Abstract
Our objective was to study the bacterial community changes that determine enhanced removal of petroleum hydrocarbons from soils subjected to bioaugmentation with the hydrocarbon-degrading strains Rhodococcus erythropolis CD 130, CD 167, and their combination. To achieve this, a high-throughput sequencing of the 16S rRNA gene was performed. The changes in the bacterial community composition were most apparent the day after bacterial inoculation. These changes represented an increase in the percentage abundance of Rhodococcus and Pseudomonas genera. Surprisingly, members of the Rhodococcus genus were not present after day 91. At the end of the experiment, the bacterial communities from the CD 130, CD 167, and control soils had a similar structure. Nevertheless, the composition of the bacteria in the CD 130 + CD 167 soil was still distinct from the control. Metagenomic predictions from the 16S rRNA gene sequences showed that the introduction of bacteria had a significant influence on the predicted pathways (metabolism of xenobiotics, lipids, terpenoids, polyketides, and amino acids) on day one. On day 182, differences in the abundance of functional pathways were also detected in the CD 130 and CD 130 + CD 167 soils. Additionally, we observed that on day one, in all bioaugmented soils, the alkH gene was mainly contributed by the Rhodococcus and Mycobacterium genera, whereas in non-treated soil, this gene was contributed only by the Mycobacterium genus. Interestingly, from day 91, the Mycobacterium genus was the main contributor for the tested genes in all studied soils. Our results showed that hydrocarbon depletion from the analyzed soils resulted from the activity of the autochthonous bacteria. However, these changes in the composition and function of the indigenous bacterial community occurred under the influence of the introduced bacteria.
Highlights
Total petroleum hydrocarbons (TPH) are a broad family of organic compounds that originate from crude oil and contain many carcinogens and neurotoxic pollutants (Ławniczak et al, 2020)
As a result of applied bioaugmentation causing the changes in the structure of autochthonous bacteria, a 38.40%, 29.8%, and 29.72% hydrocarbon removal was observed on day 182 in soils CD 167, CD 130 and CD 130 + CD 167, respectively, while in the untreated soil, the decrease in TPH was only 14.77%
The presented analyses of the taxonomic and functional composition of bacteria in soil contaminated with petroleumhydrocarbons subjected to bioaugmentation provides a better understanding of the dynamics of autochthonous bacterial communities
Summary
Total petroleum hydrocarbons (TPH) are a broad family of organic compounds that originate from crude oil and contain many carcinogens and neurotoxic pollutants (Ławniczak et al, 2020). According to the European Environment Agency (2017), the pollution caused by petroleum products is considered to be one of the most serious global environmental problems. Since exploiting bacteria for the removal of organic pollutants from the environment has shown great promise, the development of an effective bioremediation strategy for soils contaminated with hydrocarbons is one of the major tasks facing environmental microbiologists. Bioaugmentation is a technique in which selected microbial strains are introduced into a contaminated environment to increase the rate of pollutant removal (Vogel, 1996). The poor survivability and adaptability of inoculants often results in the failure of a bioaugmentation strategy (Szulc et al, 2014). To extend the survival of the inoculants, the use of indigenous strains well adapted to the remediated soil, is highly recommended
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