Rhodococcus spongiicola sp. nov. and Rhodococcus xishaensis sp. nov., from marine sponges.

Two novel Rhodococcus strains, LHW50502T and LHW51113T, were isolated from marine sponges obtained on Xisha Island, Hainan Province, PR China. Rods and cocci, typical characteristics of the genus Rhodococcus, were observed. The strains contained meso-diaminopimelic acid as the diagnostic diamino acid in the cell-wall hydrolysates and galactose, arabinose, ribose and glucose as the whole-cell sugars. The major fatty acid identified was C16 : 0. MK-8(H4) was the predominat menaquinone of both strains. Stains LHW50502T and LHW51113T had almost identical (99.6 %) 16S rRNA gene sequences but shared relatively low similarities with previously characterized Rhodococcus species (well below 98.7 %). The results of phylogenetic analysis supported their closest relationship; however, the average nucleotide identity and digital DNA-DNA hybridization values between these two strains indicated that they belonged to distinct species. Taken together, the results of this study indicate that strains LHW50502T and LHW51113T represent two novel species of the genus Rhodococcus, for which the names Rhodococcus spongiicola sp. nov. (type strain LHW50502T=DSM 106291T=CCTCC AA 2018033T) and Rhodococcus xishaensis sp. nov. (type strain LHW51113T=DSM 106204T=CCTCC AA 2018034T) are proposed.

Rhodococcus spelaei sp. nov., isolated from a cave, and proposals that Rhodococcus biphenylivorans is a later synonym of Rhodococcus pyridinivorans, Rhodococcus qingshengii and Rhodococcus baikonurensis are later synonyms of Rhodococcus erythropolis, and Rhodococcus percolatus and Rhodococcus imtechensis are later synonyms of Rhodococcus opacus.

Two novel actinobacterial strains, designated C9-5T and C3-43, were isolated from soil samples of a cave in Jeju Island, Republic of Korea, and subjected to taxonomic study by a polyphasic approach. The organisms exhibited a typical rod-coccus developmental cycle during growth and grew at 10-30 °C, pH 5-9 and 0-3 % (w/v) NaCl. In 92 single-copy core gene sequence analysis, strain C9-5T was loosely associated with Rhodococcus tukisamuensis, albeit sharing low 16S rRNA gene sequence similarity (97.4 %). A combination of morphological and chemotaxonomic characteristics supported assignment with the genus Rhodococcus. With respect to 16S rRNA gene sequence similarity, the novel isolates showed the highest identity to the type strain of Rhodococcus subtropicus (98.7 % sequence similarity), followed by Rhodococcus olei (98.5 %) and Rhodococcus pedocola (98.4 %).The average nucleotide identity and digital DNA-DNA hybridization values between strain C9-5T and members of the genus Rhodococcus were ≤81.5 and ≤37.1 %, respectively. A set of physiological and chemotaxonomic properties together with overall genomic relatedness differentiated the novel isolates from members of the genus Rhodococcus, for which the name Rhodococcus spelaei sp. nov. is proposed. The type strain is C9-5T (=KACC 19822T=DSM 107558T). Based on genome analysis performed here, it is also proposed that Rhodococcus biphenylivorans Su et al. 2015 is a later heterotypic synonym of Rhodococcus pyridinivorans Yoon et al. 2000, Rhodococcus qingshengii Xu et al. 2007 and Rhodococcus baikonurensis Li et al. 2004 are later heterotypic synonyms of Rhodococcus erythropolis (Gray and Thornton 1928) Goodfellow and Alderson 1979 (Approved Lists 1980), and Rhodococcus percolatus Briglia et al. 1996 and Rhodococcus imtechensis Ghosh et al. 2006 are later heterotypic synonyms of Rhodococcus opacus Klatte et al. 1995.

A bifunctional enzyme belonging to cytochrome P450 family involved in the O-dealkylation and N-dealkoxymethylation toward chloroacetanilide herbicides in Rhodococcus sp. B2.

BACKGROUND: The chloroacetamide herbicides pretilachlor is an emerging pollutant. Due to the large amount of use, its presence in the environment threatens human health. However, the molecular mechanism of pretilachlor degradation remains unknown. RESULTS: Now, Rhodococcus sp. B2 was isolated from rice field and shown to degrade pretilachlor. The maximum pretilachlor degradation efficiency (86.1%) was observed at a culture time of 5 d, an initial substrate concentration 50 mg/L, pH 6.98, and 30.1 °C. One novel metabolite N-hydroxyethyl-2-chloro-N-(2, 6-diethyl-phenyl)-acetamide was identified by gas chromatography-mass spectrometry (GC-MS). Draft genome comparison demonstrated that a 32,147-bp DNA fragment, harboring gene cluster (EthRABCDB2), was absent from the mutant strain TB2 which could not degrade pretilachlor. The Eth gene cluster, encodes an AraC/XylS family transcriptional regulator (EthRB2), a ferredoxin reductase (EthAB2), a cytochrome P450 monooxygenase (EthBB2), a ferredoxin (EthCB2) and a 10-kDa protein of unknown function (EthDB2). Complementation with EthABCDB2 and EthABDB2, but not EthABCB2 in strain TB2 restored its ability to degrade chloroacetamide herbicides. Subsequently, codon optimization of EthABCDB2 was performed, after which the optimized components were separately expressed in Escherichia coli, and purified using Ni-affinity chromatography. A mixture of EthABCDB2 or EthABDB2 but not EthABCB2 catalyzed the N-dealkoxymethylation of alachlor, acetochlor, butachlor, and propisochlor and O-dealkylation of pretilachlor, revealing that EthDB2 acted as a ferredoxin in strain B2. EthABDB2 displayed maximal activity at 30 °C and pH 7.5. CONCLUSIONS: This is the first report of a P450 family oxygenase catalyzing the O-dealkylation and N-dealkoxymethylation of pretilachlor and propisochlor, respectively. And the results of the present study provide a microbial resource for the remediation of chloroacetamide herbicides-contaminated sites.

Complete genome sequencing and comparative CAZyme analysis of Rhodococcus sp. PAMC28705 and PAMC28707 provide insight into their biotechnological and phytopathogenic potential.

Study of carbohydrate-active enzymes (CAZymes) can reveal information about the lifestyle and behavior of an organism. Rhodococcus species is well known for xenobiotic metabolism; however, their carbohydrate utilization ability has been less discussed till date. This study aimed to present the CAZyme analysis of two Rhodococcus strains, PAMC28705 and PAMC28707, isolated from lichens in Antarctica, and compare them with other Rhodococcus, Mycobacterium, and Corynebacterium strains. Genome-wide computational analysis was performed using various tools. Results showed similarities in CAZymes across all the studied genera. All three genera showed potential for significant polysaccharide utilization, including starch, cellulose, and pectin referring their biotechnological potential. Keeping in mind the pathogenic strains listed across all three genera, CAZymes associated to pathogenicity were analyzed too. Cutinase enzyme, which has been associated with phytopathogenicity, was abundant in all the studied organisms. CAZyme gene cluster of Rhodococcus sp. PAMC28705 and Rhodococcus sp. PAMC28707 showed the insertion of cutinase in the cluster, further supporting their possible phytopathogenic properties.

Sequence analysis of 16S rDNA, gyrB and alkB genes of plant-associated Rhodococcus species from Tunisia.

The genus Rhodococcus contains several species with agricultural, biotechnological and ecological importance. Within this genus, many phyllosphere, rhizosphere and endosphere strains are plant growth promoting bacteria, whereas strains designated as R. fascians are plant pathogens. In this study, we isolated 47 Rhodococcus strains from a range of herbaceous and woody plant species. Phylogenetic analysis based on 16S rDNA, gyrB and alkB genes was used to compare our strains with type strains of Rhodococcus. For most of our strains, sequence similarity of the 16S rDNA, gyrB and alkB regions to type strains ranged from 98-100 %. Results of the concatenated gene sequence comparisons identified 18 strains of R. fascians and three strains of R. kroppenstedtii. The remaining strains were unclassified, and may represent novel species of Rhodococcus. Phylogenetic analysis based on gyrB sequences provided a more precise classification of our strains to species level than 16S rDNA sequences, whereas analysis of alkB sequences was unable to identify strains with orange-coloured colonies to species level.

Rhodococcus cavernicola sp. nov., isolated from a cave, and Rhodococcus degradans is a later heterosynonym of Rhodococcus qingshengii.

A Gram-reaction-positive, strictly aerobic, catalase-positive, oxidase-negative, non-motile actinobacterium, designated C1-24T, was isolated from a soil sample collected inside a natural cave. The organism exhibited a rod-coccus developmental cycle during its growth phase. Results of 16S rRNA gene-based phylogenetic analysis showed that the novel strain belonged to the genus Rhodococcus and formed a distinct sublineage at the base of the radiation including a Rhodococcus enclensis-Rhodococcus kroppenstedtii-Rhodococcus corynebacterioides-Rhodococcus trifoli cluster. In the results of phylogenomic analysis, the novel strain was loosely associated to Rhodococcus corynebacterioides. The closest relatives were Rhodococcus qingshengii (98.01 % 16S rRNA gene sequence similarity) and Rhodococcus degradans (98.01 %). The genome size was 5.66 Mbp and the DNA G+C content was 64.30 mol%. Whole-cell hydrolysates contained meso-diaminopimelic acid, arabinose and galactose as the diagnostic diamino acid and sugars. MK-8(H2) was the predominant menaquinone. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, an unidentified glycolipid and three unidentified phospholipids. Mycolic acids were present. The major fatty acids were C16 : 0, C18 : 1 ω9c, C16 : 1 ω7c and/or C16 : 1 ω6c and 10-methyl C18 : 0. Digital DNA-DNA hybridization and average nucleotide identity values revealed that the novel strain should be assigned to a different species. Based on the combined data obtained here, strain C1-24T (=KACC 19964T=DSM 109484T) represents a new species of the genus Rhodococcus, for which Rhodococcus cavernicola sp. nov. is proposed. Also, it is proposed that R. degradans is a later heterosynonym of R. qingshengii based on analyses of 16S rRNA gene and whole-genome sequences.

Rhodococcus oryzae sp. nov., a novel actinobacterium isolated from rhizosphere soil of rice (Oryza sativa L.).

A Gram-stain-positive, non-motile, creamy-white actinobacterium, which has an elementary branching rod-coccus life cycle was isolated from the rhizosphere soil of rice (Oryza sativa L.) collected from Northeast Agricultural University in Harbin, Heilongjiang province, north-east PR China, and its taxonomic status was examined by using a polyphasic approach. Results from the 16S rRNA gene sequence study showed that the isolate, designated strain NEAU-CX67T, belonged to the genus Rhodococcus and formed a cluster with Rhodococcus maanshanensis DSM 44675T, Rhodococcus kronopolitis NEAU-ML12T and Rhodococcus tukisamuensis JCM 11308T (98.3, 98.1 and 97.7% gene sequence similarity, respectively). The major fatty acids were C16 : 0, 10-methyl C18 : 0, C18 : 1 ω9c and C16 : 1 ω7c. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannoside. The major isoprenoid quinone was MK-8(H2). Whole-cell hydrolysates contained meso-diaminopimelic acid. Arabinose, galactose and ribose were detected as diagnostic sugars from whole-cell hydrolysates. Mycolic acids were detected. The genomic DNA G+C content of strain NEAU-CX67T was 64.6 mol%. Strain NEAU-CX67T exhibited low average nucleotide identity and digital DNA-DNA hybridization values with R. maanshanensis DSM 44675T (92.1 and 45.4 %) and R. tukisamuensis JCM 11308T (81.9 and 24.4 %). On the basis of results of phylogenetic, genotypic, physiological and chemotaxonomic analysis, strain NEAU-CX67T is considered to represent a novel species of the genus Rhodococcus for which the name Rhodococcus oryzae sp. nov. is proposed. The type strain is NEAU-CX67T (=DSM 107701T=CCTCC AB 2018233T).

Raman spectroscopic signatures of carotenoids and polyenes enable label-free visualization of microbial distributions within pink biofilms.

Pink biofilms are multispecies microbial communities that are commonly found in moist household environments. The development of this pink stain is problematic from an aesthetic point of view, but more importantly, it raises hygienic concerns because they may serve as a potential reservoir of opportunistic pathogens. Although there have been several studies of pink biofilms using molecular analysis and confocal laser scanning microscopy, little is known about the spatial distributions of constituent microorganisms within pink biofilms, a crucial factor associated with the characteristics of pink biofilms. Here we show that Raman spectroscopic signatures of intracellular carotenoids and polyenes enable us to visualize pigmented microorganisms within pink biofilms in a label-free manner. We measured space-resolved Raman spectra of a pink biofilm collected from a bathroom, which clearly show resonance Raman bands of carotenoids. Multivariate analysis of the Raman hyperspectral imaging data revealed the presence of typical carotenoids and structurally similar but different polyenes, whose spatial distributions within the pink biofilm were found to be mutually exclusive. Raman measurements on individual microbial cells isolated from the pink biofilm confirmed that these distributions probed by carotenoid/polyene Raman signatures are attributable to different pigmented microorganisms. The present results suggest that Raman microspectroscopy with a focus on microbial pigments such as carotenoids is a powerful nondestructive method for studying multispecies biofilms in various environments.

A new Rhodococcus aetherivorans strain isolated from lubricant-contaminated soil as a prospective phenol-biodegrading agent.

Microbe-based decontamination of phenol-polluted environments has significant advantages over physical and chemical approaches by being relatively cheaper and ensuring complete phenol degradation. There is a need to search for commercially prospective bacterial strains that are resistant to phenol and other co-pollutants, e.g. oil hydrocarbons, in contaminated environments, and able to carry out efficient phenol biodegradation at a variable range of concentrations. This research characterizes the phenol-biodegrading ability of a new actinobacteria strain isolated from a lubricant-contaminated soil environment. Phenotypic and phylogenetic analyses showed that the novel strain UCM Ac-603 belonged to the species Rhodococcus aetherivorans, and phenol degrading ability was quantitatively characterized for the first time. R. aetherivorans UCM Ac-603 tolerated and assimilated phenol (100% of supplied concentration) and various hydrocarbons (56.2-94.4%) as sole carbon sources. Additional nutrient supplementation was not required for degradation and this organism could grow at a phenol concentration of 500 mg L-1 without inhibition. Complete phenol assimilation occurred after 4 days at an initial concentration of 1750 mg L-1 for freely-suspended cells and at 2000 mg L-1 for vermiculite-immobilized cells: 99.9% assimilation of phenol was possible from a total concentration of 3000 mg L-1 supplied at daily fractional phenol additions of 750 mg L-1 over 4 days. In terms of phenol degradation rates, R. aetherivorans UCM Ac-602 showed efficient phenol degradation over a wide range of initial concentrations with the rates (e.g. 35.7 mg L-1 h-1 at 500 mg L-1 phenol, and 18.2 mg L-1 h-1 at 1750 mg L-1 phenol) significantly exceeding (1.2-5 times) reported data for almost all other phenol-assimilating bacteria. Such efficient phenol degradation ability compared to currently known strains and other beneficial characteristics of R. aetherivorans UCM Ac-602 suggest it is a promising candidate for bioremediation of phenol-contaminated environments.

Influence of pressure and dispersant on oil biodegradation by a newly isolated Rhodococcus strain from deep-sea sediments of the gulf of Mexico.

A new Rhodococcus strain, capable of degrading crude oil, was isolated from the Gulf of Mexico deep-sea sediment and was investigated for its biodegradation characteristics under atmospheric as well as under deep-sea pressure (1500 m = 15 MPa). Additionally, the effect of dispersant (Corexit EC9500A) addition was studied. Rhodococcus sp. PC20 was shown to degrade 60.5 ±â€¯10.7% of the saturated and aromatic fraction of crude oil at atmospheric pressure and 74.2 ±â€¯9.1% at deep-sea level pressure within 96 h. Degradation rates, especially for monoaromatic hydrocarbons, were significantly higher at elevated pressure compared to atmospheric pressure. This study found a growth inhibiting effect at a dispersant to oil ratio of 1:100 and higher. This effect of the dispersant was enhanced when elevated pressure was applied.

Microaerobic conditions caused the overwhelming dominance of Acinetobacter spp. and the marginalization of Rhodococcus spp. in diesel fuel/crude oil mixture-amended enrichment cultures.

The aim of the present study was to reveal how different microbial communities evolve in diesel fuel/crude oil-contaminated environments under aerobic and microaerobic conditions. To investigate this question, aerobic and microaerobic bacterial enrichments amended with a diesel fuel/crude oil mixture were established and analysed. The representative aerobic enrichment community was dominated by Gammaproteobacteria (64.5%) with high an abundance of Betaproteobacteriales (36.5%), followed by Alphaproteobacteria (8.7%), Actinobacteria (5.6%), and Candidatus Saccharibacteria (4.5%). The most abundant alkane monooxygenase (alkB) genotypes in this enrichment could be linked to members of the genus Rhodococcus and to a novel Gammaproteobacterium, for which we generated a high-quality draft genome using genome-resolved metagenomics of the enrichment culture. Contrarily, in the microaerobic enrichment, Gammaproteobacteria (99%) overwhelmingly dominated the microbial community with a high abundance of the genera Acinetobacter (66.3%), Pseudomonas (11%) and Acidovorax (11%). Under microaerobic conditions, the vast majority of alkB gene sequences could be linked to Pseudomonas veronii. Consequently, results shed light on the fact that the excellent aliphatic hydrocarbon degrading Rhodococcus species favour clear aerobic conditions, while oxygen-limited conditions can facilitate the high abundance of Acinetobacter species in aliphatic hydrocarbon-contaminated subsurface environments.

Rhodococcus induced false-positive galactomannan (GM), a biomarker of fungal presentation, in patients with peritoneal dialysis: case reports.

BACKGROUND: Galactomannan index (GMI) at a level higher than 0.5 provides high sensitivity and specificity for the diagnosis of fungal peritonitis. Here, we report the false-positive of GMI in peritoneal dialysis (PD) effluent (PDE) due to Rhodococcus peritonitis in PD patients. CASE PRESENTATION: GMI in PDE of case #1 and case #2 were 1.53 and 0.76, respectively, while serum GMI of both cases was less than 0.5. In addition, GMI from the specimens obtained directly from the stationary phase of Rhodococcus colonies were 1.27 and 1.56, which were isolated from case #1 and #2, accordingly. CONCLUSION: High GMI in PDE of PD patients is not specific just for fungal infections but may also be secondary to other infections, such as Rhodococcus spp., especially in endemic areas.

Detection of Nocardia, Streptomyces and Rhodococcus from bronchoalveolar lavage specimens of patients with HIV by Multiplex PCR Assay.

BACKGROUND: Nocardia, Streptomyces and Rhodococcus are life threatening opportunistic pathogens under immunodeficiency conditions, particularly among patients infected with HIV. Rapid and accurate detection of these infections can improve immune health quality, patient management and appropriate treatment. The aim of this study was to design a novel multiplex-PCR assay for rapid diagnosis of these three organisms directly from bronchoalveolar lavage (BAL) specimens of patients infected with HIV. METHODS: The genus specific primers were designed for direct-detection of Nocardia, Streptomyces and Rhodococcus in a single tube multiplex PCR. This PCR specifically amplified the target genes from pure cultures. It subsequently was applied on BAL specimens of 29 HIV positive patients that had previously been culture negative for actinomycete bacteria, of which Nocardia, Streptomyces and Rhodococcus are members. RESULTS: Of 29 respiratory clinical specimens, there were positive for Nocardia spp. and one was positive for Streptomyces spp using the multiplex PCR assay. The sequencing of the PCR products identified the species as Nocardia cyriacigeorgica (n=2), Nocardia farcinica and Streptomyces albus. CONCLUSION: This novel multiplex PCR assay yielded reliable results for accurate identification of Nocardia, Streptomyces and Rhodococcus from BAL while the results of bacterial culture were negative.

Rhodococcus subtropicus sp. nov., a new actinobacterium isolated from a cave.

A novel Gram-stain-positive actinobacterial strain, designated C9-28T, was isolated from soil sampled in a natural cave on Jeju Island, Republic of Korea. Strain C9-28T morphologically exhibited a rod-coccus life cycle and grew at 10-37 °C (optimum, 30 °C), pH 6-9 (optimum, pH 7) and 0-3 % (optimum, absence of NaCl). In the maximum-likelihood tree based on 16S rRNA gene sequences, strain C9-28T formed a sublineage between a Rhodococcus equi-Rhodococcus soli-Rhodococcus agglutinans clade and the type strain of Rhodococcus defluvii. The closest relatives of strain C9-28T were the type strains of R. defluvii (98.88 % 16S rRNA gene sequence similarity), R. equi (98.88 %) and R. soli (98.60 %). The phylogenomic tree based on whole genome sequences supported the distinct position of the novel strain within the genus Rhodococcus. The following chemotaxonomic characteristics also supported the assignment to the genus: meso-diaminopimelic acid; arabinose and galactose in whole-cell hydrolysates; the predominant menaquinone of MK-8(H2); and polar lipids including diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, three unidentified glycolipids and two unidentified lipids. The predominant cellular fatty acids were C16 : 0, summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), C18 : 1ω9c and C14 : 0. Based on the values of average nucleotide identity and digital DNA-DNA hybridization from whole genome sequences, and in vitro DNA-DNA hybridization between the isolate and the closest relatives, strain C9-28T (=KACC 19823T=DSM 107559T) represents a novel species of the genus Rhodococcus, for which the name Rhodococcussubtropicus sp. nov. is proposed.

Characterization of trehalose lipids produced by a unique environmental isolate bacterium Rhodococcus qingshengii strain FF.

AIMS: The aim of this study was to elucidate the chemical properties and applications of trehalose lipids produced by Rhodococcus qingshengii strain FF and optimize its production yield. METHODS AND RESULTS: Strain FF was identified as R. qingshengii. It was observed to produce biosurfactants in the presence of n-hexadecane. The biosurfactants were identified as the mixture of trehalose triesters and trehalose tetraesters, mainly consisting of TrehC12 C3 C6 C12 :10, TrehC11 C8 C6 :6, TrehC11 C6 C4 :5 and TrehC6 C4 C6 :5 based on the analysis of thin layer chromatography, Fourier transform infrared and flight tandem mass spectrometry. The best carbon source and nitrogen source for producing trehalose lipids was the mixture of n-hexadecane and oleic acid (m : m = 1 : 1) and the organic nitrogen, urea. Under this condition, the production of trehalose lipids could reach 7·97 g l-1 . The crude trehalose lipids showed extremely high surface-active properties and were proven to promote the degradation of naphthalene. CONCLUSIONS: The trehalose lipids produced by R. qingshengii strain FF exhibited high surfactant activity under various conditions and were proven to promote the degradation of naphthalene. SIGNIFICANCE AND IMPACT OF THE STUDY: Rhodococcus qingshengii strain FF is a potential candidate for bioremediation. The trehalose lipids might be used as unique biosurfactants in cosmetic industries, biological formulations and other applications.

Screening, partial purification of antivibriosis metabolite sterol-glycosides from Rhodococcus sp. against aquaculture associated pathogens.

The present study probed the antimicrobial potential of a rare mangrove associated actinomycetes against an array of aquatic bacterial pathogens causing disease outbreak in fin and shellfish. Antibacterial activity results implied that the mangrove associated actinomycetes RAS7 exhibited striking inhibitory activity against the tested aquatic bacterial pathogens. Identification of strain RAS7 through polyphasic and 16S rRNA sequencing affirmed that the strain belongs to Rhodococcus sp. Optimization of culture conditions for antibacterial activity by Rhodococcus sp. inferred that it grew well and exerted notable antagonistic activity in medium supplied with 1% galactose and peptone as carbon and nitrogen sources. Similarly, the strain grown in 0.1% tyrosine, 1% NaCl, pH 7.5 and temperature 35 °C recorded maximum bioactivity against the test pathogens. The crude ethyl acetate extract of Rhodococcus sp. at 200  µg/ml recorded markedly pronounced growth inhibitory activity ranged between 14 and 29 mm. The cytotoxic effect of crude extract against brine shrimp Artemia salina nauplii registered LC50 value of 134.294 µg/ml after 24 h of exposure. The secondary metabolite was separated using Ethyl acetate: Methanol (7:3) as solvent system through TLC. The TLC autobiogram mapped the active spot in TLC with Rf value of 0.84. Analysis of chemical constituents and FT-IR spectral analysis substantiated that the active principle in bioassay guided fraction was sterol-glycosides.

Desorption and solubilization of anthracene by a rhamnolipid biosurfactant from Rhodococcus fascians.

The rhamnolipid biosurfactant-producing bacterium, strain SDRB-G7, was isolated from the sediment of Sindu-ri beach and identified as Rhodococcus fascians based on a phylogenetic analysis. Optimal activity, with the highest yield (2.441 g/L) and surface tension-reducing activity (24.38 mN/m), was observed when the cells were grown on olive oil as their sole source of carbon at pH 8.0. The rhamnolipid biosurfactant showed environmental stability at a variety of NaCl concentrations (2-20%) and pH values (2-12) even under acidic conditions. Of the initial anthracene, 66% was solubilized by 100% crude biosurfactant. Furthermore, 100% crude biosurfactant desorbed 81% of the anthracene in sediment into the aqueous phase. These results suggest that the rhamnolipid biosurfactant produced from R. fascians SDRB-G7 is a promising candidate for polycyclic aromatic hydrocarbon (PAH) removal from the sediment and can be an effective agent for processes that bioremediate PAHs such as surfactant-enhanced remediation. PRACTITIONER POINTS: Biosurfactants can accelerate desorption of PAHs and improve their solubility. BS-producing R. fascians SDRB-G7 was selected by screening of biochemical tests. Solubility of anthracene was enhanced by rhamnolipid produced by strain SDRB-G7. Microbial surfactant is a promising alternative for bioremediation of PAH-polluted sites.