kèo nhà cái 188bet Testing antibacterial effect of silver nanoparticles on sulfate-reducing bacteria

Summary

In kèo nhà cái 188bet oil and gas industry, sulfate-reducing bacteria can generate hydrogen sulfide (H2S) in their growth, thus decreasing kèo nhà cái 188bet commercial value of crude oil, causing metal equipment corrosion and seriously affecting kèo nhà cái 188bet economic efficiency and kèo nhà cái 188bet health of workers on drilling rigs. Because of their strong antibacterial and environmental friendly characteristics, silver nanoparticles have been studied and applied in various sectors world-wide. This paper presents some initial research results on kèo nhà cái 188bet synthesis of silver nanoparticles (NPs) with kèo nhà cái 188bet mean silver nanoparticle size of 18 - 21nm being effective to reduce bacterial numbers from 106tb/ml to < 10tb/ml (99%). This activity was tested on sulfate-reducing bacteria EPC-KK2 - Desulfomicrobium baculatum which was isolated from crude oil samples taken from Bach Ho field.

Key words: Silver nanoparticle, biocide, sulfate-reducing bacteria, Bach Ho field.

1.    Introduction

kèo nhà cái 188bet sulfate reducing bacteria (SRB) are anaerobic bacteria that produce H2S. This type of bacteria can survive in extreme environments such as high temperature, high pressure, high salinity, to alkaline or acidic environment and is especially quite common in oil fields and exploitation wells. kèo nhà cái 188bet SRB produce H2S that is acidifying, leading to a reduction in kèo nhà cái 188bet commercial value of crude oil, corrosion of metalworking equipment, piping, and kèo nhà cái 188bet health of workers on drilling rigs [1, 2]. Under favourable conditions, desulfurising bacteria can develop biofilm membranes that occlude kèo nhà cái 188bet reservoir, which reduces kèo nhà cái 188bet ability of kèo nhà cái 188bet water to pump.

Currently, popular biocides being used are aldehydes or cyclic amines in combination with cationic active substances, which are highly toxic to humans and kèo nhà cái 188bet environment. When these biocides are used for a long time kèo nhà cái 188bet phenomenon of“grease” will occur. It is therefore in need of a new biocide with better antibacterial effect and being more environmentally friendly.

Silver NPs is a new material that is known for its superior disinfection ability and has many applications in life. Silver NPs are very small in size and have very large surface area. They can penetrate easily into microbial cells, alter biochemical mechanisms, inactivate microbial metabolism, and finally destroy them [3].

kèo nhà cái 188bet antibacterial mechanism of silver NPs is kèo nhà cái 188bet  result of kèo nhà cái 188bet conversion of silver atoms on kèo nhà cái 188bet surface of silver NPs to free Ag+ and free ions that will affect bacteria. Some mechanisms of silver NPs action on bacteria are being understood, for example silver ions inhibit kèo nhà cái 188bet ability of oxygen to travel through kèo nhà cái 188bet cell wall due to its ability to bind to kèo nhà cái 188bet peptidoglycan (cell-wall component), leading to cell death [4]. In animals without cell walls, they are unaffected by exposure to these ions. In kèo nhà cái 188bet other mechanism, silver ions can pass through kèo nhà cái 188bet cell membrane into kèo nhà cái 188bet cell and react with sulfhydryl - SH group of kèo nhà cái 188bet oxygen-converting enzyme molecule, neutralising kèo nhà cái 188bet enzyme that inhibits bacterial cell respiration. In addition, silver ions are capable of binding to DNA bases and neutralising kèo nhà cái 188bet charge of phosphate, preventing DNA replication [5 - 8].

Antibacteria with silver NPs is a new research direction in kèo nhà cái 188bet manufacture of biocides for use in kèo nhà cái 188bet oil and gas industry. This article presents some  results  of  synthesis of silver NPs and testing bactericidal ability of silver NPs on desulfurising bacteria isolated from Bach Ho crude oil samples.

2.    Materials and methods

    Materials and equipment

    Materials

In this study, all reagents of producing silver NPs colloids were of analytical grades and used as received without further purification. Silver nitrate AgNO3 (99.98%) was used as kèo nhà cái 188bet silver precursor, which was obtained from  Merck (Germany). Sodium borohydride NaBH4 (96.5%) was obtained from Chemical Ltd., whereas kèo nhà cái 188bet sodium citrate Na3C6H5O7 (99.0%) from Sigma Aldrich was used as producing agents. All kèo nhà cái 188bet aqueous solutions were prepared in double distilled water.

kèo nhà cái 188bet improved Postgate’s B bacterial culture medium was used for bacterial culture KH2PO4 0.5g/l; Na2SO4 1g/l; NH4Cl 1g/l; MgSO4 2g/l; NaCl 4g/l; CaCl2 0.1g/l; marine water 200ml; distilled water 800ml; C3H5NaO3 2g/l; pH 7.2g/l; C2H3NaO2.3H2O 1.75g/l;

FeSO4 0.5g/l; yeast extract 0.5g/l; kèo nhà cái 188bet medium should be autoclaved for 15 minutes at 121oC (250oF). kèo nhà cái 188bet pH should be adjusted with NaHCO3.

SRB strain was isolated from MSP10 crude oil sample of Bach Ho field and identified by analysing and sequencing 16S rRNA genes.

    Equipments

kèo nhà cái 188bet UV-visible spectra were recorded over kèo nhà cái 188bet range of 200 - 800nm by Thermo Evolution 300. kèo nhà cái 188bet size and morphology of silver nanoparticle colloids were investigated using transmitted electron microscope (TEM) Philips CM 120. Particle size measuring device by laser light scattering LA-950.

    Methods

kèo nhà cái 188bet chemical reduction method is used  for  kèo nhà cái 188bet production of silver NPs from AgNO3, with kèo nhà cái 188bet reducing agent NaBH4 or Na3C6H5O7 [9]. kèo nhà cái 188bet reduction process for silver NPs is shown in Figure 1.

 Evaluating kèo nhà cái 188bet dispersibility of silver NPs: Silver NPs were diluted at different concentrations and UV-VIS spectra were measured to evaluate kèo nhà cái 188bet existence and contraction of silver NPs.

Isolation and identification of SRB: Bacteria were isolated from Bach Ho oil samples. SRB was isolated on Postgate’s B medium and purified to kèo nhà cái 188bet mono-assay by means of critical dilution. SRB strain was Gram stained and its cell shape was observed under kèo nhà cái 188bet optical microscope.

kèo nhà cái 188bet bacterial strain was cultured and enriched, and identified by analysing and sequencing of 16S rRNA genes.

kèo nhà cái 188bet biocide efficiency was tested according to bacterial growth after exposure to silver NPs according to API RP38 standard.

3.    Results and discussion

    Preparation of silver nanoparticle solution

    Selection of reducing agents

kèo nhà cái 188bet results in Figures 2 and 3 show that kèo nhà cái 188bet particle sizes of products obtained from Na3Cit (Na3C6H5O7) reductant are larger than those from NaBH4. When Na3Cit was used, kèo nhà cái 188bet absorption wavelength of kèo nhà cái 188bet silver NPs colloid went up to 450nm under UV-VIS spectrometer and kèo nhà cái 188bet efficiency of reaction reduced significantly comparing to NaBH4.

Figure 1. Diagram of silver nanoparticle preparation

Figure 2. UV-VIS spectrophotometric and TEM image of silver NPs with Na3Cit
 

Figure 3. UV-VIS spectrum and TEM image of silver NPs with NaBH4

Figure 4. UV-VIS spectra of silver nanoparticle samples (AgNPs 30, 31, 33)

Figure 5. UV-VIS spectra of silver NPs solution samples with concentration ratios stabilised/AgNO3: 0.05; 0.275 and 0.5

Figure 6. Silver NPs solution in different concentrations

Figure 7. UV-VIS spectra of silver nanoparticles AgNPs 27 at concentrations of 0.1 , 0.3 , 0.5 , 1 and 1.5

Figure 8. TEM of AgNPs 32

It means that kèo nhà cái 188bet reduction capacity of Ag+ ions to Ago by NaBH is higher than Na Cit. As a result, NaBH was comparing to AgNO3. Figure 5 shows kèo nhà cái 188bet UV-VIS spectrographic chromatograms of silver NPs colloids with NaBH4 to AgNO3 ratios being 2:1; 3:1; 4:1 at 0.380; 0.900; 0.683 peak heights respectively. It means that kèo nhà cái 188bet content of reducing agents would considerably affect kèo nhà cái 188bet numbers of silver NPs produced (Figure 4). kèo nhà cái 188bet results showed that kèo nhà cái 188bet highest concentration of silver NPs colloid was chosen for kèo nhà cái 188bet synthesis of silver NPs.

    Silver nanoparticle preparation conditions

-    Effect of NaBH4/AgNO3 concentration ratio
In order to achieve kèo nhà cái 188bet highest reaction efficiency, kèo nhà cái 188bet NaBH4 reductant must be used in excess amount obtained at NaBH4 to AgNO3 ratio of 3:1.

-    Effect of kèo nhà cái 188bet stabilising agent/AgNO3 ratio

kèo nhà cái 188bet results in Figure 5 indicated that kèo nhà cái 188bet UV-VIS absorption peak height of products obtained from a 0.05 ratio of stabilising agent to AgNO3 is much lower than that from 0.275 and 0.5 ratios. It can be explained that too low stabilising agent concentration  will  not create mixed molecular surrounding silver NPs, and this is kèo nhà cái 188bet reason why kèo nhà cái 188bet nanoparticle size increases and kèo nhà cái 188bet number of silver NPs decreases. kèo nhà cái 188bet highest UV-VIS absorption peak was obtained from kèo nhà cái 188bet 0.5 ratio of stabilising agent to AgNO3.

    Evaluation of silver NPs colloid characteristics

Silver NPs colloids were prepared at  different concentrations from 0.2 to 2,000ppm (Figure 6). UV-VIS absorption spectrometer of range of silver NPs concentrations was shown in Figure 7. kèo nhà cái 188bet diluted samples all reached a peak of 400nm which indicated that kèo nhà cái 188bet properties of silver NPs were not affected by kèo nhà cái 188bet dilution in water.

kèo nhà cái 188bet TEM image of silver NPs at 2,000ppm (Figure 8) showed that kèo nhà cái 188bet size of silver NPs was at approximately 15 ± 4nm. These nanoparticles meet kèo nhà cái 188bet requirements of size which is effective for biocide (< 100nm).

Figure 9 showedtheresultsofsizedistribution of silver NPs at concentration, 2000ppm, and kèo nhà cái 188bet mean size is around 19nm.

    Isolation and identification of bacteria

kèo nhà cái 188bet EPC-KK2 sulfate reducing strain was isolated from oil sample MSP10-1014. On kèo nhà cái 188bet microscope, these cells are short rod shaped, Gram-negative bacteria, planktonic. This type of bacteria is anaerobic, and anaerobic respiration uses sulfate as kèo nhà cái 188bet final electron acceptor, producing H2S. They grow on lactate substrates. Optimum conditions of growth include: appropriate temperature is 30 - 32oC; pH is 7.5; and salt concentration of NaCl is 2.5g/l.

kèo nhà cái 188bet EPC-KK2 strain was classified and identified by analysing and sequencing 16S rRNA genes.

kèo nhà cái 188bet    results    of    gene    analysis    (Figure 10) of EPC-KK2 showed that kèo nhà cái 188bet amplified genomes were similar to Desulfomicrobium baculatum KF536747.1 (Figure 11). From kèo nhà cái 188bet results of sequencing 16S rRNA genes and  kèo nhà cái 188bet cell   morphology   (Figure   12),   EPC-KK2   can be identified as Bacteria; Proteobacteria; Deltaproteobacteria; Desulfovibrionales; Desulfomicrobiaceae; Desulfomicrobium baculatum.

Figure 9. Size distribution of AgNPs 27 in solution

Figure 10. Sequence genes of strain EPC-KK2

Figure 11. Phylogenetic position of EPC-KK2 species with relatives based on16S rRNA sequences General characteristics of kèo nhà cái 188bet bacterium Desulfomicrobium baculatum:

Cells: rod or  ellipsoidal-shaped  cells, 0.5 - 0.9 x 1.3 - 2.9μm, with round ends, either singly or in pairs [10]. Gram- negative stain reaction and having cell- wall structure. Cells are motile, usually by a single polar flagellum. Endospores are not formed.

Growth condition: anaerobic, pre- reduced medium or reducing agent required in medium for growth. Growth can occur by anaerobic respiration with sulfate or sulfoxy-anions as terminal electron acceptor, producing H2S. 
Optimal temperature from 25 - 30oC.

Substrates used: simple organic compounds that serve as electron donors during sulfate respiration include lactate, pyruvate,  ethanol,  formate  and hydrogen. Sulfate respiration with lactate as electron donors is incomplete, with kèo nhà cái 188bet formation of acetate and CO2. Hydrogenase is present. Cells  contain  b- and c-type cytochromes. Metabolism can also be fermentative on simple organic substrates, including pyruvate, malate or fumarate; carbohydrates are not fermented. No specific vitamins are required [10].

    Antibacterial effect of silver NPs

There are a number of theories on kèo nhà cái 188bet antibacterial ability of silver NPs colloid, in which kèo nhà cái 188bet absorbed theory is most convincing. kèo nhà cái 188bet main idea of kèo nhà cái 188bet theory is that kèo nhà cái 188bet bacterial cell is inactive due to kèo nhà cái 188bet electron storage between kèo nhà cái 188bet negative charged surface of kèo nhà cái 188bet cell and kèo nhà cái 188bet Ag+ ions which have been absorbed to it. These ions would penetrate into kèo nhà cái 188bet inside of kèo nhà cái 188bet bacterial cell and inactivate them. 

Table 1. kèo nhà cái 188bet effect of NPs size and concentration of AgNPs colloids on EPC-KK2

Table 2. Test on antibacterial concentrations of AgNPs 25 with EPC-KK2

Table 3. Test on antibacterial concentrations of AgNPs 27 with EPC-KK2

kèo nhà cái 188bet silver NPs samples  collected  are  tested  with  kèo nhà cái 188bet antibacterial effect based on their particle sizes. According to announced  studies,  kèo nhà cái 188bet  size  of  silver  NPs is an important factor that affects kèo nhà cái 188bet antibacterial property. For different size of silver NPs, kèo nhà cái 188bet activities of kèo nhà cái 188bet solution on kèo nhà cái 188bet bacteria are very different [8]. Overall, kèo nhà cái 188bet size of kèo nhà cái 188bet silver NPs that is effective for bacteria is within kèo nhà cái 188bet range of 1 to 50nm. For kèo nhà cái 188bet isolated strain,    kèo nhà cái 188bet size of silver NPs is within 1 - 50nm. kèo nhà cái 188bet effective concentration of silver NPs solution on different bacteria varies. Normally, kèo nhà cái 188bet  minimum  inhibited  concentration of silver NPs solution is about 10 - 75ppm. kèo nhà cái 188bet silver NPs solutions which are prepared and tested in kèo nhà cái 188bet study include: AgNPs 25, AgNPs 27, AgNPs 31, and AgNPs 34. These solutions did not show precipitation and were tested with kèo nhà cái 188bet EPC-KK2 type. kèo nhà cái 188bet results are shown in Table 1.

Figure 12. Sulfate reducing bacteria EPC-KK2 under Leica DM750 microscope

Table 1 shows kèo nhà cái 188bet ability of silver NPs colloid AgNPs 25 and AgNPs 27 to kill EPC-KK2 strain with kèo nhà cái 188bet mean particle size < 25nm. AgNPs 31 and AgNPs 34 with kèo nhà cái 188bet mean particle size > 25nm did not kill EPC-KK2 strain, effectively.

With kèo nhà cái 188bet silver NPs size < 25nm, kèo nhà cái 188bet antibacterial effect of AgNPs 25 and AgNPs 27 were observed at different concentration between 0 - 30ppm. kèo nhà cái 188bet results in Tables 2 and 3 show that EPC-KK2 was not observed after kèo nhà cái 188bet experiment with AgNPs 25 and AgNPs 27 samples at kèo nhà cái 188bet concentration of 20ppm.

Figure 13. EPC-KK2 strain grown again in test of silver NPs

Figure 14. EPC-KK2 strain killed in test of silver NPs

Pictures of kèo nhà cái 188bet cultivated EPC-KK2 strain in kèo nhà cái 188bet experiment to assess kèo nhà cái 188bet antibacterial ability of silver NPs colloid are shown in Figures 13 and 14.
kèo nhà cái 188bet results of kèo nhà cái 188bet  tests  show  that  kèo nhà cái 188bet antibacterial ability of AgNPs 27 and AgNPs 25 samples are highly effective at kèo nhà cái 188bet concentration of 20ppm for kèo nhà cái 188bet EPC- KK2 strain.
4.    Conclusion
kèo nhà cái 188bet EPC-KK2 strain, which was isolated from kèo nhà cái 188bet Bach Ho crude oil samples and classified as Desulfomicrobium baculatum, was used to evaluate kèo nhà cái 188bet antibacterial effectiveness of silver NPs colloid. Silver NPs (mean silver NPs size 18 -  21nm)  were effective to reduce kèo nhà cái 188bet antibacterial activity from 106tb/ml to < 10tb/ml (99%) at 20ppm. kèo nhà cái 188bet results showed that silver NPs are highly effective in killing SRB. This would create a new approach for applying silver NPs as biocide in Vietnam's oil and gas industry. References
1.    Lai Thuy Hien, Dang Phuong Nga. Physiological and biochemical properties  of some sulfate-reducing bacteria strains isolated from Bach Ho oil field. Journal of Biology. 1998; 20(2): p. 33 - 38.
 2.    Lai   Thuy   Hien,    Le    Phi    Nga.    Study    on metal    corrosion    potential    of     Desulfovibrio    vulgaris.      Journal       of       Biology.       1992;        14(4): p. 26 - 29.
3.    Catalina Marambio-Jones, Eric M.V.Hoek.  A  review of kèo nhà cái 188bet antibacterial effects of silver nanomaterials and potential implications for human health and kèo nhà cái 188bet environment. Journal of Nanoparticle Research. 2010; 12(5): p. 1531 - 1551.
4.    T.A.Brown, D.G.Smith. kèo nhà cái 188bet effects of silver nitrate on kèo nhà cái 188bet growth and ultrastructure of kèo nhà cái 188bet yeast Cryptococcus albidus. Microbios Letters. 1976; 3: p. 155 - 162.
5.    M.R.Richards, H.A.Odelola, B.Anderson. Effect of silver on whole cells and spheroplasts of a silver resistant Pseudomonas aeruginosa. Microbios. 1984; 39(157 - 158): p. 151 - 157.
6.    Yakabe Yoshikuni, Sano Takayuki, Ushio Hidetoshi, Yasunaga Tatsuya. Kinetic studies of kèo nhà cái 188bet interaction between silver ion and deoxyribonucleic acid. Chemistry Letters. 1980; 9(4): p. 373 - 376.
 7.    Reed M.Izatt, James J.Christensen, J.Howard Rytting. Sites and thermodynamic quantities associated with proton and metal ion interaction with ribonucleic acid, deoxyribonucleic acid, and their constituent bases, nucleosides, and nucleotides. Chemical Reviews. 1971; 71(5): p. 439 - 481.
8.    Gianluigi Franci, Annarita Falanga, Stefania Galdiero, Luciana Palomba, Mahendra Rai, Giancarlo Morelli, Massimiliano Galdiero. Silver nanoparticles as potential  antibacterial  agents.  Molecules.  2015;  20(5): p. 8856 - 8874.
9.    Shuai He, Honglin Chen, Zanru Guo, Biqing Wang, Chongli Tang, Yujun Feng. High-concentration silver colloid stabilized by a cationic geminisurfactant. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2013; 429: p. 98 - 105.
10.    George M.Garrity. Bergey’s manual of systematic bacteriology (2nd edition). Springer Science & Business Media, USA. 2001; 2: p. 944 - 945.