SDS-degrading bacteria attach to riverine sediment in response to the surfactant or its primary biodegradation product dodecan-1-ol

New Fe3O4-Based Coatings with Enhanced Anti-Biofilm Activity for Medical Devices

With the increasing use of invasive, interventional, indwelling, and implanted medical devices, healthcare-associated infections caused by pathogenic biofilms have become a major cause of morbidity and mortality. Herein, we present the fabrication, characterization, and in vitro evaluation of biocompatibility and anti-biofilm properties of new coatings based on Fe3O4 nanoparticles (NPs) loaded with usnic acid (UA) and ceftriaxone (CEF). Sodium lauryl sulfate (SLS) was employed as a stabilizer and modulator of the polarity, dispersibility, shape, and anti-biofilm properties of the magnetite nanoparticles. The resulting Fe3O4 functionalized NPs, namely Fe3O4@SLS, Fe3O4@SLS/UA, and Fe3O4@SLS/CEF, respectively, were prepared by co-precipitation method and fully characterized by XRD, TEM, SAED, SEM, FTIR, and TGA. They were further used to produce nanostructured coatings by matrix-assisted pulsed laser evaporation (MAPLE) technique. The biocompatibility of the coatings was assessed by measuring the cell viability, lactate dehydrogenase release, and nitric oxide level in the culture medium and by evaluating the actin cytoskeleton morphology of murine pre-osteoblasts. All prepared nanostructured coatings exhibited good biocompatibility. Biofilm growth inhibition ability was tested at 24 h and 48 h against Staphylococcus aureus and Pseudomonas aeruginosa as representative models for Gram-positive and Gram-negative bacteria. The coatings demonstrated good biocompatibility, promoting osteoblast adhesion, migration, and growth without significant impact on cell viability or morphology, highlighting their potential for developing safe and effective antibacterial surfaces.

The structure of biodegradable surfactants shaped the microbial community, antimicrobial resistance, and potential for horizontal gene transfer

While most household surfactants are biodegradable in aerobic conditions, their biodegradability may obscure their environmental risks. The presence of surfactants in a biological treatment process can lead to the proliferation of antimicrobial-resistance genes (ARG) in the biomass. Surfactants can be cationic, anionic, or zwitterionic, and these different classes may have different effects on the proliferation ARG. Cationic hexadecyltrimethyl-ammonium (CTAB), anionic sodium dodecyl sulfate (SDS), and zwitterionic 3-(decyldimethylammonio)-propanesulfonate inner salt (DAPS) were used to represent the three classes of surfactants in domestic household clean-up products. This study focused on the removal of these surfactants by the O₂-based Membrane Biofilm Reactor (O_2-MBfR) for hotspot scenarios (∼1 mM) and how the three classes of surfactants affected the microbial community's structure and ARG. Given sufficient O₂ delivery, the MBfR provided at least 98% surfactant removal. The presence and biodegradation for each surfactant uniquely shaped the biofilms' microbial communities and the presence of ARG. CTAB had by far the strongest impact and the higher ARG abundance. In particular, Pseudomonas and Stenotrophomonas, the two main genera in the biofilm treating CTAB, were highly correlated to the abundance of ARG for efflux pumps and antibiotic inactivation. CTAB also led to more functional genes relevant to the Type-IV secretion system and protection against oxidative stress, which also could encourage horizontal gene transfer. Our findings highlight that the biodegradation of quaternary ammonium surfactants, while beneficial, can pose public health concerns from its ability to promote the proliferation of ARG.

Sulfate Ester Detergent Degradation in Pseudomonas aeruginosa Is Subject to both Positive and Negative Regulation

Bacteria using toxic chemicals, such as detergents, as growth substrates face the challenge of exposing themselves to cell-damaging effects that require protection mechanisms, which demand energy delivered from catabolism of the toxic compound. Thus, adaptations are necessary for ensuring the rapid onset of substrate degradation and the integrity of the cells. Pseudomonas aeruginosa strain PAO1 can use the toxic detergent sodium dodecyl sulfate (SDS) as a growth substrate and employs, among others, cell aggregation as a protection mechanism. The degradation itself is also a protection mechanism and has to be rapidly induced upon contact to SDS. In this study, gene regulation of the enzymes initiating SDS degradation in strain PAO1 was studied. The gene and an atypical DNA-binding site of the LysR-type regulator SdsB1 were identified and shown to activate expression of the alkylsulfatase SdsA1 initiating SDS degradation. Further degradation of the resulting 1-dodecanol is catalyzed by enzymes encoded by laoCBA, which were shown to form an operon. Expression of this operon is regulated by the TetR-type repressor LaoR. Studies with purified LaoR identified its DNA-binding site and 1-dodecanoyl coenzyme A as the ligand causing detachment of LaoR from the DNA. Transcriptional studies revealed that the sulfate ester detergent sodium lauryl ether sulfate (SLES) induced expression of sdsA1 and the lao operon. Growth experiments revealed an essential involvement of the alkylsulfatase SdsA1 for SLES degradation. This study revealed that the genes for the enzymes initiating the degradation of toxic sulfate-ester detergents are induced stepwise by a positive and a negative regulator in P. aeruginosa strain PAO1.IMPORTANCE Bacterial degradation of toxic compounds is important not only for bioremediation but also for the colonization of hostile anthropogenic environments in which biocides are being used. This study with Pseudomonas aeruginosa expands our knowledge of gene regulation of the enzymes initiating degradation of sulfate ester detergents, which occurs in many hygiene and household products and, consequently, also in wastewater. As an opportunistic pathogen, P. aeruginosa causes severe hygienic problems because of its pronounced biocide resistance and its metabolic versatility, often combined with its pronounced biofilm formation. Knowledge about the regulation of detergent degradation, especially regarding the ligands of DNA-binding regulators, may lead to the rational development of specific inhibitors for restricting growth and biofilm formation of P. aeruginosa in hygienic settings. In addition, it may also contribute to optimizing bioremediation strategies not only for detergents but also for alkanes, which when degraded merge with sulfate ester degradation at the level of long-chain alcohols.

LaoABCR, a Novel System for Oxidation of Long-Chain Alcohols Derived from SDS and Alkane Degradation in Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa strain PAO1 is able to use a variety of organic pollutants as growth substrates, including the anionic detergent sodium dodecyl sulfate (SDS) and long-chain alkanes. While the enzymes initiating SDS and alkane degradation are well known, the subsequent enzymatic steps for degradation of the derived primary long-chain alcohols have not yet been identified. By evaluating genes specifically induced during growth with SDS, a gene cluster encoding a putative alcohol dehydrogenase (PA0364/LaoA), a probable inner membrane protein (PA0365/LaoB), and a presumable aldehyde dehydrogenase (PA0366/LaoC) was identified and designated the Lao (long-chain-alcohol/aldehyde-oxidation) system. Growth experiments with deletion mutants with SDS, 1-dodecanol, and alkanes revealed that LaoA and LaoB are involved in the degradation of primary long-chain alcohols. Moreover, detection of 1-dodecanol oxidation in cell extracts by activity staining revealed an interdependency of LaoA and LaoB for efficient 1-dodecanol oxidation. An in silico analysis yielded no well-characterized homologue proteins for LaoA and LaoB. Furthermore, a gene adjacent to the lao gene cluster encodes a putative transcriptional regulator (PA0367/LaoR). A laoR deletion mutant exhibited constitutive expression of LaoA and LaoB, indicating that LaoR is a repressor for the expression of laoABC Taken together, these results showed that the proteins LaoA and LaoB constitute a novel oxidation system for long-chain alcohols derived from pollutants.IMPORTANCE The versatile and highly adaptive bacterium Pseudomonas aeruginosa is able to colonize a variety of habitats, including anthropogenic environments, where it is often challenged with toxic compounds. Its ability to degrade such compounds and to use them as growth substrates can significantly enhance spreading of this opportunistic pathogen in hygienic settings, such as clinics or water distribution systems. Thus, knowledge about the metabolism of P. aeruginosa can contribute to novel approaches for preventing its growth and reducing nosocomial infections. As the Lao system is important for the degradation of two different classes of pollutants, the identification of these novel enzymes can be a useful contribution for developing effective antibacterial strategies.

Characterization of SDS-degrading Delftia acidovorans and in situ monitoring of its temporal succession in SDS-contaminated surface waters

Incomplete removal of sodium dodecyl sulfate (SDS) in wastewater treatment plants may result in SDS residues escaping and finding their way into receiving water bodies like rivers, lakes, and sea. Introduction of effective microorganisms into the aerobic treatment facilities can reduce unpleasant by-products and SDS residues. Selecting effective microorganisms for SDS treatment is a big challenge. Current study reports the isolation, identification, and in situ monitoring of an effective SDS-degrading isolate from detergent-polluted river waters. Screening was carried out by the conventional enrichment culture technique and the isolate was tentatively identified by using fatty acid methyl ester and 16S ribosomal RNA (rRNA) sequence analyses. Fatty acids produced by the isolate investigated were assumed as typical for the genus Comamonas. 16S rRNA sequence analysis also confirmed that the isolate had 95% homology with Delftia acidovorans known as Comamonas or Pseudomonas acidovorans previously. D. acidovorans exhibited optimum growth at SDS concentration of 1 g l(-1) but tolerated up to 10 g l(-1) SDS. 87% of 1.0 g l(-1) pure SDS was degraded after 11 days of incubation. The temporal succession of D. acidovorans in detergent-polluted river water was also monitored in situ by using Comamonas-specific fluorescein-labeled Cte probe. Being able to degrade SDS and populate in SDS-polluted surface waters, D. acidovorans isolates seem to be very helpful in elimination of SDS.

Plasmid-mediated biodegradation of the anionic surfactant sodium dodecyl sulphate, by Pseudomonas aeruginosa S7

Sodium dodecyl sulphate (SDS), an anionic surfactant, has been used extensively due to its low cost and excellent foaming properties. Fifteen different bacterial isolates capable of degrading SDS were isolated from detergent contaminated soil by enrichment culture technique and the degradation efficiency was assessed by Methylene Blue Active Substances (MBAS) assay. The most efficient SDS degrading isolate was selected and identified as Pseudomonas aeruginosa S7. The selected isolate was found to harbor a single 6-kb plasmid. Acridine orange, ethidium bromide, SDS and elevated temperatures of incubation failed to cure the plasmid. The cured derivatives of SDS degrading Pseudomonas aeruginosa were obtained only when ethidium bromide and elevated temperature (40 °C) were used together. Transformation of E. coli DH5α with plasmid isolated from S7 resulted in subsequent growth of the transformants on minimal salt media with SDS (0.1%) as the sole source of carbon. The SDS degradation ability of S7 and the transformant was found to be similar as assessed by Methylene Blue Active Substance Assay. The antibiotic resistance profiles of S7, competent DH5α and transformant were analyzed and it was noted that the transfer of antibiotic resistance correlated with the transfer of plasmid as well as SDS degrading property.

Cell aggregation of Pseudomonas aeruginosa strain PAO1 as an energy-dependent stress response during growth with sodium dodecyl sulfate

Pseudomonas aeruginosa strain PAO1 grew with the detergent sodium dodecyl sulfate (SDS). The growth started with the formation of macroscopic cell aggregates which consisted of respiring cells embedded in an extracellular matrix composed of acidic polysaccharides and DNA. Damaged and uncultivable cells accumulated in these aggregates compared to those cells that remained suspended. We investigated the response of suspended cells to SDS under different conditions. At high energy supply, the cells responded with a decrease in optical density and in viable counts, release of protein and DNA, and formation of macroscopic aggregates. This response was not observed if the energy supply was reduced by inhibiting respiration with KCN, or if cells not induced for SDS degradation were exposed to SDS. Exposure to SDS caused cell lysis without aggregation if cells were completely deprived of energy, either by applying anoxic conditions, by addition of CCCP, or by addition of KCN to a mutant defective in cyanide-insensitive respiration. Aggregated cells showed a more than 100-fold higher survival rate after exposure to SDS plus CCCP than suspended cells. Our results demonstrate that cell aggregation is an energy-dependent response of P. aeruginosa to detergent stress which might serve as a survival strategy during growth with SDS.

Biological activity and environmental impact of anionic surfactants

The newest results concerning the biological activity and environmental fate of anionic surfactants are collected and critically evaluated. The chemical and physicochemical parameters related to the biological activity and the field of application are briefly discussed. Examples on the effect of anionic surfactants on the cell membranes, on the activity of enzymes, on the binding to various proteins and to other cell components and on their human toxicity are presented and the possible mode of action is elucidated. The sources of environmental pollution caused by anionic surfactants are listed and the methods developed for their removal from liquid, semiliquid and solid matrices are collected. Both the beneficial and adversary effects of anionic surfactants on the environment are reported and critically discussed. It was concluded that the role of anionic surfactants in the environment is ambiguous: they can cause serous environmental pollution with toxic effect on living organisms; otherwise, they can promote the decomposition and/or removal of other inorganic and organic pollutants from the environment. The relationship between their chemical structure, physicochemical parameters, biological activity and environmental impact is notwell understood. A considerable number of data are needed for the development of new anionic surfactants and for the successful application of the existing ones to reduce the adversary and to promote beneficial effects.

The response of a bacterial biofilm community in a simulated industrial cooling water system to treatment with an anionic dispersant

The effect of a dispersant on the microbial community in a simulated open recirculating cooling water system was determined by continuous operation of the system over two consecutive periods of 196 and 252 d, respectively. An open recirculating cooling water system feeding a modified Robbin's Device with synthetic cooling water to simulate the environment of an industrial cooling water system was set up. Planktonic and biofilm (mild steel and Nylon(R)) samples were taken weekly in 1997 (196-d period) and fortnightly in 1998 (252-d period). Each biofilm was scraped off and diluted in 10-ml 1 x phosphate-buffered saline (PBS). Serial dilutions were performed and plated onto R2A agar (pH 8.0) to obtain the predominant culturable bacteria. The diversity was determined by allocating groups according to colony morphology, diameter and colour. Diversity was calculated according to the Shannon-Weaver Index. During the first run (1997), dispersant was added on day 57 to a final concentration of 15 mg l-1 for 49 d, stopped for 49 d and dosed at 30 mg l-1 for 41 d. The second run entailed adding dispersant to a final concentration of 30 mg l-1 on day 98 for 70 d, stopping dosing for 56 d and resuming dosing at 30 mg l-1 for another 28 d. The 2-year evaluation period demonstrated that the biofilm-removing action of the dispersant decreased to a point where it was not effective at all. Our results showed that the synthetic dispersant evaluated was only effective initially, but was ineffective in controlling biofouling on Nylon, and to a lesser degree on mild steel at the recommended (15 mg l-1) as well as at double the recommended concentration in the long term. The release of cells from biofilms observed when dispersant dosing was terminated, supports the notion that a community attaching in the presence of the surface active agent was selected for. The decreased efficacy may therefore be due to a selection of strains able to remain attached and/or attach in the presence of the dispersant as demonstrated by shifts in the biofilm communities on both Nylon and mild steel.

Lipophilic compounds in biotechnology--interactions with cells and technological problems

Lipophilic compounds are of significant importance in modern biotechnology. Centerly of interest are the biodegradation as well as the biotransformation of such lipophilic and often water-immiscible substances. Both whole cells and/or enzymes are used for these processes. It is obvious that a wide range of problems arise in an application of such complex systems consisting of biocatalysts substrate(s), product(s), water, (in some cases water-immiscible organic solvents): (i) interactions between lipophilic compounds and the membranes resulting in the change of some physiological characteristics of the living system; (ii) problems in the transport of these compounds (substrates and/or products) within the complex structured reaction systems; (iii) the problem of increasing the solubility of the lipophilic and mostly water-immiscible compounds with a minimum of inhibition effects on the processes; (iv) the presence of lipophilic components may also cause changes of the transport processes within the system (e.g. immobilized cells) resulting in changed yield or activity of the biological system. These problems are critically discussed in this review in relation to the known modes of interaction of lipophilic compounds with membranes, the bioavailability of the substrates, and the cases of steroid biotransformations. An outlook of future aspects in research, development and application of such processes is given.

Re-evaluation of the hypothesis that biodegradable surfactants stimulate surface attachment of competent bacteria

The hypothesis that biodegradable surfactants stimulate the attachment of biodegradation-competent bacteria to surfaces has been re-evaluated using a variant of the surfactant-degrading bacterium Pseudomonas sp. DES1 designated Pseudomonas sp. DES2. This variant was identical to the parental strain in terms of its carbon-utilization patterns and alcohol dehydrogenase and alkylsulfatase complements (enzymes involved in surfactant biodegradation), but differed markedly in its growth characteristics when using sodium dodecyl triethoxysulfate or triethylene glycol dodecyl ether as secondary carbon sources. Pseudomonas sp. DES1 exhibited diauxie in these surfactant-based culture media in contrast to Pseudomonas sp. DES2, which exhibited single-phase growth. Pseudomonas sp. DES2 did not attach to river sediment in a microcosm system when challenged with a dose of either surfactant, although it did biodegrade the substrate. In contrast, Pseudomonas sp. DES1 attached to the river sediment whilst biodegrading the test substrate. It is concluded that the ether-scission system, which is responsible for primary biodegradation of both substrates, is deregulated in Pseudomonas sp. DES2 in contrast to that in Pseudomonas sp. DES1, and that, contrary, to a previous hypothesis, biodegradable surfactants do not necessarily stimulate the attachment of biodegradation-competent bacteria during their biodegradation.

Charge-transfer chromatographic study of the interaction of antibiotics with sodium dodecylsulfate

The interaction of 29 antibiotics with the anionic surfactant sodium dodecylsulfate (SDS) was studied by charge-transfer reversed-phase chromatography carried out on impregnated silica layers using water-methanol mixtures as eluents. The hydrophobicity of antibiotics and the relative strength of SDS-antibiotic interaction was calculated separately for each antibiotic-SDS pair. SDS interacted with 17 antibiotics where the antibiotic-SDS complex was either more hydrophilic or more hydrophobic than the uncomplexed molecule. The relative strength of interaction depended considerably on the molecular structure of the antibiotics. No significant linear correlation was found between the hydrophobicity parameters of antibiotics and their capacity to interact with SDS. Stepwise regression analysis proved that the inductive effect of substituents, their electron-withdrawing power and proton-acceptor capacity exert a significance influence on the strength of interaction.