Bacterial Solution Research Articles

Photodynamic Therapy With Resveratrol and an Nd:YAG Laser for Enterococcus faecalis Elimination.

Enterococcus faecalis is the leading cause of endodontic treatment failures. Despite various conventional disinfection approaches, microorganisms often persist in root canals. Photodynamic therapy (PDT) is an adjunct antimicrobial strategy employing a nontoxic photosensitizer (PS) and light source. This study evaluated the antimicrobial effect of PDT using an Nd:YAG laser and resveratrol (RSV) with or without pigment, and confirmed that RSV is nontoxic as a PS. We employed laser irradiation at a 3W output power, using RSV and red pigment as the PS, on an E. faecalis bacterial solution. Subsequently, colony-forming units were quantified. The impact of RSV on osteoblasts was measured using an MTT assay. E. faecalis counts declined after laser irradiation. The combined application of laser irradiation with RSV, red pigment, or both showed a reduction compared to no irradiation and control groups without RSV and red pigment. The 50% cytotoxic concentration against osteoblast cells from mice incubated with RSV for 48 h was 162 μM. The value with RSV and laser was 201 μM and that with RSV and red pigment was 199 μM. The value with RSV, laser and red pigment was 357 μM. The combination of Nd:YAG laser irradiation and RSV as the PS with pigment was efficacious for E. faecalis elimination without inducing any toxic effects on osteoblasts. This combination holds potential as a root canal irrigation strategy.

Investigation on Self-Healing Concrete Using Bacillus Subtilis Bacteria

Cracking is a common occurrence in concrete, primarily attributed to its relatively low tensile strength due to External loads which induce high tensile stresses. Immediate and proper treatment is essential to prevent the expansion of cracks, as their unchecked growth may lead to higher repair costs. Bacterially induced calcium carbonate precipitation emerges as an eco-friendly alternative for crack repair. This technique involves the metabolic activities of specific bacteria in concrete, resulting in microbial mineral precipitation. In this study an attempt has been made to define bacterial concrete and its behavior such as self-healing by minor cracks induced in the samples. Concrete cubes of M20, M25 and M30 have been casted with three dosages of bacterial solution (Bascillus Subtilis) as 60 ml, 75 ml & 90 ml per cube (150 mm size). It has been observed that the compressive strength of bacterial concrete has increased slightly as compared to conventional concrete for each dose. The best performance in compressive strength enhancement has been observed for 75 ml dose and best self-healing has been observed for 90 ml dose of bacterial solution (per cube) in bacterial concrete. Ultrasonic pulse velocity test shows excellent quality for all samples of bacterial concrete.

Impact of in vitro lens deposition and removal on bacterial adhesion to orthokeratology contact lenses

PurposeThe purpose of this study was to explore the impact of several contact lens (CL) care solutions on the removal of proteins and lipids, and how deposit removal impacts bacterial adhesion and solution disinfection. MethodsLysozyme and lipid deposition on three ortho-k (rigid) and two soft CL materials were evaluated using an ELISA kit and gas chromatography respectively. Bacterial adhesion to a fluorosilicone acrylate material using Pseudomonas aeruginosa with various compositions of artificial tear solutions (ATS), including with denatured proteins, was also investigated. The impact of deposition of the different formulations of ATS on biofilm formation was explored using cover slips. Finally, the lysozyme and lipid cleaning efficacy and disinfection efficacy against P. aeruginosa and Staphylococcus aureus of four different contact lens care solutions were studied using qualitative analysis. ResultsWhile maximum lysozyme deposition was observed with the fluorosilicone acrylate material (327.25 ± 54.25 µg/lens), the highest amount of lipid deposition was recorded with a fluoro-siloxanyl styrene material (134.71 ± 19.87 µg/lens). Adhesion of P. aeruginosa to fluorosilicone acrylate lenses and biofilm formation on cover slips were significantly greater with the addition of denatured proteins and lipids. Of the four contact lens care solutions investigated, the solution based on povidone-iodine removed both denatured lysozyme and lipid deposits and could effectively disinfect against P. aeruginosa and S. aureus when contaminated with denatured proteins and lipids. In contrast, the peroxide-based solution was able to inhibit P. aeruginosa growth only, while the two multipurpose solutions were unable to disinfect lenses contaminated with denatured proteins and lipids. ConclusionBacterial adhesion and biofilm formation is influenced by components within artificial tear solutions depositing on lenses, including denatured proteins and lipids, which also affects disinfection. The ability of different solutions to remove these deposits should be considered when selecting systems to clean and disinfect ortho-k lenses.

Functional results of surgical treatment of macular holes fully preserving the internal limiting membrane as compared with the traditional method

Purpose: to assess the functional results of surgical treatment of macular holes (MH) using the authors’ developed technology preserving the internal limiting membrane (ILM) and compare them with the results of traditional surgery technology involving ILM peeling.Material and methods: 150 MH patients aged 50 to 82 were divided into 2 groups: the main group who underwent surgical MH treatment with ILM preservation and the control group, whose traditional surgical treatment involved ILM peeling. After vitrectomy, the main group patients’ macular areas were treated with a bacterial collagenase solution (1 kU) for three minutes, whereupon it was washed out, the vitreal cavity was dried and treated with platelet-rich plasma. In the control group, ILM was stained and removed, whereupon platelet-rich plasma was applied in the air medium. The anatomical result was assessed by optical coherence tomography data. To assess the functional results, the patients were tested for the best corrected visual acuity (BCVA) and subjected to microperimetry. The observation period was 24 months.Results: in all cases, a significant increase in BCVA was achieved after surgical treatment. After 6 months, the control group showed a tendency to a BCVA decrease, while in the main group BCVA remained stable. In the main group, not a single case showed a decrease in the total retinal photosensitivity below the threshold level of the norm of 24 dB, whilst in the control group, 35 cases (47 %) revealed a retinal sensitivity decrease below 24 dB. The total retinal sensitivity turned out to be significantly lower in the control group as compared to the main group over the entire observation period (p < 0.05). Postoperative scotomas were significantly more frequent after ILM peeling. Absolute scotomas were detected in 7 control group cases, whilst in the main group they were not noted in any case.Conclusion. The developed technology makes it possible to practically eliminate the formation of absolute scotomas and to significantly reduce the formation of relative scotomas in the postoperative period, as well as improve functional results against the traditional method of surgical treatment of MH with ILM peeling.

Establishment and validation of a callus tissue transformation system for German chamomile (Matricaria chamomilla L.)

BackgroundGerman chamomile (Matricaria chamomilla L.) is an important medicinal plant, and the essential oils in the flowers have various biological activities. Genetic transformation systems are important for plant quality improvement and molecular research. To the best of our knowledge, a genetic transformation system has not yet been reported for German chamomile.ResultsIn this study, we developed Agrobacterium-mediated transformation protocols for German chamomile callus tissues. This involved optimizing key parameters, such as hygromycin and cefotaxime concentrations, bacterial density, and infection and co-culture durations. We also performed gas chromatography–mass spectrometry analysis to identify volatile compounds in non-transgenic and transgenic callus and hairy root tissues. Furthermore, to compare and verify the callus transformation system of German chamomile, we transferred McFPS to the hairy roots of German chamomile. The results showed that the optimal conditions for Agrobacterium-mediated callus tissue transformation were as follows: explant, petiole; cefotaxime concentration, 300 mg/L; hygromycin concentration, 10 mg/L; and bacterial solution concentration, OD600 = 0.6; callus transformation efficiency was the highest when the co-culture time was 3 days.ConclusionsEstablishment of a high-efficiency callus transformation system will lay the foundation for gene function identification in German chamomile.

An experimental study of the effects of bacteria on asphaltene adsorption and wettability alteration of dolomite and quartz

The adsorption of asphaltene on the rock surface and the changes in its wettability are very relevant issues in flow assurance and oil recovery studies, and for carbonate reservoirs, they are even more important. During microbial enhanced oil recovery (MEOR) processes, wettability alteration is considered a crucial mechanism leading to improved oil recovery. Therefore, it is essential to understand the mechanisms of surface wettability changes by bacteria and biosurfactants and find new and reliable methods to prevent asphaltene adsorption. Hence, the main aim of this research was to investigate the effect of a mixture of thiobacillus thiooxidans and thiobacillus ferooxidans microorganisms with an optimum effective temperature of around 30 °C (referred to as mesophilic bacteria), as well as a mixture of two moderate thermophiles Sulfobacillus thermosulfidooxidans for operating temperatures around 50 °C (referred to as moderately thermophilic bacteria) on the adsorption of asphaltene samples isolated from two different crude oils onto main reservoir minerals (i.e., quartz and dolomite). The results indicated that after two weeks of mineral aging in moderate thermophilic bacteria, the adsorption of asphaltene on both minerals increased between 180 and 290%. Fourier-transform infrared spectroscopy (FTIR) analysis for quartz and dolomite samples demonstrated that after aging in bacterial solution, bonds related to the adsorption of bacterial cells and biosurfactant production appear, which are the main factors of change in wettability. Alteration in wettability towards hydrophilicity expands hydrogen bonds on the surface, thus improving asphaltene adsorption due to polar interaction. Asphaltene 1 changed the contact angle of dolomite from 53.85° to 90.51° and asphaltene 2 from 53.85° to 100.41°. However, both strains of bacteria caused a strong water-wetting effect on the dolomite rock samples. The influence of moderate thermophilic bacteria on surface wettability is more significant than that of mesophilic bacteria, which may be caused by the high protein content of these bacteria, which expands hydrogen bonding with the surface. Adsorption of asphaltenes on dolomite rocks previously aged with bacteria showed that the wetted rock samples retained their water-wet state. This study highlights the dual impact of the used microorganisms. On one hand, they significantly reduce contact angles and shift wettability towards a strongly water-wet condition, a crucial positive factor for MEOR. On the other hand, these microorganisms can elevate the adsorption of asphaltenes on reservoir rock minerals, posing a potential challenge in the form of formation damage, particularly in low-permeability reservoirs.

Synthesis and application of a new multi-functional biopolymer-based aerogel loaded with bistriazole derivative as highly efficient adsorbent and disinfectant

Herein, we exploited xanthan gum (XG) and cationic dextran (CD) in designing a novel porous aerogel (XCD) loaded with different concentrations of a new bistriazole derivative (CPSC). The CPSC was deposited into and onto the pores of aerogels. The neat aerogel removed both AB40 dye and Cu2+ efficiently. Adding 0.5 g of CPSC to the neat aerogel (XCD-0.50 sample) improved slightly the adsorption of Cu2+ and has no effect on the adsorption of AB40 dye. XCD-0.50 removed almost completely 10 mg/L of AB40 dye in 10 min using 0.5 g/L at pHi 6 while for Cu2+ longer contact time (90 min) and higher dosage (2.0 g/L) were required to remove 10 mg/L solution at pHi 5. Relative to literature, the Langmuir adsorption capacity of XCD-0.5 toward AB40 dye (436 mg/g) was the highest and toward Cu2+ (60 mg/g) was comparable to others. The aerogel XCD-0.50 was regenerable and reusable for three cycles with reasonable efficiency. By submerging a bacterial solution (106 CFU/mL) in the XCD-0.75 aerogel for 90 min, an impressive 6-log decrease in the number of bacteria was obtained under ideal circumstances. Crucially, toxicity test clearly confirmed that the prepared aerogels had non-toxic impact. Across all investigated bacterial species, XCD-0.75 continuously achieved a 6-log CFU decrease after 180 min, demonstrating its efficacy in the context of disinfection experiment. The results of the study highlight the extraordinary potential of the biopolymer aerogel loaded with CPSC as a potent adsorbent and disinfectant. They show significant removal of toxic trace elements and dyes, along with microbial reduction in industrial wastewater, underscoring the aerogel's potential use in water treatment.

Toluidine blue O photosensitizer combined with caffeic acid improves antibacterial performance by increasing the permeability of cell membrane

Photodynamic therapy has always been an antibacterial tool for solving multi-drug resistant bacteria problem, but the side effects and the low efficiency due to the high aggregation and low solubility of photosensitizers limit its application. Due to the anti-inflammatory effect of caffeic acid, two novel photosensitizers (CA-1-TBO, CA-TBO) were synthesized by conjugating caffeic acid with toluidine blue O (TBO). The structures have been characterized by 1HNMR and high-resolution mass spectrometry. The UV-vis absorption, fluorescence spectra and the octanol-water partition coefficient of two photosensitizers were measured to evaluate their photophysical properties and hydrophilic/hydrophobic properties. Compared with parent TBO, the two modified photosensitizers have shown a higher quantum yield and kinetics constants of singlet oxygen, which has been supported by the simulation results of density functional theory. As drug-resistant representatives of gram-positive and gram-negative bacteria, respectively, S. aureus and P. aeruginosa have been used for in vitro antibacterial experiments. The sterilization efficiencies of the two modified photosensitizers far exceed that of parent TBO. The results of the octanol-water partition coefficient and fluorescence quantification showed that modified photosensitizers CA-1-TBO and CA-TBO could be more accumulated than parent TBO. Based on scanning electron microscopy images, protein gel electrophoresis, and the conductivity of the bacterial solution, the possible mechanism of improved antibacterial photodynamic efficiencies could be induced by membrane permeability due to the caffeic acid effect. The findings demonstrate the significant potential of natural phenolic compounds in the development of photosensitizer molecules with characteristics such as more efficient, biocompatible and less side effects.

Mycoplasma synoviae induce spleen tissue damage and inflammatory response of chicken through oxidative stress and apoptosis

ABSTRACT Mycoplasma synovium (MS) is a prominent avian pathogen known to elicit robust inflammatory responses in birds while evading immune detection, often leading to chronic infection and immune compromise. The mechanisms underpinning MS-mediated splenic tissue damage in chickens, however, remain undefined. In our investigation with 7-day-old SPF chickens, we administered an MS-Y bacterial solution (200 µl, 1 × 109 CCU/ml) through eye and nose droplets, collecting spleen samples on days 3, 6, and 12 post-infection. Comprehensive analyses utilizing histopathology, electron microscopy, TUNEL assay, qRT-PCR, and western blot were employed. Results demonstrated that MS-infection downregulated T-SOD, GSH-PX, and CAT, while concurrently elevating iNOS, NO, and MDA levels. Evidently, MS-induced oxidative stress compromised the spleen’s antioxidant defences. Histological examinations pinpointed splenic damage characterized by lymphocyte reduction and increased inflammatory cell infiltration. Ultrastructural observations revealed clear apoptotic markers, including mitochondrial perturbations and nuclear anomalies. Importantly, MS induced significant spleen tissue apoptosis, as supported by TUNEL assay outputs and gene expression profiles associated with apoptosis. Concurrently, we observed upregulated expressions of mRNAs and proteins affiliated with the NF-κB/MAPK signalling cascade (p < 0.05). Collectively, our data elucidate that MS infection induces splenic apoptosis and oxidative disturbances, perturbs tissue integrity, and potentiates the NF-κB/MAPK-mediated inflammatory cascade.

A Biochemical Corrosion Monitoring Sensor with a Silver/Carbon Comb Structure for the Detection of Living Escherichia coli.

For the detection and monitoring of live bacteria, we propose a biochemical corrosion monitoring (BCM) sensor that measures galvanic current by using a Ag/C sensor comprising silver and carbon comb electrodes. The deposition of an Escherichia coli suspension containing an LB liquid medium on the Ag/C sensor increased the galvanic current. The time required for the current to reach 20 nA is defined as T20. T20 tends to decrease as the initial number of E. coli in the E. coli solution increases. A linear relationship was obtained between the logarithm of the E. coli count and T20 in a bacterial count range of 1-108 cfu/mL under culture conditions in which the growth rate of the bacteria was constant. Hence, the number of live E. coli could be determined from T20. Ag2S precipitation was observed on the surface of the Ag electrode of the Ag/C sensor, where an increase in the current was observed. This generation of galvanic current was attributed to the reaction between a small amount of free H2S metabolized by E. coli in the bacterial solution during its growth process and Ag-the sensor anode. The Ag/C sensor can detect a free H2S concentration of 0.041 μM in the E. coli solution. This novel biochemical sensor can monitor the growth behavior of living organisms without damaging them.

Filamentous marine Gram-positive Nocardiopsis dassonvillei biofilm as biocathode and its electron transfer mechanism

This study investigated electrochemical characteristics of Gram-positive, Nocardiopsis dassonvillei B17 facultative bacterium in bioelectrochemical systems. The results demonstrated that anodic and cathodic reaction rates were catalyzed by this bacterium, especially by utilization of aluminium alloy as a substrate. Cyclic voltammogram results depicted an increase of peak current and surface area through biofilm development, confirming its importance on catalysis of redox reactions. Phenazine derivatives were detected and their electron mediating behavior was evaluated exogenously. A symmetrical redox peak in the range of −59 to −159 mV/SHE was observed in cyclic voltammogram of bacterial solution supplemented with 12 μM phenazine, a result consistent with cyclic voltammogram of a 5-d biofilm, confirming its importance as an electron mediator in extracellular electron transfer. Furthermore, the dependency of bacterial catalysis and polarization potential were studied. These results suggested that B17 biofilm behaved as a biocathode and transferred electrons to bacterial cells through a mechanism associated with electron mediators.

Phytochemical Analysis and Evaluation of Antioxidant and Antibacterial Activities of Kratom-Containing Formulations of Ya-Gae-Bid-Na-Ron

Objective: This study aimed to evaluate the antioxidant and antibacterial activities of Ya-Gae-Bid-Na-Ron (YGBNR).Material and Methods: YGBNR formulations were prepared using kratom collected from different provinces in Thailand. Mitragynine content was determined using high-performance liquid chromatography (HPLC), while total phenolic content (TPC), total tannin content (TTC), and total flavonoid content (TFC) were determined using colorimetric methods. Antioxidant power was estimated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric-reducing antioxidant power (FRAP) assays. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of YGBNR were determined using a broth dilution technique and plating of the bacterial solution, respectively.Results: Mitragynine content, TPC, TTC, and TFC varied among different sources of kratom. DPPH assay indicated that YGBNR had an average IC50 of 0.44±0.04 mg/mL, and the FRAP assay ranged from 61.48±0.55 to 102.98±0.94 mg gallic acid equivalent (GAE), per gram of dry extract. YGBNR extracts did not exhibit any antibacterial activity. However, the volatile oil fraction showed MIC against Escherichia coli and Pseudomonas aeruginosa at a concentration of 3 mg/mL.Conclusion: Phytochemical analysis revealed the abundance of phenolic compounds in YGBNR. YGBNR exhibits promising antioxidant potential, but does not exert any antibacterial activity.

The evolution characteristics of water absorption, hydration products and microstructure of supersulfated cement containing phosphogypsum by microbial induced carbonate precipitation

In this paper, microbial induced calcite precipitation (MICP) was adopted as a modifying technology for surface property enhancement of supersulfated cement (SSC) containing phosphogypsum (PG). A series of tests including waster absorption test, mercury intrusion porosimetry (MIP), X-ray diffractometry (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were conducted to investigate the modification mechanism of SSC containing PG. The results indicate that the enhancement of surface properties is highly dependent on the modification methods and conditions. The effect of surface treatments on the reduction of water absorption and the refine of pore structure is superior to that of the direct-addition method (DM). After surface treatment, the content of ettringite slightly drops, while the calcite content rises significantly. TM with the volume ratio of bacterial solution to cementation solution of 1:1 leads to the formation of more bio calcite with spherical or square particles, which can fill the inner pores and surface holes of the surface layer. The increase of treatment cycle has a limited effect on the increase of calcite content, while can refine the pore structure and reduce the absorption coefficient when the treatment cycle was 9. DM has a great influence on the alkalinity of SSC mortar, which can significantly reduce the content of ettringite and slightly increase the calcite content and it also changes the morphology of ettringite in matrix.

Experimental study on the mechanical properties and cementation mechanism of microbial cemented fine tailings backfill

The extensive exploitation of metal mines has resulted in the generation of vast quantities of fine tailings, posing significant environmental challenges such as surface subsidence and deposition. The conventional cemented backfill technology, which has been widely used for tailings processing, requires substantial cement consumption and thus leads to escalated economic costs and carbon emissions. In this paper, we propose a pollution-free alternative, Microbial-Induced Calcite Precipitation (MICP) technology, as a promising solution for sustainable mine filling. The study employs microscopic and macroscopic analysis techniques, including laser diffraction particle size (LDPS) analysis, scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), to investigate the inner structure and mechanical properties of the microbial cemented fine tailing backfill (MCFB). Key parameters such as unconfined compressive strength (UCS), CaCO3 content and porosity are examined, with a focus on the effects of bacterial solution dosage and curing time. The results reveal that the MICP-processed fine tailings exhibit an increase in particle size by approximately 292.1% compared to their original size. Furthermore, MCFB specimens demonstrates significantly enhanced UCS and decreasing porosity under comparable conditions, surpassing the performance of traditional cemented fine tailings backfill (CFB) specimens. Microscopic analysis highlights that the strength development in MCFB predominantly arises from the cementation effects of MICP-induced CaCO3, primarily in the form of calcite, rather than the cementation effects resulting from hydration products (C-S-H) in conventional CFB.

Effect of Bio-Cementation with Rice Husk Ash on Permeability of Silty Sand

The scarcity of competent soils in the desired locations has forced geotechnical engineers to look for soil stabilization that is sustainable and environment-friendly. In this regard, bio-cementation technology has received a lot of interest in this area because of its benefits over traditional soil stabilization techniques. The present study aims to examine the influence of the bio-cementation technique with and without Rice Husk Ash (RHA) on the permeability property of silty sand. Biocemented soil samples were prepared with various combinations of the bacterial solution (0.5, 1.0, and 1.5 optical density (OD)) and cementation solution (0.5, 1.0, and 1.5 molarity) at 0, 3, 7, 14, and 28 curing days. The RHA, an agricultural waste with good pozzolanic qualities, was added to the control soil and the biocemented soil samples at 5, 10, and 15% by weight. A falling head permeability test was employed in this study. The test results showed that the permeability of the soil decreased when the bio-cementation technique, with or without RHA, was applied. The permeability of the soil decreased with increasing BS and CS concentrations in all curing days. A greater decrease in the permeability value was seen when the RHA additive was added to the bio-cemented soil. The results of the micro-analysis tests were also in support of this reduction. Overall, the addition of RHA up to 10% with 1.0 OD BS and 1.0M CS at a 14-day curing period was noted to optimally reduce the permeability property of the soil. Doi: 10.28991/CEJ-2023-09-11-016 Full Text: PDF

Capture antibody imitator MnO2 nanozyme-based dual-signal immunochromatographic assay for rapid detection of Salmonella enteritidis

The sensitive and rapid detection of foodborne pathogens is of great significance to global public health security. Here, with two-dimensional nanomaterial MnO2 NSs as the capture antibody imitator and signal reporter molecules, based on its enzyme-catalyzed signal amplification capability, a label-free, dual-signal output immunochromatographic biosensor was constructed to achieve the sensitive detection of S. enteritidis. The capture antibody imitator of MnO2 capture probe shows an outstanding capture ability, forming a stable immune complex with S. enteritidis. As an in-situ catalytic amplification colorimetric signal trigger, MnO2 NSs exert oxidase-like enzyme activity and obtain satisfactory detection sensitivity. It is worth noting that the proposed dual-signal ICA has high analytical performances for S. enteritidis during the concentration range of 103-107 cfu mL−1 both in standard bacterial solutions and food matrixes.

The behaviour of Escherichia coli and Pseudomonas aeruginosa in bottled mineral water

Microbial contamination of bottled water during the filling and capping procedure is a problem which should be avoided. The examination of the influence of carbon dioxide (CO2) on bacterial growth of Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) in bottled mineral water was the aim of this study. Commercially available glass bottles with plastic screw caps filled with natural mineral water (without additional CO2 “still” (StMW) and with CO2 “sparkling” (SpMW) were obtained from a manufacturer in the province of Styria, Austria. The artificial contamination was performed in the lab by opening the bottle with subsequent addition of a bacterial solution with a defined number of bacteria. For each bacterial strain, 12 bottles were prepared. Samples (100 mL) were taken after a specific number of days, filtrated and placed on Endo Agar for cultivation. After incubation for 24 h bacterial colonies were counted. In this study CO2 addition to bottled water reduced colony forming units of the two investigated bacterial strains over time.

Promotional Properties of ACC Deaminase-Producing Bacterial Strain DY1-3 and Its Enhancement of Maize Resistance to Salt and Drought Stresses.

Salt stress and drought stress can decrease the growth and productivity of agricultural crops. Plant growth-promoting bacteria (PGPB) may protect and promote plant growth at abiotic stress. The aim of this study was to search for bacterial strains that can help crops resist rises in drought and salt stresses, to improve crop seed resistance under drought and salt stresses, and to investigate the effect of bacterial strains that can help crop resist external stresses under different stress conditions. Pseudomonas DY1-3, a strain from the soil under the glacier moss community of Tien Shan No. 1, was selected to investigate its growth-promoting effects. Previous studies have shown that this strain is capable of producing ACC (1-aminocyclopropane-1-carboxylic acid) deaminase. In this experiment, multifunctional biochemical test assays were evaluated to determine their potential as PGPB and their bacterial growth-promoting properties and stress-resistant effects on maize plants were verified through seed germination experiments and pot experiments. The results showed that strain DY1-3 has good salt and drought tolerance, as well as the ability to melt phosphorus, fix nitrogen, and produce iron carriers, IAA, EPS, and other pro-biomasses. This study on the growth-promoting effects of the DY1-3 bacterial strain on maize seeds revealed that the germination rate, primary root length, germ length, number of root meristems, and vigor index of the maize seeds were increased after soaking them in bacterial solution under no-stress, drought-stress, and salt-stress environments. In the potting experiments, seedlings in the experimental group inoculated with DY1-3 showed increased stem thicknesses, primary root length, numbers of root meristems, and plant height compared to control seedlings using sterile water. In the study on the physiological properties of the plants related to resistance to stress, the SOD, POD, CAT, and chlorophyll contents of the seedlings in the experimental group, to which the DY1-3 strain was applied, were higher than those of the control group of seedlings to which the bacterial solution was not applied. The addition of the bacterial solution reduced the content of MDA in the experimental group seedlings, which indicated that DY1-3 could positively affect the promotion of maize seedlings and seeds against abiotic stress. In this study, it was concluded that strain DY1-3 is a valuable strain for application, which can produce a variety of pro-biotic substances to promote plant growth in stress-free environments or to help plants resist abiotic stresses. In addition to this, the strain itself has good salt and drought tolerance, making it an option to help crops grown in saline soils to withstand abiotic stresses, and a promising candidate for future application in agricultural biofertilizers.

Bio-cementation of coral sand using microbial-induced calcite precipitation with sodium alginate

Coral sand with microbial-induced calcite precipitation (MICP) is a promising material for practical engineering. This study attempts to improve the precipitation efficiency by using a modified bio-cement method based on MICP and sodium alginate (SA). It was found that adding an appropriate amount of SA in the bacterial solution could greatly improve the ability of immobilising bacteria, thus achieving an effective precipitation of calcium carbonate on the aggregate surfaces. As the SA content increased, the weight increment and unconfined compressive strength of each sample after MICP cementation initially increased and then decreased. Three main failure modes were observed, i.e., the particle unbroken failure, stepped failure, and steep drop failure. Owing to the macro pores of coral sand, the specific loss of calcium carbonate crystals produced by MICP had a significant effect on the cementation performance, while prolonging the single soaking time could favourably reduce the crystal loss. The calcium carbonate crystals occupied part of the pores between sand aggregates, but did not change the compression strength of a single aggregate significantly.

Self-assembled silk fibroin cross-linked with genipin supplements microbial carbonate precipitation in building material.

The process of microbially induced carbonate precipitation (MICP) is known to effectively improve engineering properties of building materials and so does silk fibroin (SF). Thus, in this study, an attempt was taken to see the improvement in sand, that is, basic building material coupled with MICP and SF. Urease producing Bacillus megaterium was utilized for MICP in Nutri-Calci medium. To improve the strength of SF itself in bacterial solution, it was cross-linked with genipin at the optimized concentration of 3.12 mg/mL. The Fourier transform infrared (FTIR) spectra confirmed the crosslinking of SF with genipin in bacterial solution. In order to understand how such cross-linking can improve engineering properties, sand moulds of 50 mm3 dimension were prepared that resulted in 35% and 55% more compressive strength than the one prepared with bacterial solution with SF and bacterial solution only, respectively with higher calcite content in former one. The FTIR, SEM, x-ray powder diffraction spectrometry and x-ray photoelectron spectroscopy analyses confirmed higher biomineral precipitation in bacterial solution coupled with genipin cross-linked SF. As the process of MICP is proven to replace cement partially from concrete without negatively influence mechanical properties, SF cross-linked with genipin can provide additional significance in developing low-carbon cement-based composites.