Solvent Stress Response of the Denitrifying Bacterium “ Aromatoleum aromaticum ” Strain EbN1

Abstract

The denitrifying betaproteobacterium "Aromatoleum aromaticum" strain EbN1 degrades several aromatic compounds, including ethylbenzene, toluene, p-cresol, and phenol, under anoxic conditions. The hydrophobicity of these aromatic solvents determines their toxic properties. Here, we investigated the response of strain EbN1 to aromatic substrates at semi-inhibitory (about 50% growth inhibition) concentrations under two different conditions: first, during anaerobic growth with ethylbenzene (0.32 mM) or toluene (0.74 mM); and second, when anaerobic succinate-utilizing cultures were shocked with ethylbenzene (0.5 mM), toluene (1.2 mM), p-cresol (3.0 mM), and phenol (6.5 mM) as single stressors or as a mixture (total solvent concentration, 2.7 mM). Under all tested conditions impaired growth was paralleled by decelerated nitrate-nitrite consumption. Additionally, alkylbenzene-utilizing cultures accumulated poly(3-hydroxybutyrate) (PHB) up to 10% of the cell dry weight. These physiological responses were also reflected on the proteomic level (as determined by two-dimensional difference gel electrophoresis), e.g., up-regulation of PHB granule-associated phasins, cytochrome cd 1 nitrite reductase of denitrification, and several proteins involved in oxidative (e.g., SodB) and general (e.g., ClpB) stress responses.

Anaerobic Catabolism of Aromatic Compounds: a Genetic and Genomic View

“…The products of the ebA326 to ebA335, ebA1926 to ebA1936, and ebA5762 to ebA5768 genes were specifically formed during anaerobic growth on p-ethylphenol (379), toluene (203), and phenol/p-cresol (378), respectively. The formation of ebA5762 to ebA5768 was also observed in succinate-utilizing cells suddenly stressed with phenolic compounds (351). These similar regulatory patterns support the predicted solvent-related function of the encoded proteins and point to a fine-tuned system of solvent stress tolerance in Azoarcus sp.…”

“…However, in Azoarcus sp. strain EbN1, the semi-inhibitory alkylbenzene concentrations determined for cells grown in succinate were at least 2.5-fold higher than those reported for other anaerobic biodegraders and similar to those reported for aerobic P. putida strains (351). It was shown that during anaerobic growth with 0.32 mM ethylbenzene or 0.74 mM toluene, the corresponding degradation pathways were operative in strain EbN1.…”

“…It was shown that during anaerobic growth with 0.32 mM ethylbenzene or 0.74 mM toluene, the corresponding degradation pathways were operative in strain EbN1. However, when cells grown in succinate were suddenly exposed to 0.5 mM ethylbenzene, 1.2 mM toluene, 3.0 mM p-cresol, and 6.5 mM phenol, applied as single stressors or as a mixture (total solvent concentration, 2.7 mM), the corresponding degradation pathways were not operative, and complete growth inhibition was observed (351). Thus, aromatic compound degradation seems not to contribute to the solvent tolerance of strain EbN1 (351).…”

“…Moreover, the purified DCO from T. aromatica was also enriched with an additional protein that was identified as being an aconitase-like protein (349). Since both catalase and aconitase enzymes, which are classical oxidative stress-related proteins, have been shown to be upregulated when anaerobes are grown in the presence of several aromatic compounds (351), the hypothesis that the production of DCO may represent an additional strategy to cope with the oxidative stress conditions generated during the anaerobic catabolism of aromatic compounds (see below) sounds plausible.…”

Exploring biodegradable polymer production from marine microbes

“…PHAs are biopolymers that are beneficial to bacteria and environment; they are utilized as nutrient under stressful condition in rhizosphere, soil, and phyllosphere [175,179,[180][181][182][183], distribution of carbon sources [184][185][186][187], enhancing survival factors in stress condition; osmotic shock, solvent stress, UV irradiation, heat and cold, ethanol, H2O2, and desiccation [188][189][190][191][192][193]183,[194][195][196] and control exopolysaccharide production [197,198,191,192,199] play a vital role in different energy consuming pathways, chemotaxis, nitrogen fixation, cell motility and aerotaxis [200,51,183,201,202], formation of cyst, germination, and sporulation [203]. Despite the PAHs producing significant advances, bacterial inoculants currently received much attention in plant growth promotion or plant production [204].…”