Analysis of microbial communities in heavy metals-contaminated soils using the metagenomic approach

Soil pollution occurring at mining sites has adverse impacts on soil microbial diversity. New approaches, such as metagenomics approach, have become a powerful tool to investigate biodiversity of soil microbial communities. In the current study, metagenomics approach was used to investigate the microbial diversity of soils contaminated with different concentrations of lead (Pb) and zinc (Zn). The contaminated soils were collected from a Pb and Zn mine. The soil total DNA was extracted and 16S rDNA genes were amplified using universal primers. The PCR amplicons were sequenced and bioinformatic analysis of metagenomes was conducted to identify prokaryotic diversity in the Pb- and Zn-contaminated soils. The results indicated that the ten most abundant bacteria in all samples were Solirubrobacter (Actinobacteria), Geobacter (Proteobacteria), Edaphobacter (Acidobacteria), Pseudomonas (Proteobacteria), Gemmatiomonas (Gemmatimonadetes), Nitrosomonas, Xanthobacter, and Sphingomonas (Proteobacteria), Pedobacter (Bacterioidetes), and Ktedonobacter (Chloroflexi), descendingly. Archaea were also numerous, and Nitrososphaerales which are important in the nitrogen cycle had the highest abundance in the samples. Although, alpha and beta diversity showed negative effects of Pb and Zn contamination on soil microbial communities, microbial diversity of the contaminated soils was not subjected to a significant change. This study provided valuable insights into microbial composition in heavy metals-contaminated soils.

The synergistic use of plant and isolated bacteria to clean up polycyclic aromatic hydrocarbons from contaminated soil

BACKGROUND

Biological methods of polycyclic aromatic hydrocarbons (PAH) contamination elimination typically involve the transformation of contaminants to non-toxic materials by microorganisms and plants and appear to be the most effective methods available.

METHODS

In this study, Bacillus licheniformis and Bacillus mojavensis isolated from oil-contaminated soils were inoculated onto Festuca arundinacea seeds before planting in the pot and 3 weeks after planting by syringe injection into the rhizospheric zone in order to study the elimination of PAHs from Festuca's rhizosphere in the greenhouse. Some physical and chemical properties of the soil, PAH concentrations, seeds germination percentage, root and shoot biomasses of the treated samples were examined.

RESULTS

The results showed that the treated samples inoculated with both bacteria had a significantly higher percentage of seed germination and root and shoot biomass compared to other treatments. The concentration of some PAHs reduced significantly (Pvalue < 0.05) in the rhizosphere of the treated samples inoculated with both bacteria compared to in contaminated soils. Concentrations of some PAHs (eg. Naphthalene, Phenanthrene, Benzo[a]anthracene and Dibenzo[a,h]anthracene) even reached below the detection limit of the method. The PAHs concentrations in the treated samples inoculated with bacteria was decreased significantly (Pvalue < 0.05). Therefore, the results showed the high efficiency of the Festuca and bacterial inoculation in eliminating PAHs from the soil.

CONCLUSION

According to the results, the partnership of Festuca with B. licheniformis and B. mojavensis isolates displayed positive effect on PAHs dissipation and can be effective cleanup technology with high performance.

The anti-biofouling effect of Lactobacillus fermentum-derived biosurfactant against Streptococcus mutans

Biofouling in the oral cavity often causes serious problems. The ability of Streptococcus mutans to synthesize extracellular glucans from sucrose using glucosyltransferases (gtfs) is vital for the initiation and progression of dental caries. Recently, it was demonstrated that some biological compounds, such as secondary metabolites of probiotic bacteria, have an anti-biofouling effect. In this study, S. mutans was investigated for the anti-biofouling effect of Lactobacillus fermentum (L.f.)-derived biosurfactant. It was hypothesized that two enzymes produced by S. mutans, glucosyltransferases B and C, would be inhibited by the L.f.-biosurfactant. When these two enzymes were inhibited, fewer biofilms (or none) were formed. RNA was extracted from a 48-h biofilm of S. mutans formed in the presence or absence of L.f. biosurfactant, and the gene expression level of gtfB/C was quantified using the real-time polymerase chain reaction (RT-PCR). L.f. biosurfactant showed substantial anti-biofouling activity because it reduced the process of attachment and biofilm production and also showed a reduction in gtfB/C gene expression (P value < 0.05).