Stenotrophomonas maltophilia is an emerging multidrug-resistant global opportunistic pathogen. The increasing incidence of nosocomial and community-acquired S. maltophilia infections is of particular concern for immunocompromised individuals, as this bacterial pathogen is associated with a significant fatality/case ratio. S. maltophilia is an environmental bacterium found in aqueous habitats, including plant rhizospheres, animals, foods, and water sources. Infections of S. maltophilia can occur in a range of organs and tissues; the organism is commonly found in respiratory tract infections. This review summarizes the current literature and presents S. maltophilia as an organism with various molecular mechanisms used for colonization and infection. S. maltophilia can be recovered from polymicrobial infections, most notably from the respiratory tract of cystic fibrosis patients, as a cocolonizer with Pseudomonas aeruginosa. Recent evidence of cell-cell communication between these pathogens has implications for the development of novel pharmacological therapies. Animal models of S. maltophilia infection have provided useful information about the type of host immune response induced by this opportunistic pathogen. Current and emerging treatments for patients infected with S. maltophilia are discussed.

Stenotrophomonas maltophilia: an Emerging Global Opportunistic Pathogen

Microbial Geotechnology is a new branch of geotechnical engineering that deals with the applications of microbiological methods to geological materials used in engineering. The aim of these applications is to improve the mechanical properties of soil so that it will be more suitable for construction or environmental purposes. Two notable applications, bioclogging and biocementation, have been explored. Bioclogging is the production of pore-filling materials through microbial means so that the porosity and hydraulic conductivity of soil can be reduced. Biocementation is the generation of particle-binding materials through microbial processes in situ so that the shear strength of soil can be increased. The most suitable microorganisms for soil bioclogging or biocementation are facultative anaerobic and microaerophilic bacteria, although anaerobic fermenting bacteria, anaerobic respiring bacteria, and obligate aerobic bacteria may also be suitable to be used in geotechnical engineering. The majority of the studies on Microbial Geotechnology at present are at the laboratory stage. Due to the complexity, the applications of Microbial Geotechnology would require an integration of microbiology, ecology, geochemistry, and geotechnical engineering knowledge.

Applications of microorganisms to geotechnical engineering for bioclogging and biocementation of soil in situ

Consideration of soil as a living ecosystem offers the potential for innovative and sustainable solutions to geotechnical problems. This is a new paradigm for many in geotechnical engineering. Realising the potential of this paradigm requires a multidisciplinary approach that embraces biology and geochemistry to develop techniques for beneficial ground modification. This paper assesses the progress, opportunities, and challenges in this emerging field. Biomediated geochemical processes, which consist of a geochemical reaction regulated by subsurface microbiology, currently being explored include mineral precipitation, gas generation, biofilm formation and biopolymer generation. For each of these processes, subsurface microbial processes are employed to create an environment conducive to the desired geochemical reactions among the minerals, organic matter, pore fluids, and gases that constitute soil. Geotechnical applications currently being explored include cementation of sands to enhance bearing capacity and liquefaction resistance, sequestration of carbon, soil erosion control, groundwater flow control, and remediation of soil and groundwater impacted by metals and radionuclides. Challenges in biomediated ground modification include upscaling processes from the laboratory to the field, in situ monitoring of reactions, reaction products and properties, developing integrated biogeochemical and geotechnical models, management of treatment by-products, establishing the durability and longevity/reversibility of the process, and education of engineers and researchers.

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Biogeochemical processes and geotechnical applications: progress, opportunities and challenges

Microbially induced calcium carbonate precipitation (MICCP) is a naturally occurring biological process in which microbes produce inorganic materials as part of their basic metabolic activities. This technology has been widely explored and promising with potential in various technical applications. In the present review, the detailed mechanism of production of calcium carbonate biominerals via ureolytic bacteria has been discussed along with role of bacteria and the sectors where these biominerals are being used. The review discusses the applications of bacterially produced carbonate biominerals for improving the durability of buildings, remediation of environment (water and soil), sequestration of atmospheric CO2, filler material in rubbers and plastics etc. The study also sheds light on benefits of bacterial biominerals over traditional agents and also the issues that lie in the path of successful commercialization of the technology of Microbially induced calcium carbonate precipitation from lab to field scale.

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Biomineralization of calcium carbonates and their engineered applications: a review

The availability of trace metals as micro-nutrients plays a very significant role on the performance and stability of agricultural biogas digesters, which are operated with energy crops, animal excreta, crop residues, organic fraction of municipal solid wastes or any other type of organic waste. The unavailability of these elements in biogas digesters is probably the first reason of poor process efficiency without any other obvious reason, despite proper management and control of other operational and environmental parameters. However, trace metal requirements of biogas digesters operated with solid biomass are not often reported in literature. Therefore, the aim of this article is to review the previous and current literature about the trace metal requirements of anaerobic biogas digesters operated with solid organic substrates for production of methane.

Trace element requirements of agricultural biogas digesters during biological conversion of renewable biomass to methane

Bioreduction of Fe(III) and biooxidation of Fe(II) can be used in wastewater engineering as an innovative biotechnology BioIronTech, which is protected for commercial applications by US patent 7393452 and Singapore patent 106658 "Compositions and methods for the treatment of wastewater and other waste". The BioIronTech process comprises the following steps: 1) anoxic bacterial reduction of Fe(III), for example in iron ore powder; 2) surface renovation of iron ore particles due to the formation of dissolved Fe 2+ ions; 3) precipitation of insoluble ferrous salts of inorganic anions (phosphate) or organic anions (phenols and organic acids); 4) (bio)oxidation of ferrous compunds with the formation of negatively, positively, or neutrally charged ferric hydroxides, which are good adsorbents of many pollutants; 5) disposal or thermal regeration of ferric (hydr)oxide. Different organic substances can be used as electron donors in bioreduction of Fe(III). Ferrous ions and fresh ferrous or ferric hydroxides that are produced after iron bioreduction and (bio)oxidation adsorb and precipitate diferent negatively charged molecules, for example chlorinated compounds of sucralose production wastewater or other halogenated organics, as well as phenols, organic acids, phosphate, and sulphide. Reject water (return liquor) from the stage of sewage sludge dewatering on municipal wastewater treatment plants represents from 10 to 50% of phosphorus load when being recycled to the aeration tank. BioIronTech process can remove/recover more than 90% of phosphorous from this reject water thus replacing the conventional process of phosphate precipitation by ferric/ferrous salts, which are 20-100 times more expensive than iron ore, which is used in BioIronTech process. BioIronTech process can remarkably improve the aerobic and anaerobic treatments of municipal and industrial wastewaters, especially anaerobic digestion of lipid- and sulphate-containing food-processing wastewater. It can also remove the recalcitrant compounds from industrial wastewater, enhance sustainability and quality of water resources, restore eutrophicated lakes due to removal of phosphate, ammonium, and pesticides from water, and recover ammonium and phosphate from municipal and food-processing wastes.

Wastewater engineering applications of BioIronTech process based on the biogeochemical cycle of iron bioreduction and (bio)oxidation

The biotechnological production of construction biomaterials is a sustainable process because renewable agricultural and biotechnological biomass residues are used as organic raw materials and as the components of composite biocement. In some geotechnical processes, microorganisms themselves are performing useful function. There are at least eight types of construction-related biotechnological processes classified by the results of the microbial treatment of soil: bioaggregation of soil particles, biocrusting of soil surface, biocoating of solid surface, bioclogging of soil, porous material or fractured rocks, biocementation of soil or porous material, biodesaturation of soil, bioencapsulation of clay/soft soil/particles, and bioremediation of polluted ground.

Biotechnological Improvement of Construction Ground and Construction Materials

Fast decontamination of chemical, biological, radiological, or nuclear pollutants of land and demolished infrastructure must be carried out following the industrial accidents, military actions, or terrorist attacks. Biotechnological decontamination is more acceptable in some cases than physical or chemical methods due to its environmental safety, lower cost, and deep penetration of decontamination solution in the soil pores or concrete cracks. The dispersion of the land and infrastructure pollutants to environment can be decreased using microbially mediated adsorption and precipitation of radioactive pollutants, fixation of the bacteriological pollutants, and biochemical biodegradation of the chemical pollutants. One of the most effective ways is the immobilization of the pollutants using bioaggregation of the soil particles, bioclogging of the pores and cracks, biocrusting of the soil surface, and biocoating of the concrete surface.

Biotechnological immobilization of chemical, biological, and radioactive pollutants on land and infrastructure demolition waste after industrial accident, military action, or terrorist attack

Biocements and biogrouts are developing extensively as new materials alternative to cement and toxic chemical grouts. The most popular type of biocement is a mixture of urease-producing bacteria, urea and calcium salt. Thus, development of biotechnology to produce biomass of urease-active bacteria for large-scale biocementation is an important biotechnological task. Two strains of urease-producing bacteria, Yaniella sp. VS8 and Bacillus sp. VS1 that synthesized inducible and constitutive urease, respectively, were used in the present study. It was shown that low cost biomass of urease-active bacteria can be produced from the hydrolyzed excessive activated sludge of municipal wastewater treatment plant. The biomass of Yaniella sp. VS8 grown in this medium diminished the hydraulic conductivity of sand from 4.8A—10 -4 m/s to 5âˆ™10 -8 m/s after several biotreatments with solution of 1.5 M urea and 0.75M ÐiÐ°Cl 2 .

Production of Bioagent for Calcium-Based Biocement

Artificial oasis could be supported by the trapping and retaining rainfall water by impermeable layer of artificial material. In case of average annual rainfall in Arabian or Pakistani Deserts of 100 mm the watershed area must be at least 1000 ha to ensure rainfall water supply for consumption and irrigation in the artificial oasis of 100 ha area. Minimum cost for the sealing of 1000 ha of the sand slopes with 1 mm geosynthetic liner is about 112 mln Saudi Arabian Riyal, which could be not acceptable price for 100 ha of artificial oasis land. However, this cost could be diminished to 17 mln Saudi Arabian Riyal if to coat watershed slopes with 1 mm of biocemented sand crust using a low viscosity solution of biocement. Conventional cementation is cheaper but it cannot be used to make 1 mm sand crust because of a high viscosity of the cement suspension. The novel biotechnological method is based on the formation of the sand surface crust for water collection and transportation on the surrounding slopes. Most environmentally friendly biotechnology for this biocementation is aerobic biooxidation of cheap calcium formate or calcium acetate. Biocementation of the sand crust could be used to make a low-cost artificial desert oasis fed by rainfall.

Viktor Stabnikov

Papers

Wastewater engineering applications of BioIronTech process based on the biogeochemical cycle of iron bioreduction and (bio)oxidation

Biotechnological Improvement of Construction Ground and Construction Materials

Biotechnological immobilization of chemical, biological, and radioactive pollutants on land and infrastructure demolition waste after industrial accident, military action, or terrorist attack

Production of Bioagent for Calcium-Based Biocement

Biocementation technology for construction of artificial oasis in sandy desert