Denaturing gradient gel electrophoresis of amplified fragments of genes coding for 16S rRNA and for the largest subunit of multicomponent phenol hydroxylase (LmPH) was used to monitor the behaviour and relative abundance of mixed phenol-degrading bacterial populations (Pseudomonas mendocina PC1, P. fluorescens strains PC18, PC20 and PC24) during degradation of phenolic compounds in phenolic leachate-and oil-amended microcosms. The analysis indicated that specific bacterial populations were selected in each microcosm. The naphthalene-degrading strain PC20 was the dominant degrader in oil-amended microcosms and strain PC1 in phenolic leachate microcosms. Strain PC20 was not detectable after cultivation in phenolic leachate microcosms. Mixed bacterial populations in oil-amended microcosms aggregated and formed clumps, whereas the same bacteria had a planktonic mode of growth in phenolic leachate microcosms. Colony hybridisation data with catabolic gene specific probes indicated that, in leachate microcosms, the relative proportions of bacteria having meta (PC1) and ortho (PC24) pathways for degradation of phenol and p-cresol changed alternately. The shifts in the composition of mixed population indicated that different pathways of metabolism of aromatic compounds dominated and that this process is an optimised response to the contaminants present in microcosms.

The Baltic Sea is vulnerable to environmental changes. With the increasing shipping activities, the risk of oil spills remains high. Archaea are widely distributed in many environments. However, the distribution and the response of archaeal communities to oil contamination have rarely been investigated in brackish habitats. Hence, we conducted a survey to investigate the distribution, diversity, composition, and species interactions of indigenous archaeal communities at oil-contaminated sites along the coast of the Gulf of Finland (GoF) using high-throughput sequencing. Surface water and littoral sediment samples were collected at presumably oil-contaminated (oil distribution facilities) and clean sites along the coastline of the GoF in the winter 2015 and the summer 2016. Another three samples of open sea surface water were taken as offshore references. Of Archaea, Euryarchaeota dominated in the surface water and the littoral sediment of the coast of the GoF, followed by Crenarchaeota (including Thaumarchaeota, Thermoprotei, and Korarchaeota based on the Greengenes database used). The unclassified sequences accounted for 5.62% of the total archaeal sequences. Our study revealed a strong dependence of the archaeal community composition on environmental variables (e.g., salinity, pH, oil concentration, TOM, electrical conductivity, and total DNA concentration) in both littoral sediment and coastal water in the GoF. The composition of archaeal communities was season and ecosystem dependent. Archaea was highly diverse in the three ecosystems (littoral sediment, coastal water, and open sea water). Littoral sediment harbored the highest diversity of archaea. Oil was often detected in the littoral sediment but rarely detected in water at those presumably contaminated sites. Although the composition of archaeal community in the littoral sediment was sensitive to low-input oil contamination, the unchanged putative functional profiles and increased interconnectivity of the archaeal core species network plausibly revealed resilience and the potential for oil degradation. Halobacteriaceae and putative cytochrome P450 pathways were significantly enriched in the oil-contaminated littoral sediment. The archaeal taxa formed highly interconnected and interactive networks, in which Halobacteriaceae, Thermococcus, and methanogens were the main components, implying a potential relevant trophic connection between hydrocarbon degradation, methanogenesis, sulfate reduction, and/or fermentative growth.

Accumulation of key catabolic intermediates during degradation of phenol, p‐cresol and benzoate was studied in two‐substrate batch cultivations by the strains Pseudomonas mendocina PC1, Pseudomonas fluorescens PC18 and P. fluorescens PC24. According to sequence analysis of 16S rRNA genes the strains belonged to different monophyletic clusters of Pseudomonas. The catechol 2,3‐dioxygenase (C23O) gene, xylE, of strain PC1 and the phenol monooxygenase gene, pheA, of PC24 were localised on the chromosome, while the C23O gene, xylE, of strain PC18 and the p‐cresol methylhydroxylase gene, pchF, of strains PC18 and PC24 were on plasmids. It was shown that, if the substrates were degraded from mixtures using either catechol meta, catechol ortho or catechol ortho and protocatechuate ortho pathways, then both substrates were catabolised simultaneously (nondiauxic growth) without the accumulation of intermediates. Exceptionally, degradation of phenol and benzoate via the catechol ortho pathway caused irreversible accumulation of cis,cis‐muconate without detectable effect on simultaneous consumption of substrates. When the substrates were degraded from mixtures through meta and ortho catabolic pathways, the sequential consumption of substrates (diauxic growth) was observed due to the reversible accumulation of the catabolic intermediates p‐hydroxybenzoate or catechol. Regulation of parallel catabolic pathways by the accumulation of catabolic intermediates depended on the concentration of growth substrates. At low concentrations simultaneous degradation occurred and the antagonistic effect of p‐hydroxybenzoate on the degradation of phenol was diminished. In strain PC18 only the accumulation of p‐hydroxybenzoate during growth on a phenol–p‐cresol mixture seems to be directly metabolically regulated because phenol also induces the catabolic pathway for p‐cresol degradation. Partial sequencing of the pchF genes of strains PC18 and PC24 showed considerable differences.

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