Application of bioemulsifiers in soil oil bioremediation processes. Future prospects

Biodegradation is one of the primary mechanisms for elimination of petroleum and other hydrocarbon pollutants from the environment. It is considered an environmentally acceptable way of eliminating oils and fuel because the majority of hydrocarbons in crude oils and refined products are biodegradable. Petroleum hydrocarbon compounds bind to soil components and are difficult to remove and degrade. Bioemulsifiers can emulsify hydrocarbons enhancing their water solubility and increasing the displacement of oily substances from soil particles. For these reasons, inclusion of bioemulsifiers in a bioremediation treatment of a hydrocarbon polluted environment could be really advantageous. There is a useful diversity of bioemulsifiers due to the wide variety of producer microorganisms. Also their chemical compositions and functional properties can be strongly influenced by environmental conditions. The effectiveness of the bioemulsifiers as biostimulating agent in oil bioremediation processes has been demonstrated by several authors in different experimental assays. For example, they have shown to be really efficient in combination with other products frequently used in oil bioremediation such as they are inorganic fertilizer (NPK) and oleophilic fertilizer (i.e. S200C). On the other hand, the bioemulsifiers have shown to be more efficient in the treatment of soil with high percentage of clay. Finally, it has been proved their efficacy in other biotechnological processes such as in situ treatment and biopiles. This paper reviews literature concerning the application of bioemulsifiers in the bioremediation of soil polluted with hydrocarbons, and summarizes aspects of the current knowledge about their industrial application in bioremediation processes.

Removal and degradation characteristics of quinolone antibiotics in laboratory-scale activated sludge reactors under aerobic, nitrifying and anoxic conditions

This work describes the removal of 6 quinolone antibiotics from wastewaters under different redox conditions (aerobic, nitrifying and anoxic) through batch experiments in laboratory scale activated sludge reactors using mixed liquor from a membrane bioreactor pilot plant (MBR). The main removal pathways for antibiotics from wastewaters involved in each treatment are described. Mass balances indicated that sorption on sludge played a dominating role in the elimination of antibiotics. Sorption potential depended on the redox conditions, being lower in nitrifying (Kd, 414-876 L kg(-1)) and anoxic (Kd, 471-930 L kg(-1)) sludge in comparison with aerobic sludge (Kd, 534-1137 L kg(-1)). Kd was higher for piperazinylic quinolones. Redox conditions also influenced biodegradation, a secondary pathway, which followed first-order kinetics with degradation rates constants ranging from 1.8·10(-3) to 8.2·10(-3) h(-1). Biodegradation rates under anoxic conditions were negligible. The experimental results have also demonstrated much higher removal efficiency by biodegradation (36.2-60.0%) under nitrifying conditions in comparison with aerobic conditions (14.9-43.8%). The addition of allylthiourea, an ammonia monooxygenase inhibitor, inhibited nitrification completely and reduced significantly the biodegradation of target antibiotics (16.5-29.3%). The residual biodegradation in the presence of allylthiourea may be due to the activity of heterotrophs in the enriched nitrifier culture. The removal of the selected antibiotics under the studied redox conditions depended significantly on the bacteria composition of the sludge. These results suggest that despite the known persistence of this group of antibiotics it is possible to enhance their degradation using nitrifying conditions, which at adequate working conditions as high SRT, typical in MBR, become a promising alternative for improving quinolones removal from environment.

Effect of dissolved oxygen concentration on nitrate removal from groundwater using a denitrifying submerged filter

A unidirectional submerged filter system was employed to purify groundwater contaminated with nitrate by biological denitrification. The influence of the concentration of dissolved oxygen (DO) in the process was tested using ethanol, methanol and sucrose as carbon sources. Inorganic-nitrogen removal, growth of the biofilm, platable denitrifying bacteria and nitrate reducing bacteria in biofilm were studied. With regard to the type of electron donor used, the presence of oxygen decreased the removal efficiency of inorganic nitrogen and caused an increase of nitrite concentration in the treated water. These negative effects depended on utilised carbon source. Biological denitrification with alcohols such as ethanol and methanol was less affected by DO than with sucrose. The development of the biofilm was also influenced by the DO concentration as excess O(2) caused reduced biofilm growth. These biofilms developed in oxygen presence had a smaller bacterial density and a lower denitrifying bacteria versus nitrate reducing bacteria ratio, which led to an unfavorable inorganic nitrogen removal and presence of nitrite in the treated water. All these effects are more pronounced when sucrose is used as carbon source.

Selection and identification of bacteria isolated from waste crude oil with polycyclic aromatic hydrocarbons removal capacities

Fifteen bacterial strains isolated from solid waste oil samples were selected due to their capacity of growing in the presence of hydrocarbons. The isolates were identified by PCR of the 16S rDNA gene using fD1 and rD1 primers. The majority of the strains belonged to genera Bacillus, Bacillus pumilus (eight strains) and Bacillus subtilis (two strains). Besides, three strains were identified as Micrococcus luteus, one as Alcaligenes faecalis and one strain as Enterobacter sp. Growth of the above-mentioned strains in mineral liquid media amended with naphthalene, phenanthrene, fluoranthene or pyrene as sole carbon source was studied and our results showed that these strains can tolerate and remove different polycyclic aromatic hydrocarbons that may be toxic in the environment polluted with hydrocarbons. Finally, the capacity of certain strains to emulsify octane, xilene, toluene, mineral oil and crude oil, and its ability to remove hydrocarbons, look promising for its application in bioremediation technologies.

Production of B-group vitamins by two Azotobacter strains with phenolic compounds as sole carbon source under diazotrophic and adiazotrophic conditions

Azotobacter vinelandii strain ATCC 12837 and A. chroococcum strain H23 (CECT 4435) were able to grow on N-free or NH4Cl-amended chemically-defined (Burk's) media, with protocatechuic acid (1-2 mmol 1(-1)) or sodium p-hydroxybenzoate (1-10 mmol 1(-1)) as sole carbon (C) sources. At a concentration of 2 mmol 1(-1), both substrates supported nitrogen fixation (acetylene reduction assay) at similar or higher rates than bacteria grown in control media amended with 2 mmol 1(-1) sodium succinate as C source. The two strains produced the B-group vitamins niacin, pantothenic acid, thiamine, riboflavin and biotin after 72 h of growth in chemically-defined media with 2 mmol 1(-1) protocatechuic acid, sodium phydroxybenzoate or sodium succinate as sole C source, either in N-free media or in media amended with 0.1% NH4Cl. Quantitative production of all vitamins was affected by the use of the different C and N substrates.

Arthrobacter siccitolerans sp. nov., a highly desiccation-tolerant, xeroprotectant-producing strain isolated from dry soil

A novel desiccation-tolerant, xeroprotectant-producing bacterium, designated strain 4J27(T), was isolated from a Nerium oleander rhizosphere subjected to seasonal drought in Granada, Spain. Phylogenetic analysis based on 16S rRNA gene sequencing placed the isolate within the genus Arthrobacter, its closest relative being Arthrobacter phenanthrenivorans Shep3 DSM 18606(T), with which it showed 99.23 % 16S rRNA gene sequence similarity. DNA-DNA hybridization measurements showed less than 25 % relatedness between strain 4J27(T) and Arthrobacter phenanthrenivorans DSM 18606(T). The DNA base composition of strain 4J27(T) was 65.3 mol%. The main fatty acids were anteiso C15 : 0, anteiso C17 : 0, C16 : 0 and iso C16 : 0 and the major menaquinone was MK-9 (H2). The peptidoglycan type was A3α with an l-Lys-l-Ser-l-Thr-l-Ala interpeptide bridge. The bacterium tested positive for catalase activity and negative for oxidase activity. Phylogenetic, chemotaxonomic and phenotypic analyses indicated that the desiccation-tolerant strain 4J27(T) represents a novel species within the genus Arthrobacter, for which the name Arthrobacter siccitolerans is proposed. The type strain is 4J27(T) ( = CECT 8257(T) = LMG 27359(T)).

Community structure, population dynamics and diversity of fungi in a full-scale membrane bioreactor (MBR) for urban wastewater treatment

Community structure, population dynamics and diversity of fungi were monitored in a full-scale membrane bioreactor (MBR) operated throughout four experimental phases (Summer 2009, Autumn 2009, Summer 2010 and Winter, 2012) under different conditions, using the 18S-rRNA gene and the intergenic transcribed spacer (ITS2-region) as molecular markers, and a combination of temperature-gradient gel electrophoresis and 454-pyrosequencing. Both total and metabolically-active fungal populations were fingerprinted, by amplification of molecular markers from community DNA and retrotranscribed RNA, respectively. Fingerprinting and 454-pyrosequencing evidenced that the MBR sheltered a dynamic fungal community composed of a low number of species, in accordance with the knowledge of fungal diversity in freshwater environments, and displaying a medium-high level of functional organization with few numerically dominant phylotypes. Population shifts were experienced in strong correlation with the changes of environmental variables and operation parameters, with pH contributing the highest level of explanation. Phylotypes assigned to nine different fungal Phyla were detected, although the community was mainly composed of Ascomycota, Basidiomycota and Chytridiomycota/Blastocladiomycota. Prevailing fungal phylotypes were affiliated to Saccharomycetes and Chytridiomycetes/Blastocladiomycetes, which displayed antagonistic trends in their relative abundance throughout the experimental period. Fungi identified in the activated sludge were closely related to genera of relevance for the degradation of organic matter and trace-organic contaminants, as well as genera of dimorphic fungi potentially able to produce plant operational issues such as foaming or biofouling. Phylotypes closely related to genera of human and plant pathogenic fungi were also detected.

TGGE analysis of the diversity of ammonia-oxidizing and denitrifying bacteria in submerged filter biofilms for the treatment of urban wastewater

The spatial and temporal diversity of the bacterial community-forming biofilms in a pilot-scale submerged biofilter used for the treatment of urban wastewater was analyzed by a temperature-gradient gel electrophoresis (TGGE) approach. TGGE profiles based on partial sequence of the 16S rRNA gene showed that the community composition of the biofilms remained fairly stable along the column system and during the whole time of operation of the biofilter (more than 1 year). Community-profiling based on the amplification and separation of partial ammonia monooxygenase (amoA) and nitrous oxide reductase (nosZ) genes demonstrated that ammonia-oxidizing and denitrifying bacteria coexisted in both the anoxic and the aerated parts of the system. Several amoA and nosZ bands separated by TGGE were reamplified and sequenced, in order to further analyze the composition of these microbial communities in the biofilm. Phylogeny inferred from amoA/AmoA revealed the prevalence of Nitrosomonas species with five sequences affiliated to Nitrosomonas oligotropha, six sequences affiliated to Nitrosomonas europaea, and three sequences that showed only 75.7-76.1% identity of the DNA sequence with the closest described species (Nitrosomonas nitrosa). According to literature, this low identity value is indicative of previously undiscovered species. Eighteen new partial nosZ sequences were obtained which were mostly related to nosZ of gamma-proteobacteria (Pseudomonas) or clustered in the periphery of previously known denitrifying alpha-proteobacteria (Bradyrhizobium and Azospirillum).

Influence of carbon source on nitrate removal of contaminated groundwater in a denitrifying submerged filter

The effectiveness of three selected carbon sources (sucrose, ethanol and methanol) on submerged filters for the removal of nitrate from contaminated groundwater (100mg NO3(-)/litre), was studied. Process yields, nitrite accumulation, biomass production and growth of denitrifying bacteria were compared. Process yields, represented as ratio C/N were 2.5, 1.08 and 1.1 for sucrose, ethanol and methanol assays, respectively, making sucrose the least efficient carbon source. Nitrite accumulation in treated groundwater was more notable for sucrose assays, reaching values of 5mg NO2(-)/l. However, when ethanol or methanol were used as carbon sources, nitrite accumulation in treated water was practically zero during the experiments. On the other hand, a greater biomass production was observed in these assays with sucrose, causing clogging of the filter. Higher density of denitrifying bacteria in the biofilm, observed when ethanol and methanol were amended to the influent, suggested that these carbon sources increased the denitrification activity compared with the experiments performed with sucrose. Since methanol is toxic, ethanol is considered the most suitable carbon source out of the three tested, under the experimental conditions.

Dominance of sphingomonads in a copper-exposed biofilm community for groundwater treatment

The structure, biological activity and microbial biodiversity of a biofilm used for the removal of copper from groundwater were studied and compared with those of a biofilm grown under copper-free conditions. A laboratory-scale submerged fixed biofilter was fed with groundwater (2.3 l h(-1)) artificially polluted with Cu(II) (15 mg l(-1)) and amended with sucrose (150 mg l(-1)) as carbon source. Between 73 and 90 % of the Cu(II) was removed from water during long-term operation (over 200 days). The biofilm was a complex ecosystem, consisting of eukaryotic and prokaryotic micro-organisms. Scanning electron microscopy revealed marked structural changes in the biofilm induced by Cu(II), compared to the biofilm grown in absence of the heavy metal. Analysis of cell-bound extracellular polymeric substances (EPS) demonstrated a significant modification of the composition of cell envelopes in response to Cu(II). Transmission electron microscopy and energy-dispersive X-ray microanalysis (EDX) showed that copper bioaccumulated in the EPS matrix by becoming bound to phosphates and/or silicates, whereas copper accumulated only intracytoplasmically in cells of eukaryotic microbes. Cu(II) also decreased sucrose consumption, ATP content and alkaline phosphatase activity of the biofilm. A detailed study of the bacterial community composition was conducted by 16S rRNA-based temperature gradient gel electrophoresis (TGGE) profiling, which showed spatial and temporal stability of the species diversity of copper-exposed biofilms during biofilter operation. PCR reamplification and sequencing of 14 TGGE bands showed the prevalence of alphaproteobacteria, with most sequences (78 %) affiliated to the Sphingomonadaceae. The major cultivable colony type in plate counts of the copper-exposed biofilm was also identified as that of Sphingomonas sp. These data confirm a major role of these organisms in the composition of the Cu(II)-removing community.

Xeroprotectants for the stabilization of biomaterials

With the advancement of science and technology, it is crucial to have effective preservation methods for the stable long-term storage of biological material (biomaterials). As an alternative to cryopreservation, various techniques have been developed, which are based on the survival mechanism of anhydrobiotic organisms. In this sense, it has been found that the synthesis of xeroprotectants can effectively stabilize biomaterials in a dry state. The most widely studied xeroprotectant is trehalose, which has excellent properties for the stabilization of certain proteins, bacteria, and biological membranes. There have also been attempts to apply trehalose to the stabilization of eukaryotic cells but without conclusive results. Consequently, a xeroprotectant or method that is useful for the stable drying of a particular biomaterial might not necessarily be suitable for another one. This article provides an overview of recent advances in the use of new techniques to stabilize biomaterials and compare xeroprotectants with other more standard methods.

Effects of culture conditions on the production of polyhydroxyalkanoates by Azotobacter chroococcum H23 in media containing a high concentration of alpechín (wastewater from olive oil mills) as primary carbon source

Large amounts of homopolymers containing beta-hydroxybutyrate (PHB) and copolymers containing beta-hydroxyvalerate (P[HB-co-HV]) are produced by Azotobacter chroococcum strain H23 when growing in culture media amended with alpechín (wastewater from olive oil mills) as the sole carbon source. Copolymer was formed when valerate (pentanoate) was added as a precursor to the alpechín medium, but it was not formed with the addition of propionate as a precursor. A. chroococcum formed homo- and copolymers of polyhydroxyalkanoates (PHAs) up to 80% of the cell dry weight, when grown on NH(4)(+)-medium supplemented with 60% (v/v) alpechín, after 48 h of incubation at 100 rev min(-1) and 30 degrees C. Production of PHAs by strain H23 using alpechín looks promising, as the use of a cheap substrate for the production of these materials is essential if bioplastics are to become competitive products.

Effect of the concentration of suspended solids on the enzymatic activities and biodiversity of a submerged membrane bioreactor for aerobic treatment of domestic wastewater

A pilot-scale submerged membrane bioreactor was used for the treatment of domestic wastewater in order to study the influence of the variations in the concentration of volatile suspended solids (VSS) on the enzymatic activities (acid and alkaline phosphatases, glucosidase, protease, esterase, and dehydrogenase) and biodiversity of the bacterial community in the sludge. The influence of VSS concentration was evaluated in two separated experiments, which were carried out in two different seasons of the year (experiment 1 through spring-summer and experiment 2 through autumn-winter). Cluster analysis of the temperature gradient gel electrophoresis (TGGE) profiles demonstrated that the community composition was significantly different in both experiments. Within the same experiment, the bacterial community experienced sequential shifts as the biomass accumulated, as shown by the evolution of the population profiles through time as VSS concentration increased. All enzymatic activities studied were significantly lower during experiment 2, except for glucosidase. Concentrations of VSS over 8 g/l induced a strong descent of all enzymatic activities, which overlapped with a significant modification of the community composition. Sequences of the major TGGE bands were identified as representatives of the Alpha-proteobacteria, filamentous bacteria (Thiotrix), and nitrite oxidizers (Nitrospira). Some sequences which were poorly related to any validated bacterial taxon were obtained.

Biological and technical study of a partial-SHARON reactor at laboratory scale: effect of hydraulic retention time

This study was on the technical and biological characteristics of a partial-SHARON submerged-filter bioreactor of 3 L. The main focus was the influence of the hydraulic retention time (HRT) on biofilms. For this purpose, we used molecular tools based on the partial 16S rRNA genes. The results showed that the HRT may affect the nitrification processes of a bioreactor using synthetic wastewater containing 600 mg/L of ammonia. It was found that an HRT of 0.5 day transformed 100 % of the ammonium into nitrite. However, when the HRT was decreased to 0.4 day, there was a significant reduction (35 %) in the quantity of ammonia transformed, which confirmed the complexity of the system operation. Moreover, a PCR-TGGE approach highlighted the differences observed. The results obtained showed that an HRT of 0.5 day reduced bacterial biodiversity in the biofilms, which were mainly formed by Nitrosomonas and Diaphorobacter. In contrast, an HRT of 0.4 day facilitated the formation of heterogeneous biofilms formed by nitrifying bacteria, such as Nitrosomonas sp., Nitrosospira sp., and Nitrosovibrio sp.).

Surfactant activity of a naphthalene degrading Bacillus pumilus strain isolated from oil sludge

We studied the growth, biosurfactant activities and petroleum hydrocarbon compounds utilisation of strain 28-11 isolated from a solid waste oil. The isolate was identified as Bacillus pumilus. It grew well in the presence of 0.1% (w/v) of crude oil and naphthalene under aerobic conditions and utilised these substances as carbon and energy source. The capacity of strain 28-11 to emulsify crude oil and its ability to remove hydrocarbons looks promising for its application in environmental technologies.

Structure of archaeal communities in membrane-bioreactor and submerged-biofilter wastewater treatment plants

A cultivation independent approach (PCR-TGGE) was used to evaluate the occurrence of Archaea in four wastewater treatments based on technologies other than activated sludge, and to comparatively analyze their community structure. TGGE fingerprints (based on partial archaeal 16S-rRNA amplicons) were obtained from sludge samples taken from a pilot-scale aerated MBR fed with urban wastewater and operated under two different sets of conditions (MBR1 and MBR2 treatments), and also from biofilms sampled from two pilot-scale submerged biofilters (SBs) consisting of one aerated and one anoxic column each, fed with urban (USB treatment) or industrial (ISB treatment) wastewater, respectively. Analysis of TGGE fingerprints revealed clear and significant differences of the community structure of Archaea between the wastewater treatments studied, primarily according to wastewater origin and the type of technology. Thirty-two different band classes were detected among the 23 sludge and biofilm samples analyzed, from which five were selected as dominant or distinctive of the four treatments studied. Sixteen predominant TGGE bands were identified, revealing that all of them were related to methanogenic Archaea. Neither other Euryarchaeota groups nor Crenarchaeota members were identified amongst the 16S-rRNA fragments sequenced from separated TGGE bands.

Full-scale photobioreactor for biotreatment of olive washing water: Structure and diversity of the microalgae-bacteria consortium

The performance of a full-scale photobioreactor (PBR) for the treatment of olive washing water (OWW) was evaluated under different HRTs (5-2days). The system was able to treat up to 3926L OWWday^-1, and consisted of an activated-carbon pretreatment column and a tubular PBR unit (80 tubes, 98.17L volume, 2-m height, 0.25m diameter). PBR was an effective and environmentally friendly method for the removal of phenols, COD, BOD₅, turbidity and color from OWW (average efficiencies 94.84±0.55%, 85.86±1.24%, 99.12±0.17%, 95.86±0.98% and 87.24±0.91%, respectively). The diversity of total bacteria and microalgae in the PBR was analyzed using Illumina-sequencing, evaluating the efficiency of two DNA extraction methods. A stable microalgae-bacteria consortium was developed throughout the whole experimentation period, regardless of changes in HRT, temperature or solar radiation. MDS analyses revealed that the interplay between green algae (Sphaeropleales), cyanobacteria (Hapalosiphon) and Proteobacteria (Rhodopseudomonas, Azotobacter) played important roles in OWW bioremediation.

Growth of moderately halophilic bacteria isolated from sea water using phenol as the sole carbon source

Moderately halophilic bacteria utilizing phenol as the sole carbon source were isolated by selective enrichment from sea water. The isolate (Gram-negative motile rods) was identified as Deleya venusta. It grew well in the presence of up to 1600 mg/L of phenol and 8% NaCl under aerobic conditions. When the cells were treated with chloramphenicol prior to the addition of phenol they did not utilize added phenol, even after prolonged incubation. Thus, the enzymes necessary for phenol metabolism appeared to be inducible.

Identification of bacteria isolated from an oligotrophic lake with pesticide removal capacities

We studied the growth and capacities for pesticides removal of bacterial strains isolated from the Laguna Grande, an oligotrophic lake at the South of Spain (Archidona, Málaga). Strains were isolated from water samples amended with 10 and 50 microg/ml of nine pesticides: organochlorinated insecticides (aldrin and lindane), organophosphorous insecticides (dimetoate, methyl-parathion and methidation), s-triazine herbicides (simazine and atrazine), fungicide (captan) and diflubenzuron (1-(-4-chlorophenyl)-3-(2,6-difluorobenzoyl urea), a chitinase inhibitor. The majority of the strains belonged to the genera Pseudomonas and Aeromonas and only 9% of the total of strains were Gram positive. From all the strains isolated, only 22 showed a wide growth range in all the pesticides tested and 4 of them were chosen for pesticide removal studies. The genetic identification of these strains showed their affiliation to Pseudomonas pseudoalcaligenes, Micrococcus luteus, Bacillus sp. and Exiguobacterium aurantiacum. These last two strains were those that showed the highest pesticide removal capacities and a high bacterial growth.

Calcified leiomyoma of deep soft tissue. Report of a case in childhood

This report illustrates a calcified leiomyoma of deep soft tissue in the left leg of a 6-year-old boy. The tumour was composed of spindle cells arranged in interlacing bundles, between which were multiple small and large areas of calcification. Tumour cells were positive for vimentin, desmin and smooth muscle actin. Ultrastructurally, the cells showed numerous pinocytotic vesicles and bundles of intracytoplasmic filaments with smooth muscle dense bodies. Only four calcified leiomyomas have been previously reported in the deep soft tissues of limbs. Here we report a new case and suggest a new pathogenetic scheme involving alkaline phosphatase in the origin of these calcifications.

Analysis of community composition of biofilms in a submerged filter system for the removal of ammonia and phenol from industrial wastewater

The bacterial diversity of a submerged filter, used for the removal of ammonia and phenol from an industrial wastewater with high salinity, was studied by a cultivation-independent approach based on PCR/TGGE (temperature-gradient gel electrophoresis). The wastewater treatment plant (laboratory scale) combined the nitrification and denitrification processes and consisted of two separated columns (one anoxic and one aerated) connected through a valve. The spatial diversity of bacterial communities in the plant biofilms was analysed by taking samples at four different heights in the system. TGGE profiles of PCR-amplified sequences of the 16 S rRNA gene (V3-hypervariable region) showed significant variations of the bacterial diversity, mainly depending on the concentration of O2 along the system. Several bands separated by TGGE were reamplified and sequenced, in order to explore the composition of the microbial communities in the biofilms. Most of the sequenced bands (10 out of 13) were closely related to the 16 S rRNA gene of marine α-proteobacteria, mainly grouping in the periphery of the genus Roseobacter. Other sequences were related to those of γ-proteobacteria, the nitrite oxidizer Nitrospira marina and anaerobic phenol-degrading bacteria of the Desulfobacteraceae.

Liberation of amino acids by heterotrophic nitrogen fixing bacteria

Large amounts of amino acids are produced by nitrogen-fixing bacteria such as Azotobacter, Azospirillum, Rhizobium, Mesorhizobium and Sinorhizobium when growing in culture media amended with different carbon and nitrogen sources. This kind of bacteria live in close association with plant roots enhanced plant growth mainly as a result of their ability to fix nitrogen, improving shoot and root development suppression of pathogenic bacteria and fungi, and increase of available P concentration. Also, it has been strongly evidenced that production of biologically substances such as amino acids by these rhizobacteria are involved in many of the processes that explain plant-grown promotion. This paper reviews literature concerning amino acids production by nitrogen-fixing bacteria. The role of amino acids in microbial interactions in the rhizosphere and establishment of plant bacterial association is also discussed.

Effect of salinity on enzymatic activities in a submerged fixed bed biofilm reactor for municipal sewage treatment

The effect of salinity on the hydrolytic enzymatic activities (acid phosphatase, alkaline phosphatase, glucosidase, protease and esterase) released by the microorganisms in a submerged fixed bed bioreactor for real urban wastewater treatment was investigated. The influence of salt (NaCl) on the enzymatic activities was evaluated in four different experiments with concentrations of NaCl of 0, 3.7, 24.1 and 44.1g/L, remaining constant all other operating parameters of the bioreactor. The results show that enzymatic activities were reduced when the salinity was increased in the influent and consequently the biotransformation of organic matter in the submerged fixed bed bioreactor significantly decreased. A redundancy analysis was performed to evaluate the relationships between enzymatic activities and physic-chemical parameters analyzed in the influent. According to the results obtained with the Monte Carlo permutation test, salinity and sampling day significantly contributed to explain the variation of enzymatic activities, showing a negative correlation.

D,L-Hydantoinase activity of an Ochrobactrum anthropi strain

AIMS

A microorganism with the ability to release methionine from D,L-(2-methylthioethyl) hydantoin (strain 245) was isolated from soil. The aim of this study was the identification of the strain and the adjustment of the conditions of growth and of the enzymatic reaction, in order to achieve high specific activities of bioconversion of the hydantoin.

METHODS AND RESULTS

Strain 245 was identified as Ochrobactrum anthropi. The strain grew at alkaline pH (up to 10.0) and its hydantoinase activity was found to be inducible by the substrate D,L-(2-methylthioethyl) hydantoin. The enzyme is also alkalostable, with a pH optimum of 9.0. Under these conditions, hydantoinase activity was significantly enhanced and its half life prolonged when 200 mmol l-1 ammonium and phosphate were added. The addition of Ca2+, Na+, Cu2+, Co2+, Mg2+, Zn2+ or Fe3+ (0.5 mmol l-1) to the reaction mixture increased the hydantoinase activity of strain 245 up to tenfold after 24 h of incubation, compared with unamended controls.

CONCLUSION

The adequate adjustment of some environmental parameters (pH, addition of inducer, presence of ammonium, phosphate, heavy metals and other ions) can considerably increase the D, L-hydantoinase activity of strain 245.

SIGNIFICANCE AND IMPACT OF THE STUDY

The findings reported here set up the initial conditions for a further application of strain 245 in the production of methionine from hydantoine.

Microbial community structure and dynamics in a pilot-scale submerged membrane bioreactor aerobically treating domestic wastewater under real operation conditions

A pilot scale submerged ultra-filtration membrane bioreactor (MBR) was used for the aerobic treatment of domestic wastewater over 9 months of year 2006 (28th March to 21st December). The MBR was installed at a municipal wastewater facility (EMASAGRA, Granada, Spain) and was fed with real wastewater. The experimental work was divided in 4 stages run under different sets of operation conditions. Operation parameters (total and volatile suspended solids, dissolved oxygen concentration) and environmental variables (temperature, pH, COD and BOD(5) of influent water) were daily monitored. In all the experiments conducted, the MBR generated an effluent of optimal quality complying with the requirements of the European Law (91/271/CEE 1991). A cultivation-independent approach (polymerase chain reaction-temperature gradient gel electrophoresis, PCR-TGGE) was used to analyze changes in the structure of the bacterial communities in the sludge. Cluster analysis of TGGE profiles demonstrated significant differences in community structure related to variations of the operation parameters and environmental factors. Canonical correspondence analysis (CCA) suggested that temperature, hydraulic retention time and concentration of volatile suspended solids were the factors mostly influencing community structure. 23 prominent TGGE bands were successfully reamplified and sequenced, allowing gaining insight into the identities of predominantly present bacterial populations in the sludge. Retrieved partial 16S-rRNA gene sequences were mostly related to the alpha-Proteobacteria, beta-Proteobacteria and gamma-Proteobacteria classes. The community established in the MBR in each of the four stages of operation significantly differed in species composition and the sludge generated displayed dissimilar rates of mineralization, but these differences did not influence the performance of the bioreactor (quality of the permeate). These data indicate that the flexibility of the bacterial community in the sludge and its ability to get adapted to environmental changes play an important role for the stable performance of MBRs.