Modelización de la dinámica de los microorganismos anaerobios sintróficos oxidantes del ácido acético (SAO)

In the anaerobic digestion process, the most sensitive step is the methanogenesis. The main methane producing organisms are the acetoclastic methanogenic archaea that degrade the acetic acid to methane. These microorganisms are very sensitive to high concentrations of ammonia, which leads to operation problems. Recently, it has been studied a microorganism that also has the ability to degrade acetate, SAO bacteria, less sensitive to ammonia and favoring the methane production through the hydrogenotrophic methanogens. In the present project, a study of the SAO bacteria was made, in order toadd them in the ADM1 model. These microorganisms are able to oxidize acetic anaerobically to hydrogen and carbon dioxide. The reaction is very sensitive to the partial pressure of H2, needing the presence of hydrogenotrophic methanogenic archaea, which consume the H2 generated and transform to methane. Once the population SAO was implemented in the model, the kinetic parameters of these new bacteria were identified by using experimental data and optimizing the sum of the square of differences between these data and values predicted by the model. The experimental data came from simultaneous batch test with different initial concentrations of ammonium, acetate and hydrogen, using an inoculum from a biogas plant whose behavior suggested the possible presence of SAO. Moreover, the variable stoichiometry model was studied because the SAO organisms are very sensitive to the reaction thermodynamics. That model was compared with the ADM1 model, which in the results seems that could not fulfill the second law of thermodynamics, simulating reactions which are endergonic in the reality. The results indicate the interest of modifying the ADM1 model to consider the presence of the SAO microorganisms. The fitting to the experimental data, using the modified ADM1 model, corroborate the presence of an appreciable initial concentration of SAO in the samples, with higher concentrations than those of acetoclastic methanogenic archaea.En la digestió anaeròbia una de les etapes més sensibles és la metanogènesi. Els principals organismes productors de metà, les arqueobacteris metanogènics acetoclástics, que degraden l'àcid acètic a metà, són molt sensibles a concentracions elevades d'amoníac, el que comporta problemes en el procés. Per intentar solucionar aquest inconvenient i comprendre millor el procés, recentment s'estan estudiant més a fons els bacteris SAO. Aquestes també tenen la capacitat de degradar l'acètic i són menys sensibles al amoníac. A diferència de les acetoclástiques, els SAO transformen l'acetat en hidrogen i diòxid de carboni. L'H2 produït és transformat en metà per arqueobacteris metanogènics hidrogenófils. A més, els SAO són molt sensibles a la pressió parcial d'hidrogen, pel que és imprescindible per al seu desenvolupament el consum d'H2 per part de les metanogènics hidrogenófils. En el present treball s'ha realitzat un estudi dels bacteris SAO, per tal de poder implementar la seva dinàmica en el model ADM1. Un cop implementada, es va procedir a la identificació de paràmetres utilitzant dades experimentals d'assaigs discontinus simultanis, amb diferents concentracions inicials d'amoni, acetat i hidrogen, utilitzant un inòcul procedent d'una planta de biogàs el comportament suggeria la possible presència de SAO. D'altra banda, com els organismes SAO són molt sensibles a la termodinàmica de la reacció, es va estudiar el model adoptant estequiometria variable i es va comparar amb el model ADM1. Aquest últim, segons els resultats, podria no complir el segon principi de la termodinàmica, produint reaccions endergòniques. Els resultats obtinguts indiquen l'interès en modificar el model de referència ADM1 perquè contempli la presència de microorganismes SAO. Els ajustos a les dades experimentals, realitzats mitjançant el model ADM1 modificat, corroboren la presència d'una concentració inicial apreciable de SAO en les mostres estudiades, amb concentracions superiors a les de arqueobacteris metanogènics acetoclástics.En la digestión anaerobia una de las etapas más sensibles es la metanogénesis. Los principales organismos productores de metano, las arqueas metanogénicas acetoclásticas, que degradan el ácido acético a metano, son muy sensibles a concentraciones elevadas de amoniaco, lo que conlleva problemas en el proceso. Para intentar solucionar este inconveniente y comprender mejor el proceso, recientemente se están estudiando más a fondo las bacterias SAO. Estas también poseen la capacidad de degradar el acético y son menos sensibles al amoniaco. A diferencia de las acetoclásticas, SAO transforma el acetato en hidrógeno y dióxido de carbono. El H2 producido es transformado en metano por arqueas metanogénicas hidrogenófilas. Además, SAO son muy sensibles a la presión parcial de hidrógeno, por lo que es imprescindible para su desarrollo el consumo de H2 por parte de las metanogénicas hidrogenófilas. En el presente trabajo se ha realizado un estudio de las bacterias SAO, con el fin de poder implementar su dinámica en el modelo ADM1. Una vez implementada, se procedió a la identificación de parámetros utilizando datos experimentales de ensayos discontinuos simultáneos, con diferentes concentraciones iniciales de amonio, acetato e hidrógeno, utilizando un inóculo procedente de una planta de biogás cuyo comportamiento sugería la posible presencia de SAO. Por otra parte, como los organismos SAO son muy sensibles a la termodinámica de la reacción, se estudió el modelo adoptando estequiometría variable y se comparó con el modelo ADM1. Este último, según los resultados, podría no cumplir el segundo principio de la termodinámica, produciendo reacciones endergónicas. Los resultados obtenidos indican el interés en modificar el modelo de referencia ADM1 para que contemple la presencia de microorganismos SAO. Los ajustes a los datos experimentales, realizados mediante el modelo ADM1 modificado, corroboran la presencia de una concentración inicial apreciable de SAO en las muestras estudiadas, con concentraciones superiores a las de arqueas metanogénicas acetoclásticas

Modelling the dynamics of valerate acetogenesis by modified ADM1 with variable stoichiometry and t hermodynamic control

The thermodynamics analysis of hevalerate and propionateacetogenesi sindicaes thatthisprocessi snotfavouredathighac etateconcen tr atio n aPostprint (published version

mcr -Colistin Resistance Genes Mobilized by IncX4, IncHI2, and IncI2 Plasmids in Escherichia coli of Pigs and White Stork in Spain

Colistin has become the last-line antimicrobial for the treatment of multidrug resistant (MDR) Enterobacterales in human medicine. To date, several colistin resistance genes have been described. Of them mcr -1 is disseminated worldwide in Escherichia coli of human and animal origin. The aim of this study was to characterize mcr -mediated resistance plasmids from E. coli of animal origin in Spain. From our strain collection, 70 E. coli of pig origin collected between 2005 and 2014 (10 per year, except for years 2009-2010-2013) were randomly selected and screened for the presence of mcr -genes. Additionally, 20 E. coli isolated in 2011 from white storks (Ciconia ciconia) from the same urban household waste landfill associated colony were also included. Whole genome sequencing of mcr -positive isolates was carried out on a MiSeq (Illumina). Hybrid whole genome sequencing strategy combining nanopore and Illumina technologies were performed in a selection of isolates to close the genomes and plasmids and identify the presence of antimicrobial resistance genes. Minimum inhibitory concentration (MIC) was used to assess the susceptibility to colistin. Mating experiments were carried out to evaluate transferability of the mcr -genes. A total of 19 mcr -1 and one mcr -4 positive isolates were detected, 15 from pigs distributed during the study period, and five from storks collected in 2011. No other mcr -variants were found. The MICs for colistin ranged between 4 and >4 mg/L. High diversity of STs were detected among the mcr-1 positive E. coli isolates, with only ST-10 shared between pigs and white storks. Except for one isolate, all were genotypic and phenotypically MDR, and five of them also harbored cephalosporin resistance genes (bla , bla , and three bla ). mcr -1 genes were mobilizable by conjugation, associated with IncX4, IncHI2, and IncI2 plasmids. In our study, mcr -1 genes have been circulating in pig farms since 2005 harbored by a variety of E. coli clones. Its persistence may be driven by co-selection since plasmids containing mcr -1 also exhibit resistance to multiple drugs used in veterinary medicine. Furthermore, this is the first report of the presence of mcr -1 gene in isolates from white storks in Spain. This finding highlights the potential importance of wildlife that forage at urban household waste landfills in the transmission and spread of colistin resistance genes

Single-locus-sequence-based typing of the mgpB gene reveals transmission dynamics in mycoplasma genitalium

Sexually transmitted infections (STIs) by Mycoplasma genitalium are a major problem worldwide, especially given their marked and rapid propensity for developing antimicrobial resistance. Since very few treatment options exist, clinicians face an important challenge in the management of the infection. In this scenario, little is known regarding the transmission dynamics of M. genitalium and the epidemiology of antimicrobial resistance. This mgpB-based molecular typing study, conducted among 54 asymptomatically infected individuals prospectively recruited from an STI screening service, reveals two distinct epidemiological clusters that significantly correlate with sexual conduct in heterosexuals and men who have sex with men (MSM), respectively. This well-defined structuration suggests the presence of two independent sexual networks with little connectivity between them. On the other hand, the study demonstrates the multiclonal feature of the emergence of antibiotic resistance in M. genitalium to both macrolides and fluoroquinolones. The high prevalence of macrolide resistance in M. genitalium among MSM, influenced by dense network connectivity and strong antibiotic selective pressure, may correspond to allodemics affecting other STIs such as gonorrhea, syphilis and enteric pathogens. Collaterally, the structural and functional impact of mutations in the mgpB gene, encoding the major adhesin P140 (MgpB), may require further investigation.This work was partially supported by an “Ayuda SEIMC” grant from the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC)

Increasing trend of antimicrobial resistance in Shigella associated with MSM transmission in Barcelona, 2020-21 : outbreak of XRD Shigella sonnei and dissemination of ESBL-producing Shigella flexneri

Several countries have recently reported the detection of ESBL-producing Shigella sonnei associated with transmission among MSM. In a previous study by our group, 2.8% of Shigella spp. obtained from MSM in Barcelona between 2015 and 2019 were ESBL producers. To describe and characterize the emerging ESBL-producing Shigella spp. associated with sexual transmission among MSM detected from 2020 to 2021 in Barcelona, elucidating their connectivity with contemporaneous ESBL-producing Shigella spp. from other countries. From 2020 to 2021, we identified that among MSM, 68% of S. sonnei were XDR harbouring bla and 14% of Shigella flexneri were MDR harbouring bla . WGS analysis showed that the ESBL-producing S. sonnei were part of a monophyletic cluster, which included isolates responsible for the prolonged outbreak occurring in the UK. Our data also reveal the first emergence and clonal dissemination of ESBL-producing and fluoroquinolone-resistant S. flexneri 2a among MSM. We report an increasing trend of antimicrobial resistance in Shigella spp. among MSM in Barcelona since 2021, mainly as a consequence of the dissemination of XDR ESBL-producing S. sonnei, previously reported in the UK. These results highlight the importance of international collaborative surveillance of MDR/XDR S. sonnei and S. flexneri for rapid identification of their emergence and the prevention of the transmission of these pathogens

Increasing trend of antimicrobial resistance in Shigella associated with MSM transmission in Barcelona, 2020–21: outbreak of XRD Shigella sonnei and dissemination of ESBL-producing Shigella flexneri

Antimicrobial resistance; Shigella sonnei; Sexually transmitted infectionResistencia antimicrobiana; Shigella sonnei; Infección de transmisión sexualResistència antimicrobiana; Shigella sonnei; Infecció de transmissió sexualBackground Several countries have recently reported the detection of ESBL-producing Shigella sonnei associated with transmission among MSM. In a previous study by our group, 2.8% of Shigella spp. obtained from MSM in Barcelona between 2015 and 2019 were ESBL producers. Objectives To describe and characterize the emerging ESBL-producing Shigella spp. associated with sexual transmission among MSM detected from 2020 to 2021 in Barcelona, elucidating their connectivity with contemporaneous ESBL-producing Shigella spp. from other countries. Results From 2020 to 2021, we identified that among MSM, 68% of S. sonnei were XDR harbouring blaCTX-M-27 and 14% of Shigella flexneri were MDR harbouring blaCTX-M-27. WGS analysis showed that the ESBL-producing S. sonnei were part of a monophyletic cluster, which included isolates responsible for the prolonged outbreak occurring in the UK. Our data also reveal the first emergence and clonal dissemination of ESBL-producing and fluoroquinolone-resistant S. flexneri 2a among MSM. Conclusions We report an increasing trend of antimicrobial resistance in Shigella spp. among MSM in Barcelona since 2021, mainly as a consequence of the dissemination of XDR ESBL-producing S. sonnei, previously reported in the UK. These results highlight the importance of international collaborative surveillance of MDR/XDR S. sonnei and S. flexneri for rapid identification of their emergence and the prevention of the transmission of these pathogens.This work was partially supported by the ‘Ministerio de Economía y Competitividad’, ‘Instituto de Salud Carlos III’, and co-financed by the European Regional Development Fund (ERDF) ‘A Way to Achieve Europe’ (Spanish Network for Research in Infectious Diseases, grant number RD16/0016/0003) and by the Centro de Investigación Biomédica en Red (CIBER de Enfermedades Infecciosas, grant no. CB21/13/00054). A.M.M. is supported by a grant from the ‘Fondo de Investigación Sanitaria’ (Contratos Predoctorales de Formación en Investigación, grant number FI19/00315)

Pertactin-Deficient Bordetella pertussis with Unusual Mechanism of Pertactin Disruption, Spain, 1986-2018

Bordetella pertussis not expressing pertactin has increased in countries using acellular pertussis vaccines (ACV). The deficiency is mostly caused by pertactin gene disruption by IS481. To assess the effect of the transition from whole-cell vaccine to ACV on the emergence of B. pertussis not expressing pertactin in Spain, we studied 342 isolates collected during 1986-2018. We identified 93 pertactin-deficient isolates. All were detected after introduction of ACV and represented 38% of isolates collected during the ACV period; 58.1% belonged to a genetic cluster of isolates carrying the unusual prn::del(-292, 1340) mutation. Pertactin inactivation by IS481 insertion was identified in 23.7% of pertactin-deficient isolates, arising independently multiple times and in different phylogenetic branches. Our findings support the emergence and dissemination of a cluster of B. pertussis with an infrequent mechanism of pertactin disruption in Spain, probably resulting from introduction of ACV.This work was supported by the Ministerio de Economía y Competitividad, Instituto de Salud Carlos III, and cofinanced by the European Regional Development Fund “A Way to Achieve Europe” (Spanish Network for Research in Infectious Diseases, grant no. FIS PI18/00703) and by the Centro de Investigación Biomédica en Red (CIBER de Enfermedades Infecciosas), the Red Española de Investigación en Patología Infecciosa (grant no. CB21/13/00054). A.M.C. is supported by the Agència de Gestió d’Ajuts Universitaris i de Recerca de la Generalitat de Catalunya at Vall d’Hebron Institut de Recerca (Ajuts per a la Contractació de Personal Investigador FI, grant no. 2020FI_B2_00145) and by the Spanish Network for Research in Infectious Diseases (grant no. RD16/ 0016/0003). A.M.M. is supported by a grant from the Fondo de Investigación Sanitaria at Vall d’Hebron Institut de Recerca (Contratos Predoctorales de Formación en Investigación, grant no. FI19/00315).S

Spread of a SARS-CoV-2 variant through Europe in the summer of 2020.

Following its emergence in late 2019, the spread of SARS-CoV-21,2 has been tracked by phylogenetic analysis of viral genome sequences in unprecedented detail3–5. Although the virus spread globally in early 2020 before borders closed, intercontinental travel has since been greatly reduced. However, travel within Europe resumed in the summer of 2020. Here we report on a SARS-CoV-2 variant, 20E (EU1), that was identified in Spain in early summer 2020 and subsequently spread across Europe. We find no evidence that this variant has increased transmissibility, but instead demonstrate how rising incidence in Spain, resumption of travel, and lack of effective screening and containment may explain the variant’s success. Despite travel restrictions, we estimate that 20E (EU1) was introduced hundreds of times to European countries by summertime travellers, which is likely to have undermined local efforts to minimize infection with SARS-CoV-2. Our results illustrate how a variant can rapidly become dominant even in the absence of a substantial transmission advantage in favourable epidemiological settings. Genomic surveillance is critical for understanding how travel can affect transmission of SARS-CoV-2, and thus for informing future containment strategies as travel resumes. © 2021, The Author(s), under exclusive licence to Springer Nature Limited

Modelización de la dinámica de los microorganismos anaerobios sintróficos oxidantes del ácido acético (SAO)

In the anaerobic digestion process, the most sensitive step is the methanogenesis. The main methane producing organisms are the acetoclastic methanogenic archaea that degrade the acetic acid to methane. These microorganisms are very sensitive to high concentrations of ammonia, which leads to operation problems. Recently, it has been studied a microorganism that also has the ability to degrade acetate, SAO bacteria, less sensitive to ammonia and favoring the methane production through the hydrogenotrophic methanogens. In the present project, a study of the SAO bacteria was made, in order toadd them in the ADM1 model. These microorganisms are able to oxidize acetic anaerobically to hydrogen and carbon dioxide. The reaction is very sensitive to the partial pressure of H2, needing the presence of hydrogenotrophic methanogenic archaea, which consume the H2 generated and transform to methane. Once the population SAO was implemented in the model, the kinetic parameters of these new bacteria were identified by using experimental data and optimizing the sum of the square of differences between these data and values predicted by the model. The experimental data came from simultaneous batch test with different initial concentrations of ammonium, acetate and hydrogen, using an inoculum from a biogas plant whose behavior suggested the possible presence of SAO. Moreover, the variable stoichiometry model was studied because the SAO organisms are very sensitive to the reaction thermodynamics. That model was compared with the ADM1 model, which in the results seems that could not fulfill the second law of thermodynamics, simulating reactions which are endergonic in the reality. The results indicate the interest of modifying the ADM1 model to consider the presence of the SAO microorganisms. The fitting to the experimental data, using the modified ADM1 model, corroborate the presence of an appreciable initial concentration of SAO in the samples, with higher concentrations than those of acetoclastic methanogenic archaea.En la digestió anaeròbia una de les etapes més sensibles és la metanogènesi. Els principals organismes productors de metà, les arqueobacteris metanogènics acetoclástics, que degraden l'àcid acètic a metà, són molt sensibles a concentracions elevades d'amoníac, el que comporta problemes en el procés. Per intentar solucionar aquest inconvenient i comprendre millor el procés, recentment s'estan estudiant més a fons els bacteris SAO. Aquestes també tenen la capacitat de degradar l'acètic i són menys sensibles al amoníac. A diferència de les acetoclástiques, els SAO transformen l'acetat en hidrogen i diòxid de carboni. L'H2 produït és transformat en metà per arqueobacteris metanogènics hidrogenófils. A més, els SAO són molt sensibles a la pressió parcial d'hidrogen, pel que és imprescindible per al seu desenvolupament el consum d'H2 per part de les metanogènics hidrogenófils. En el present treball s'ha realitzat un estudi dels bacteris SAO, per tal de poder implementar la seva dinàmica en el model ADM1. Un cop implementada, es va procedir a la identificació de paràmetres utilitzant dades experimentals d'assaigs discontinus simultanis, amb diferents concentracions inicials d'amoni, acetat i hidrogen, utilitzant un inòcul procedent d'una planta de biogàs el comportament suggeria la possible presència de SAO. D'altra banda, com els organismes SAO són molt sensibles a la termodinàmica de la reacció, es va estudiar el model adoptant estequiometria variable i es va comparar amb el model ADM1. Aquest últim, segons els resultats, podria no complir el segon principi de la termodinàmica, produint reaccions endergòniques. Els resultats obtinguts indiquen l'interès en modificar el model de referència ADM1 perquè contempli la presència de microorganismes SAO. Els ajustos a les dades experimentals, realitzats mitjançant el model ADM1 modificat, corroboren la presència d'una concentració inicial apreciable de SAO en les mostres estudiades, amb concentracions superiors a les de arqueobacteris metanogènics acetoclástics.En la digestión anaerobia una de las etapas más sensibles es la metanogénesis. Los principales organismos productores de metano, las arqueas metanogénicas acetoclásticas, que degradan el ácido acético a metano, son muy sensibles a concentraciones elevadas de amoniaco, lo que conlleva problemas en el proceso. Para intentar solucionar este inconveniente y comprender mejor el proceso, recientemente se están estudiando más a fondo las bacterias SAO. Estas también poseen la capacidad de degradar el acético y son menos sensibles al amoniaco. A diferencia de las acetoclásticas, SAO transforma el acetato en hidrógeno y dióxido de carbono. El H2 producido es transformado en metano por arqueas metanogénicas hidrogenófilas. Además, SAO son muy sensibles a la presión parcial de hidrógeno, por lo que es imprescindible para su desarrollo el consumo de H2 por parte de las metanogénicas hidrogenófilas. En el presente trabajo se ha realizado un estudio de las bacterias SAO, con el fin de poder implementar su dinámica en el modelo ADM1. Una vez implementada, se procedió a la identificación de parámetros utilizando datos experimentales de ensayos discontinuos simultáneos, con diferentes concentraciones iniciales de amonio, acetato e hidrógeno, utilizando un inóculo procedente de una planta de biogás cuyo comportamiento sugería la posible presencia de SAO. Por otra parte, como los organismos SAO son muy sensibles a la termodinámica de la reacción, se estudió el modelo adoptando estequiometría variable y se comparó con el modelo ADM1. Este último, según los resultados, podría no cumplir el segundo principio de la termodinámica, produciendo reacciones endergónicas. Los resultados obtenidos indican el interés en modificar el modelo de referencia ADM1 para que contemple la presencia de microorganismos SAO. Los ajustes a los datos experimentales, realizados mediante el modelo ADM1 modificado, corroboran la presencia de una concentración inicial apreciable de SAO en las muestras estudiadas, con concentraciones superiores a las de arqueas metanogénicas acetoclásticas

Modelización de la dinámica de los microorganismos anaerobios sintróficos oxidantes del ácido acético (SAO)

In the anaerobic digestion process, the most sensitive step is the methanogenesis. The main methane producing organisms are the acetoclastic methanogenic archaea that degrade the acetic acid to methane. These microorganisms are very sensitive to high concentrations of ammonia, which leads to operation problems. Recently, it has been studied a microorganism that also has the ability to degrade acetate, SAO bacteria, less sensitive to ammonia and favoring the methane production through the hydrogenotrophic methanogens. In the present project, a study of the SAO bacteria was made, in order toadd them in the ADM1 model. These microorganisms are able to oxidize acetic anaerobically to hydrogen and carbon dioxide. The reaction is very sensitive to the partial pressure of H2, needing the presence of hydrogenotrophic methanogenic archaea, which consume the H2 generated and transform to methane. Once the population SAO was implemented in the model, the kinetic parameters of these new bacteria were identified by using experimental data and optimizing the sum of the square of differences between these data and values predicted by the model. The experimental data came from simultaneous batch test with different initial concentrations of ammonium, acetate and hydrogen, using an inoculum from a biogas plant whose behavior suggested the possible presence of SAO. Moreover, the variable stoichiometry model was studied because the SAO organisms are very sensitive to the reaction thermodynamics. That model was compared with the ADM1 model, which in the results seems that could not fulfill the second law of thermodynamics, simulating reactions which are endergonic in the reality. The results indicate the interest of modifying the ADM1 model to consider the presence of the SAO microorganisms. The fitting to the experimental data, using the modified ADM1 model, corroborate the presence of an appreciable initial concentration of SAO in the samples, with higher concentrations than those of acetoclastic methanogenic archaea.En la digestió anaeròbia una de les etapes més sensibles és la metanogènesi. Els principals organismes productors de metà, les arqueobacteris metanogènics acetoclástics, que degraden l'àcid acètic a metà, són molt sensibles a concentracions elevades d'amoníac, el que comporta problemes en el procés. Per intentar solucionar aquest inconvenient i comprendre millor el procés, recentment s'estan estudiant més a fons els bacteris SAO. Aquestes també tenen la capacitat de degradar l'acètic i són menys sensibles al amoníac. A diferència de les acetoclástiques, els SAO transformen l'acetat en hidrogen i diòxid de carboni. L'H2 produït és transformat en metà per arqueobacteris metanogènics hidrogenófils. A més, els SAO són molt sensibles a la pressió parcial d'hidrogen, pel que és imprescindible per al seu desenvolupament el consum d'H2 per part de les metanogènics hidrogenófils. En el present treball s'ha realitzat un estudi dels bacteris SAO, per tal de poder implementar la seva dinàmica en el model ADM1. Un cop implementada, es va procedir a la identificació de paràmetres utilitzant dades experimentals d'assaigs discontinus simultanis, amb diferents concentracions inicials d'amoni, acetat i hidrogen, utilitzant un inòcul procedent d'una planta de biogàs el comportament suggeria la possible presència de SAO. D'altra banda, com els organismes SAO són molt sensibles a la termodinàmica de la reacció, es va estudiar el model adoptant estequiometria variable i es va comparar amb el model ADM1. Aquest últim, segons els resultats, podria no complir el segon principi de la termodinàmica, produint reaccions endergòniques. Els resultats obtinguts indiquen l'interès en modificar el model de referència ADM1 perquè contempli la presència de microorganismes SAO. Els ajustos a les dades experimentals, realitzats mitjançant el model ADM1 modificat, corroboren la presència d'una concentració inicial apreciable de SAO en les mostres estudiades, amb concentracions superiors a les de arqueobacteris metanogènics acetoclástics.En la digestión anaerobia una de las etapas más sensibles es la metanogénesis. Los principales organismos productores de metano, las arqueas metanogénicas acetoclásticas, que degradan el ácido acético a metano, son muy sensibles a concentraciones elevadas de amoniaco, lo que conlleva problemas en el proceso. Para intentar solucionar este inconveniente y comprender mejor el proceso, recientemente se están estudiando más a fondo las bacterias SAO. Estas también poseen la capacidad de degradar el acético y son menos sensibles al amoniaco. A diferencia de las acetoclásticas, SAO transforma el acetato en hidrógeno y dióxido de carbono. El H2 producido es transformado en metano por arqueas metanogénicas hidrogenófilas. Además, SAO son muy sensibles a la presión parcial de hidrógeno, por lo que es imprescindible para su desarrollo el consumo de H2 por parte de las metanogénicas hidrogenófilas. En el presente trabajo se ha realizado un estudio de las bacterias SAO, con el fin de poder implementar su dinámica en el modelo ADM1. Una vez implementada, se procedió a la identificación de parámetros utilizando datos experimentales de ensayos discontinuos simultáneos, con diferentes concentraciones iniciales de amonio, acetato e hidrógeno, utilizando un inóculo procedente de una planta de biogás cuyo comportamiento sugería la posible presencia de SAO. Por otra parte, como los organismos SAO son muy sensibles a la termodinámica de la reacción, se estudió el modelo adoptando estequiometría variable y se comparó con el modelo ADM1. Este último, según los resultados, podría no cumplir el segundo principio de la termodinámica, produciendo reacciones endergónicas. Los resultados obtenidos indican el interés en modificar el modelo de referencia ADM1 para que contemple la presencia de microorganismos SAO. Los ajustes a los datos experimentales, realizados mediante el modelo ADM1 modificado, corroboran la presencia de una concentración inicial apreciable de SAO en las muestras estudiadas, con concentraciones superiores a las de arqueas metanogénicas acetoclásticas