Strain S1 Research Articles

Plant Growth‐Promoting Bacteria Associated With Some Salt‐Tolerant Plants

ABSTRACTGiven the benefits of bacteria associated with the rhizosphere and phytoplane of halophytes, this research focused on examining the plant growth‐promoting characteristics of bacteria isolated from Cressa cretica, Suaeda aegyptiaca, and Alhagi graecorum. From the 33 isolates tested, 9 exhibited plant growth‐promoting traits. Bacillus rugosus strain CS5 and Bacillus sp. strain SS4 exhibited the notable growth inhibition of the pathogenic fungus Fusarium oxysporum, with values of 47% and 45%, respectively. Bacillus sp. strains SS4 and CS1 demonstrated impressive results in solubilizing phosphorus and zinc, respectively, achieving concentrations of 259 and 271 mg L−1. Additionally, Staphylococcus xylosus strain SR2, Bacillus sp. strain SS4, and Bacillus paralicheniformis strain CR1 thrived in nitrogen‐free media. The Priestia filamentosa strain AL4 showed the greatest HCN production, whereas B. paralicheniformis strain CR1 was notable for higher auxin production. The Bacillus sp. strains SS4 and CS1 exhibited greater tolerance than other isolates in a medium containing 600 mM of NaCl. Additionally, inoculating these isolates into soil significantly alleviated the salinity and drought stress on Zea mays seedlings. These findings suggest that further investigation into these strains as microbial inoculants could be beneficial for mitigating salt and drought stress in plants.

Enhancing riboflavin production by modulating the expression of the rib operon in Bacillus subtilis

Riboflavin is an essential vitamin for humans and animals, with its annual demand experiencing a consistent upward trajectory. In recent years, newly constructed riboflavin producing strains are difficult to reach the level of industrial strains. Therefore, developing competitive strains is crucial for advancing the riboflavin industry. The expression level of the rib operon is strongly correlated with riboflavin biosynthesis. The strain S12, which overexpressed the rib operon of B. subtilis using plasmids with approximately 8 copies, achieved a 53.9 % increase in riboflavin biosynthesis during shake-flask fermentation. However, the strain cannot grow normally in a 7.5-L bioreactor. The expression of rib operon may have competed with cell growth for GTP or produced toxic intermediate ArP. Therefore, the strain S16 replaced ribA in rib operon with a monofunctional DHBP synthase, increased 20 % of riboflavicn production in a 7.5-L bioreactor. Furthermore, the strain S24, which overexpressed the rib operon using the phase-dependent promoter PyqgZ, attained a riboflavin production of 29 g/L in a 7.5-L bioreactor, achieving the highest reported riboflavin production to date. This study reports for the first time using the phase-dependent promoter for overexpression of rib operon, effectively regulated the relationship between cell growth and riboflavin production.

Decoding the Impact of a Bacterial Strain of Micrococcus luteus on Arabidopsis Growth and Stress Tolerance.

Microbes produce various bioactive metabolites that can influence plant growth and stress tolerance. In this study, a plant growth-promoting rhizobacterium (PGPR), strain S14, was identified as Micrococcus luteus (designated as MlS14) using de novo whole-genome assembly. The MlS14 genome revealed major gene clusters for the synthesis of indole-3-acetic acid (IAA), terpenoids, and carotenoids. MlS14 produced significant amounts of IAA, and its volatile organic compounds (VOCs), specifically terpenoids, exhibited antifungal activity, suppressing the growth of pathogenic fungi. The presence of yellow pigment in the bacterial colony indicated carotenoid production. Treatment with MlS14 activated the expression of β-glucuronidase (GUS) driven by a promoter containing auxin-responsive elements. The application of MlS14 reshaped the root architecture of Arabidopsis seedlings, causing shorter primary roots, increased lateral root growth, and longer, denser root hairs; these characteristics are typically controlled by elevated exogenous IAA levels. MlS14 positively regulated seedling growth by enhancing photosynthesis, activating antioxidant enzymes, and promoting the production of secondary metabolites with reactive oxygen species (ROS) scavenging activity. Pretreatment with MlS14 reduced H2O2 and malondialdehyde (MDA) levels in seedlings under drought and heat stress, resulting in greater fresh weight during the post-stress period. Additionally, exposure to MlS14 stabilized chlorophyll content and growth rate in seedlings under salt stress. MlS14 transcriptionally upregulated genes involved in antioxidant defense and photosynthesis. Furthermore, genes linked to various hormone signaling pathways, such as abscisic acid (ABA), auxin, jasmonic acid (JA), and salicylic acid (SA), displayed increased expression levels, with those involved in ABA synthesis, using carotenoids as precursors, being the most highly induced. Furthermore, MlS14 treatment increased the expression of several transcription factors associated with stress responses, with DREB2A showing the highest level of induction. In conclusion, MlS14 played significant roles in promoting plant growth and stress tolerance. Metabolites such as IAA and carotenoids may function as positive regulators of plant metabolism and hormone signaling pathways essential for growth and adaptation to abiotic stress.

Probiotic properties, whole-genome sequence analysis, and safety assessment of BreviBacillus borstelensis S8

In previous studies, BreviBacillus borstelensis S8 exhibited favorable enzyme production characteristics. In this study, the whole genome of Br borstelenensis S8 was sequenced to analyze its genomic sequence information and functions, investigating its genotype and potential probiotic properties. The whole genome sequence of S8 was determined to be 5,559,180 bp with an average GC content of 51.5%. A total of 5406 protein-coding genes were identified and annotated using NCBI Prokaryotic Genome Annotation. By comparing it with the complete genome sequences of Bacillus cereus strains, 1911 orthologous gene families were recognized. Genome analysis revealed the absence of active antibiotic resistance genes, virulence factor genes, and toxin-encoding genes. Safety assessments included hemolytic assays, antibiotic resistance tests, and evaluations of biogenic amine production. Functional gene analysis highlighted S8's metabolic pathways based on its genomic features. The presence of adhesion-related genes, stress response genes (e.g., acid and bile salts), antimicrobial gene clusters, and genes involved in vitamin and essential amino acid synthesis in the genome showcased the probiotic potential of S8. Simultaneously, analysis of hemolytic activity, biogenic amines production ability, acid and bile salt tolerance for the strain S8 also demonstrated its probiotic traits. The genomic exploration and probiotic activity of S8 revealed its potential as a probiotic, offering valuable genomic insights and a foundation for its safe utilization in the food industry.

Synergistic suppression of grey mold on cut rose flower by combined application of methyl jasmonate and lipopeptides from Bacillus altitudinis

Roses are the most popular cut flowers that are widely used in various occasions and celebrations, yet can also be easily infected by grey mold caused by Botrytis cinerea; a notorious pathogen in the cut flower industry. A wide range of methods, including fungicides, have been used to control B. cinerea. Environmentally benign methods are increasingly sought after to minimize disease incidence. In this study, we evaluated 10 strains of Bacillus across eight species for their action against B. cinerea. Strains TM22A (Bacillus altitudinis) and S2 (Bacillus subtilis) were identified to be effective in disease suppression. Lipopeptides (LPs) were isolated from two strains, and their activity for inhibiting the growth of B. cinerea was tested. Additionally, methyl jasmonate (MeJA), a natural growth regulator, was evaluated for disease suppression using a in planta assay. Subsequently, LPs from TM22A and MeJA, alone or in combination, were evaluated for disease occurrence in cut rose flowers. Results showed that either LPs or MeJA at concentrations of 250 μmol/L significantly reduced lesion size and disease incidence. The combined application of LPs from TM22A with MeJA further reduced the disease occurrence in cut rose flowers. Furthermore, the activities of POD, PPO, PAL, CAT, and SOD enzymes were much higher in flowers treated with combined application of LPs from TM22A with MeJA. The enhanced suppression of B. cinerea is attributed to the antifungal effects of LPs and MeJA and activation of antioxidant enzymes. This study suggests that the combined application of LPs from TM22A with MeJA could be an environmentally friendly approach for control of grey mold disease in cut roses.

Evaluation of Probiotics Ability to Enhance Population Density, Growth Rate, and Neonates Production of Moina micrura in Different Environmental Parameters

Salinity, light intensity, and oxygen concentration are key environmental factors that significantly affect biological processes and the composition and dispersion of Moina biomass. Evaluating the effectiveness of probiotic enrichment in improving population density, growth rate, and neonate production can provide valuable details on the effectiveness of probiotics in enhancing the resilience and viability of Moina micrura under suboptimal circumstances. The purpose of this research project is to assess the efficacy of two probiotics, Bacillus pocheonensis strain S2 and Lysinibacillus fusiformis strain A1, in improving the population density, growth rate, and reproductive output in M. micrura across various environmental conditions. Moina micrura were treated with each probiotic at a volume of 5 x 105 CFU/ml under different levels of salinity (0, 2, 4, and 6 ppt), light intensity (800, 1,000, 1,500, and 2,000 lux), and oxygen concentration (80, 70, 60, and 50%). The results indicated that M. micrura treated with L. fusiformis A1 at 0 ppt attained the highest population density (6 ± 0.90 Ind./ml), growth rate (0.355 ± 0.030 µ), and number of offspring production (5 ± 0.75 Ind./ml). The highest point of population density (5 ± 0.07 Ind./ml), growth rate (0.381 ± 0.002 µ) and number of offspring (7 ± 0.41 Ind./ml) of M. micrura were obtained while treated with B. pocheonensis S2 at light intensity of 1,500 lux. Similarly, the highest population density (5 ± 0.60 Ind./ml), growth rate (0.365 ± 0.190 µ), and offspring production (2 ± 0.25 Ind./ml) of M. micrura were observed during enrichment with B. pocheonensis S2 at 70% oxygen concentration. Therefore, these results suggested that the optimum conditions for enriching M. micrura with B. pocheonensis S2 are salinity of 0 ppt, 70% oxygen concentration, and a light intensity level of 1,500 lux.

The quorum sensing SinI/SinR-TraI/TraR systems promote Pb stabilization by Ensifer adhaerens S24 in the Pb-polluted aquatic environment

In this study, the Pb-resistant Ensifer adhaerens strain S24, which contains quorum sensing (QS) systems responsible for N-acyl homoserine lactone (AHL) production, was investigated for QS system-mediated Pb stabilization and the underlying mechanisms. Whole-genome sequence analysis revealed the QS SinI/R and TraI/R systems in strain S24. Subsequently, strains S24 and the S24∆sinI/R, S24∆traI/R, S24∆traI/R/sinR, and S24∆sinI/R-traI/R/sinR mutants were constructed and compared for QS SinI/SinR-TraI/TraR system-mediated Pb stabilization in the solution and the mechanisms involved. After 5 days of incubation, strain S24 significantly decreased the Pb concentration in the Pb-contaminated solution compared with the mutants. The S24∆sinI/R-traI/R/sinR mutant exhibited reduced Pb stabilization and AHL activity than the other mutants. The S24∆sinI/R-traI/R/sinR mutant had significantly greater Pb concentrations in the solution and lower cell surface-adsorbed and extracellular precipitated Pb (PbS) contents as well as lower expression of H2S-producing genes of metC and sseA than did strain S24. Furthermore, the S24∆sinI/R-traI/R/sinR mutant displayed reduced interactions between the hydroxyl, amino, carboxyl, and ether groups and Pb, compared with strain S24. These findings implied the vital role of the SinI/SinR-TraI/TraR systems in strain S24 for Pb stabilization through enhanced cell surface adsorption and extracellular precipitation in Pb-polluted aquatic environments.

Mitigating the detrimental impacts of low- and high-density polyethylene microplastics using a novel microbial consortium on a soil-plant system: Insights and interactions

The accumulation of polyethylene microplastics (PE-MPs) in soil has raised considerable concerns; however, the effects of their persistence and mitigation on agroecosystems have not been explored. This study aimed to assess the detrimental effects of PE-MPs on a soil-plant system and evaluate their mitigation using a novel microbial consortium (MC). We incorporated low-density polyethylene (LDPE) and high-density polyethylene (HDPE) at two different concentrations, along with a control (0 %, 1 %, and 2 % w/w) into the sandy loam soil for a duration of 135 days. The samples were also treated with a novel MC and incubated for 135 days. The MC comprised three bacterial strains (Ralstonia pickettii (MW290933) strain SHAn2, Pseudomonas putida strain ShA, and Lysinibacillus xylanilyticus XDB9 (T) strain S7–10F), and a fungal strain (Aspergillus niger strain F1–16S). Sunflowers were subsequently cultivated, and physiological growth parameters were measured. The results showed that adding 2 % LDPE significantly decreased soil pH by 1.06 units compared to the control. Moreover, adding 2 % HDPE resulted in a more significant decrease in soil electrical conductivity (EC) relative to LDPE and the control. A dose-dependent increase in dissolved organic carbon (DOC) was observed, with the highest DOC found in 2 % LDPE. The addition of higher dosages of LDPE reduced soil bulk density (BD) more than HDPE. The addition of 2 % HDPE increased the water drop penetration time (WDPT) but decreased the mean weight diameter of soil aggregates (MWD) and water-stable aggregates (WSA) compared to LDPE. The results also revealed that higher levels of LDPE enhanced soil basal respiration (BR) and microbial carbon biomass (MBC). The interaction of MC and higher MP percentages considerably reduced soil pH, EC, BD, and WDPT but significantly increased soil DOC, MWD, WSA, BR, and MBC. Regarding plant growth, incorporating 2 % PE-MPs significantly reduced physiological responses of sunflower: chlorophyll content (Chl; −15.2 %), Fv/Fm ratio (-25.3 %), shoot dry weight (ShD; −31.3 %), root dry weight (RD; −40 %), leaf area (LA; −38.4 %), and stem diameter (StemD; −25 %) compared to the control; however, the addition of novel MC considerably reduced and ameliorated the harmful effects of 2 % PE-MPs on the investigated plant growth responses.

Clinical and Histopathological Evolution of Acute Intraperitoneal Infection by Streptococcus agalactiae Serotypes Ib and III in Nile Tilapia

Streptococcus agalactiae is a highly invasive bacterium that causes significant economic losses in tilapia aquaculture around the world. Furthermore, it is a pathogen for mammals, including humans, emphasizing its importance in One Health. The aim of this work was to evaluate the evolution of clinical and histopathological lesions caused by acute infection with two serotypes of S. agalactiae. For this, two strains isolated from natural outbreaks in Brazilian aquaculture farms (S13, serotype Ib; S73, serotype III) were used to challenge juvenile Nile tilapia (Oreochromis niloticus) intraperitoneally. Target organ samples were collected ten times, between 1 and 96 h post-infection, for microbiological and histopathological analyses. Anorexia was the first clinical sign and the first death occurred at 24 and 30 h in the fish infected with strains S13 and S73, respectively. Serotype Ib initially caused more pronounced lesions in the nervous system; however, serotype III lesions progressed more aggressively, reaching the same severity as those of serotype Ib. This trend was repeated in the mortality curve after 32 h. These results elucidated the important stages in the pathogenesis of S. agalactiae serotypes Ib and III in tilapia and suggest “tips and tricks” to improve the positive culture rate in the clinical diagnosis of infections in some tissues.

Role of Arthrospira Platensis in Preventing and Treating High-Fat Diet-Induced Hypercholesterolemia in Adult Rats.

Hyperlipidaemia is a recognised risk factor for cardiovascular disease. In this study, the antihyperlipidaemic properties of spirulina (Arthrospira platensis, strain S2 from Serbia) were tested in adult Wistar rats before and after induction of hypercholesterolaemia by a high-fat diet (HFD) to compare the preventive with the curative effect. Total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), alanine transaminase (ALT) and aspartate transaminase (AST) levels were measured in the blood samples. The chemical composition (lipids, proteins and cholesterol) and the content of bile acids in the faeces of the animals were also analysed. Feeding rats with an atherogenic diet for 10 weeks led to the successful development of hyperlipidaemia, as serum TC and LDL-C levels as well as lipids, cholesterol and bile acids in the animals' faeces were significantly increased. Pre- and post-treatment with spirulina led to a reduction in serum LDL, TC and ALT levels. Administration of spirulina resulted in both a significant increase in primary bile acids excretion and a decrease in bile acids metabolism, with pre-treatment being more effective than post-treatment in some cases. These results suggest that increased excretion of bile acids as well as an effect on the gut microbiota may be the mechanism responsible for the anti-hyperlipidaemic activity of the tested spirulina strain.

Antifungal Properties of Streptomyces bacillaris S8 for Biological Control Applications.

Soybean (Glycine max), a crucial global crop, experiences yearly yield reduction due to diseases such as anthracnose (Colletotrichum truncatum) and root rot (Fusarium spp.). The use of fungicides, which have traditionally been employed to control these phytopathogens, is now facing challenges due to the emergence of fungicide-resistant strains. Streptomyces bacillaris S8 strain S8 is previously known to produce valinomycin t through a nonribosomal peptide synthetase (NRPS) pathway. The objective of this study was to evaluate the antifungal activity of S. bacillaris S8 against C. truncatum and Fusarium sp., assessing its efficacy against soybean pathogens. The results indicate that strain S8 effectively controlled both above-ground and underground soybean diseases, using the NRPS and NRPS-related compound, suggesting its potential as a biological control in plant-microbe interactions. These findings underscore the pivotal role of the stain S8 in fostering healthy soybean microbial communities and emphasize the significance of microbiota structure studies in unveiling potent biocontrol agents.

Organic matter degradation in the deep, sulfidic waters of the Black Sea: insights into the ecophysiology of novel anaerobic bacteria

BackgroundRecent studies have reported the identity and functions of key anaerobes involved in the degradation of organic matter (OM) in deep (> 1000 m) sulfidic marine habitats. However, due to the lack of available isolates, detailed investigation of their physiology has been precluded. In this study, we cultivated and characterized the ecophysiology of a wide range of novel anaerobes potentially involved in OM degradation in deep (2000 m depth) sulfidic waters of the Black Sea.ResultsWe have successfully cultivated a diverse group of novel anaerobes belonging to various phyla, including Fusobacteriota (strain S5), Bacillota (strains A1T and A2), Spirochaetota (strains M1T, M2, and S2), Bacteroidota (strains B1T, B2, S6, L6, SYP, and M2P), Cloacimonadota (Cloa-SY6), Planctomycetota (Plnct-SY6), Mycoplasmatota (Izemo-BS), Chloroflexota (Chflx-SY6), and Desulfobacterota (strains S3T and S3-i). These microorganisms were able to grow at an elevated hydrostatic pressure of up to 50 MPa.Moreover, this study revealed that different anaerobes were specialized in degrading specific types of OM. Strains affiliated with the phyla Fusobacteriota, Bacillota, Planctomycetota, and Mycoplasmatota were found to be specialized in the degradation of cellulose, cellobiose, chitin, and DNA, respectively, while strains affiliated with Spirochaetota, Bacteroidota, Cloacimonadota, and Chloroflexota preferred to ferment less complex forms of OM. We also identified members of the phylum Desulfobacterota as terminal oxidizers, potentially involved in the consumption of hydrogen produced during fermentation. These results were supported by the identification of genes in the (meta)genomes of the cultivated microbial taxa which encode proteins of specific metabolic pathways. Additionally, we analyzed the composition of membrane lipids of selected taxa, which could be critical for their survival in the harsh environment of the deep sulfidic waters and could potentially be used as biosignatures for these strains in the sulfidic waters of the Black Sea.ConclusionsThis is the first report that demonstrates the cultivation and ecophysiology of such a diverse group of microorganisms from any sulfidic marine habitat. Collectively, this study provides a step forward in our understanding of the microbes thriving in the extreme conditions of the deep sulfidic waters of the Black Sea.Exyq52VguUrmavAnxe2qURVideo

Antagonistic and enzymatic activities of Bacillus species isolated from the fish gastrointestinal tract as potential probiotics use in Artemia culture.

Probiotics have been used successfully in aquaculture to enhance disease resistance, nutrition, and/or growth of cultured organisms. Six strains of Bacillus were isolated from the intestinal tracts of fish and recognised by conventional biochemical traits. The six isolated strains were Bacillus cereus and Bacillus subtilis using MALDI-TOF-MS technique. The probiotic properties of these Bacillus strains were studied. The tested bacillus strains exhibit antibacterial activity against the different pathogens. The strain S5 gave the important inhibition zones against most pathogens (20.5, 20.33, 23, and 21 mm against Vibrio alginolyticus, Vibrio parahaemolyticus, Staphylococcus aureus, and Salmonella typhimurium, respectively). According to our results, all Bacillus strains have extracellular components that can stop pathogenic bacteria from growing. The enzymatic characterization showed that the tested strains can produce several biotechnological enzymes such as α-glucosidase, naphtol-AS-BI-Phosphohydrolase, esterase lipase, acid phosphatase, alkaline phosphatase, amylase, lipase, caseinase, and lecithinase. All Bacillus strains were adhesive to polystyrene. The adding Bacillus strains to the Artemia culture exerted significantly greater effects on the survival of Artemia. The challenge test on Artemia culture showed that the protection against pathogenic Vibrio was improved. These findings allow us to recommend the examined strains as prospective probiotic options for the Artemia culture, which will be used as food additives to improve the culture conditions of crustacean larvae and marine fish.

Improving dryland maize productivity and water efficiency with heterotrophic ammonia-oxidizing bacteria via nitrification and cytokinin activity

A two-year field experiment conducted under dryland conditions in semi-humid and drought-prone regions of China aimed to assess the effect of ammonia-oxidizing bacterial on maize water use efficiency and yield. A heterotrophic ammonia-oxidizing bacteria (HAOB) strain S2_8_1 was used. Six treatments were applied: (1) no irrigation + HAOB strain (DI), (2) no irrigation + blank culture medium (DM), (3) no irrigation control (DCK), (4) irrigation + HAOB (WI), (5) irrigation + blank culture medium (WM), and (6) irrigation control (WCK). Results revealed that HAOB treatment increased maize growth, yield, and water use efficiency over controls, regardless of whether the year was wet or dry. This improvement was attributed to the accelerated nitrification in the rhizosphere soil due to HAOB inoculation, which subsequently led to increased levels of leaf cytokinins. Overall, these findings suggest that HAOB inoculation holds promise as a strategy to boost water use efficiency and maize productivity in dryland agriculture.

The Effect of Azotobacter on Growth and Yield of Water Spinach in Growing Media Containing Gold Mine Tailings

Gold mining provides economic benefits but results in the conversion of agricultural land and produces low-fertility tailings. Efforts to remediate tailings can be done through the utilization of the biofertilizer bacteria Azotobacter sp., which is capable of producing exopolysaccharides. This study aims to study the effects of biofertilizers containing a consortium of Azotobacter sp. strains S5, S6a, and S9 in enhancing the growth and yield of water spinach plants in growth media containing gold mine tailings. The experiment used a randomized complete block design with four treatments and six replications. The treatments consisted of; (A) control, (B) 1% biofertilizer, (C) 5% biofertilizer, and (D) 10% biofertilizer. The results of the experiment showed that the dosage of 5% biofertilizers increased plant height, leaf count, and fresh weight of plants, while the 10% biofertilizer increased the stem diameter. The findings of this experiment emphasize the importance of biofertilizers in enhancing the growth and yield of water spinach plants in media with low fertility.

Non-Pigmented Antarctic Yeasts and Their Resistance to Toxic Metals

Despite the key role in biogeochemical processes and in the functioning of terrestrial ecosystems, yeasts of Antarctic regions still remain insufficiently studied. The study and analysis of the composition of Antarctic microbial communities remains relevant and is carried out using molecular biological approaches. The investigation of their resistance to toxic metal ions is essential to select industrially promising strains that can contribute to the development of new methods of metals detoxification via microorganisms. Aim. To determine the taxonomic position of non-pigmented Antarctic yeasts and investigate their resistance to toxic metal ions. Methods. The objects of the research are yeasts isolated from Antarctic phytocenoses. They were grown on malt wort (pH 5.0–5.5, temperature 18–20 °C). Isolation of genomic DNA was performed via the commercial DNA-sorb kit. Amplification of DNA was carried out using primers NL1 and NL4. Phylogenetic analysis was conducted by construction of trees (dendrograms) showing the position of the studied strains among closely related and typical species. The resistance of yeasts to toxic metal ions was established by cultivation in the concentration gradient of Ni2+, Co2+, CrO42-, and Сu2+. The ecophysiological traits of the isolated yeast strains including psychro- and halotolerance were determined. Results. Phylogenetic analysis showed a high percentage of similarity (99.5–99.6 %) of sequences of 18S rRNA genes of Antarctic yeast strains with the yeast sequences from the GenBank database. Psychrotolerant and halotolerant Antarctic yeast strains S11 and S12 were identified as Leucosporidium scottii and Debaryomyces hansenii, respectively. The studied yeast strains were found to be the most resistant to metal ions Ni2+ and Co2+. Strain of L. scottii S11 grew at 800 mg/L of Co2+, and D. hansenii S12 – at 750 mg/L of Ni2+. The yeasts were the least resistant to CrO42-: the L. scottii S11 and D. hansenii S12 strains grew at concentrations of 25 mg/L and 150 mg/L, respectively. In the presence of Cu2+, they grew at the same concentration – 600 mg/L. The combined action of toxic metal ions resulted in the increased toxic effects on the studied yeasts. Conclusions. The nucleotide sequences of 18S rRNA gene fragment of yeast strains S11 and S12 were included in the GenBank database under the numbers LT220858 and LT220859. Metal-resistant psychrotolerant yeast strains can be used to evaluate the metals content in polar regions as well as to bioremediate metal-contaminated ecosystems. However, further research is needed to develop and optimize bioremediation processes.

Analysis and modeling of two-dimensional piezoelectric semiconductor shell theory

In recent years, there has been a surge in research on piezoelectric semiconductors (PSs). However, studies specifically focused on two-dimensional PS structures remain scarce. In this paper, based on the principle of the virtual work method, the condition of charge continuity and the first-order thickness shear theory, we have established a two-dimensional model to investigate the electromechanical properties of two-dimensional PS shells. The basic field quantities, including the displacement, the electric potential and the carrier concentration perturbations were Fourier expanded along the width direction, and then the governing equations were successfully derived. The differential quadrature method was used to obtain numerical results for the PS shells with different loading modes and structural configurations. It was found that the inhomogeneous shear strain S13 is the key to the potential change in the PS shell structure. The emergence of the potential barriers and wells in the shell structure of PS is well explained. In addition, the position of the potential barriers can be modulated by varying the magnitude of the load, which provides a reference for the design of thin-film devices.

Characterization of a hemolytic and antibiotic-resistant Pseudomonas aeruginosa strain S3 pathogenic to fish isolated from Mahananda River in India.

Virulent strain Pseudomonas aeruginosa isolated from Mahananda River exhibited the highest hemolytic activity and virulence factors and was pathogenic to fish as clinical signs of hemorrhagic spots, loss of scales, and fin erosions were found. S3 was cytotoxic to the human liver cell line (WRL-68) in the trypan blue dye exclusion assay. Genotype characterization using whole genome analysis showed that S3 was similar to P. aeruginosa PAO1. The draft genome sequence had an estimated length of 62,69,783 bp, a GC content of 66.3%, and contained 5916 coding sequences. Eight genes across the genome were predicted to be related to hemolysin action. Antibiotic resistance genes such as class C and class D beta-lactamases, fosA, APH, and catB were detected, along with the strong presence of multiple efflux system genes. This study shows that river water is contaminated by pathogenic P. aeruginosa harboring an array of virulence and antibiotic resistance genes which warrants periodic monitoring to prevent disease outbreaks.

Degradation of pyrene by Xanthobacteraceae bacterium strain S3 isolated from the rhizosphere sediment of Vallisneria natans: active conditions, metabolite identification, and proposed pathways.

Polycyclic aromatic hydrocarbons (PAHs) were typical environmental contaminants that accumulated continuously in sediment. Microbial degradation is the main way of PAH degradation in the natural environment. Therefore, expanding the available pool of microbial resources and investigating the molecular degrading mechanisms of PAHs are critical to the efficient control of PAH-polluted sites. Here, a strain (identified as Xanthobacteraceae bacterium) with the ability to degrade pyrene was screened from the rhizosphere sediment of Vallisneria natans. Response surface analysis showed that the strain could degrade pyrene at pH 5-7, NaCl addition 0-1.5%, and temperature 25-40°C, and the maximum pyrene degradation (~ 95.4%) was obtained under the optimum conditions (pH 7.0, temperature 28.5°C, and NaCl-free addition) after 72h. Also, it was observed that the effect of temperature on the degradation ratio was the most significant. Furthermore, eighteen metabolites were identified by mass spectrometry, among which (2Z)-2-hydroxy-3-(4-oxo-4H-phenalen-3-yl) prop-2-enoic acid, 7-(carboxymethyl)-8-formyl-1-naphthyl acetic acid, phthalic acid, naphthalene-1,2-diol, and phenol were the main metabolites. And the degradation pathway of pyrene was proposed, suggesting that pyrene undergoes initial ortho-cleavage under the catalysis of metapyrocatechase to form (2Z)-2-hydroxy-3-(4-oxo-4H-phenalen-3-yl) prop-2-enoic acid. Subsequently, this intermediate was progressively oxidized and degraded to phthalic acid or phenol, which could enter the tricarboxylic acid cycle. Furthermore, the pyrene biodegradation by the strain followed the first-order kinetic model and the degradation rate changed from fast to slow, with the rate remaining mostly slow in the later stages. The slow biodegradation rate was probably caused by a significant amount of phenol accumulation in the initial stage of degradation, which resulted in a decrease in bacterial activity or death.

Traditional Bulgarian Fermented Foods as a Source of Beneficial Lactic Acid Bacteria.

Traditional Bulgarian fermented foods are prominent for their uniqueness of local ingredients, production methods, and endemic microbial species. The present research investigated the diversity and beneficial biological potential of lactic acid bacteria (LAB) isolated from various types of unique Bulgarian fermented foods. Species identification was performed via 16S rDNA sequencing. Biological activity was evaluated by determining antibacterial activity (via agar well diffusion assay), H2O2 production, spectrophotometrically determined auto- and co-aggregation, microbial adhesion to hydrocarbon, and biofilm formation. The biosafety of the isolated lactic acid bacteria was established based on hemolytic activity and phenotypic and genotypic antibiotic susceptibility. Forty-five strains were isolated from fermented foods (sauerkraut, fermented green tomatoes, fermented cucumbers, kefir, white cheese, and Izvara (curdled milk)). Five species were detected: Lactiplantibacillus plantarum, Levilactobacillus koreensis, Levilactobacillus brevis, Lactobacillus helveticus, and Levilactobacillus yonginensis. The most prominent species was L. plantarum, at 47%. For the first time, L. koreensis and L. yonginensis, isolated from unique Bulgarian fermented foods, are reported in this study. The antibacterial effect of the cell-free supernatants was evaluated. An antagonistic effect was observed against Escherichia coli (57%) and Salmonella enterica subsp. enterica serotype Enteritidis (19%) for several L. plantarum strains. Only one L. brevis (Sauerkraut, S15) strain showed activity against E. coli. The best autoaggregation ability at hour 4 was observed for L. koreensis (fermented cucumbers, FC4) (48%) and L. brevis S2 (44%). The highest percentage of co-aggregation with Candida albicans, at hou 4 in the experiments, was observed for strains L. koreensis (fermented green tomato, FGT1) (70%), L. plantarum strains S2 (54%), S13 (51%), and S6 (50%), while at hour 24 for strains L. koreensis FGT1 (95%), L. brevis (Kefir, K7) (89%), L. plantarum S2 (72%), and L. koreensis FC2 (70%). Seven of the isolated LAB strains showed hydrophobicity above 40%. Our results showed that the ability of biofilm formation is strain-dependent. No hemolytic activity was detected. The antibiotic resistance to 10 antibiotics from different groups was tested phenotypically and genotypically. No amplification products were observed in any strains, confirming that the isolates did not carry antibiotic-resistance genes. Traditional fermented Bulgarian foods can be considered functional foods and beneficial LAB sources.