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Sex is an important factor affecting bacterial diversity in insects (Xu et al. 2016, J. Insect Phy, 95: 110–117). Divergence in some life-history traits between males and females could provide differential opportunities for bacterial colonization (Tang et al. 2012, FEMS Microb Ecol 80: 659–670). Blister beetles include almost 3000 species (Riccieri et al. 2022, Syst Ent 1-12) and are characterized by sexual dimorphism in body content of the toxic terpene cantharidin (CA). CA is produced and exuded by blister beetles in yellowish oily hemolymph droplets from leg and antennal joints as a defensive strategy (Gisondi et al. 2019, Entomol Sci 22: 258-263). Although the latest steps of CA production are still elusive (Fratini et al. 2021, BMC Genomics 22: 808), males are known to produce more CA than females and accumulate large amounts of this terpene in their reproductive organs (Carrel et al. 1993, Experientia 49: 171–174). Females are especially attracted by males with high amount of CA, which is transferred to females upon mating for protecting eggs from predators or parasites (Sierra et al. 1976, Experientia 32: 142-144). Through 16S metabarcoding we compared the bacterial composition between males and females in five species of blister beetles (Hycleus polymorphus, Mylabris variabilis, Lydus trimaculatus, Zonitis flava, Meloe proscarabeus). Gammaproteobacteria, Bacilli, Actinobacteria and Alphaproteobacteria were the most prevalent classes of bacteria in all species. Overall, we observed a sexual dimorphism in the microbial component in all examined species, with males harboring lower values of microbial alpha-diversity, as in other insects (Wan et al. 2020, Animals 10: 2352). Plausible roles of sex-specific microbes are hypothesized and, as in other terpene-producing beetles (i.e., Paederus fuscipennis, Song et al. 2022, Insect Mol Biol 1-14), the potential involvement of bacteria in the de novo biogenesis of CA in blister beetles is discussed.

Pollution of agricultural soils by excessive petroleum hydrocarbons (PHs) has recently become a severe world-wide environmental issue. Various approaches have been recently employed to biodegrade PHs and detoxify soils. In the present study, an experimental mesocosm was developed in a bioslurry reactor. Six treatments were applied to degrade PHs-and detoxify contaminated soil by adding external stimulants such as nutrients, activated sludge, synthetic surfactant, and long-chain rhamnolipids. The comparative analysis revealed that the combi-nation of activated sludge, nutrients, and biosurfactant showed a 79.4% reduction in TPHs after 10 days in the mesocosm experiment. The lowest reduction in total PHs (48.5 %) was attained in the nutrient-supplied meso-cosms. The consortia's kinetic analyses of PHs revealed the lowest half-life time (t1/2 = 4.1 days), the highest biodegradation rate constants (k = 0.17 day1), and the reaction rate data from each bioremediation method was fitted with a first-order reaction rate model. The 16S rRNA gene amplicon and sequencing revealed that Strep-tomyces, Nocardioides, Arthrobacter, Pseudomonas, and Bacillus were the main oxidative species as PHs degraders. The highest relative abundances were in Arthrobacter, Pseudomonas, and Bacillus. The phytotoxicity studies proved that there was a significant decrease in the toxicity of soil after the biotreatment. According to the findings of this study, adding external stimulants such as activated sludge, nutrients, and biosurfactants enhanced the degradation of PHs in the soil in bioslurry enhancement as a promising approach to pilot scale.

Petroleum hydrocarbons (PHs) are used as raw materials in many industries and primary energy sources. However, excessive PHs act as soil pollutants, posing serious threats to living organisms. Various ex-situ or in-situ chemical and biological methods are applied to restore polluted soil. However, most of the chemical treatment methods are expensive, environmentally unfriendly, and sometimes inefficient. That attracts scientists and researchers to develop and select new strategists to remediate polluted soil through risk-based analysis and eco-friendly manner. This review discusses the sources of PHs, properties, distribution, transport, and fate in the environment, internal and external factors affecting the soil remediation and restoration process, and its effective re-utilization for agriculture. Bioremediation is an eco-friendly method for degrading PHs, specifically by using microorganisms. Next-generation sequencing (NGS) technologies are being used to monitor contaminated sites. Currently, these new technologies have caused a paradigm shift by giving new insights into the microbially mediated biodegradation processes by targeting rRNA are discussed concisely. The recent development of risk-based management for soil contamination and its challenges and future perspectives are also discussed. Furthermore, nanotechnology seems very promising for effective soil remediation, but its success depends on its cost-effectiveness. This review paper suggests using bio-electrochemical systems that utilize electro-chemically active microorganisms to remediate and restore polluted soil with PHs that would be eco-friendlier and help tailor-made effective and sustainable remediation technologies.

Petroleum-contaminated soil is a global problem that must be faced with novel and green technologies in the near future. Considering the toxicity of fossil-based surfactants, microbial surface-active compounds (SACs) have shown various advantages, including high remobilization of hydrocarbons, low toxicity, biodegradability, sus-tainability, and others. Their main criticisms are the downstream costs (i.e., extraction, purification), the pathogenic character of some biosurfactant producers, the low yield obtained, and heterogeneity (i.e., the number and abundance of congeners). The use of surfactants at low concentrations is of great interest for efficient and controllable bioremoval of pollutants from porous soil media without harming the autochthonous microbial communities and pollutants' degraders. In the absence of valid benchmarking studies among numerous bio-surfactants' classes, novel rhamnolipids (RLs) by non-Pseudomonas aeruginosa producers also deserve in-depth investigations in the future. Herein, the main RL producers with a nonpathogenic character, with lower yields and safe capacities, were highlighted, which would be very advantageous for applying the circular economy across soil remediation sites, even at a large-scale. This review emphasizes the main current knowledge regarding the use of these glycolipids within the emerging soil remediation technologies, including soil washing, biore-mediation, phytoremediators, bio-electrochemical systems, nanoparticle technologies, and others. The main prospects that should be addressed towards tackling RL costs by including safe producers and their broths moving towards replacing chemical surfactants, at least partly, were discussed. This review enhances the un-derstanding of the novel RL-soil treatments and provides critical information to accelerate the transition to a circular economy within biosurfactant-based soil remediation technologies.

This study aims to isolate and characterize a novel rhamnolipid producer within the recent bioremediation approaches for treating hydrocarbon-contaminated soils in Algeria. In this context, from a hydrocarbon-contaminated soil, a newly bacterium designated LGMS7 was screened and identified, belonged to the Pseudomonas genus, and was closely related to Pseudomonas mucidolens, with a 16S rRNA sequence similarity of 99.05%. This strain was found to use different hydrocarbons and oils as a sole carbon and energy source for growth. It showed a stable emulsification index E24 (%) of 66.66% ± 3.46 when growing in mineral salts medium (MSM) supplemented with 2% (v/v) glycerol after incubation for 6days at 30°C. Interestingly, it was also able to reduce the surface tension of the cell-free supernatant to around 30 ± 0.65mNm−1 with a critical micelle concentration (CMC) of 800mgl−1. It was found to be able to produce around 1260 ± 0.57mgl−1 as the yield of rhamnolipid production. Its biosurfactant has demonstrated excellent stability against pH (pH 2.0–12.0), salinity (0–150gl−1), and temperature (−20 to 121°C). Based on various chromatographic and spectroscopic techniques (i.e., TLC, FTIR, 1H-NMR), it was found to belong to the glycolipid class (i.e., rhamnolipids). Taken altogether, the strain LGMS7 and its biosurfactant display interesting biotechnological capabilities for the bioremediation of hydrocarbon-contaminated sites. To the best of our knowledge, this is the first study that described the production of biosurfactants by Pseudomonas mucidolens species.

A strain NAPH6 of Pseudomonas aeruginosa, isolated from contaminated seawater taken from the fishing harbor of Sfax, Tunisia, was able to degrade almost completly the naphthalene (200 mg/l) and the aliphatic hydrocarbons of crude oil (1%, v/v), after 7 and 20 days of culture, respectively, at 30 g/l NaCl. Moreover, the isolated NAPH6 exhibited a notable potentiality to synthesize biological surfactants (BS-NAPH6) on inexpensive carbon sources. The Fourier Transform Infrared (FTIR) analysis suggested that BS-NAPH6 belonged to the glycolipid family. Besides, BS-NAPH6 displayed a high steadiness against a wide spectrum of pHs, temperatures and salinities. The treatment of human HEK293 cells by different concentrations of BS-NAPH6 displayed that this latter exhibited no cytotoxic effect at concentrations below 200 μg/mL. Furthermore, the application of BS-NAPH6 in hydrocarbons removal from polluted soil, demonstrated that it was more efficient than tested chemical surfactants. Interestingly, BS-NAPH6 highlighted a significant healing activity on the wound site in a rat model compared to a commercial cream. Due to their attractive biological properties, strain NAPH6 as well as its biosurfactant BS-NAPH6 are considered as promising candidates for various applications including environmental and biomedical ones.

Abstract Within the circular economy framework, our study aims to assess the rhamnolipid production from winery and olive oil residues as low-cost carbon sources by nonpathogenic strains. After evaluating various agricultural residues from those two sectors, Burkholderia thailandensis E264 was found to use the raw soluble fraction of nonfermented (white) grape marcs (NF), as the sole carbon and energy source, and simultaneously, reducing the surface tension to around 35 mN/m. Interestingly, this strain showed a rhamnolipid production up to 1070 mg/L (13.37 mg/g of NF), with a higher purity, on those grape marcs, predominately Rha-Rha C14-C14, in MSM medium. On olive oil residues, the rhamnolipid yield of using olive mill pomace (OMP) at 2% (w/v) was around 300 mg/L (15 mg/g of OMP) with a similar CMC of 500 mg/L. To the best of our knowledge, our study indicated for the first time that a nonpathogenic bacterium is able to produce long-chain rhamnolipids in MSM medium supplemented with winery residues, as sole carbon and energy source. Key points • Winery and olive oil residues are used for producing long-chain rhamnolipids (RLs). • Both higher RL yields and purity were obtained on nonfermented grape marcs as substrates. • Long-chain RLs revealed stabilities over a wide range of pH, temperatures, and salinities

Vineyard and olive farming are deeply rooted in the economy, culture, and even the welfare of Mediterranean countries. Although numerous approaches and methods were developed to valorize their agricultural residues, several challenges remain to overcome moving towards the Circular Economy (CE). Conventional treatments of winery and olive mill wastes are becoming increasingly expensive, demanding significant amounts of effort, resources, and energy for safe waste discharge. Therefore, the need to recycle, reuse, and recover energy and valuable biocompounds from the wastes of these two sectors become apparent. In the context of increasing waste production, climate change, coupled with dramatic rises in demand from a much larger global population and customers, CE offers the prospect of a better future. Microbes are able to produce diverse biosurfactants (BS) containing both hydrophilic and hydrophobic moieties that could interact with surfaces, lower surface and interfacial tensions, form micelles, and emulsify immiscible substances. Among several BS classes, rhamnolipids are glycolipids produced by some gram-negative bacteria with various potential applications in numerous fields, including bioremediation of contaminated soils. In contrast to several biosurfactants, this particular class of glycolipids is among the economically competitive biomolecules with its synthetic equivalents. For that, we highlighted the main opportunities, the challenges, and the future aspects towards the production of this particular type of glycolipids using winery and olive oil wastes. Therefore, we proposed the critical points that should be assumed through the path of successful strategies for rhamnolipid production using these two potential agricultural residues. This review might help at boosting the current attempts to find novel CE models. Graphic Abstract: [Figure not available: see fulltext.]

This study aims to isolate and characterize a novel rhamnolipid producer within the recent bioremediation approaches for treating hydrocarbon-contaminated soils in Algeria. In this context, from a hydrocarbon-contaminated soil, a newly bacterium designated LGMS7 was screened and identified, belonged to the Pseudomonas genus, and was closely related to Pseudomonas mucidolens, with a 16S rRNA sequence similarity of 99.05%. This strain was found to use different hydrocarbons and oils as a sole carbon and energy source for growth. It showed a stable emulsification index E(24) (%) of 66.66% ± 3.46 when growing in mineral salts medium (MSM) supplemented with 2% (v/v) glycerol after incubation for 6 days at 30 °C. Interestingly, it was also able to reduce the surface tension of the cell-free supernatant to around 30 ± 0.65 mN m(−1) with a critical micelle concentration (CMC) of 800 mg l(−1). It was found to be able to produce around 1260 ± 0.57 mg l(−1) as the yield of rhamnolipid production. Its biosurfactant has demonstrated excellent stability against pH (pH 2.0–12.0), salinity (0–150 g l(−1)), and temperature (−20 to 121 °C). Based on various chromatographic and spectroscopic techniques (i.e., TLC, FTIR, (1)H-NMR), it was found to belong to the glycolipid class (i.e., rhamnolipids). Taken altogether, the strain LGMS7 and its biosurfactant display interesting biotechnological capabilities for the bioremediation of hydrocarbon-contaminated sites. To the best of our knowledge, this is the first study that described the production of biosurfactants by Pseudomonas mucidolens species. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02751-6.

A newly marine Halomonas pacifica strain Cnaph3 was isolated, as a naphthalene degrader and biosurfactant producer, from contaminated seawater collected in Ataya’s fishing harbor, located in Kerkennah Islands, Tunisia. Chromatography flame ionization detector analysis revealed that 98.8% of naphthalene (200 mg/L) was degraded after 7 days of incubation, at 30 g/L NaCl and 37 °C. Strain Cnaph3 showed also a noticeable capacity to grow on a wide range of aliphatic, aromatic, and complex hydrocarbons. Interestingly, strain Cnaph3 showed a significant potential to produce biosurfactants in the presence of all tested substrates, particularly on glycerol (1%, v/v). Electrospray ionization analysis of the biosurfactant, designated Bios-Cnaph3, suggested a lipopeptide composition. The critical micelle concentration of Bios-Cnaph3 was about 500 mg/L. At this concentration, the surface tension of the water was reduced to 27.6 mN/m. Furthermore, Bios-Cnaph3 displayed interesting stabilities over a wide range of temperatures (4–105 °C), salinities (0–100 g/L NaCl), and pH (2.2–12.5). In addition, it showed promising capacities to remove used motor oil from contaminated soils. The biodegradation and biosurfactant-production potential of the Halomonas sp. strain Cnaph3 would present this strain as a favorite agent for bioremediation of hydrocarbon-contaminated sites under saline conditions. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13205-020-2085-x) contains supplementary material, which is available to authorized users.

BACKGROUND We showed previously that a Staphylococcus capitis strain SH6 was found to be able to degrade several malodorous mercaptans and simultaneously reduce the surface tension. RESULTS Herein, we revealed the capacity of strain SH6 to grow on various hydrocarbons, used as the only carbon and energy sources. Based on GC-MS analyses, the substantial ability to degrade up to 45% and 64% of aliphatic hydrocarbons (n-alkanes) of crude oil and waste motor oil, respectively, after 30 days of incubation at 37 °C and 180 rpm, was shown. Moreover, the properties of biosurfactant produced by strain SH6 grown on different oil substrates; diesel oil and waste motor oil, were studied. Biosurfactants exhibited enhanced emulsification capacities and significant stabilities over a wide range of salinity (20-150 g/l), temperature (-20-100 °C), pH (2-12) and also a promising abilities in crude oil removal from contaminated soils. Their CMC were of 800 mg/l. FTIR analyses suggested the lipopetide nature of biosurfactants. CONCLUSION Overall, the stabilities of biosurfactants under a wide pH range, high temperatures and variable concentrations of salt, as well as its emulsifying properties, suggest potential applications in bioremediation processes.

The aim of this study was to isolate and characterize a newly isolated bacterium, designated strain W10, a polycyclic aromatic hydrocarbon (PAHs) degrader and biosurfactant producer, belonged to Pseudomonas genus and closely related to Pseudomonas aeruginosa, with the 16 rRNA gene sequence similarity of 99.1%. Based on GC-MS analyses, it degraded around 80% of phenanthrene, used as the sole carbon and energy source, at an initial concentration of 200 mg l−1, after 30 days of incubation at 37 °C and 180 rpm, reducing the surface tension (ST) from 56.1 to 42 mN m−1 after 4 days of incubation. Furthermore, strain W10 utilized about 10%, 20%, 90%, and 99% of hexadecane (C16), pyrene, fluoranthene, and crude oil, respectively, after 30 days of incubation at 37 °C and 180 rpm. During the growth of strain W10 on phenanthrene and fluoranthene, some metabolites were identified, supporting the biodegradation pathways of the two PAHs. Interestingly, strain W10 showed also a significant potential to produce surface-active agents reducing the surface tension to 32 mN m−1 and reaching a production around 2 g l−1 after 48 h of incubation, in the presence of olive oil (1%,v/v) as substrate, at 37 °C and 180 rpm. Its biosurfactant, namely BSW10, showed an interesting emulsification activity and a high stability over a wide range of salinity (0–150 g l−1), temperature (0–100 °C), pH (2–12) and thus a promising abilities in used motor oil and crude oil removal from contaminated soils. Overall, these results provide evidence that strain W10 and its biosurfactant (BSW10) could be potential candidates for further bioremediation applications.

The present study investigates the purification and physico-chemical characterization of an extracellular protease from the Aeribacillus pallidus strain VP3 previously isolated from a geothermal oil-field (Sfax, Tunisia). The maximum protease activity recorded after 22 h of incubation at 45 °C was 3000 U/ml. Pure enzyme, designated as SPVP, was obtained after ammonium sulfate fractionation (40–60%)-dialysis followed by heat-treatment (70 °C for 30 min) and UNO Q-6 FPLC anion-exchange chromatography. The purified enzyme is a monomer of molecular mass about 29 kDa. The sequence of the 25 NH2-terminal residues of SPVP showed a high homology with those of Bacillus proteases. The almost complete inhibition by PMSF and DIFP confirmed that SPVP is a member of serine protease family. Its optima of pH and temperature were pH 10 and 60 °C, respectively. Its half-life times at 70 and 80 °C were 8 and 4 h, respectively. Its catalytic efficiency was higher than those of SAPCG, Alcalase Ultra 2.5 L, and Thermolysin type X. SPVP exhibited excellent stability to detergents and wash performance analysis revealed that it could remove blood-stains effectively and high resistance against organic solvents. These properties make SPVP a potential candidate for applications in detergent formulations and non-aqueous peptide biocatalysis.

The capacities of a biosurfactant producing and polycyclic aromatic hydrocarbon (PAH) utilizing bacterium, namely, strain 1C, isolated from an Algerian contaminated soil, were investigated. Strain 1C belonged to the Paenibacillus genus and was closely related to the specie Paenibacillus popilliae, with 16S rRNA gene sequence similarity of 98.4%. It was able to produce biosurfactant using olive oil as substrate. The biosurfactant production was shown by surface tension (32.6mN/m) after 24h of incubation at 45°C and 150rpm. The biosurfactant(s) retained its properties during exposure to elevated temperatures (70°C), relatively high salinity (20% NaCl), and a wide range of pH values (2–10). The infrared spectroscopy (FTIR) revealed that its chemical structure belonged to lipopeptide class. The critical micelle concentration (CMC) of this biosurfactant was about 0.5g/l with 29.4mN/m. In addition, the surface active compound(s) produced by strain 1C enhanced PAH solubility and showed a significant antimicrobial activity against pathogens. In addition to its biosurfactant production, strain 1C was shown to be able to utilize PAHs as the sole carbon and energy sources. Strain 1C as hydrocarbonoclastic bacteria and its interesting surface active agent may be used for cleaning the environments polluted with polyaromatic hydrocarbons.

In this study, we aimed to optimize the cultural and nutritional conditions for protease production by Lysinibacillus fusiformis strain C250R in submerged fermentation process using statistical methodology. The most significant factors (gruel, wheat bran, yeast extract, and FeSO4) were identified by Plackett-Burman design. Response surface methodology (RSM) was used to determine the optimum levels of the screened factors and their interaction. Under the optimized conditions, protease yield 3100U/mL was 4.5 folds higher than those obtained by the use of the initial conditions (680U/mL). Additionally, a new extracellular 51kDa-protease, designated SAPLF, was purified and biochemically characterized from strain C250R. It shows optimum activity at 70°C and pH 10. Its half-life times at 70 and 80°C were 10 and 6-h, respectively. Irreversible inhibition of enzyme activity of SAPLF with serine protease inhibitors demonstrated that it belongs to the serine protease family. Interestingly, its catalytic efficiency was higher than that of SPVP from Aeribacillus pallidus strain VP3 and Alcalase Ultra 2.5L from Bacillus licheniformis. This study demonstrated that SAPLF has a high detergent compatibility and an excellent stain removal compared to Alcalase Ultra 2.5L; which offers an interesting potential for its application in the laundry detergent industry.

The phenanthrene (PHE) degradation by a halotolerant bacterial consortium enriched from production water of Sercina oilfield in Tunisia was investigated. The consortium PHMM utilized PHE (200 mg/L), as a sole carbon source, in the presence of a wide range of NaCl concentrations, from 1 to 5% (w/v). The maximum growth rate was obtained at 500 mg/L of PHE. A PHE metabolism was assayed by using FTIR, UV and GC–MS analyses. Results revealed that the consortium PHMM metabolized PHE via protochatechuate pathway since intermediates such as naphthalenol and phthalic acid were detected. Phylogenetic analysis showed that the adapted consortium PHMM was composed by two dominant bacterial strains, identified as Pseudomonas sp. (strain PH1) and Staphylococcus sp. (strain PH2). All the results indicated that the microorganisms from the Tunisian oilfield have a promising application in bioremediation of petrochemical contaminated environments and could be potentially useful for the study of PAHs biodegradation.

A moderately thermophilic bacterium, designated strain CAN55, was isolated from the gas-washing wastewaters of the phosphate industry, located in Sfax, Tunisia, after enrichment on 1-decanethiol, a mercaptan used as the sole carbon and energy source. Strain CAN55 belonged to the Bacillus genus and was closely related to Bacillus licheniformis, with 16S rRNA gene sequence similarity of 99.2%. It was able to degrade 83% of 1-decanethiol (3 mM), and 39% of decyl disulfide, the product of spontaneous autoxidation, after 14 days of incubation at 55 °C, and without yeast extract added. Strain CAN55 was also capable of degrading 70% of 1-dodecanethiol (3 mM) after 14 days of incubation at 55 °C. During the growth on decanethiol and dodecanethiol, the decrease of surface tensions of cell-free culture supernatants from 55.1 to 40 mN/m and from 56.1 to 41 mN/m, respectively, after 26 h of incubation at 55 °C, was an agreement with the production of biosurfactant(s). In addition, strain CAN55 degraded 1-heptanethiol and cyclohexylmercaptan thus suggesting that this isolate may be useful for the bioremediation of mercaptan contaminated sites.

Industrial biofouling-problems associated with the accumulation of microorganisms from flowing water and fluids on processing surfaces can cause severe problems. A Pseudomonas aeruginosa strain W10 was isolated from industrial setting and found to produce predominantly di-rhamnolipids (Rha-Rha-C10-C10) with a yield of around 10 g L-1 and a critical micelle concentration (CMC) of 80 mg L-1 . P. aeruginosa W10 rhamnolipids were able to disrupt up to 99% of 48 h pre-formed biofilms of the Gram-positive organisms Bacillus licheniformis CAN55, Staphylococcus capitis SH6, and a mixed culture (strains CAN55, SH6, and W10), under static conditions, at concentrations of 0.1, 0.5, and 1 mg ml-1 on a stainless steel surface commonly used in industrial process pipelines. CFU measurements and LIVE/DEAD BacLight staining confirmed these observations. Furthermore, a purified di-rhamnolipid fraction was found to be responsible for the microbial inhibition of B. licheniformis strain CAN55. This study provides evidence that rhamnolipids may have valuable applications in preventing biofilms and biofouling in industrial plants and, in a wider context, may also apply to metal medical devices.

Biosurfactants are naturally occurring surface active compounds that have mainly been exploited for environmental applications and consumer products, with their biomedical efficacy an emerging area of research. Rhamnolipids area major group of biosurfactants that have been reported for their antimicrobial and antibiofilm efficacy. One of the main limiting factors for scaled up production and downstream applications of rhamnolipids is the fact that they are predominantly produced from the opportunistic pathogen Pseudomonas aeruginosa. In this article, we have reported the production and characterisation of long chain rhamnolipids from non-pathogenic Burkholderia thailandensis E264 (ATCC 700388). We have also investigated the antibacterial and antibiofilm properties of these rhamnolipids against some oral pathogens (Streptococcus oralis, Actinomyces naeslundii, Neisseria mucosa and Streptococcus sanguinis), important for oral health and hygiene. Treating these bacteria with different concentrations of long chain rhamnolipids resulted in a reduction of 3–4 log of bacterial viability, placing these rhamnolipids close to being classified as biocidal. Investigating long chain rhamnolipid efficacy as antibiofilm agents for prospective oral-related applications revealed good potency against oral-bacteria biofilms in a co-incubation experiments, in a pre-coated surface format, in disrupting immature biofilms and has shown excellent combination effect with Lauryl Sodium Sulphate which resulted in a drastic decrease in its minimal inhibitory concentration against different bacteria. Investigating the rhamnolipid permeabilization effect along with their ability to induce the formation of reactive oxygen species has shed light on the mechanism through which inhibition/killing of bacteria may occur.

A physico-chemical characterization of seawater taken from the fishing harbour of Sfax, Tunisia, revealed a contamination by organic and inorganic micropollutants. An aerobic marine halotolerant Bacillus stratosphericus strain FLU5 was isolated after enrichment on fluoranthene, a persistent and toxic polycyclic aromatic hydrocarbon (PAH). GC-MS analyses showed that strain FLU5 was capable of degrading almost 45 % of fluoranthene (100 mg l(-1)), without yeast extract added, after 30 days of incubation at 30 g l(-1) NaCl and 37 °C. In addition, the isolate FLU5 showed a remarkable capacity to grow on a wide range of aliphatic, aromatic and complex hydrocarbons. This strain could also synthesize a biosurfactant which was capable of reducing the surface tension of the cell-free medium, during the growth on fluoranthene. The biodegradative abilities of PAHs are promising and can be used to perform the bioremediation strategies of seawaters and marine sediments contaminated by hydrocarbons.

There are increasing concerns over the harmful effects of the phosphate industry on human health and quality of life worldwide, including the Tunisian Chemical Group (GCT) in Sfax, which generates various malodorous gas fractions, such as hydrogen sulfide (H2S) and fetid mercaptans, causing nuisance to employees and local residents. Accordingly, the present study aimed to investigate the ability of an adapted microbial consortium isolated from the gas-washing wastewaters (GWWs) generated from GCT to degrade hazardous and malodorous mercaptans. A novel mesophilic bacterial strain (SH6), which was noted to display particularly high mercaptan degradation potential, was isolated from the adapted consortium growing on those GWWs and several malodorous mercaptans after enrichment on 1-dodecanethiol. The results from 16 rRNA gene sequencing and identity analysis revealed that the SH6 isolate belonged to Staphylococcus genus, with a high sequence similarity to Staphylococcus capitis (99.7%). The SH6 strain was able to completely degrade 1-dodecanethiol, used as the sole carbon and energy source, after 72h of incubation at 37°C and 180rpm. A decrease in the surface tension of cell-free culture supernatants was observed during the oxidation of dodecanethiol, suggesting the production of surface-active compounds. The stain was also able to grow on other mercaptans, such as 1,8-octanedithiol and 2,3-butanedithiol, which further supports its potential candidacy for application in the bioremediation of mercaptan-contaminated sites. Overall, the findings of the present study indicate that the SH6 strain might offer promising opportunities for the development of more adapted, efficient and cost-effective bio-disodoration strategies.

Hydrogen sulfide (H2S) and thiols (RSH) generated by the phosphate industry cause harmful effects on human health and quality of life. The present study aims to investigate and evaluate a bacterial strain CAT37 isolated from gas-washing wastewaters in terms of its properties and ability to degrade malodorous thiols. Gas-washing wastewater samples were submitted to physicochemical analyses and used for the isolation of thiol-degrading bacteria. The results from gas chromatography-mass spectrometry (GC-MS) analysis revealed that the isolated strain CAT37 was able to oxidize ~99% of each thiol, decanethiol and dodecanethiol used as sole carbon and energy sources after 30 days of incubation at 37° C. The strain CAT37 displayed a biodegradative potential on several thiols known by their toxicity and odors. The results from phylogenetic and phenotypic analysis revealed that the CAT37 isolate belonged to the genus Brevibacillus, showing the highest sequence similarity to Brevibacillus agri. Overall, the results indicated that the strain CAT37 exhibited a number of attractive biodegradation abilities against thiols and could be considered a promising candidate for industrial application in future thiol biodeodorization strategies.