the presence of lead, zinc and TPH (0.893, 0.599 and 0.488), respectively, assessed using Pearson Correlation coefficient factor. Next Generation Sequencing of soil bacterial 16S rRNA, revealed a lack of dominate genera; however, despite the variation in soil type, a few genera including Azospirillum spp. and Conexibacter were present in most soil samples (85% and 82% of all soils, respectively). Likewise, many genera of hydrocarbon-degrading bacteria were identified in all soil samples. Streptomyces spp. was presented in 93% of the samples with abundance between 7% and 40%. In contrast, Acinetobacter spp. was found in only one sample but was a dominant member of (45%) of the microbial community. In addition, some bacterial genera were correlated to the presence of the heavy metals, such as Geodermatophilus spp., Rhodovibrio spp. and Rubrobacter spp. which were correlated with copper, lead and zinc, respectively. This study concludes that TPH and heavy metal co-contamination significantly elevated the associated toxicity. This is an important consideration when carrying out risk assessment associated with natural attenuation. This study also improves knowledge about the dynamics of microbial communities in mixed contamination scenarios.

Per- and polyfluoroalkyl substances (PFASs) have received increasing attention due to their widespread presence in diverse environments including wastewater treatment plants (WWTPs) and their potential adverse health effects. Perfluorooctanoic acid (PFOA) is one of the most detected forms of PFASs in WWTPs. However, there is still a paucity of knowledge about the effect of PFASs on microorganisms of the key component of WWTP, activated sludge. In this study, lab-scale microcosm experiments were established to evaluate the influences of PFOA on activated sludge microbes under aerobic and anaerobic conditions. The diversity, structure, and microbe-microbe interaction of microbial community were determined by 16S rRNA gene amplicon sequencing and co-occurrence network analysis. After 90 days of exposure to PFOA, activated sludge microbial richness decreased under both aerobic and anaerobic conditions. Specifically, under aerobic condition, Rhodopseudomonas (mean relative abundance 3.6%), Flavobacterium (2.4%), and Ignavibacterium (6.6%) were enriched in PFOA-spiked activated sludge compared with that in the unspiked sludge (2.6%, 0.1%, and 1.9%, respectively). By contrast, after 90 days of exposure to PFOA, Eubacterium (2.1%), Hyphomicrobium (1.8%), and Methyloversatilis (1.2%) were enriched under anaerobic condition, and more abundant than that in the control sludge (0.4%, 1.5%, and 0.6%, respectively). These genera were the potential PFOA-resistant members. In addition, Azospirillum and Sporomusa were the most connected taxa in PFOA-aerobic and PFOA-anaerobic networks, respectively. Prediction of the functional gene showed that PFOA inhibited some gene expression of sludge microbes, such as transcription, amino acid transport and metabolism, and energy production and conversion. In summary, continued exposure to PFOA induced substantial shifts of the sludge bacterial diversity and composition under both aerobic and anaerobic conditions.

Heavy metal contamination plays a major role in water pollution. It needs remediation without raising the issues of secondary waste generation and their related issues. Heavy metal residues adversely affect soil and water quality. Their leachate would disturb the whole ecological system. It needs remediation to avoid the effect on soil and water. Azospirillium biofertilizer has the ability to reduce hazardous components without disturbing the growth of the plant. Hence, the use of low-cost biosorbent was proposed for heavy metal removal. The investigations showed excellent removal of heavy metals like copper (Cu) and chromium (Cr) using Azospirillium biofertilizer. These materials showed efficient removal of Cu and Cr at 94% and 70%, respectively. Separation was dependent upon the interaction between sorbent and sorbate, which makes separation tunable for the removal of the desired material from effluent or other streams. Parameter optimization like temperature, adsorbent dose, time, pH, and agitation speed was studied for both metals. At optimum parameters, Langmuir capacity was found to be 35.71 mg/g and 5.58 mg/g of copper and chromium. Experimental data was best fitted to Langmuir isotherm, and the pseudo-second-order kinetic model was suitable for the study of both metals.

Presence of heavy metals in industrial discharge warrants the adoption of efficient and cost-effective treatment technologies. In this work, lichen Parmotrema tinctorum biomass was utilized as biosorbent for removal of Ni (II) from metal finishing industry effluents. Optimal adsorption was observed at pH 7, stirring speed of 300 rpm, 120 min incubation from independent batch experiments. Adsorption isotherm at optimal conditions followed Langmuir model (R² > 0.974) with a maximum adsorption capacity of 33.92 mg g⁻¹. Adsorption kinetics could be described with pseudo-first-order model (R² > 0.98). Fourier transform infrared spectroscopy of pristine and metal loaded P. tinctorum biomass indicated electrostatics and ionic interaction in the adsorption process. Biosorbent treated water showed no inhibition against agriculturally important microorganisms like Phosphobacter sp. and Azospirillum sp. in microbial toxicity assay. Similarly, biosorbent treated water offered better germination and growth for Vigna radiata than the untreated water in greenhouse phytotoxicity assessment. Though the result suggests detoxification of industrial effluents following P. tinctorum biosorption, reusability of treated wastewater in agricultural practice warrants multi-tiered ecotoxicity assessment, and long-term environmental impact analysis.

The Voltri Massif is an ophiolitic complex located in the Ligurian Alps close to the city of Genova (Northern Italy) where several springs discharge high pH (up to 11.7), low salinity waters produced by the active serpentinization of the ultramafic basement. Mixing of these hyperalkaline waters with the river waters along with the uptake of atmospheric carbon dioxide forms brownish carbonate precipitates covering the bedrock at the springs. Diverse archaeal and bacterial communities were detected in these carbonate precipitates using 454 pyrosequencing analyses of 16S ribosomal RNA (rRNA) genes. Archaeal communities were dominated by members of potential methane-producing and/or methane-oxidizing Methanobacteriales and Methanosarcinales (Euryarchaeota) together with ammonia-oxidizing Nitrososphaerales (Thaumarchaeota) similar to those found in other serpentinization-driven submarine and terrestrial ecosystems. Bacterial communities consisted of members of the Proteobacteria, Actinobacteria, Planctomycetes, Bacteroidetes, Chloroflexi, and Verrucomicrobia phyla, altogether accounting for 92.2 % of total retrieved bacterial 16S rRNA gene sequences. Amongst Bacteria, potential chemolithotrophy was mainly associated with Alpha- and Betaproteobacteria classes, including nitrogen-fixing, methane-oxidizing or hydrogen-oxidizing representatives of the genera Azospirillum, Methylosinus, and Hydrogenophaga/‘Serpentinomonas’, respectively. Besides, potential chemoorganotrophy was attributed mainly to representatives of Actinobacteria and Planctomycetales phyla. The reported 16S rRNA gene data strongly suggested that hydrogen, methane, and nitrogen-based chemolithotrophy can sustain growth of the microbial communities inhabiting the carbonate precipitates in the hyperalkaline springs of the Voltri Massif, similarly to what was previously observed in other serpentinite-hosted ecosystems.

Biofilms harboring simultaneously anoxygenic and oxygenic phototrophic bacteria, diazotrophic bacteria, and hydrocarbon-utilizing bacteria were established on glass slides suspended in pristine and oily seawater. Via denaturing gradient gel electrophoresis analysis on PCR-amplified rRNA gene sequence fragments from the extracted DNA from biofilms, followed by band amplification, biofilm composition was determined. The biofilms contained anoxygenic phototrophs belonging to alphaproteobacteria; pico- and filamentous cyanobacteria (oxygenic phototrophs); two species of the diazotroph Azospirillum; and two hydrocarbon-utilizing gammaproteobacterial genera, Cycloclasticus and Oleibacter. The coexistence of all these microbial taxa with different physiologies in the biofilm makes the whole community nutritionally self-sufficient and adequately aerated, a condition quite suitable for the microbial biodegradation of aquatic pollutant hydrocarbons.

The retention of aquatic plant debris in freshwater systems favors a reduction in soluble reactive phosphorus (P) in overlying water through microbe-mediated mechanisms in sediment. For a more complete view of the changes in sediment microbial structure and functioning when receiving plant debris, the enzyme activities and microbial community structure in sediments incubated with or without plant debris were investigated. Significantly higher fluorescein diacetate (FDA) hydrolysis, alkaline phosphatase, polyphenol oxidase, cellulase, β-glucosidase, and dehydrogenase activities were observed with plant debris treatment. High-throughput pyrosequencing showed that the number of total operational taxonomic units (OTUs) of bacteria estimated by using the Chao1 analysis was 2064 (in the control) and 1821 (with the plant debris treatment). The Shannon index, functional organization, and Venn diagrams revealed that the enriched OTUs in plant debris-treated community were less diversified than those in the control sample. The prominent bacterial phyla Firmicutes and Bacteroidetes were more diverse after plant debris addition. At the class level, the relative abundance of Alphaproteobacteria increased by 114% when plant debris was added, whereas the relative abundances of Beta-, Delta-, and Gammaproteobacteria decreased by 42, 78, and 86%, respectively. Azospirillum and Dechloromonas, the dominant phylogenetic groups at the genus level, increased with plant debris addition. Our study showed the importance of the above microbial genera in plant debris-mediated P retention in sediment.

The presence and composition of soil microbial communities has been shown to have a large impact on plant–plant interactions and consequently plant diversity and composition. The goal of the present study was to evaluate impact of arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing bacteria, which constitutes an essential link between the soil and the plant’s roots. A greenhouse pot experiment was conducted to evaluate the feasibility of using selected microbes to improve Hieracium pilosella and Medicago sativa growth on Zn–Pb-rich site. Results of studies revealed that biomass, the dry mass of shoots and roots, increased significantly when plants were inoculated with mycorrhizal fungi and nitrogen-fixing bacteria. The addition of Azospirillum sp. and Nostoc edaphicum without mycorrhiza suppressed plant growth. Single bacterial inoculation alone does not have a positive effect on M. sativa growth, while co-inoculation with AMF improved plant growth. Plant vitality (expressed by the performance index) was improved by the addition of microbes. However, our results indicated that even dry heat sterilization of the substratum created imbalanced relationships between soil-plant and plants and associated microorganisms. The studies indicated that AMF and N₂-fixers can improve revegetation of heavy metal-rich industrial sites, if the selection of interacting symbionts is properly conducted.