Acid Production Ability Research Articles

Exogenous salicylic acid mediated herbicide (Paraquat) resistance in cyanobacterial biofertilizer Microchaete sp. NCCU-342.

Paddy field farming remains the dominant form of growing rice in modern times as the rice is the staple food for over half the world's population and is closely associated with food security and political stability of many countries. Record increase in rice production have been observed since the start of the Green Revolution. India is one of the largest paddy producer and exporter in the world. However, constant use of chemical herbicide like paraquat had shown adverse impact on the rice yield. Non-target organisms of the habitat including cyanobacterial paddy biofertilizer face the herbicide toxicity and are unable to perform efficiently their role as biofertilizer. Therefore, in the present study, an attempt has been made to enhance the paraquat resistance in rice biofertilizer (Microchaete sp. NCCU-342) by exogenous addition of salicylic acid. Paraquat showed toxicity in Microchaete sp. NCCU-342 in a dose-dependent manner. Concentration of paraquat >1.0 μM exhibited lethal effect since the beginning. Through successive narrow range experiment, LD50 value of paraquat was obtained as 0.6 μM. Biomass exposed to paraquat (LD50 value) and salicylic acid (0.3 mM) showed mitigation in free radical production (2.20 % MDA and 1.69 % H2O2) and enhancement in the activity of the antioxidant enzymes activity, i.e. SOD, CAT, APX (137.76 %, 87.45 %, 118 %, respectively) and osmolytes (3.8 % proline and 21.51% sucrose). Thus, for sustainable agricultural practice, especially for paddy field cyanobacterial biofertilizer, application of salicylic acid or organism with higher salicylic acid production ability may be an alternative to overcome the paraquat toxicity.

Synergistic effects of plant growth promoting rhizobacteria and silicon dioxide nano-particles for amelioration of drought stress in wheat

Drought tolerant plant growth-promoting rhizobacteria (PGPR) can confer drought tolerance in plants, when inoculated, and this effect can be more pronounced by their combined application with silicon oxide nanoparticles (SiO2 NPs). In this research, drought-tolerant and plant growth-promoting rhizobacterial strains were isolated from the rhizospheric soil of wheat plants growing in the arid region of Pakistan. Out of 30 isolated strains, three rhizobacterial strains were selected based on their drought tolerance, higher phytohormones (indole acetic acid (IAA), abscisic acid (ABA), and cytokinin (CK), and osmolyte (proline and sugar) production ability. These strains were identified as Bacillus sp. Azospirillum lipoferum and Azospirillum brasilense by 16S rRNA sequencing and accession numbers (MT482404, MT742664, and MT 742666, respectively) were obtained. Inoculation of these strains, alone and in combination, improved the germination attributes of wheat seeds under drought stress conditions. However, the combination of all three bacterial strains gave the best results. SiO2 NPs were prepared from silicon dioxide and characterized by scanning electron microscopy (SEM), Energy dispersive X-rays pattern (EDX), and UV–visible spectrum. The effect of SiO2 NPs was also tested on wheat seeds under drought stress and it was observed that SiO2 NPs (150 mg/L) create pronounced drought ameliorative potential in wheat seedlings. In the pot experiment, the combined application of SiO2 NPs and PGPR exhibited a synergistic role and improved the growth and yield of wheat. The interaction between SiO2 NPs and bacterial combination improved biomass (fresh and dry weight), and chlorophyll-a, b content by 138.78%, 65.70%, 128.57%, and 283.33% respectively as compared to untreated but drought exposed plants. They also improved relative water content (71.66%), gas exchange attributes, increased nutrients uptake, and osmolytes production of wheat. Up-regulation of antioxidant enzymes; superoxide dismutase (60.49%), peroxidase (55.99%), and catalase (81.69%) was also observed. This research work suggested that the application of SiO2 NPs and PGPR strains induced drought tolerance in wheat by modulating different physiological and metabolic processes in plants which ultimately improved the growth and yield of wheat under drought stress.

Isolation and characterization of a novel Lactobacillus plantarum MMB-07 from traditional Suanyu for Acanthogobius hasta fermentation

As one of Lianyungang's most famous specialties, Acanthogobius hasta is delicious and nutritious fish, but is extremely susceptible to spoilage during transportation and storage. In this study, Lactobacillus plantarum MMB-07 was isolated from traditional fermented sour fish to reduce losses and improve the utilization and food value of A. hasta. L. plantarum MMB-07 had good ability of acid production and acid resistance. Moreover, it could also inhibit common pathogens in food or aquatic products to ensure the safety of fermented products. MMB-07 was used to ferment A.hasta and obtain fermented Suanyu rich in nutrition value and good flavor. The volatile base nitrogen was 18.44mg/100g and the fermented fish meat maintained second-grade freshness. Thiobarbituric acid assay was 0.90mg/kg and fat in fish meat was oxidized to a low degree. The studies indicated that MMB-07 has a high application prospect in low salt fermented fish.

Lactic acid production ability of Lactobacillus sp. from four tropical fruits using their by-products as carbon source

The present work was aimed at studying the technological properties of lactobacilli isolated from four tropical fruits (banana, papaya, pineapple, and orange) sold in Dschang (a city of the Menoua Division, West-Cameroon), as well as their ability to produce lactic acid (LA) from by-products of these fruits. After isolation and preliminary identification, homofermentative isolates were investigated for acidifying, amylolytic, cellulolytic activities as well as exopolysaccharides production. The chemical composition of the by-products was determined prior to fermentation assays and the most promising isolates were identified by 16S rRNA gene sequencing. From the 54 homofermentative lactobacilli obtained, 9 isolates were pre-selected based on their higher acidifying activity in MRS-Glucose medium. They all showed amylolytic activity, with the most important activity (54.26 ± 0.10 μg of reducing sugar/ml/min) recorded by isolate O31. Relatively to their cellulolytic activity, isolate 1B9 showed the best activity, displaying a production rate of 7.98 ± 0.40 μg glucose/ml/min, while none of them produced exopolysaccharides. The proximate analysis showed that the fruit-derived by-products contained proteins (0.40 ± 0.06% DM to 1.54 ± 0.06% DM), carbohydrates (61.75 ± 0.75% DM to 71.94 ± 2.02% DM) that are main nutrient needs for bacterial growth. Banana-derived and pineapple-derived by-products showed the highest LA production rates with values, 26.37 ± 0.05 g/l (isolate 3A5) and 26.29 ± 0.38 g/l (isolate 1B9) respectively after 16 h of fermentation. Based on the principal component analysis, isolates O31, 1B9, 3A5, 3A9 and 4O8 were selected as the most promising isolates and were identified as Lactobacillus plantarum strains. According to the obtained results, lactobacilli from tropical fruits displayed properties of commerical interest and can be promising candidates in the valorisation of by-products from tropical fruits through LA production.

Bioremediation of petroleum contaminated soil through biosurfactant and Pseudomonas sp. SA3 amended design treatments.

Toxicity of agricultural soil due to petroleum contamination has become a serious issue in recent times. Petrol oil exhibits toxic effects in agricultural crops due to the presence of various hazardous hydrocarbons. The degradation of petroleum hydrocarbon has been widely studied by the researchers that signify the requirement of effective treatments for the detoxification of petroleum contaminated soil and their reuse for growing crops. Hence, with this intention in the present study secondary metabolites "biosurfactant" (natural surfactant) along with the potent plant growth promoting (PGP) bacterial strain Pseudomonas sp. SA3 was used in the designed treatments for growing agricultural crop. The biosurfactant produced by the strain has the emulsification capacity of 43% and surface tension reduction ability to 34.5mN/m whereas the plant growth promoting traits demonstrates 93.46µg/mL phosphate solubilisation ability, siderophores (iron chelating compound) production upto 69.41% units and 81.41µg/mL indole acetic acid (IAA) production ability. Further, the results of the design treatments signifies that treatments amended with the strain SA3 and biosurfactant is effective in the management of petroleum contaminated soil indicating treatment EX 5 (1kg soil+1L water+Pseudomonas sp. SA3+300mL crude biosurfactant), as an efficient treatment in increment of phytochemical constituents and 10-15% enhancement in growth parameters as compared to negative control. Hence, the developed treatments can be efficaciously used for the management of petroleum contaminated soil for agronomy.

Combined Use of Two Trichoderma Strains to Promote Growth of Pakchoi (Brassica chinensis L.)

Trichoderma spp., which widely exist in nature, are always used as plant growth-promoting stimulants. However, there is little reporting about the combined use of Trichoderma strains to promote growth of plants. We explored two different Trichoderma strains (Trichoderma atroviride LX-7 and Trichoderma citrinoviride HT-1) and a mixture of the two on the growth-promoting effects of pakchoi. In this study, in vitro-promoting traits of two Trichoderma strains were determined, and six treatments were used: T. atroviride LX-7, T. citrinoviride HT-1, different mixtures of these two (1:1, 1:2 and 2:1) and no inoculation in the seed germination and pot experiment. The results showed that T.atroviride LX-7 and T. citrinoviride HT-1 had the ability of siderophore and indol acetic acid (IAA) production, and LX-7 had the capacity for potassium solubilization. The highest seed germination percentage (GP), germination energy (GE), germination index (GI), vitality index (VI) and growth of radicles and plumules was observed in the LX-7 + HT-1 (1:1) combination, the highest biomass and quality of plants was observed in the LX-7 + HT-1 (1:2) inoculation (followed by a single LX-7 or HT-1 strain inoculation), while the lowest values were obtained in the untreated seeds or plants. On the basis of this study, combined use of two Trichoderma strains had greater benefits for growth and quality of pakchoi, making this formulation attractive for future field applications.

Dendrobium candidum extract on the bioactive and fermentation properties of Lactobacillus rhamnosus GG in fermented milk

Dendrobium candidum has a long medicinal history and good nutritional value. It has been used in the health food industry. However, the effect of D. candidum on the biological activity and the fermentation of probiotics need further study. This study evaluated the effect of D. candidum extract (DCE) on the chemical, viable bacteria count, and acid production capacity of milk fermented using probiotics. The tolerance of Lactobacillus rhamnosus GG (LGG) to simulated gastrointestinal fluids, the ability of the strain to scavenge free radicals, adhesion capacity, and antibacterial activity were measured. The differences in volatile flavor substances and sensory properties of fermented milk with and without DCE added were measured. The results showed that DCE supplementation increased the use of proteins and carbohydrates by LGG, and rate of carbohydrate using LGG increased by 25%. The growth and acid production ability of the strain were increased. The number of viable bacteria in the fermented milk with DCE supplementation was >8.5 log CFU/mL, and the survival rates of LGG in simulated gastric and intestinal juices were improved. O2− and hydroxyl radicals in the fermented milk samples with DCE added were significantly decreased. In addition, DCE did not significantly affect the flavor quality of fermented milk. DCE supplements are a promising type of transfer protection agent.

Probiotic potential of γ-aminobutyric acid (GABA)–producing yeast and its influence on the quality of cheese

Kazakh cheese is a traditional dairy product in Xinjiang, China. To study the function and potential probiotic characteristics of yeast in Kazakh cheese and its contribution to cheese fermentation, we screened the γ-aminobutyric acid (GABA)-producing yeasts Pichia kudriavzevii 1-21, Kluyveromyces marxianus B13-5, Saccharomyces cerevisiae DL6-20, and Kluyveromyces lactis DY1-10. We investigated the potential probiotic properties of these strains and their use in cheese fermentation (cheeses designated CSP, CSM, CSS, and CSI, respectively); a control with no added yeast was designated CS. The results showed that the 4 yeast strains all showed high self-polymerization (2- and 24-h autoaggregation capacity of >80 and 90%, respectively), hydrophobicity (40-92% variation, low hydrophobicity in xylene, but within the range of probiotics), and the ability to survive the gastrointestinal tract (survival rate >75% after simulation), indicating the probiotic ability of the strains in vitro. The GABA production capacity of the CSM cheese increased (to 95.6 mg/100 g), but its protein content did not change significantly, and amino acid degradation was obvious. The GABA production capacity of the CSS cheese decreased (to 450 mg/kg); its protein content declined, and its amino acid content increased. Except for water and protein, we found no obvious differences in most physical and chemical indicators. Kluyveromyces marxianus B13-5 helped to form the desired texture. Multivariate statistical analysis showed that fermentation of the cheese with the 4 yeasts improved the production of esters and alcohols. The CSS cheese had good aroma production performance, because S. cerevisiae DL6-20 produced high concentrations of isoamyl alcohol, hexanoic acid ethyl ester, benzyl alcohol, octanoic acid ethyl ester, 3-hydroxy-2-butanone, and hexanoic acid; the content of 2-methyl-propanoic acid was low. Compared with the CSP cheese, the CSI and CSM cheeses had a fruitier aroma and a milder odor, but the CSI and CSM cheeses had high concentrations of ethyl acetate, butanoic acid, ethyl ester, 3-methyl-1-butanol-acetate, ethyl hexanoate, ethyl octanoate, acetic acid 2-phenylethyl ester, and ethyl lactate; concentrations of 3-methyl-butanoic acid, propanoic acid, acetic acid, and butanoic acid were low. The CSP cheese had stronger acid-producing ability. The order of fragrance production performance was CSS > CSI, CSM > CSP > CS. Research into the fermentation mechanisms of GABA-producing yeast in cheese will provide a theoretical basis for the quality control and industrial production of Kazakh cheese.

Inoculation with Rhizobacteria Enhanced Tolerance of Tomato (Solanum lycopersicum L.) Plants in Response to Cadmium Stress

In this study, cadmium (Cd)-tolerant bacteria Serratia sp. D23 (D23) and Sphingomonas sp. D36 (D36) were isolated from Cd-contaminated rhizospheric soil. Both strains have indole-3-acetic acid production, phosphate solubilization and siderophores production ability. A hydroponic experiment was performed to evaluate the effect of D23 and D36 on Cd toxicity and Cd content in tomato plants. The results indicated that under Cd-stressed condition, D23 and D36 inoculation increased photosynthetic pigment content in tomato leaves and decreased malonyldialdehyde level in tomato roots (p < 0.05). Both strains could alleviate Cd-induced inhibition of dry mass accumulation, D23 inoculation increased the root and leaf dry mass by 44.95% and 99.13%, while D36 treatment increased the root and leaf dry mass by 41.56% and 46.81%, respectively. Besides, D23 treatment reduced the Cd content in tomato root by 46.70%, and D36 inoculation reduced the Cd content in root and leaf by and 27.63% and 35.41%. Moreover, the expression of stress-related genes, including Hsp90, MT2 and Nramp3 were enhanced by bacterial inoculation. The subcellular localization of Cd and the activity of antioxidant enzyme were also influenced by D23 and D36 colonization. Taken together, rhizobacteria D23 and D36 could alleviate Cd toxicity and reduce Cd concentration in tomato plants via alleviating oxidative stress, modulating Cd subcellular localization and upregulating stress-related gene expression. This study provides evidence of enhancing Cd tolerance in tomato plants via rhizosphere bacteria and will be helpful to establish bacterial-assisted approach for alleviating heavy metal toxicity in plants.

Effects of Methyl Donors on L-Tryptophan Fermentation

Methyl donors, a class of compounds that supply methyl groups to methyl acceptors, play important roles in the function, growth, and proliferation of cells; however, the methyl donor content in cells is not sufficient to meet their normal needs. In L-tryptophan production with E. coli, the growth and acid-producing ability of E. coli cells are weak due to the presence of exogenous plasmids that inhibit the growth of E. coli, and reduce the efficiency of exogenous gene expression. Therefore, the effect of methyl donors on L-tryptophan production was investigated. Among the methyl donors tested, choline chloride showed the most significant effect in promoting fermentation, followed by methionine. The optimum addition method involved the addition of 1.5 g/L methionine to the culture medium, combined with continuous feeding with a glucose solution containing 1 g/L choline chloride. The final tryptophan titer reached 53.5 g/L; the highest biomass of bacteria reached 51.8 g/L; and the main by-product, acetic acid, was reduced to 2.23 g/L, which had a significant impact on the fermentation results.

Linoleic acid induces different metabolic modes in two Bifidobacterium breve strains with different conjugated linoleic acid-producing abilities

Frequently, Bifidobacterium breve strains are found to be CLA-producers. Previous studies revealed that free linoleic acid inhibited the growth of bifidobacterial strains, however, the reason why bifidobacteria with different CLA-producing abilities exhibit similar adaptive modes to linoleic acid (LA) stress is still unknown. We used B. breve strains CCFM683 and CCFM1025, which exhibit 85% and 0% CLA conversion rates, respectively, together with metabonomics analyses, to elucidate the putative factors involved in the protection against LA stress. We found that the pathways involved in amino acid, carbohydrate, and fatty acid metabolisms were much more active in B. breve CCFM1025. Moreover, l-cysteine, l-methionine, mannitol, and 18-hydroxy-oleate accumulated to a much higher level in B. breve CCFM1025, probably providing primary protection. In particular, the levels of several antioxidant compounds, including l-ascorbate, glutathione, ubiquinol-6, 3-demethylubiquinol-7, and demethylmenaquinol-7, were much higher in B. breve CCFM1025, suggesting that these antioxidants may provide a primary protective effect to the strain without CLA-producing abilities.

Relationship between sucrose concentration and bacteria proportion in a multispecies biofilm

ABSTRACT Objective: The aim of this study was to evaluate the relationship between sucrose concentration and bacteria proportion in a multispecies biofilm model. Methods: Streptococcus mutans (S. mutans), Streptococcus oralis (S. oralis), and Actinomyces naeslundii (A. naeslundii) were chose to form a multispecies biofilm. Different concentration (0–40%) of sucrose was introduced to the multispecies biofilm 3 times per day (30 min per time). And then the bacteria proportion and acid production of the biofilms were analyzed. Results: Increasing sucrose level increased CFU count of S. mutans up to a certain concentration (5% sucrose), after which the number of S. mutans slightly decreased, but the CFU counts of S. oralis and A. naeslundii continually decreased with sucrose concentration increase, especially, from 5% sucrose, the reduction was significant, and S. mutans became the dominant species in the biofilms. Furthermore, the acid production ability of the multispecies biofilm gradually increased and slightly decreased with sucrose concentration increased, and the turning concentration was 5%. Conclusion: Our findings suggest that increasing sucrose level could increase the competitiveness of S. mutans in the multispecies biofilm, which may shift the biofilm to a more cariogenic one, and 5% sucrose formed a most cariogenic biofilm in this study.

Screening of dominant strains in red sour soup from Miao nationality and the optimization of inoculating fermentation conditions.

Red sour soup is a traditional fermented product in southwest China. Currently, the existing production process mainly adopts the method of natural fermentation, with long fermentation cycles and poor stability between batches. Rapid establishment of dominant strains can accelerate the formation of lactic acid, which can inhibit the growth of miscellaneous bacteria. It is also helpful for the inhibition of nitrite accumulation, shortening of fermentation. In this study, the dominant strain H9, with lactic acid‐producing ability, was isolated from the natural fermented red sour soup, and was identified as Lactobacillus buchneri, based on the 16s rRNA sequence analysis and biochemical identification. Then, the optimization of fermentation conditions was performed using L. buchneri H9 strain as external bacteria. The optimized fermentation conditions were temperature of 22°C, starch dosage of 11.24 g/L, and initial inoculation of 3.5 × 108 cfu/L. The concentration of lactic acid reached 8.029 g/L after 8 days of inoculating fermentation, which exceeded 6.221 g/L for 20 days of natural fermentation. Compared with natural fermentation, the peak of nitrite during inoculating fermentation appeared earlier and the peak height was lower. While the nitrite content in inoculating fermentation decreased to safety threshold more quickly. The volatile flavor compounds analysis showed that 41 types of volatile compounds were detected in the inoculating fermentation product, while 45 in the natural fermentation product. Over 88% compounds were overlapped, which means similar flavor between two fermentation products. These results provide a sufficient scientific basis for the industrialized production of inoculating fermentation of red sour soup.

Isolation of Lactic acid bacteria showing antagonistic activity against Streptococcus mutans

Streptococcus mutans is a major pathogen that initiates dental plaque and dental caries due to its strong acid production and biofilm-forming ability. Recent studies showed that lactic acid bacteria (LAB), exert useful properties which make them become potential tools to fight against S. mutans and its relating diseases. The current study aimed to isolate and screen for LAB strains that could inhibit S. mutans growth as well as its biofilm production. Using the spread plate technique, fifty-one LAB strains were isolated from fermented vegetables and healthy human saliva. From that, fourteen isolates showed the inhibitory effect on S. mutans growth in well-diffusion assay. These strains were then screened on the ability in reducing S. mutans biofilm formation by colorimetric assay. Next, potential LAB was evaluated on some probiotic characteristics including saliva amylase tolerance, acid tolerance, bile tolerance as well as antibiotic susceptibility properties. As a result, four strains showed the most promising features were further tested for the ability to reduce Streptococcus mutans biofilm by scanning electron microscopy (SEM) observation and by expression analysis of biofilm-forming genes (gtfB and luxS) using RT-qPCR method. Finally, these four strains were identified to species level using API® 50 CHL kit and 16S rDNA sequencing method. The result showed that two strains belong to L. plantarums, one belongs to L. brevis and the other is Weisella confusa. This study was successful in isolating LAB that showed promising probiotic effects against S. mutans.

Lactobacillus delbrueckii is the key functional microorganism of natural fermented tofu sour water involved in the traditional coagulation of Chinese Huizhou Mao-tofu

Mao-tofu is traditionally coagulated by natural fermented tofu sour water (NFTSW), which contains large numbers of microorganisms from the environment. Nonetheless, the microorganisms accountable for coagulation require further analysis and characterization. Our aim was to evaluate the bacteria in NFTSW that carry out the traditional fermentation process of Mao-tofu by using polymerase chain reaction-denaturing gradient gel electrophoresis. Results show that Lactobacillus ultunensis, Enterococcus bulliens, Lactobacillus graminis, Lactobacillus delbrueckii, Lactobacillus delbrueckii subsp. lactis, and Lactobacillus mucosae are the primary bacteria involved in brewing. Furthermore, 6 types of lactic acid bacteria were sequestered from NFTSW by methodology dependent on culture and their acid-producing abilities were analyzed. The results indicated that strain L1, which was identified as Lactobacillus delbrueckii, produced the highest lactic acid content of 2.85 g/100 mL. Simulated coagulation further confirmed that strain L1 was preferable for Mao-tofu coagulation through the evaluation of textural properties, volatile flavour compounds, and sensory characteristics. The results suggested that Lactobacillus delbrueckii might be the core functional microorganism significantly contributing to flavor compound synthesis during the traditional production of Chinese Huizhou Mao-tofu. The research method we used in this investigation may encourage detection of the main microorganisms with different roles involved in other food fermentation processes.

EVALUATION OF POMEGRANATE PEEL AS A SUBSTRATE FOR CITRIC ACID PRODUCTION BY ASPERGILLUS NIGER

Objective: The present study aimed to evaluate dried pomegranate peels as a substrate for citric acid production by Aspergillus niger.&#x0D; Methods: The morphological study of Aspergillus niger was carried out by wet mount with lactophenol cotton blue and slide culture method. A preliminary qualitative screening of citric acid-producing ability of this fungal strain was also performed by using the Czapek-Dox agar medium containing Bromocresol green. Dried and finely powdered Pomegranate peel was used as a principal substrate for the production of citric acid by submerged fermentation. Classical method of citric acid recovery involved a precipitation technique using calcium hydroxide followed by filtration and subsequent treatment with sulphuric acid. The citric acid produced was also chemically detected and titrimetrically estimated by 0.1 N NaOH.&#x0D; Results: The present experiment demonstrated that pomegranate peels may serve as an inexpensive medium for the production of citric acid with a yield of 19.39 g/l by using Aspergillus niger.&#x0D; Conclusion: This study provided an alternative basis to recycle the fruit peel waste of pomegranate in order to achieve industrially feasible and environmentally sustainable bio-production of pharmaceutically significant citric acid.

A high Mn(II)-tolerance strain, Bacillus thuringiensis HM7, isolated from manganese ore and its biosorption characteristics.

Microorganisms play a significant part in detoxifying and immobilizing excessive metals. The present research isolated a strain (HM7) with high Mn(II) tolerance from Mn(II)-contaminated soil samples. The 16S rDNA sequence analysis showed that HM7 had a 99% similarity to Bacillus thuringiensis, which can survive under a high concentration 4,000 mg/L of Mn(II), and the highest removal rate was up to 95.04% at the concentration of 400 mg/L. The highest Mn(II) removal rate was detected at the contact time 72 h, temperature 30 °C, and pH 5.0, while the differences in strain growth and Mn(II) removal rate among different inoculation doses were insignificant. Scanning electron microscopy indicated B. thuringiensis HM7 cells appeared irregular and cracked under Mn(II) stress. Fourier transform infrared exhibited that functional groups like carboxyl, hydroxyl, amino, sulfhydryl groups, and amide bands might take part in the complexation of Mn(II). In addition, HM7 suggested the ability of indoleacetic acid production, siderophore production, and P’ solubilization potential. Therefore, HM7 might have a potential to promote metal absorption by changing the form of heavy metals, and the experiments supported the application of B. thuringiensis HM7 as a biological adsorbent in Mn(II) contaminated environment remediation.

Resumptive Streptococcus mutans Persisters Induced From Dimethylaminododecyl Methacrylate Elevated the Cariogenic Virulence by Up-Regulating the Quorum-Sensing and VicRK Pathway Genes.

Bacterial persistence has become a worldwide health problem due to its ability to cause the recalcitrance and relapse of infections. The existence of bacterial persistence and their possible mechanisms have been widely reported. However, the following regrowth of persister cells is not clear although the awakening of dormant surviving persisters is the key to reinitialize bacterial infection. In this study, we investigated the growth character and cariogenic virulence during the recovery of Streptococcus mutans drug-tolerant persister cells induced by a novel quaternary ammonium: dimethylaminododecyl methacrylate (DMADDM). A remarkable lag phase was observed in S. mutans persisters when regrew at the first 24 h compared to normal cells. During the entire recovery state, persisters are metabolically active to increase the production of both water-soluble and water-insoluble glucan. The shortage of cell number in persisters resulted in the decrease of lactic acid production, but persisters gradually recovered the normal acid production ability after 72 h. The up-regulated expression of gtf and vicR was in line with comDE circuit and consistent with the virulence change during the regrowth stage. Our findings proved that lethal dosages of DMADDM induced drug-tolerant S. mutans persisters in biofilm, which had a prolonged lag phase and elevated cariogenic virulence during regrowth. The recovery and elevated virulence of persisters were regulated by quorum-sensing and VicRK pathway. This alarmed the elevated cariogenicity of persisters and highlighted the critical requirement for the drug-tolerance evaluation when developing new oral antimicrobial agents. To the best of our knowledge, we characterized the regrowth and cariogenic virulence variation of S. mutans persisters induced by quaternary ammonium for the first time. Our findings suggest that S. mutans persisters with the elevated cariogenic virulence during their regrowth stage highlighted the need of new strategy to overcome bacterial persistence. Meanwhile, the prolonged lag phase and the involvement of quorum-sensing system in the regrowth of S. mutans persisters may provide the potential targets.

Screening of plant growth-promoting endophytic bacteria from the roots of the medicinal plant Aloe vera

This work aimed to test the hypothesis that the root bacteria of Aloe vera (Asphodelaceae) present multifunctionality with potential in biotechnology for plant growth. A total of 129 endophytic bacteria from three environments, a field, a garden, and nursery were isolated and evaluated for indole-3-acetic acid-producing ability. Thirty-two of the total bacteria isolates were evaluated for siderophore production, phosphate solubilization and antibiosis to phytopathogenic fungi. The phylogenetic analysis revealed the presence of four groups: Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria. The functional trait for indole-3-acetic acid (IAA) synthesis was observed in 32 of the isolates, with emphasis on the 135 V Enterobacter tabaci strain, which revealed the highest production (225.2 μg mL−1). The results found for Bayóvar phosphate solubilization were not expressive, with the highest values observed for the bacterium 149H Paraburkholderia sp. (45.7 mg L−1). The 3 V isolate Brevibacillus agri presented 45.6% antagonism against Sclerotinia sclerotiorum. The greatest inhibition of the phytopathogens Fusarium sp. and Rhizoctonia sp. was observed with 149H Paraburkholderia sp. and 348 V E. tabaci, respectively. Studies evaluating to evaluate the potential of endophytic bacteria of A. vera for plant growth promotion are rare and our results indicate that the isolates 135 V and 348 V E. tabaci and 149H Paraburkholderia sp. have potential for to be field-tested as growth promoter inoculants.

Oxidative Degradation of Methylene Blue via PDS-Based Advanced Oxidation Process Using Natural Pyrite.

H2O2- and PDS-based reactions are two typical advanced oxidation processes (AOPs). In this paper, a comparative study of H2O2/PDS-based AOPs employing natural pyrite as a catalyst to degrade methylene blue (MB) was reported. The adaptive pH range in pyrite/PDS extended from 3 to 11, in contrast to the narrow effective pH range of 3–7 in pyrite/H2O2. As a result of the iron leaching, a synergistic effect of both homogeneous and heterogeneous catalysis was observed in pyrite/PDS, whereas heterogeneous catalytic oxidation dominated pyrite/H2O2. Furthermore, the batch results showed that the MB removal by pyrite/PDS was highly dependent on chemical conditions (e.g., pH, pyrite and PDS concentration, temperature). Powerful SO4•− was generated by pyrite rapidly under acidic or weakly acidic conditions, while SO4•− and PDS were assumed by OH− under alkaline condition. The lower pyrite loading (from 0.1 to 0.5 g/L) was affected the removal efficiency obviously, while the scavenging of SO4•− did not seem to be remarkable with the excessive amounts of pyrite (>0.5 g/L). Excessive amounts of PDS (>2 mmol/L) might negatively affect the pyrite/PDS system. The reaction temperature that increased from 20 to 40 °C had a positive effect on the degradation of MB. SEM and XRD showed that the passivation of catalyst did not occur due to the strong acid-production ability of pyrite/PDS, inhibiting the formation of Fe-oxide covering the pyrite surface.