Unique Carbon Source Research Articles

Acinetobacter baylyi ADP1 growth performance and lipid accumulation on different carbon sources.

Acinetobacter baylyi ADP1 is a microorganism with the potential to produce storage lipids. Here, a systematic study was carried out to evaluate growth performance and accumulation of wax esters and triacylglycerols using glycerol, xylose, glucose, acetate, ethanol, and pyruvate as carbon sources. High specific growth rates (μ) were found in gluconeogenic carbon sources (ethanol, acetate, and pyruvate: 0.94 ± 0.18, 0.93 ± 0.06, and 0.61 ± 0.01 h-1, respectively), and low in glucose (0.25 ± 0.01 h-1). Interestingly, these μ values were sustained in a broad range of concentrations of glucose (0.5-50 g L-1), pyruvate (3-10 g L-1), and acetate (0.3-2 g L-1), suggesting a high tolerance to glucose and pyruvate. It was observed that ADP1 is not able to use glycerol or xylose as unique carbon sources. On the other hand, ADP1 showed sensitivity to osmotic upshifts, noted by the lysis at the beginning of cultivations on different carbon sources. However, ADP1 is adapted to relatively high substrate concentrations as indicated by the minimal inhibitory concentrations (MICs) determined at 24 h of cultivations: 350, 50, 80, and 15 g L-1 for glucose, ethanol, pyruvate, and acetate, respectively. Remarkably, ADP1 co-utilized glucose, acetate, ethanol, and pyruvate. Finally, the accumulation of storage lipids, wax esters (WEs), and triacylglycerols (TAGs) showed to be substrate dependent. Under nitrogen-limiting conditions, the TAGs:WEs (mol:mol) accumulation ratios were 1:4.9 in pyruvate and 1:1.6 in glucose, the WEs were mainly accumulated in acetate. In ethanol, no accumulation of lipids was detected.

Hypoxic Conditions in Crown Galls Induce Plant Anaerobic Responses That Support Tumor Proliferation.

Agrobacterium tumefaciens infection of wounded plant tissues causes the formation of crown gall tumors. Upon infection, genes encoded on the A. tumefaciens tumor inducing plasmid are integrated in the plant genome to induce the biosynthesis of auxin and cytokinin, leading to uncontrolled cell division. Additional sequences present on the bacterial T-DNA encode for opine biosynthesis genes, which induce the production of opines that act as a unique carbon and nitrogen source for Agrobacterium. Crown galls therefore become a very strong sink for photosynthate. Here we found that the increased metabolic demand in crown galls causes an increase in oxygen consumption rate, which leads to a steep drop in the internal oxygen concentration. Consistent with this, plant hypoxia-responsive genes were found to be significantly upregulated in crown galls compared to uninfected stem tissue. Following this observation, we aimed at understanding whether the low-oxygen response pathway, mediated by group VII ethylene response factor (ERF-VII) transcription factors, plays a role in the development of crown galls. We found that quintuple knock-out mutants of all ERF-VII members, which are incapable of inducing the hypoxic response, show reduced crown gall symptoms. Conversely, mutant genotypes characterized by constitutively high levels of hypoxia-associated transcripts, displayed more severe crown gall symptoms. Based on these results, we concluded that uncontrolled cell proliferation of crown galls established hypoxic conditions, thereby requiring adequate anaerobic responses of the plant tissue to support tumor growth.

Integrated Experimental and Computational Analyses Reveal Differential Metabolic Functionality in Antibiotic-Resistant Pseudomonas aeruginosa.

Metabolic adaptations accompanying the development of antibiotic resistance in bacteria remain poorly understood. To study this relationship, we profiled the growth of lab-evolved antibiotic-resistantlineages of the opportunistic pathogen Pseudomonas aeruginosa across 190 unique carbon sources. Our data revealed that the evolution of antibiotic resistance resulted in systems-level changes to growth dynamics and metabolic phenotype. A genome-scale metabolic network reconstruction of P.aeruginosa was paired with whole-genome sequencing data to predict genes contributing to observed changes in metabolism. We experimentally validated computational predictions to identify mutations in resistant P.aeruginosa affecting loss of catabolic function. Finally, we found a shared metabolic phenotype between lab-evolved P.aeruginosa and clinical isolates with similar mutational landscapes. Our results build upon previous knowledge of antibiotic-induced metabolic adaptation and provide a framework for the identification of metabolic limitations in antibiotic-resistant pathogens.

Different schemas of saccharification and fermentation for bioethanol production from Opuntia ficus-indica cladode flour with wild strains

In the present work, two wild microorganisms were studied for saccharification and fermentation. A wild Acinetobacter pittii isolated from decaying cladodes (Opuntia ficus-indica) was capable of producing extracellular cellulases and a wild yeast Kluyveromyces marxianus isolated from termite was capable of producing alcohol. In Mexico, there are surpluses of cladode production and where it is essential to take advantage and use this carbon source for alcohol production due to currently fossil fuels depletion. Separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF) and semi-simultaneous saccharification and fermentation (SSSF) for cellulase and alcohol production using Opuntia ficus-indica cladode as a unique carbon source was evaluated. In SHF process the best conditions for FPase activity (Filter paper activity for total cellulases) were 37 °C and pH 6.5 obtaining 0.67±0.02 U/ml and 0.61±0.03 U/ml for Acinetobacter pittii and Kluyveromyces marxianus, respectively. For alcohol production, the best conditions were 40 °C and pH 5.5 obtaining 12.95±0.3 g/L with K. marxianus while A. pittii did not produce significant alcohol concentration. Both processes were made with agitation (200 rpm). The SSF process was made with both microorganisms inoculated at the same time at 37 °C and without agitation. The maximum FPase activity of 0.28±0.004 U/ml and the maximum alcohol concentration was 7.5±0.27 g/L. Finally, an SSSF was performed, initially with A. pittii at 37 °C and after 8 h K. marxianus was then inoculated with temperature switched to 40 °C, the all process was performed without agitation. The maximum FPase activity was 0.45±0.001 U/ml, and the maximum alcohol concentration was 11.7±0.02 g/L. There was a significant difference (ANOVA) between SHF and SSSF in alcohol production. The best process for FPase activity and alcohol production is separate hydrolysis and fermentation using only yeast Kluyveromyces marxianus.

Pseudomonas aeruginosa mutants defective in glucose uptake have pleiotropic phenotype and altered virulence in non-mammal infection models

Pseudomonas spp. are endowed with a complex pathway for glucose uptake that relies on multiple transporters. In this work we report the construction and characterization of Pseudomonas aeruginosa single and multiple mutants with unmarked deletions of genes encoding outer membrane (OM) and inner membrane (IM) proteins involved in glucose uptake. We found that a triple ΔgltKGF ΔgntP ΔkguT mutant lacking all known IM transporters (named GUN for Glucose Uptake Null) is unable to grow on glucose as unique carbon source. More than 500 genes controlling both metabolic functions and virulence traits show differential expression in GUN relative to the parental strain. Consistent with transcriptomic data, the GUN mutant displays a pleiotropic phenotype. Notably, the genome-wide transcriptional profile and most phenotypic traits differ between the GUN mutant and the wild type strain irrespective of the presence of glucose, suggesting that the investigated genes may have additional roles besides glucose transport. Finally, mutants carrying single or multiple deletions in the glucose uptake genes showed attenuated virulence relative to the wild type strain in Galleria mellonella, but not in Caenorhabditis elegans infection model, supporting the notion that metabolic functions may deeply impact P. aeruginosa adaptation to specific environments found inside the host.

Growth inhibition of Colletotrichum gloeosporioides and Phytophthora capsici by native Mexican Trichoderma strains

An integrated evaluation to determine the potential of Trichoderma against two important phytopathogens is described in the present research. Phytophthora capsici and Colletotrichum gloeosporioides were the phytopathogens used in the assay to evaluate the inhibition potential by Trichoderma. Trichoderma harzianum, Trichoderma longibranchiatum, Trichoderma yunnanense, Trichoderma asperellum (T2-10 and T2-31) and Trichoderma sp. were evaluated. The Trichoderma strains showed a percentage of inhibition on P. capsici and C. gloeosporioides up to 22.5%. P. capsici was mycoparasitized by all Trichoderma strains evaluated and also C. gloeosporioides, except when it was evaluated against T. longibranchiatum. When there was a mycoparasitism, it was 100% over phytopathogen biomass. The production of cellulases and chitinases using sugarcane bagasse and chitin from shrimp shell as unique carbon source were evaluated. The best production of endoglucanase was showed by T. harzianum (40.8 U/g), exoglucanase by Trichoderma sp. and T. harzianum (2.9 and 2.5 U/g, respectively), by last the best value of chitinases was 22.1, 20.5 and 20.1 U/g showed by T. asperellum (T2-31), T. longibranchiatum and Trichoderma sp., respectively. All Trichoderma strains evaluated showed to be an excellent potential agent to be used as control pest against C. gloeosporioides and P. capsici.

Temporal Expression Dynamics of Plant Biomass-Degrading Enzymes by a Synthetic Bacterial Consortium Growing on Sugarcane Bagasse.

Plant biomass (PB) is an important source of sugars useful for biofuel production, whose degradation efficiency depends on synergistic and dynamic interactions of different enzymes. Here, using a metatranscriptomics-based approach, we explored the expression of PB-degrading enzymes in a five-species synthetic bacterial consortium during cultivation on sugarcane bagasse as a unique carbon source. By analyzing the temporal expression dynamics of a selection of enzymes we revealed the functional role of each consortium member and disentangled the potential interactions between them. Based on normalized expression values and the taxonomic affiliation of all the transcripts within thirty carbohydrate-active enzyme (CAZy) families, we observed a successional profile. For instance, endo-glucanases/-xylanases (e.g., GH8, GH10, and GH16) were significantly expressed at 12 h, whereas exo-glucanases (e.g., GH6 and GH48) and α-arabinosidases/β-xylosidases (e.g., GH43) were highly expressed at 48 h. Indeed, a significant peak of extracellular β-xylosidase activity was observed at this stage. Moreover, we observed a higher expression of several CAZy families at 12–48 h, suggesting easy access to the main plant polysaccharides. Based on this evidence, we predicted that the highest level of collaboration between strains takes place at the initial stages of growth. Here, Paenibacillus, Brevundimonas, and Chryseobacterium were the most important contributors, whereas Stenotrophomonas was highly active at the end of the culture (96–192 h) without contributing to a large extent to the expression of lignocellulolytic enzymes. Our results contribute to the understanding of enzymatic and ecological mechanisms within PB-degrading microbial consortia, yielding new perspectives to improve the PB saccharification processes.

Pretreatment of saline antibiotic wastewater using marine microalga

A green microalga Chlorella sp. isolated from marine environment was investigated for its potential to pretreat saline antibiotic wastewater containing amoxicillin (AMX). Through Biolog EcoPlate assay, the Chlorella sp. showed its unique carbon source metabolic patterns under autotrophic condition. In addition, the microalga could effectively remove AMX (>99%) under initial AMX concentrations ranging from 10 to 150 mg/L through a treatability test. In the continuous AMX treatment using a lab-scale membrane photobioreactor (MPBR), a stable AMX removal efficiency of 85.6 ± 3.8% was observed. Moreover, with the aid of a subsequent bacterial treatment, the microalgal-bacterial process (the Chlorella sp. pretreatment followed by either intertidal wetland sediment or activated sludge) can achieve simultaneous AMX removal of >99% and total organic carbon (TOC) removal of ∼80%. In general, the microalgal pretreatment showed its great potential in effective removal of antibiotic residues, which could greatly enhance the overall treatment efficiency of saline antibiotic wastewater.

Workflow Based on the Combination of Isotopic Tracer Experiments to Investigate Microbial Metabolism of Multiple Nutrient Sources.

Studies in the field of microbiology rely on the implementation of a wide range of methodologies. In particular, the development of appropriate methods substantially contributes to providing extensive knowledge of the metabolism of microorganisms growing in chemically defined media containing unique nitrogen and carbon sources. In contrast, the management through metabolism of multiple nutrient sources, despite their broad presence in natural or industrial environments, remains virtually unexplored. This situation is mainly due to the lack of suitable methodologies, which hinders investigations. We report an experimental strategy to quantitatively and comprehensively explore how metabolism operates when a nutrient is provided as a mixture of different molecules, i.e., a complex resource. Here, we describe its application for assessing the partitioning of multiple nitrogen sources through the yeast metabolic network. The workflow combines information obtained during stable isotope tracer experiments using selected 13C- or 15N-labeled substrates. It first consists of parallel and reproducible fermentations in the same medium, which includes a mixture of N-containing molecules; however,a selected nitrogen source is labeled each time. A combination of analytical procedures (HPLC, GC-MS) is implemented to assess the labeling patterns of targeted compounds and to quantify the consumption and recovery of substrates in other metabolites. An integrated analysis of the complete dataset provides an overview of the fate of consumed substrates within cells. This approach requires an accurate protocol for the collection of samples-facilitated by a robot-assisted system for online monitoring of fermentations-and the achievement of numerous time-consuming analyses. Despite these constraints, it allowed understanding, for the first time, the partitioning of multiple nitrogen sources throughout the yeast metabolic network. We elucidated the redistribution of nitrogen from more abundant sources toward other N-compounds and determined the metabolic origins of volatile molecules and proteinogenic amino acids.

Contribution of the β-glucosidase BglC to the onset of the pathogenic lifestyle of Streptomyces scabies.

Common scab disease on root and tuber plants is caused by Streptomyces scabies and related species which use the cellulose synthase inhibitor thaxtomin A as the main phytotoxin. Thaxtomin production is primarily triggered by the import of cello-oligosaccharides. Once inside the cell, the fate of the cello-oligosaccharides is dichotomized: (i) the fuelling of glycolysis with glucose for the saprophytic lifestyle through the action of β-glucosidase(s) (BGs); and (ii) elicitation of the pathogenic lifestyle by the inhibition of CebR-mediated transcriptional repression of thaxtomin biosynthetic genes. Here, we investigated the role of scab57721, encoding a putative BG (BglC), in the onset of the pathogenicity of S.scabies. Enzymatic assays showed that BglC was able to release glucose from cellobiose, cellotriose and all other cello-oligosaccharides tested. Its inactivation resulted in a phenotype opposite to that expected, as reduced production of thaxtomin was monitored when the mutant was cultivated on medium containing cello-oligosaccharides as unique carbon source. This unexpected phenotype could be attributed to the highly increased activity of alternative intracellular BGs, probably as a compensation for bglC inactivation, which then prevented cellobiose and cellotriose accumulation to reduce the activity of CebR. In contrast, when the bglC null mutant was cultivated on medium devoid of cello-oligosaccharides, it instead constitutively produced thaxtomin. This observed hypervirulent phenotype does not fit with the proposed model of the cello-oligosaccharide-mediated induction of thaxtomin production, and suggests that the role of BglC in the route to the pathogenic lifestyle of S.scabies is more complex than currently presented.

Effect of sulfonylurea tribenuron methyl herbicide on soil Actinobacteria growth and characterization of resistant strains.

Repeated application of pesticides disturbs microbial communities and cause dysfunctions on soil biological processes. Granstar® 75 DF is one of the most used sulfonylurea herbicides on cereal crops; it contains 75% of tribenuron-methyl. Assessing the changes on soil microbiota, particularly on the most abundant bacterial groups, will be a useful approach to determine the impact of Granstar® herbicide. For this purpose, we analyzed Actinobacteria, which are known for their diversity, abundance, and aptitude to resist to xenobiotic substances. Using a selective medium for Actinobacteria, 42 strains were isolated from both untreated and Granstar® treated soils. The number of isolates recovered from the treated agricultural soil was fewer than that isolated from the corresponding untreated soil, suggesting a negative effect of Granstar® herbicide on Actinobacteria community. Even so, the number of strains isolated from untreated and treated forest soil was quite similar. Among the isolates, resistant strains, tolerating high doses of Granstar® ranging from 0.3 to 0.6% (v/v), were obtained. The two most resistant strains (SRK12 and SRK17) were isolated from treated soils showing the importance of prior exposure to herbicides for bacterial adaptation. SRK12 and SRK17 strains showed different morphological features. The phylogenetic analysis, based on 16S rRNA gene sequencing, clustered the SRK12 strain with four Streptomyces type strains (S. vinaceusdrappus, S. mutabilis, S. ghanaensis and S. enissocaesilis), while SRK17 strain was closely related to Streptomyces africanus. Both strains were unable to grow on tribenuron methyl as unique source of carbon, despite its advanced dissipation. On the other hand, when glucose was added to tribenuron methyl, the bacterial development was evident with even an improvement of the tribenuron methyl degradation. In all cases, as tribenuron methyl disappeared, two compounds were detected with increased concentrations. These by-products appeared to be persistent and were not degraded either chemically or by the studied strains. Based on these observations, we suggested that bacterial activity on carbon substrates could be directly involved in the partial breakdown of tribenuron methyl, by generating the required acidity for the first step of the hydrolysis. Such a process would be interesting to consider in bioremediation of neutral and alkaline tribenuron methyl-polluted soils.

Bacteria Associated to Plants Naturally Selected in a Historical PCB Polluted Soil Show Potential to Sustain Natural Attenuation.

The exploitation of the association between plants and microorganisms is a promising approach able to boost natural attenuation processes for soil clean-up in vast polluted areas characterized by mixed chemical contamination. We aimed to explore the selection of root-associated bacterial communities driven by different plant species spontaneously established in abandoned agricultural soils within a historical polluted site in north Italy. The site is highly contaminated by chlorinated persistent organic pollutants, mainly constituted by polychlorobiphenyls (PCBs), together with heavy metals and metalloids, in variable concentrations and uneven distribution. The overall structure of the non-vegetated and root-associated soil fractions bacterial communities was described by high-throughput sequencing of the 16S rRNA gene, and a collection of 165 rhizobacterial isolates able to use biphenyl as unique carbon source was assayed for plant growth promotion (PGP) traits and bioremediation potential. The results showed that the recruitment of specific bacterial communities in the root-associated soil fractions was driven by both soil fractions and plant species, explaining 21 and 18% of the total bacterial microbiome variation, respectively. PCR-based detection in the soil metagenome of bacterial bphA gene, encoding for the biphenyl dioxygenase α subunit, indicated that the soil in the site possesses metabolic traits linked to PCB degradation. Biphenyl-utilizing bacteria isolated from the rhizosphere of the three different plant species showed low phylogenetic diversity and well represented functional traits, in terms of PGP and bioremediation potential. On average, 72% of the strains harbored the bphA gene and/or displayed catechol 2,3-dioxygenase activity, involved in aromatic ring cleavage. PGP traits, including 1-aminocyclopropane-1-carboxylic acid deaminase activity potentially associated to plant stress tolerance induction, were widely distributed among the isolates according to in vitro assays. PGP tested in vivo on tomato plants using eleven selected bacterial isolates, confirmed the promotion and protection potential of the rhizosphere bacteria. Different spontaneous plant species naturally selected in a historical chronically polluted site showed to determine the enrichment of peculiar bacterial communities in the soil fractions associated to the roots. All the rhizosphere communities, nevertheless, hosted bacteria with degradation/detoxification and PGP potential, putatively sustaining the natural attenuation process.

Potential of Chlorella vulgaris to Abate Flue Gas

The likely use of continuous cultures of Chlorella vulgaris for flue gas abatement was studied. Firstly, no pH-controlled photo-bioreactors were operated in order to understand the tolerance of this microalgae to high CO2 concentrations in the airstream. Thus, the effect in biomass productivity, CO2 fixation and biochemical composition of different percentage of pure CO2 (ranging 1–12%) in the air supply was investigated. When the inlet CO2 concentration varied from 1 to 10%, no statistical differences were found (ANOVA, p < 0.05) in the rate of carbon assimilation (0.6–0.8 g L−1 d). In all the cases, biomass presented a high content both proteins and lipids (40 and 25% respectively). However, when cultures were supplied with 12% of pure CO2 in the airstream, pH drastically dropped and cultures were not viable. Next, the potential use of CO2 contained in a simulated flue gas as a unique source of carbon was evaluated. Thus a mix of gases mimicking those presented in an exhausted stream of a power plant was used to aerate constantly the cultures. In this condition, cultures were only viable either when the simulated flue gas stream was diluted twelve times with air (resulting a constant supply of 1% CO2 in the airstream) or no diluted but being used by pulse to control the pH of the culture. In both cases, cultures achieved a steady state, rendering 0.7 and 0.9 g CO2 assimilated L−1 d−1 respectively. Biomass presented high content of proteins and lipids (40% respectively) in both conditions. These results suggest that the use of exhausted gases can make more economically feasible the production of microalgae and generate a valuable biomass rich in proteins and lipids.

Pre-cultivation with Selected Prebiotics Enhances the Survival and the Stress Response of Lactobacillus rhamnosus Strains in Simulated Gastrointestinal Transit.

In our study, we dwelled upon combinations of lactobacilli/prebiotics, considering four different strains belonging to the Lactobacillus rhamnosus species, including Lactobacillus rhamnosus GG (LGG), and different prebiotics often found in commercial synbiotic products, such as inulin, lactulose and polyols mannitol and sorbitol. In the first step of the research, the survival, the growth kinetic parameters and the protein expression of Lb. rhamnosus strains cultivated in presence of the different prebiotics as a unique carbon source were evaluated. In the second step, the influence of pre-cultivation in medium added of metabolizable prebiotics on the strains survival to simulated gastrointestinal (GI) transit, assayed without prebiotics addition, was estimated. Our results showed that the presence in the medium of certain low fermented prebiotics, specific for each strain, represents a stress factor that significantly affects the growth of Lb. rhamnosus strains, inducing the up-regulation of several proteins. In detail, all added prebiotics used as unique carbon source caused a growth retard compared with glucose, as testified by increased values of the lag phase and decreased values of the μmax. Mannitol evidenced intermediate μmax values between those registered with glucose and those detected with the other assayed prebiotics. Moreover, the cultivation with prebiotics induced the over expression of 7 protein bands. Interestingly, we found a correlation between the up-regulation of two specific stress proteins, called P4 (ATP-binding subunit Clpx) and P7 (GrpE), and the death kinetic parameters (resistance and cells viability) registered during the simulated GI transit of strains pre-cultivated with specific, low fermented prebiotics. Specifically, the highest resistance and gastric-vitality scores were highlighted for the strain AT195 when pre-cultivated in presence of sorbitol. Conversely, the lowest values were found in the case of DSM20021 pre-cultivated with mannitol. Among the up-regulated stress proteins, P7 resulted involved in the response to the starvation. Finally, it is possible to conclude that the pre-cultivation with certain prebiotics as a unique carbon source represents a strain-specific, sub-lethal stress able to enhance the resistance of Lb. rhamnosus strains and consequently their viability under simulated GI transit.

Selection of Biodegrading Phytosterol Strains.

The phytosterol-biotransforming strains were selected from Mycobacterium sp., using a high concentration of β-sitosterol. The selection was made by culturing the strains in a medium enriched with 14g β-sitosterol/L as the unique source of carbon. During 2months, the bacterial cultures were transferred successively. The extraction of the biotransformation products was made with methanol and ethyl acetate. The qualitative and quantitative analysis was made by means of thin-layer chromatography, gas-liquid chromatography (GLC), and GLC-mass spectrometry. Under these conditions, it was observed that after seven transfers, the strains Mycobacterium sp. MB-3683 and the Mycobacterium fortuitum B-11045 increased their biotransformation capacity from 20% to 64% and from 34% to 55%, respectively. The products in the highest proportion identified for each trial were androstenedione and androstadienedione. The results suggest that the high substrate concentration could be a selective mechanism to obtain strains more efficient in the biotransformation of β-sitosterol into steroidal bases.

Cholesterol plays a larger role during Mycobacterium tuberculosis in vitro dormancy and reactivation than previously suspected

It is known that cholesterol plays a key role for Mycobacterium tuberculosis (Mtb) adaptation and survival within the host, thus contributing to the establishment of dormancy. It has been extensively demonstrated that fatty acids are the main energy source of Mtb during infection and dormancy, and it has been proposed that these molecules are implicated in reactivation of bacilli from a dormant state. We used in vitro models to analyze Mtb gene expression during dormancy and reactivation when fatty acids and cholesterol are the unique carbon source in the media. Our results suggest that cholesterol might function as a signal to trigger Mtb expression of some genes required for stress protection earlier than the one induced by fatty acids alone, indicating that cholesterol is very favorable for its development. This process is so conducive that cholesterol-adapted bacilli can reactivate their growth after NRP2 dormancy state even 10 min post ventilation. Thus, we hypothesize that cholesterol is not only involved in Mtb dormancy but that it also plays a critical role for favorable and almost immediate reactivation from an in vitro long-lasting dormant state induced by hypoxia.

Biosurfactant production by the crude oil degrading Stenotrophomonas sp. B-2: chemical characterization, biological activities and environmental applications.

In this work, biosurfactant-producing microorganisms were isolated from hydrocarbon-contaminated water collected from Tunisian oilfield. After enrichment and isolation, different bacterial strains were preliminary studied for their biosurfactant/bioemulsifier properties when using crude oil as the unique carbon source. In particular, the isolate strain B-2, a Gram-negative, rod-shaped bacterium, efficiently emulsified crude oil. The extracellular biosurfactant product from this strain presented an emulsification activity above 70% and a hydrophobicity of 71%. In addition, a diameter of 6cm was observed in the oil displacement test. The characterization of B-2 strain using 16S rDNA sequencing enables us to find a high degree of similarity with various members of the genus Stenotrophomonas (with a percentage of similarity of 99%). The emulsification activity of Stenotrophomonas biosurfactant B-2 was maintained in a wide range of pH (2 to 6), temperature (4 to 55°C), and salinity (0 to 50gL-1) conditions. It also enhanced the solubility of phenanthrene in water and could be used in the re-mobilization of hydrocarbon-contaminated environment. In addition, this biosurfactant exhibited antimicrobial and antioxidant properties. Infrared spectroscopy suggested potential lipidic and peptidic moieties, and mass spectrometry-based analyses showed that the biosurfactant contains mainly cyclic peptidic structures belonging to the class of diketopiperazines. Therefore, the B-2 strain is a promising biosurfactant-producing microorganism and its derived biosurfactant presents a wide range of industrial applications.

Nitrogen-enriched carbon sheets derived from egg white by using expanded perlite template and its high-performance supercapacitors

Nitrogen-enriched carbon sheets were synthesized using egg white as a unique carbon source and expanded perlite as a novel template. The as-prepared material was further used as an electrode material for supercapacitor applications, demonstrating excellent supercapacitance with a maximum gravimetric specific capacitance of 302 F g−1 at 0.5 A g−1 in a 3-electrode setup for a sample carbonized at 850 °C and activated for 6 h. Moreover, the carbon sheet-based capacitor with 2-symmetric electrodes showed an excellent cycle life (2% loss at 0.1 A g−1 after 10 000 cycles). The excellent performance may be attributed to the combination of the 3D carbon structure and the highly concentrated doped nitrogen component from the natural egg source for superior pseudocapacitance.

Biodegradation of crude oil by individual bacterial strains and a mixed bacterial consortium.

Three bacterial isolates identified as Alcanivorax borkumensis SK2, Rhodococcus erythropolis HS4 and Pseudomonas stutzeri SDM, based on 16S rRNA gene sequences, were isolated from crude oil enrichments of natural seawater. Single strains and four bacterial consortia designed by mixing the single bacterial cultures respectively in the following ratios: (Alcanivorax: Pseudomonas, 1:1), (Alcanivorax: Rhodococcus, 1:1), (Pseudomonas: Rhodococcus, 1:1), and (Alcanivorax: Pseudomonas: Rhodococcus, 1:1:1), were analyzed in order to evaluate their oil degrading capability. All experiments were carried out in microcosms systems containing seawater (with and without addition of inorganic nutrients) and crude oil (unique carbon source). Measures of total and live bacterial abundance, Card-FISH and quali-, quantitative analysis of hydrocarbons (GC-FID) were carried out in order to elucidate the co-operative action of mixed microbial populations in the process of biodegradation of crude oil. All data obtained confirmed the fundamental role of bacteria belonging to Alcanivorax genus in the degradation of linear hydrocarbons in oil polluted environments.

Impact of hydrocarbons, PCBs and heavy metals on bacterial communities in Lerma River, Salamanca, Mexico: Investigation of hydrocarbon degradation potential

Freshwater contamination usually comes from runoff water or direct wastewater discharges to the environment. This paper presents a case study which reveals the impact of these types of contamination on the sediment bacterial population. A small stretch of Lerma River Basin, heavily impacted by industrial activities and urban wastewater release, was studied. Due to industrial inputs, the sediments are characterized by strong hydrocarbon concentrations, ranging from 2 935 to 28 430μg·kg−1 of total polyaromatic hydrocarbons (PAHs). These sediments are also impacted by heavy metals (e.g., 9.6μg·kg−1 of Cd and 246μg·kg−1 of Cu, about 8 times the maximum recommended values for environmental samples) and polychlorinated biphenyls (ranging from 54 to 123μg·kg−1 of total PCBs). The bacterial diversity on 6 sediment samples, taken from upstream to downstream of the main industrial and urban contamination sources, was assessed through TRFLP. Even though the high PAH concentrations are hazardous to aquatic life, they are not the only factor driving bacterial community composition in this ecosystem. Urban discharges, leading to hypoxia and low pH, also strongly influenced bacterial community structure. The bacterial bioprospection of these samples, using PAH as unique carbon source, yielded 8 hydrocarbonoclastic strains. By sequencing the 16S rDNA gene, these were identified as similar to Mycobacterium goodii, Pseudomonas aeruginosa, Pseudomonas lundensis or Aeromonas veronii. These strains showed high capacity to degrade naphthalene (between 92 and 100% at 200mg·L−1), pyrene (up to 72% at 100mg·L−1) and/or fluoranthene (52% at 50mg·L−1) as their only carbon source on in vitro experiments. These hydrocarbonoclastic bacteria were detected even in the samples upstream of the city of Salamanca, suggesting chronical contamination, already in place longer before. Such microorganisms are clearly potential candidates for hydrocarbon degradation in the treatment of oil discharges.