Assessment on Strength Characteristics of Microbial Concrete by using Bacillus Subtilis as Self-healing Agent: A Critical Review

Concrete is one of the most widely used construction materials by mankind and it is the main material used for the infrastructure development of every country. Microbial concrete, as the name suggest is an improvisation provided to cement using living microbes which are capable of doing so. Using microbes such as Bacillus subtilis which has the properties of bio-calcification can secrete calcium carbonate as an extra cellular product.  Thus, filling the pores and the cracks internally, it makes the structure more compact and resistive to seepage. In this experimental investigation, the performance of microbial concrete exposed to plain water. Concrete specimens of 100 mm cubical size were cast and cured for 7, 14, 28, 60, 90 days in plain water with and without using bacterial water. Using a spectrophotometer to measure the optical density at 600 nm (OD600) of a bacterial culture to monitor bacterial growth has always been a central technique in microbiology. Concrete specimens having OD600 0.107, 0.20, 0.637 and 1.221 have been studied in plain water. The specimens were taken out periodically and subjected to compressive & tensile strength tests. From the investigation, it has been revealed that microbial concrete having OD600 0.637 shows better resistance against strength deterioration under all curing conditions and curing ages. Concrete specimens were also subjected to Ultrasonic Pulse Velocity (UPV) test. From this test, it has been observed that specimens having OD600 0.637 shows better velocity. The higher pulse velocity can therefore be used to assess the quality and uniformity of the materia

The Utilization of Bacillus Subtilis Bacteria to Improve the Mechanical Properties of Concrete

The utilization of concrete as a building material is well-known worldwide and increasing continuously due to its sustainability, low maintenance cost, durability, performance, etc. The ingredients of concrete, its constructional methodology, and exposure conditions have been observed to be moderating and improving daily but the focus of this research is on the laboratory investigation of Bacterial Concrete which is the technology established on the application of the mineral producing microbes like Bacillus subtilis which have the properties of bio-calcification and the ability to precipitate CaCO3 effectively inside concrete structures. This CaCO3 precipitation is able to fill the pores and cracks internally and this subsequently makes the structure to become more compact. Nutrient Broth (NB) media was employed for the growth and spore formation of Bacillus subtilis bacteria in this experimental study and four different bacterial culture densities including 0.107, 0.2, 0.637, and 1.221 were estimated at OD600 and directly added to the concrete matrix using the previously fixed water to culture ratio of 0.5:0.5. Moreover, 100 mm cubical concrete specimens were cast, subjected to compressive and tensile strength tests for different curing ages, and finally compared with Conventional Concrete with OD600=0. A significant increase was observed in the mechanical strengths due to the addition of Bacillus subtilis bacteria in concretes with a culture density of 0.637. Furthermore, cylindrical concrete specimens with 100 mm diameter and 200 mm height were prepared for Ultrasonic Pulse Velocity (UPV) analysis and the results showed specimens prepared with culture density of 0.637 have higher pulse velocity than other microbial groups. A UPV vs. compressive strength relationship curve was, however, later proposed for different strengths of concrete

Depulping of fruits and soaking the seeds enhances the seed germination and initial growth performance of Terminalia beleria Roxb. seedlings

The study describes the effects of depulping the fruits and soaking the seeds of Terminalia belerica Roxb. on seed germination and seedling growth in nursery condition. Around half of the freshly collected fruits of T. belerica were depulped by rotting the fleshy pulp in water. Depulped seeds or intact fruits were dried in sun following storage in airtight container. Effects pre-sowing treatments were explored by soaking the dry intact fruits or depulped seeds in cold water for 0, 24, 48 and 72 h and sowed in polybags filled with soil mixed with decomposed cow dung. The study revealed that depulping of fruits and soaking the seeds significantly enhanced the seed germination and seedling growth performance in nursery condition. The fastest seed germination was observed in depulped seeds soaked in cold water for 72 h (DT3) and slowest germination was in intact fruits without treatment (IT0). The highest germination percentage (93) was observed in depulped seeds soaked in cold water for 48 h (DT2) followed by 85.6% in depulped seeds soaked in water for 24 h (DT1), which was significantly higher than the other treatments including the control (36.7). Although growth parameters such as shoot length, root length, total height, leaf number, leaf area and collar diameter of the seedlings were maximum in the seedlings developed through DT3, the vigor index was maximum in DT2 and minimum in IT0. Total dry mass per seedling was also maximum in the seedlings developed from the treatment DT3. Considered the imbibition period, germination percentage, growth performance including vigor index and total biomass produced per seedling, depulping the fruits and soaking the dry seeds in cold water for 48 h was recommended for obtaining maximum seed germination and seedling growth performance

Early detection of biofilm formation of selected bacterial isolates through a new screening method using 'image J'

Aim: The cells growing in biofilms are physiologically distinct even from the same microorganism in the planktonic state. Although mixed-species biofilms predominate in most of the environments, single-species biofilms exist in a large variety of infections, on the surface of medical implants and parts of the machineries in the food industries. Convenient method and early detection of these biofilms are therefore, necessary to avoid or prevent the important implants from the bacterial biofilm formation. Therefore present research was undertaken with the aim to establish an in vitro method for early detection and screening of biofilm with easily applicable image J. Methodology and results: Eight bacterial colonies were isolated from the poultry wastes (PW), dental plaques (DP) and hospital effluents (HE). Among them, three isolates were finally selected for the study based on their source of origin, colony characteristics and the biofilm forming ability determined by test tube assay. The isolates were provisionally identified as Salmonella arizonae (from PW), Micrococcus luteus (from DP) and Aerococcus viridians (from HE) and examined for their biofilm forming ability through a novel in vitro method, cover slip assay. The images of crystal violet stained biofilms of the isolates on the surface of the cover slips were captured and analysed by image-processing software image J. The results of the cover slip assay were then compared with those from test tube assays to conform the efficacy and reliability of the method for screening and evaluating biofilm formation. The results suggest that the novel in vitro method for biofilm screening by cover slip assay is effective for evaluating selected bacterial biofilms. The ability to form biofilm was not specifically correlated with the colony characteristics but the initial attachment for early development of the biofilm was significantly correlated with their motility. Conclusion, significance and impact of study: The method of biofilm screening with the cover slip assay used in this study is novel, very simple but powerful and effective method, is expected to have significant impact and gain additional interest among the scientists for biofilm screening and study

Effects of deforestation on physicochemical properties and microbial population of soils in a South-East Asian tropical forest

The study was conducted in deforested land and adjacent natural forest in Chittagong Forest South Division, Bangladesh, to explore the effects of deforestation on physico-chemical properties of soil and the soil microbial population. Soil samples from surface (0-10 cm depth) or subsurface (10-20 cm depth) of two hill positions (top and bottom) of deforested land and an adjacent natural forest were collected and analysed for their physico-chemical properties and microbial population. The study reveals that there was no significant (p≤0.05) difference in soil texture for soil surfaces or hill positions between the deforested land and natural forest. However, significantly (p≤0.05) low moisture content and high pH was observed in both the surfaces and hill position in deforested land compared to the natural forest. The microbial community i.e., the fungal and bacterial population was also significantly (p≤0.05) lower in both surfaces (0-10 cm and 10-20 cm) of hill positions in the deforested land compared to natural forest. Fungal population ranged from 59 to 76 million g-1 and 78 to 153 million g-1 of dry soil in deforested land and in natural forest, respectively, whereas bacterial population ranged from 70 to 146 million g-1 in deforested land and from 127 to 218 million g-1 in natural forest. A total of seven genera of fungi were primarily identified from the soils of natural forest and six from the deforested land. The six common genera of identified fungi in both the land used were Mucor, Aspergillus, Rhizopus, Fusarium, Penicillium and Trichoderma and the different one was Colletotrichum from the natural forest. Three genera of bacteria coccus, Streptococcus and Basillus were noticed in natural forest and two genera (coccus and Streptococcus) were recorded from deforested land

An Experimental Study of the Physio-Mechanical and Microstructural Performances of Escherichia Coli Bacteria-Based Bio-Concrete

A balanced mixture of cement, sand, stone or brick chips, and water is carefully allowed to form concrete, a man-made building material. These elements can be adjusted appropriately to produce concrete with a variety of qualities. Although concrete may endure compressive forces, like natural stone, tensile forces can cause it to crack. As a result, crack formation is a frequent occurrence in concrete, allowing various foreign chemicals and water to enter the structures and shortening their life span. The likelihood of cracking grows with time due to variations in humidity and temperature. It can be exceedingly expensive to maintain or repair concrete construction items. The use of bio-concrete for the construction of durable structures has shown to be quite advantageous in this perspective. It is beneficial for improving the properties of concrete as well as lowering maintenance costs. In this investigation, concrete samples measuring 100×100×100 mm were made and periodically tested for compressive and split tensile strength testing. Following a 28-day curing period, the concrete treated with Escherichia coli bacteria had compressive and split tensile strengths that were 10% and 23% higher than identical bacteria-free. The non-destructive test on cylindrical samples was then conducted to evaluate the material qualities. The mortar samples of crystalline structures were also validated by SEM examination. In order to properly and reliably anticipate the strength of concrete, the RSM model was also formulated

Determination of pond water quality for aquaculture and ecosystem management

Fish is the main source of animal protein for the common people of Bangladesh. About 37% of the inland fishes are obtained from the closed water fish culture where ponds play vital roles in the production system. The present study was carried out to determine the water quality (physico-chemical and biological factors) of five uncultivated or under cultivated ponds in the Chittagong University campus, Bangladesh, for aquaculture and ecosystem management. Temperature, pH, EC, BOD, COD, TSS, turbidity, NO2-, PO4 -, free CO2, CO3 -, HCO3-, Cl-, total viable bacterial count and total coliform were determined. Isolation and identification of Escherichia coli and Salmonella sp. from the water samples were performed to investigate the antibiotic sensitivity. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against ciprofloxacin was also investigated. The findings reveal that there was no significant difference in temperature (19°C to 20°C), pH (6.7 to 7.4), electrical conductivity and Cl- values in the water among the ponds and that was within the range of the requirements for the fish cultivation. Both turbidity and total dissolved solids was highest in the uncultivated botanical garden pond 2 (BGP2). BOD, COD, NO2- , PO 4-2, HCO3-, and free CO2 concentration was beyond the permissible limits for aquaculture. Total viable count and total coliform ranged from 1.3 × 10 4 to 6.6 × 10 5 cfu ml-1 and from 0.0205×10 2 to 1.10×10 2 ml-1 respectively, among the ponds where both these parameters were highest in the naturally polluted BGP2. Most of the isolated E. coli and Salmonella sp. were sensitive but few showed resistance against the antibiotics, especially in BGP1, where fishes were cultivated commercially

Propagation of an endangered gymnosperm tree species (Podocarpus neriifolius D. Don.) by stem cuttings in non-mist propagator

Podocarpus neriifolius D. Don. (Podocarpaceae), an endangered and the only indigenous gymnosperm tree species, grows naturally in Bangladesh. Seed-based propagation of this species is challenging owing to its inadequate number of mother trees and irregular seed-setting attribute from among a few trees scattered throughout the country. This study weighs the significance and multiplication potentials of this species through rejuvenated stem cuttings with or without the application of Indole Butyric Acid (IBA). The rooting ability of the cuttings was evaluated by treating the cutting bases with 0%, 0.2%, 0.4% and 0.8% (w/v) IBA solution prior to place them in a low cost, non-mist propagation system. Steckling performances of the rooted cuttings were evaluated in the nursery conditions. The study found that the species was amenable to rooting with IBA treatments. The highest rooting percentage (61.3 ± 3.3 %; n = 90) and number of roots per cutting (9.8 ± 1.32; n = 90 ) were obtained in the 0.8% IBA treatment; however, the longest root and shoot, as well as the highest initial growth performances were obtained in 0.4% IBA treatment. Therefore, rejuvenated stem cuttings treated with 0.4% or 0.8% IBA solution in a non-mist propagator could potentially be an effective method for the clonal propagation of these tree species

Antimicrobial and catalytic applications of TiO2 nanoparticles prepared from titanium(IV)-Schiff base complexes as precursor

Attempts have been made to synthesis titanium dioxide (TiO2) nanoparticles using titanium (IV) complexes of Schiff base (TiOL) as a precursor where Schiff base ligand (L) act as a dibasic tetradentate one. TiO2 nanoparticles were synthesized by the direct calcination of titanium complexes at 500 °C for 3 hours. The analytical tools such as FT-IR, XRD, EDS, and SEM provided evidences in favor of the formation of TiO2 nanoparticles. Antimicrobial study showed that all prepared TiO2 nanoparticles have inhibition capacity on the growth against selected plant pathogenic fungi as well as some selected human pathogenic bacteria. Moreover, these TiO2 nanoparticles have catalytic capacity for the remarkable degradation (54.0%) of organic dye (Mordent brown 48) as well as industrial dye solutions