Impact of Zn and Cu on the development of phenanthrene catabolism in soil

Characterization of the Phenanthrene-Degrading Sphingobium yanoikuyae SJTF8 in Heavy Metal Co-Existing Liquid Medium and Analysis of Its Metabolic Pathway

Polycyclic aromatic hydrocarbons (PAHs) are common organic pollutants with great carcinogenic threaten, and metal/PAH-contaminated environments represent one of the most difficult remedial challenges. In this work, Sphingobium yanoikuyae SJTF8 was isolated and identified with great and stable PAH-degrading efficiency even under stress conditions. It could utilize typical PAHs (naphthalene, phenanthrene, and anthracene) and heterocyclic and halogenated aromatic compounds (dibenzothiophene and 9-bromophenanthrene) as the sole carbon source. It could degrade over 98% of 500 mg/L phenanthrene in 4 days, and the cis-3,4-dihydrophenanthrene-3,4-diol was the first-step intermediate. Notably, strain SJTF8 showed great tolerance to heavy metals and acidic pH. Supplements of 0.30 mM of Cu2+, 1.15 mM of Zn2+, and 0.01 mM of Cd2+ had little effect on its cell growth and phenanthrene degradation; phenanthrene of 250 mg/L could still be degraded completely in 48 h. Further, the whole genome sequence of S. yanoikuyae SJTF8 was obtained, and three plasmids were found. The potential genes participating in stress-tolerance and PAH-degradation were annotated and were found mostly distributed in plasmids 1 and 2. Elimination of plasmid 2 resulted in the loss of the PAH-degradation ability. On the basis of genome mining results, the possible degrading pathway and the metabolites of S. yanoikuyae SJTF8 to phenanthrene were predicted.

Impact of digestate and its fractions on mineralization of 14C-phenanthrene in aged soil

The impact of whole digestate (WD) and its fractions (solid [SD] and liquid [LD]) on ¹⁴C-phenanthrene mineralization in soil over 90 d contact time was investigated. The ¹⁴C-phenanthrene spiked soil was aged for 1, 30, 60 and 90 d. Analysis of water-soluble nitrogen, phosphorus, total (organic and inorganic) carbon, and quantitative bacterial count were conducted at each time point to assess their impact on mineralization of ¹⁴C-phenanthrene in soils. Indigenous catabolic activity (total extents, maximum rates and lag phases) of ¹⁴C-phenanthrene mineralization were measured using respirometric soil slurry assay. The soil amended with WD outperformed the SD and LD fractions as well as showed a shorter lag phase, higher rate and extent of mineralization throughout the study. The digestates improved (P < 0.05) the microbial population and nutritive content of the soil. However, findings showed that spiking soil with phenanthrene generally reduced the growth of microbial populations from 1 to 90 d and gave a lower nutritive content in comparison with the non-spiked soil. Also, soil fertility and bacteria count were major factors driving ¹⁴C-phenanthrene mineralization. Particularly, the non-phenanthrene degraders positively influenced the cumulative mineralization of ¹⁴C-phenanthrene after 60 d incubation. Therefore, the digestates (residue from anaerobic digestion) especially WD, which enhanced ¹⁴C-phenanthrene mineralization of the soil without minimal basal salts medium nor additional degraders should be further exploited for sustainable bioremediation of PAHs contaminated soil.

Changes in Arsenic and Copper Bioavailability and Oxytetracycline Degradation during the Composting Process

This research focuses on the effects of the composting process on oxytetracycline antibiotic degradation and the bioavailability of arsenic and copper. A compost experiment was conducted using cow and pig manure contaminated with oxytetracycline, and copper and arsenic salts. The changes in physicochemical properties, oxytetracycline concentration, and the germination index were measured. Copper and arsenic were estimated by sequential chemical extraction. We also detected the effects of compost properties, oxytetracycline concentration, and heavy metal (loid)s on the germination index through simple regression analysis. The results showed that the composting process positively and significantly affected heavy metal(loid)s bioavailability, oxytetracycline degradation, and the germination index. Oxytetracycline concentration declined in all treatments, and the decline was more evident in cows' manure. The copper and arsenic bioavailable fraction decreased significantly, while the low bioavailability fraction increased. The germination index increased above 50%, which showed that the compost was free of toxic substances. This result also showed that the compost properties had the most significant impact on the germination index, and their regression had the highest R2 values (0.84 and 0.99) in the cow and pig manure treatments, respectively. In conclusion, the composting process provides an economical method for oxytetracycline degradation and heavy metal(loid)s bioavailability reduction.

Influence of a mixture of metals on PAHs biodegradation processes in soils

In order to assess the effect of mixed pollutants, the influence of different concentration levels of a mixture of metals (Cr, Co, Pb, Mn, Ni, Cu, Zn) on the biodegradation of some PAHs (phenanthrene, fluoranthene, pyrene, benzo[b]fluoranthene and benzo[a]pyrene) in soil samples was evaluated. To do so, groups of microcosms of a natural soil from the region of Sabadell (Barcelona, Spain) were prepared as a reproduction of the native environment at laboratory scale, under controlled conditions. Mixtures of PAHs and metals were carefully selected, according to soil characterization and microbiological growth preliminary assays, and were added to microcosms. These microcosms were analyzed at various times, along two months, to obtain PAHs dissipation time-courses. A first-order kinetic modelling allowed obtaining different rate constants and DT50 values as a function of the metal levels introduced in microcosms. As a general observation, the higher the concentration of metals, the lower the biodegradation of PAHs of 3-4 rings (phenanthrene, fluoranthene and pyrene). On the other hand, no important effect on the biodegradation of higher molecular weight PAHs (benzo[b]fluoranthene and benzo[a]pyrene) was observed at the different concentration levels of metals tested.

Bioremediation of multi-polluted soil by spent mushroom (Agaricus bisporus) substrate: Polycyclic aromatic hydrocarbons degradation and Pb availability

This study investigates the effect of three spent Agaricus bisporus substrate (SAS) application methods on bioremediation of soil multi-polluted with Pb and PAH from close to a shooting range with respect natural attenuation (SM). The remediation treatments involve (i) use of sterilized SAS to biostimulate the inherent soil microbiota (SSAS) and two bioaugmentation possibilities (ii) its use without previous treatment to inoculate A. bisporus and inherent microbiota (SAS) or (iii) SAS sterilization and further A. bisporus re-inoculation (Abisp). The efficiency of each bioremediation microcosm was evaluated by: fungal activity, heterotrophic and PAH-degrading bacterial population, PAH removal, Pb mobility and soil eco-toxicity. Biostimulation of the native soil microbiology (SSAS) achieved similar levels of PAH biodegradation as SM and poor soil detoxification. Bioaugmented microcosms produced higher PAH removal and eco-toxicity reduction via different routes. SAS increased the PAH-degrading bacterial population, but lowered fungal activity. Abisp was a good inoculum carrier for A. bisporus exhibiting high levels of ligninolytic activity, the total and PAH-degrading bacteria population increased with incubation time. The three SAS applications produced slight Pb mobilization (<0.3%). SAS sterilization and further A. bisporus re-inoculation (Abisp) proved the best application method to remove PAH, mainly BaP, and detoxify the multi-polluted soil.