Desulfovibrio brasiliensis sp. nov., a moderate halophilic sulfate-reducing bacterium from Lagoa Vermelha (Brazil) mediating dolomite formation

A novel halotolerant sulfate-reducing bacterium, Desulfovibrio brasiliensis strain LVform1, was isolated from sediments of a dolomite-forming hypersaline coastal lagoon, Lagoa Vermelha, in the state of Rio de Janeiro, Brazil. The cells are vibrio-shaped and 0.30 to 0.45μm by 1.0 to 3.5μm in size. These bacteria mediate the precipitation of dolomite [CaMg(CO3)2] in culture experiments. The strain was identified as a member of the genus Desulfovibrio in the δ-subclass of the Proteobacteria on the basis of its 16S rRNA gene sequence, its physiological and morphological properties. Strain LVform1 is obligate sodium-dependent and grows at NaCl concentrations of up to 15%. The 16S rRNA sequence revealed that this strain is closely related to Desulfovibrio halophilus (96.2% similarity) and to Desulfovibrio oxyclinae (96.8% similarity), which were both isolated from Solar Lake, a hypersaline coastal lake in the Sinai, Egypt. Strain LVform1 is barotolerant, growing under pressures of up to 370bar (37MPa). We propose strain LVform1 to be the type strain of a novel species of the genus Desulfovibrio, Desulfovibrio brasiliensis (type strain LVform1 = DSMZ No. 15816 and JCM No. 12178). The GenBank/EMBL accession number for the 16S rDNA sequence of strain LVform1 is AJ54468

Use of carrier materials to immobilise and supply cementation medium for microbially mediated self-healing in biocement

Microbially induced calcium carbonate precipitation (MICP) has been attracting growing interest in respect of its use for biocementation, as a means of improving the engineering properties of granular soil. Recent studies have demonstrated the potential of MICP to enable self-healing of biocement, through the injection of nutrients and precursor chemicals required for MICP into degraded biocement. This paper documents the early stages of research into the development of an autonomous self-healing system for biocement, whereby the nutrients and precursor chemicals are provided from within the biocement matrix. This system has the potential to improve the durability and sustainability of geotechnical structures. The effectiveness of a variety of carrier materials for the immobilisation and release of the nutrients and precursor chemicals, also referred to as the cementation medium, has been explored. Materials tested include expanded perlite, diatomaceous earth and natural fibres such as jute and coir. Studies have subsequently been undertaken to investigate the effect of these carrier materials on the MICP process, in aqueous solutions and within the biocement matrix, and thus the potential to enable self-healing. Ureolytic, spore forming Sporosarcina ureae has been utilised to induce the precipitation of calcium carbonate

Development of self-healing biocement

Background: Microbially induced calcium carbonate precipitation (MICP) has been attracting growing interest in respect of its potential use for ground improvement by the process of biocementation. Recent studies have demonstrated the potential of MICP to enable self-healing, through the injection of nutrients and precursor chemicals into degraded biocement. Objectives: The focus of this three-year research project will be to develop a truly autonomous self-healing process, by facilitating the supply of nutrients and precursor chemicals from within the biocement matrix, to improve the durability and sustainability of geotechnical structures. Methods: The potential of carrier materials for the effective immobilisation and release of the nutrients and precursor chemicals required for MICP has been explored. A preliminary study has subsequently been undertaken utilising expanded perlite, within a biocement produced using Sporosarcina ureae. Calcium production during the biocementation process has been determined using ICP-OES. Results: This paper presents the results from preliminary investigations. Results obtained demonstrate that diatomaceous earth, expanded perlite and natural fibres such as jute have the potential to be utilised for the immobilisation and supply of the required nutrients and precursor chemicals to enable MICP. This combined with the proven spore forming ability of Sporosarcina ureae, indicates that in principal autonomous self-healing of biocement can be achieved

Development of self-healing biocement

Background: Microbially induced calcium carbonate precipitation (MICP) has been attracting growing interest in respect of its potential use for ground improvement by the process of biocementation. Recent studies have demonstrated the potential of MICP to enable self-healing, through the injection of nutrients and precursor chemicals into degraded biocement. Objectives: The focus of this three-year research project will be to develop a truly autonomous self-healing process, by facilitating the supply of nutrients and precursor chemicals from within the biocement matrix, to improve the durability and sustainability of geotechnical structures. Methods: The potential of carrier materials for the effective immobilisation and release of the nutrients and precursor chemicals required for MICP has been explored. A preliminary study has subsequently been undertaken utilising expanded perlite, within a biocement produced using Sporosarcina ureae. Calcium production during the biocementation process has been determined using ICP-OES. Results: This paper presents the results from preliminary investigations. Results obtained demonstrate that diatomaceous earth, expanded perlite and natural fibres such as jute have the potential to be utilised for the immobilisation and supply of the required nutrients and precursor chemicals to enable MICP. This combined with the proven spore forming ability of Sporosarcina ureae, indicates that in principal autonomous self-healing of biocement can be achieved

Diversity of Bacillus-like organisms isolated from deep-sea hypersaline anoxic sediments

Abstract Background The deep-sea, hypersaline anoxic brine lakes in the Mediterranean are among the most extreme environments on earth, and in one of them, the MgCl2-rich Discovery basin, the presence of active microbes is equivocal. However, thriving microbial communities have been detected especially in the chemocline between deep seawater and three NaCl-rich brine lakes, l'Atalante, Bannock and Urania. By contrast, the microbiota of these brine-lake sediments remains largely unexplored. Results Eighty nine isolates were obtained from the sediments of four deep-sea, hypersaline anoxic brine lakes in the Eastern Mediterranean Sea: l'Atalante, Bannock, Discovery and Urania basins. This culture collection was dominated by representatives of the genus Bacillus and close relatives (90% of all isolates) that were investigated further. Physiological characterization of representative strains revealed large versatility with respect to enzyme activities or substrate utilization. Two third of the isolates did not grow at in-situ salinities and were presumably present as endospores. This is supported by high numbers of endospores in Bannock, Discovery and Urania basins ranging from 3.8 × 105 to 1.2 × 106 g-1 dw sediment. However, the remaining isolates were highly halotolerant growing at salinities of up to 30% NaCl. Some of the novel isolates affiliating with the genus Pontibacillus grew well under anoxic conditions in sulfidic medium by fermentation or anaerobic respiration using dimethylsulfoxide or trimethylamine N-oxide as electron acceptor. Conclusion Some of the halophilic, facultatively anaerobic relatives of Bacillus appear well adapted to life in this hostile environment and suggest the presence of actively growing microbial communities in the NaCl-rich, deep-sea brine-lake sediments. </jats:sec

Increased microbially induced calcium carbonate precipitation (MICP) efficiency in multiple treatment sand biocementation processes by augmentation of cementation medium with ammonium chloride

The cementation medium for ureolytic microbially induced calcium carbonate precipitation (MICP) typically consists of urea and a calcium source. While some studies have augmented this basic medium, the effects of adding substrates such as ammonium chloride are unclear. The studies detailed in this paper sought to quantify the effect of the ammonium chloride augmentation of cementation medium (CM) on the process of MICP. An aqueous MICP study was initially carried out to study the effects of adding ammonium chloride to the urea–calcium cementation medium. This batch test also explored the effect of varying the concentration of calcium chloride dihydrate (calcium source) in the CM. A subsequent sand column study was undertaken, whereby multiple treatments of CM were injected over several days to produce a biocement. Six columns were prepared using F65 sand bioaugmented with Sporosarcina pasteurii, half of which were injected with the basic medium only and half with the augmented medium for treatment two onwards. Effluent displaced from columns was tested using ion chromatography and Nesslerisation to determine the calcium and ammonium ion concentrations, respectively, and hence the treatment efficiency. Conductivity and pH testing of effluent gave insights into the bacterial urease activity. The addition of 0.187 M ammonium chloride to the CM resulted in approximately 100% chemical conversion efficiency within columns, based on calcium ion measurements, compared to only 57% and 33% efficiency for treatments three and four, respectively, when using the urea–calcium medium. Columns treated with the CM containing ammonium chloride had unconfined compressive strengths which were 1.8 times higher on average than columns treated with the urea–calcium medium only

Effect of jute fibres on the process of MICP and properties of biocemented sand

There has been increasing interest, in the past decade, in bio-mediated approaches to soil improvement for geotechnical applications. Microbially induced calcium carbonate precipitation (MICP) has been investigated as a potentially sustainable method for the strengthening and stabilisation of soil structures. This paper presents the results of a study on the effect of jute fibres on both the MICP process and properties of biocemented sand. Ureolytic Sporosarcina pasteurii has been used to produce biocemented soil columns via MICP in the laboratory. Results showed that columns containing 0.75% (by weight of sand) untreated jute fibres had unconfined compressive strengths approximately six times greater on average compared to biocemented sand columns without jute fibres. Furthermore, efficiency of chemical conversion was found to be higher in columns containing jute fibres, as measured using ion chromatography. Columns containing jute had calcimeter measured CaCO3 contents at least three times those containing sand only. The results showed that incorporation of jute fibres into the biocemented sand material had a beneficial effect, resulting in stimulation of bacterial activity, thus sustaining the MICP process during the twelve-day treatment process. This study also explores the potential of jute fibres in self-healing MICP systems

Rapid development of anoxic niches in supraglacial ecosystems

Microorganisms play a significant role in changing the physical properties of the surface of the Greenland Ice Sheet. Cryoconite holes are a hotspot for this microbial activity, yet little is known about the REDOX conditions that develop within them. In this study, we used oxygen microelectrodes and microoptodes to measure for anoxic conditions at the microscale, for the first time revealing a potential niche for anaerobic microorganisms and anaerobic processes. The development of an anoxic zone 2 mm deep within a 6 mm-thick layer of cryoconite sediment was observed within an hour of disturbance, showing rapid acclimation to changing physical conditions. Long-term (half year) incubations of cryoconite material showed a peak of oxygen production and consumption after forty days and reached a low-activity, steady state by day 116, with a persisting anoxic zone beginning between 2 mm and 4 mm deep. Anaerobic microorganisms, which have received little attention to date, should therefore be considered an important component of the cryoconite ecosystem. We discuss the possible dynamics of oxygen concentrations in the supraglacial system and infer that anoxic zones are an important factor in the development of cryoconite sediment communities

Physiological capabilities of cryoconite hole microorganisms

Cryoconite holes are miniature freshwater aquatic ecosystems that harbor a relatively diverse microbial community. This microbial community can withstand the extreme conditions of the supraglacial environment, including fluctuating temperatures, extreme and varying geochemical conditions and limited nutrients. We analyzed the physiological capabilities of microbial isolates from cryoconite holes from Antarctica, Greenland, and Svalbard in selected environmental conditions: extreme pH, salinity, freeze-thaw and limited carbon sources, to identify their physiological limits. The results suggest that heterotrophic microorganisms in cryoconite holes are well adapted to fast-changing environmental conditions, by surviving multiple freeze-thaw cycles, a wide range of salinity and pH conditions and scavenging a variety of organic substrates. Under oxic and anoxic conditions, the communities grew well in temperatures up to 30°C, although in anoxic conditions the community was more successful at colder temperatures (0.2°C). The most abundant cultivable microorganisms were facultative anaerobic bacteria and yeasts. They grew in salinities up to 10% and in pH ranging from 4 to 10.5 (Antarctica), 2.5 to 10 (Svalbard), and 3 to 10 (Greenland). Their growth was sustained on at least 58 single carbon sources and there was no decrease in viability for some isolates after up to 100 consecutive freeze-thaw cycles. The elevated viability of the anaerobic community in the lowest temperatures indicates they might be key players in winter conditions or in early melt seasons, when the oxygen is potentially depleted due to limited flow of meltwater. Consequently, facultative anaerobic heterotrophs are likely important players in the reactivation of the community after the polar night. This detailed physiological investigation shows that despite inhabiting a freshwater environment, cryoconite microorganisms are able to withstand conditions not typically encountered in freshwater environments (namely high salinities or extreme pH), making them physiologically more similar to arid soil communities. The results also point to a possible resilience of the most abundant microorganisms of cryoconite holes in the face of rapid change regardless of the location