Shewanella putrefaciens is a Gram-negative bacillus and marine pathogen that rarely causes disease in humans. We report a case of osteomyelitis by this organism in a 48-year-old male patient, who presented with pain and erythema of the right foot that was initially diagnosed as cellulitis and did not revert despite treatment. He was transferred to Lima where osteomyelitis was diagnosed and started on empirical treatment with partial regression. A biopsy and culture of the compromised area found S. putrefaciens. The infection was treated according to the antibiotic sensitivity profile of the pathogen. S. putrefaciens infection represents a rare opportunistic infection of devitalized or exposed areas of the body. It is associated with residence in coastal areas and commonly affects the skin and soft tissues. Exceptional cases of osteomyelitis have been reported, but this is the first that involves the metatarsal bones. Shewanella putrefaciens es un bacilo Gram negativo, patógeno marino que rara vez ocasiona enfermedad en humanos. Se presenta un caso de osteomielitis por este microorganismo en un paciente varón de 48 años, procedente de Chimbote. Presentó dolor y eritema en el pie derecho, inicialmente diagnosticado como celulitis, pero que no revirtió pese al tratamiento. Fue transferido a Lima donde se diagnosticó osteomielitis e inició tratamiento empírico con escasa mejoría. Por ello, se realizó una biopsia y cultivo de la zona comprometida, el metatarso, en el cual se aisló Shewanella putrefaciens. Se trató de acuerdo al perfil de sensibilidad. La infección por Shewanella putrefaciens representa una rara infección oportunista, que se localiza en áreas desvitalizadas o expuestas del cuerpo. Se asocia a vivir en zonas costeras, afectando comúnmente piel y tejidos blandos. Se han reportado casos excepcionales de osteomielitis. Este es el primero que involucra metatarso.

Thèse de doctorat : Pharmacie. Chimie et microbiologie de l'eau : Nancy 1 : 2006. / Titre provenant de l'écran-titre.

Thèse de doctorat : Physique, chimie et biologie de l'environnement : Strasbourg 1 : 2008. / Texte en anglais. Titre provenant de l'écran-titre. Bibliogr. p. 180-192.

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Microbial metal reduction contributes to biogeochemical cycling, and reductive precipitation provides the basis for bioremediation strategies designed to immobilize radionuclide contaminants present in the subsurface. Facultatively anaerobic ×-proteobacteria of the genus Shewanella are present in many aquatic and terrestrial environments and are capable of respiration on a wide range of compounds as terminal electron acceptor including transition metals, uranium and transuranics. S. putrefaciens is readily cultivated in the laboratory and a genetic system was recently developed to study U(VI) reduction in this organism. U(VI) reduction-deficient S. putrefaciens point mutant Urr14 (hereafter referred to as CCMB1) was found to retain the ability to respire several alternate electron acceptors. In the present study, CCMB1 was tested on a suite of electron acceptors and found to retain growth on electron acceptors with high reduction potential (E¡¬0) [O2, Fe(III)-citrate, Mn(IV), Mn(III)-pyrophosphate, NO3-] but was impaired for anaerobic growth on electron acceptors with low E¡¬0 [NO2-, U(VI), dimethyl sulfoxide, trimethylamine N-oxide, fumarate, ×-FeOOH, SO32-, S2O32-]. Genetic complementation and sequencing analysis revealed that CCMB1 contained a point mutation (H108Y) in a CcmB homolog, an ABC transporter permease subunit required for c-type cytochrome maturation in E. coli. The periplasmic space of CCMB1 contained low levels of cytochrome c and elevated levels of free thiol equivalents (-SH), an indication that redox homeostasis was disrupted. Anaerobic growth ability, but not cytochrome c maturation activity, was restored to CCMB1 by adding exogenous disulfide bond-containing compounds (e.g., cystine) to the growth medium. To test the possibility that CcmB transports heme from the cytoplasm to the periplasm in S. putrefaciens, H108 was replaced with alanine, leucine, methionine and lysine residues via site-directed mutagenesis. Anaerobic growth, cytochrome c biosynthesis or redox homeostasis was disrupted in each of the site-directed mutants except H108M. The results of this study demonstrate, for the first time, that S. putrefaciens requires CcmB to produce c-type cytochromes under U(VI)-reducing conditions and maintain redox homeostasis during growth on electron acceptors with low E¡¬0. The present study is the first to examine CcmB activity during growth on electron acceptors with widely-ranging E¡¬0, and the results suggest that cytochrome c or free heme maintains periplasmic redox poise during growth on electron acceptors with E¡¬0 < 0.36V such as in the subsurface engineered for rapid U(VI) reduction or anoxic environments dominated by sulfate-reducing bacteria. A mechanism for CcmB heme translocation across the S. putrefaciens cytoplasmic membrane via heme coordination by H108 is proposed.

Dissimilatory iron reduction (DIR) is significant to the biogeochemical cycling of iron, carbon and other elements, and may be applied to bioremediation of organic pollutants, toxic metals, and radionuclides; however, the mechanism(s) of DIR and factors controlling its kinetics are still unclear. To provide insights into these questions, the interaction between a common dissimilatory iron reducing bacterium (DIRB)was studied, Shewanella oneidensis MR-1, and ferric iron (Fe(III)) (oxy)(hydr)oxide mineral surfaces. Firstly, atomic force microscopy was used to study how S. oneidensis MR-1 dissolved Fe(III) (oxy)(hydr)oxides and compared it to two other cases where Fe(III) (oxy)(hydr)oxides were either dissolved by a chemical reductant or by a mutant with an electron shuttling compound. Without the electron shuttling compound, the mutant is unable to respire on Fe(III) (oxy)(hydr)oxides, but with the electron shuttling compound, it can. It was found that the cells of S. oneidensis MR-1 formed microcolonies on mineral surfaces and dissolved the minerals in a non-uniform way which was consistent with the shape of microcolonies, whereas Fe(III) (oxy)(hydr)oxides were uniformly dissolved in both of the other cases. Secondly, confocal microscopy was used to study the adhesion behavior of S. oneidensis MR-1 cells on Fe(III) (oxy)(hydr)oxide surfaces across a broad range of bulk cell densities. While the cells were evenly distributed under low bulk cell densities, microcolonies were observed at high bulk cell densities. This adhesion behavior was modeled by a new, two-step adhesion isotherm which fit better than a simple Langmuir or Freundlich isotherm. The results of these studies suggest that DIR is in-part transport limited and the surface cell density may control DIR.

Mining and mineral processing generate a wide range of As-rich minerals, including scorodite (FeAsO4•2H2O), and arsenical ferrihydrite, which are common secondary minerals found in mine tailings. Scorodite and arsenical ferrihydrite are relatively stable under a wide range of physico-chemical conditions which makes them suitable arsenic sinks in mining environments. However, bacteria can reduce these minerals and release arsenic into the aqueous environment. Two dissimilatory iron and arsenic reducing bacteria, Shewanella sp. ANA-3 and Shewanella putrefaciens CN32, were used to investigate their effects on the reductive dissolution of scorodite and arsenical 6-line ferrihydrite in a chemically defined medium containing low phosphate concentrations representative of the natural environment. Analysis of the aqueous phase of all biotic reduced samples found mainly As(III), the more toxic form of As, while very little As(V) was reduced in the abiotic samples. Solid state analysis of the scorodite biotic post-reduction minerals identified scorodite, biogenic Fe(II)-As(III) compounds, parasymplesite and tooeleite, while in the biotic reduced arsenical six-line ferrihydrite, biogenic Fe(II)-As(III) compounds, hematite, akaganeite and unconfirmed magnetite were identified as secondary reduction products. Results from this research add to the body of literature on As and Fe biogeochemistry and provide very useful information for future assessments of the long term stability of As-rich minerals. L’activité minière et la transformation du minerai génèrent divers minéraux riches en arsenic, tels la scorodite (FeAsO4•2H2O) et la ferrihydrite riche en arsenic, lesquels sont des minéraux secondaires communs des résidus miniers. Comme la scorodite et la ferrihydrite riche en arsenic sont relativement stables sous une grande gamme de conditions physico-chimiques, ces minéraux peuvent potentiellement être utilisés pour stocker de façon permanente l’arsenic dans les environnements miniers. Cependant, certaines bactéries peuvent réduire ces minéraux, ce qui entraine la solubilisation de l’arsenic. Deux bactéries capables de réduire l’arsenic et le fer, soit Shewanella sp. ANA-3 et Shewanella putrefaciens CN32, ont été utilisées afin de déterminer leurs effets sur la réduction microbienne de la scorodite et de la ferrihydrite riche en As dans un milieu de culture contenant de faibles concentrations de phosphate. Les analyses de la phase aqueuse ont démontré que dans tous les systèmes biotiques, As(V) a été réduit en As(III), alors que dans les systèmes contrôles abiotiques, peu de As(V) a été réduit. L’analyse des minéraux secondaires présents à la fin réduction dans les systèmes biotiques contenant de la scorodite indique que la scorodite est encore présente, ainsi que des composés organiques riches en Fe(II) et As(III), de la parasymplésite et de la tooéleite, alors que dans les systèmes biotiques contenant de la ferrihydrite riche en As, des composés riches en Fe(II) et en As(III), de l’hématite, de l’akaganéite et de la magnétique ont été identifiés comme minéraux secondaires. Les résultats de cette étude enrichissent la littérature sur le cycle biogéochimique du Fe et de As et fournissent de l’information importante pour l’évaluation de la stabilité à long terme de minéraux riches en As.

The redox cycling of iron is intimately linked to the cycling of C, S, N, P as well as the speciation, mobility, and bioavailability of various toxic contaminants in soils and sediments. Within these environments, the cycling of iron is catalytically driven by iron-oxidizing (FeOB) and iron reducing bacteria (FeRB) which mediate the formation, transformation, and dissolution of various iron-bearing minerals. Under oxic conditions, FeOB promote the formation of iron oxides on or in close proximity of their cell walls and extracellular polymeric substances, and such composite, termed biogenic iron oxides (BIOS), offers highly reactive heterogenous sites that efficiently immobilize trace metals and contaminants alike. However, under reducing conditions, FeRB mediate the reductive dissolution of BIOS and in turn lead to the remobilization of associated contaminants. Conversely, contaminants may become immobilized by secondary iron minerals that form from the metabolic activity of FeRB. Therefore, determining the factors that influence the reactivity of BIOS, as well as the formation of secondary iron minerals is of critical importance to develop a better understanding of the geochemical cycling of iron and in turn the transport of contaminants in the environment. This thesis investigated (1) the impact of simulated diagenesis (ageing for ~5 years at 4ºC) on the mineral stability and reactivity of BIOS towards reduction by Shewanella putrefaciens CN32, (2) the effects of phosphate at an environmentally relevant (10µM) and excess (3.9mM) concentration on the rates and extent of microbial reduction of synthetic 2-line ferrihydrite and BIOS, as well as the formation of secondary iron minerals, and (3) the impact of sterilization by γ-irradiation on the mineral stability and reactivity of BIOS. It was found that simulated diagenesis did not affect the mineralogical composition of BIOS but significantly lowered the reactivity of BIOS towards microbial reduction. The concentration of phosphate was found to have contrasting effects on the rates of reduction of ferrihydrite and BIOS, but in general, excess concentration of phosphate enhanced the extent of Fe(III) reduction. The formation of a specific secondary iron mineral was also found to depend on the concentration of phosphate, as well as, in the case for BIOS, the presence of intermixed cell derived organic matter. γ-irradiation did not alter the mineralogy and reactivity of BIOS towards microbial reduction, and it was concluded to be a suitable technique to sterilize BIOS.