Optimization of bacterial sporulation using economic nutrient for self-healing concrete.

The use of heat- and alkali-resistant bacteria is essential for the biological repair of damaged concrete. Lysinibacillus boronitolerans YS11 was isolated from the rhizosphere of Miscanthus sacchariflorus. The increased pH in the urea-minus condition during the growth of the YS11 strain promoted calcium carbonate (CaCO3) formation. To identify the optimum medium that promoted the growth of the YS11 strain, a Plackett-Burman design was conducted for the screening process. Consequently, malt powder, rice bran, (NH4)2SO4, and corn syrup were chosen to enhance YS11 growth. The optimization of these four useful factors was carried out using a central composite design. To obtain higher survivability in mortar, the sporulation process is essential, and additional factors such as Mn2+, Fe2+, and Ca2+ were found to contribute to sporulation. A mixture of L. boronitolerans YS11 spore powder, cement, paste, sand, yeast extract, calcium lactate, and water showed a healing effect on a 0.3 mm mortar crack in 7 days. Furthermore, calcium carbonate precipitation was observed over the crack surface. Thus, we confirmed that mortar treated with YS11 spore powder was effective in healing micro-cracks in concrete.

Low-cost cultivation and sporulation of alkaliphilic Bacillus sp. strain AK13 for self-healing concrete.

The alkaliphilic, calcium carbonate precipitating Bacillus sp. strain AK13 can be utilized in concrete for self-repairing. A statistical experimental design was used to develop an economical medium for its mass cultivation and sporulation. Two types of screening experiment were first conducted to identify substrates that promote the growth of the AK13 strain: the first followed a one-factor-at-a-time factorial design and the second a two-level full factorial design. Based on these screening experiments, barley malt powder and mixed grain powder were identified as the substrates that most effectively promoted the growth of the AK13 strain from a range of 21 agricultural products and by-products. A quadratic statistical model was then constructed using a central composite design and the concentration of the two substrates was optimized. The estimated growth and sporulation of Bacillus sp. strain AK13 in the proposed medium were 3.08 ± 0.38 × 108 and 1.25 ± 0.12 × 108 CFU/ml, respectively, which meant that the proposed low-cost medium was approximately 45 times more effective than the commercial medium in terms of the number of cultivatable bacteria per unit price. The spores were then powdered via a spray-drying process to produce a spore powder with a spore count of 2.0 ± 0.7 × 109 CFU/g. The AK13 spore powder was mixed with cement paste, yeast extract, calcium lactate, and water. The yeast extract and calcium lactate generated the highest CFU/ml for AK13 at a 0.4:0.4 ratio compared to 0.4:0.25 (the original ratio of the B4 medium) and 0.4:0.8. Twenty-eight days after the spores were mixed into the mortar, the number of vegetative cells and spores of the AK13 strain had reached 106 CFU/g within the mortar. Cracks in the mortar under 0.29 mm were healed in 14 days. Calcium carbonate precipitation was observed on the crack surface. The mortar containing the spore powder was thus concluded to be effective in terms of healing micro-cracks.

Towards a low CO2 emission building material employing bacterial metabolism (2/2): Prospects for global warming potential reduction in the concrete industry.

The production of concrete is one of the most significant contributors to global greenhouse gas emissions. This work focuses on bio-cementation-based products and their potential to reduce global warming potential (GWP). In particular, we address a proposed bio-cementation method employing bacterial metabolism in a two-step process of limestone dissolution and recrystallisation (BioZEment). A scenario-based techno-economic analysis (TEA) is combined with a life cycle assessment (LCA), a market model and a literature review of consumers' willingness to pay, to compute the expected reduction of global GWP. Based on the LCA, the GWP of 1 ton of BioZEment is found to be 70-83% lower than conventional concrete. In the TEA, three scenarios are investigated: brick, precast and onsite production. The results indicate that brick production may be the easiest way to implement the products, but that due to high cost, the impact on global GWP will be marginal. For precast production the expected 10% higher material cost of BioZEment only produces a marginal increase in total cost. Thus, precast production has the potential to reduce global GWP from concrete production by 0-20%. Significant technological hurdles remain before BioZEment-based products can be used in onsite construction scenarios, but in this scenario, the potential GWP reduction ranges from 1 to 26%. While the potential to reduce global GWP is substantial, significant efforts need to be made both in regard to public acceptance and production methods for this potential to be unlocked.

A cost effective cultivation medium for biocalcification of Bacillus pasteurii KCTC 3558 and its effect on cement cubes properties.

Application of carbonate precipitation induced by Bacillus pasteurii for improving some properties of cement has been reported. However, it is not yet successful in commercial scale due to the high cost of cultivation medium. This is the first report on the application of effluent from chicken manure bio-gas plant, a high protein content agricultural waste, as an alternative growth medium for carbonate precipitation by B. pasteurii KCTC3558. Urease activity of B. pasteurii KCTC3558 cultured in chicken manure effluent medium and other three standard media were examined using phenate method. The highest urease production was achieved in chicken manure effluent medium (16.756Umg(-1) protein). Cost per liter of chicken manure effluent medium is up to 88.2% lower than other standard media. The most effective cultivation media was selected for carbonate precipitation study in cement cubes. Water absorption, voids, apparent density and compressive strength of cement cubes were measured according to the ASTM standard. The correlation between the increasing density and compressive strength of bacterial added cement cube was evident. The density of bacterial cement cube is 5.1% higher than control while the compressive strength of cement mixed with bacterial cells in chicken manure effluent medium increases up to 30.2% compared with control. SEM and XRD analysis also found the crystalline phase of calcium carbonate within bacterial cement which confirmed that the increasing density and compressive strength were resulted from bacterial carbonate precipitation. This study indicated that the effluent from chicken manure bio-gas plant could be used as an alternative cost effective culture medium for cultivation and biocalcification of B. pasteurii KCTC3558 in cement.

Laboratory-induced endolithic growth in calcarenites: biodeteriorating potential assessment.

This study is aimed to assess the formation of photosynthetic biofilms on and within different natural stone materials, and to analyse their biogeophysical and biogeochemical deterioration potential. This was performed by means of artificial colonisation under laboratory conditions during 3 months. Monitoring of microbial development was performed by image analysis and biofilm biomass estimation by chlorophyll extraction technique. Microscopy investigations were carried out to study relationships between microorganisms and the mineral substrata. The model applied in this work corroborated a successful survival strategy inside endolithic microhabitat, using natural phototrophic biofilm cultivation, composed by cyanobacteria and algae, which increased intrinsic porosity by active mineral dissolution. We observed the presence of mineral-like iron derivatives (e.g. maghemite) around the cells and intracellularly and the precipitation of hausmannite, suggesting manganese transformations related to the biomineralisation.

Characterization of microbial particle release from biomass and building material surfaces for inhalation exposure risk assessment.

A conceptual approach including measurements of materials at rest (step 1), measurements using a large rotating drum (step 2) or a Particle-FLEC (step 2) and measurements at a workplace (step 4) has been used to characterize the release of microbial components (bacteria, fungi, actinomycetes, endotoxin or enzymes) and particles from straw, wood chips or fungal cultures of different ages on gypsum boards. Repeated agitation or handling periods were included in step 2 and step 4. There was a low similarity between the amount of microbial components measured in step 1 and the aerosolized amount (step 2) from gypsum boards, wood chips and straw. Ratios between some microbial components measured at the workplace (step 4) and measured in step 2, showed similarities. Less than 1.3% of the total amount of microorganisms and endotoxin becomes airborne during 5 min of agitation of straw or wood chips. Most microbial components were released at higher rates during the first agitation period than during the following periods. However, differences were seen between different microbial components, and endotoxin from straw was released at the same rate in two successive agitation periods. Fungal particles smaller than spores were released from fungal colonized gypsum boards at amounts that were up to 30 times higher in the first agitation period compared with that in the following period, while fungal spores were released at amounts that were five times as high in the first period compared with that in the following period. In addition to differences between microbial components, the release patterns of microbial components were different for wood chips and straw. The time for maximum particle release to half particle release was longer for straw than for wood chips. The observation that some components, e.g. endotoxin, are released at the same rate in two successive handling steps, and that others (e.g. fungi) are mainly released initially, shows that the exposure period to different components from the same material differs in duration. The observed differences in the release patterns of different components and the differences between materials are important when preventive steps are to be taken, and it stresses the importance of applying a relevant sampling time and period in exposure assessments.

Decontamination assessment of Bacillus anthracis, Bacillus subtilis, and Geobacillus stearothermophilus spores on indoor surfaces using a hydrogen peroxide gas generator.

AIMS: To evaluate the decontamination of Bacillus anthracis, Bacillus subtilis, and Geobacillus stearothermophilus spores on indoor surface materials using hydrogen peroxide gas. METHODS AND RESULTS: Bacillus anthracis, B. subtilis, and G. stearothermophilus spores were dried on seven types of indoor surfaces and exposed to > or =1000 ppm hydrogen peroxide gas for 20 min. Hydrogen peroxide exposure significantly decreased viable B. anthracis, B. subtilis, and G. stearothermophilus spores on all test materials except G. stearothermophilus on industrial carpet. Significant differences were observed when comparing the reduction in viable spores of B. anthracis with both surrogates. The effectiveness of gaseous hydrogen peroxide on the growth of biological indicators and spore strips was evaluated in parallel as a qualitative assessment of decontamination. At 1 and 7 days postexposure, decontaminated biological indicators and spore strips exhibited no growth, while the nondecontaminated samples displayed growth. CONCLUSIONS: Significant differences in decontamination efficacy of hydrogen peroxide gas on porous and nonporous surfaces were observed when comparing the mean log reduction in B. anthracis spores with B. subtilis and G. stearothermophilus spores. SIGNIFICANCE AND IMPACT OF THE STUDY: These results provide comparative information for the decontamination of B. anthracis spores with surrogates on indoor surfaces using hydrogen peroxide gas.

[Assessment of biological corrosion of ferroconcrete of ground-based industrial structures]. / Otsenka biokorrozionnogo sostoianiia zhelezobetona nazemnykh promyshlennykh konstruktsii.

One of the objects of a nuclear plant built in 1983 and put in 15-years long dead storage with the purpose to estimate the degree of contamination by rust-hazardous microorganisms of ferroconcrete structures and to predict their biocorrosion state after putting in operation was a subject of microbiological investigation. The everywhere distribution of sulphur cycle bacteria (thionic and sulphate-reducing bacteria) on the surface and in the bulk of concrete structures, their confineness to corrosion products of concrete and bars of the investigated building have been shown. It has been demonstrated that sulphate-reducing bacteria were the most distributed group in all the sampling points. An indirect estimation of participation degree of the microbial communities in the processes of ferroconcrete biological damages has been carried out as based on the accumulation intensity of aggressive gaseous metabolites--carbon dioxide and hydrogen. Probability of deterioration of biocorrosion situation under the full-scale operation of the object has been substantiated.