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                 <b>Fig.4. RFU and RFU/OD<sub>600</sub> under the growth curve of <i>E. coli</i> with pET29a-Bs2 plasmid (J23119).</b>The first is incubated at 20℃; The second is incubated at 30℃. The third is incubated at 37℃.Under incubation at 30℃ Celsius,RFU reached their maximum values.Under incubation at 30℃ Celsius,OD<sub>600</sub> reached their maximum values.
 
                 <b>Fig.4. RFU and RFU/OD<sub>600</sub> under the growth curve of <i>E. coli</i> with pET29a-Bs2 plasmid (J23119).</b>The first is incubated at 20℃; The second is incubated at 30℃. The third is incubated at 37℃.Under incubation at 30℃ Celsius,RFU reached their maximum values.Under incubation at 30℃ Celsius,OD<sub>600</sub> reached their maximum values.
 
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Revision as of 06:44, 1 October 2024


flavin mononucleotide (FMN)-dependent fluorescent protein Bs2

Bs2 is one of the flavin mononucleotide (FMN)-based fluorescent proteins. We use 450nm as excited wavelength and 500nm as absorption of emission wavelength.
To find more about this flavin mononucleotide (FMN)-based fluorescent protein, view doi:/10.1016/j.jbiotec.2019.08.019

Results


In our project, the key promoter vgb was a microaerobic induced promoter of Vitreoscilla hemoglobin gene. Considering the gene compatibility difference between different host bacteria, we designed the pMTL-Pvgb-bs2 plasmid to determine whether the promoter vgb could work normally in Clostridium tyrobutyricum by detecting the fluorescent expression intensity of fluorescent protein Bs2.
The green fluorescent protein (GFP) has been one of the most widely used reporter in bioprocess monitoring of gene expression. However, they are not functional under anaerobic conditions, and thus cannot be employed as reporters in Clostridium. A series of flavin mononucleotide (FMN)-based fluorescent proteins (FbFPs) have been reported, which could exhibit strong signals in the absence of O2. FbFPs have been successfully used as a fluorescent label in anaerobic or facultative anaerobic bacteria, including several species of Clostridium for monitoring of protein expression, evaluation of promoter strength, and for proof-of-concept demonstration of transcriptional repression, etc.


Sequence and Features


Assembly Compatibility:
  • 10
    INCOMPATIBLE WITH RFC[10]
    Illegal PstI site found at 215
  • 12
    INCOMPATIBLE WITH RFC[12]
    Illegal PstI site found at 215
  • 21
    COMPATIBLE WITH RFC[21]
  • 23
    INCOMPATIBLE WITH RFC[23]
    Illegal PstI site found at 215
  • 25
    INCOMPATIBLE WITH RFC[25]
    Illegal PstI site found at 215
  • 1000
    COMPATIBLE WITH RFC[1000]

Group: Nanjing-BioX

Author: Yuyao Cao, Yijiu Lu

Summary: Characterization of the transcription of Bs2 gene regulated by Pfba promoter

<Characterization from Nanjing-BioX:

We constructed pMTL-Pfba-Bs2 plasmid using Pfba promoter and Bs2 gene, transformed the plasmid into Clostridium tyrobutyricum (C. tyrobutyricum) and detected the fluorescence intensity of Bs2, so as to characterize the transcription of Bs2 regulated by Pfba promoter.

Experiment Results:

(1)Plasmid construction

Using the recombinant plasmid Pthl-Bs2 as template and Bs2-F and Bs2-R as primers, VBs2 vector (5664 bp) was amplified. Using Clostridium tyrobutyricum (C. tyrobutyricum) genome as template, Pfba gene fragment (300 bp) was amplified with Pfba-F and Pfba-R as primers. Gibson assembly method was used to link the Pfba fragment to the VBs2 linearized vector. Colony PCR (400 bp) was performed on the transformed colonies, using Bs2-PF and Bs2-PR as primers. The positive colonies were transferred and plasmid was extracted. After sequencing verification, the recombinant plasmid was obtained: pMTL-Pfba-Bs2.

Table 1 Primer sequences

(2)Fluorescence intensity

By using E. coli CA434 as a donor strain, pMTL-Pfba-Bs2 plasmid was transferred to C. tyrobutyricum (notated as Pfba). The transfected C. tyrobutyricum was cultured in RCM medium till OD600 reached 0.8 and 1.2, and detected for fluorescence intensity. C. tyrobutyricum transfected with empty vector pMTL82151 was used as blank control (notated as Pcontrol).

Fig. 2 Comparison of fluorescence intensity of C. tyrobutyricum transfected with pMTL-Pfba-Bs2 and that transfected with pMTL82151 empty vector

Our results showed that compared with the blank control (4720.67 and 1474.67), Pfba achieved efficient expression of Bs2 gene with strong fluorescence intensity of 33204.00 and 24397.00 under OD600=0.8 and OD600=1.2.

Contribution of NJTech-China-A 2023 team

(1)Excitation maximum and emission peak

Currently there is limited data on bs2 in the component library.In order to apply this reporter to practical use, we made contributions to supplement its characteristics, including excitation and emission wavelengths, unit fluorescence intensity in facultative anaerobes, and photos under fluorescence microscopy.

In this study, we expressed the BS2 protein with the pET29a plasmid (containing the T7 promoter) (Fig. 1). To expand the application in facultative anaerob, we used the facultative anaerobe Escherichia coli strain BL21 as the expression vector to express the BS2 protein (Fig. 2). After 48 hours of cultivation, BS2 was fully released by sonication, and the excitation wavelength was measured to be approximately 447 nm, while the emission wavelength was approximately 521 nm using an multifunctional microplate detector (Fig. 3).



Fig. 1. Construction maps of plasmids of pET29a-BS2.
Fig. 2.Picture of solid medium under UV and fluorescence microscopic image. E. coli BL21 with pET29a-BS2 on LB solid medium with kanamycin (10μg/ml) and IPTG (0.2 mM), incubated in 37℃ for 24h observed under UV and fluorescence microscopic image taken from the exponential growth phase when OD was ∼0.8.


Fig. 3.Excitation maximum and emission peak (RFU: Relative fluorescence unit). The Ex Wavelength in nm (Em: 520) indicates that there are two peak values of excite wavelength and the stronger one is 447 nm. The Em Wavelength in nm (Ex: 447 nm) shows excluding the impact of one peak value of excite wavelength, the emission wavelength is around 521 nm.

(2)The expression of BS2 protein in the facultative anaerobe

Based on the measured excitation/emission wavelengths, we controlled the cultivation temperature and time to measure the unit fluorescence intensity changes of E. coli BL21 with pET29a-BS2. After entering the logarithmic growth phase (OD600 ~0.5), IPTG was added to induce BS2 gene expression, and the OD600 and fluorescence intensity were measured every 20 minutes. Once in the steady phase, the OD600 and fluorescence intensity were measured every 1 hour. The unit fluorescence intensity of BS2 in E. coli BL21 was determined (Fig 3).




Fig. 4. RFU and RFU/OD600 under the growth curve of E. coli BL21. (A) is incubated at 20℃; (B) is incubated at 30℃. (C) is incubated at 37℃. (A)-(B) indicates that OD600 has the minimal fluctuation at 37℃, however at 30℃ MFI maintained the highest than the other two.

Contribution of NJTech-China-A 2024 team

(1) Excitation maximum and emission peak
To enhance the relative fluorescence unit intensity, we replaced the T7 promoter with the J23119 promoter. J23119 is a prokaryotic constitutive super strong promoter expression vector plasmid, which offers several advantages: Firstly, the J23119 promoter is one of the strongest constitutive promoters reported in its wild-type form, capable of efficiently driving the expression of foreign genes in E. coli. Secondly, the addition of an UP element (designated as UPa) upstream of the core J23119 promoter further enhances expression efficiency, resulting in a 1.34-fold increase in relative fluorescence units (RFU).
Currently, there is limited data available on Bs2 within the component library. To facilitate the practical application of this reporter, we aimed to enhance its characteristics, including excitation and emission wavelengths as well as unit fluorescence intensity in facultative anaerobes.
In this study, we utilized the pET29a plasmid (J23119) (Fig. 1) to express the Bs2 protein. To broaden its application in facultative anaerobic bacteria, we employed the facultative anaerobe E.coli strain BL21 as the expression vector for the Bs2 protein (Fig. 2). After 48 hours of cultivation, the excitation wavelength of the Bs2 protein expressed by the pET29a plasmid (J23119) was found to be approximately 448 nm, while the emission wavelength measured around 509 nm (Fig. 3).

Fig.1 Construction maps of plasmids of pET29a-Bs2(J23119)

Fig.2 Picture of solid mediumE. coli BL21 with pET29a-Bs2(J23119) on LB solid medium with kanamycin (10μg/ml) and IPTG (0.2 mM), incubated in 37℃ for 24h observed under UV and fluorescence microscopic image taken from the exponential growth phase when OD600 was 0.8.


Fig.3.Excitation maximum and emission peak (RFU: Relative fluorescence unit).The Ex Wavelength in nm (Em: 520) indicates that there is one peak values of excite wavelength and it is 448 nm. The Em Wavelength in nm (Ex: 448 nm) shows excluding the impact of three peaks value of excite wavelength, the emission wavelength is around 509 nm.
(2)The expression of Bs2 protein in facultative anaerobic bacteria
Based on the measured excitation and emission wavelengths, we assessed the changes in unit fluorescence intensity of E. coli BL21 transformed with the pET29a-Bs2 plasmid (J23119) by controlling the culture temperature and duration. Once the culture reached the logarithmic growth phase (OD600 ~ 0.5), IPTG was added to induce the expression of the Bs2 gene. Both OD600 and fluorescence intensity were measured every hour during this phase. After entering the stable phase, these measurements were taken every two hours. The unit fluorescence intensity of Bs2 in E. coli BL21 was subsequently determined (Fig. 4).



Fig.4. RFU and RFU/OD600 under the growth curve of E. coli with pET29a-Bs2 plasmid (J23119).The first is incubated at 20℃; The second is incubated at 30℃. The third is incubated at 37℃.Under incubation at 30℃ Celsius,RFU reached their maximum values.Under incubation at 30℃ Celsius,OD600 reached their maximum values.

Contribution of NanjingBioX 2024 team

(1) Overview

BS2 is one of the fluorescent proteins based on flavin mononucleotide (FMN). Currently, there is limited data on BS2 in the parts library. In order to apply it in practice, we have conducted a series of studies. We placed BS2 under the control of promoter Pi23100 and achieved efficient expression of this gene in the parthenogenetic anaerobic bacterium Escherichia coli in BL21 (DE3) in the absence of inducers. The measurement conditions of BS2 were optimized to determine its optimal excitation wavelength of 400 nm and emission wavelength of about 525 nm. Finally, we found that the fluorescent protein expression system performed best at 30 °C.

(2) Experiment Results

1.Plasmid construction

The recombinant plasmid pET29a-BS2, which contains the T7 promoter, was utilized as a template for the experiment. Primers j23100-For-20240719 and j23100-Rev-20240719 were employed to linearize the vector (5721 bp), allowing for a direct one-step cloning process. Subsequently, colony PCR (734 bp) was conducted on the transformed colonies using the primers yanzheng23100-For and yanzheng23100-Rev. Positive colonies were then selected for plasmid extraction. Following sequencing verification, the recombinant plasmid pET29a-Pj23100-BS2 was successfully obtained.

Fig. 1：pET29a-Pj23100-BS2

2.Fluorescence intensity detection

To enhance its application in facultative anaerobic bacteria, we utilized the facultative anaerobic Escherichia coli strain BL21(DE3) as the expression host for BS2 protein. The recombinant plasmid pET29a-Pj23110-BS2 was introduced into the Escherichia coli strain BL21(DE3). The transformed Escherichia coli was cultured in LB medium until the OD600 reached 0.8, 1.0, and 1.2, at which point the fluorescence intensity was measured. Additionally, Escherichia coli BL21(DE3) transformed with the empty pET29a vector served as a control.

Fig.2：Comparison of RFU of Escherichia coli strain BL21(DE)3 harboring recombinant plasmid pET29a-Pj23100-BS2 and pET29a empty vector. RFU: Relative fluorescence unit; J23100: Escherichia coli BL21(DE)3 harboring pET29a-Pj23100-BS2; BL21: Escherichia coli BL21(DE)3 harboring pET29a.

Our results showed that Escherichia coli BL21(DE)3 harboring pET29a-Pj23100-BS2 achieved efficient expression of BS2 gene with higher RFU of 332.53, 596.60 and 669.68 under OD600 of 0.8, 1, and 1.2, respectively compared with the control(261.97, 287.54, 304.34).

3.Exploring the optimal excitation and emission wavelengths for BS2

After 48 hours of incubation, the fluorescence values of the engineered bacteria containing the recombinant plasmid were measured at various excitation and emission wavelengths. The results of the experiment are presented in the figure. Upon analysis, the optimal excitation wavelength was determined to be 400 nm, while the optimal emission wavelength was found to be 525 nm after excluding other emission wavelengths.

Fig. 3：Peak excitation and peak emission (RFU: Relative Fluorescence Unit).

4.Exploring the optimal expression temperature of BS2

Based on the measured excitation and emission wavelengths, we assessed the changes in the unit fluorescence intensity of E. coli BL21(DE3) harboring the plasmid pET29a-Pj23100-BS2 by varying the culture temperature and duration. Once the cells entered the logarithmic growth phase (OD600 ~ 0.5), OD600 and fluorescence intensity were measured every hour. After the cells transitioned to the stationary phase, measurements were taken every two hours. The unit fluorescence intensity of BS2 in E. coli BL21 was then analyzed. The results indicated that the fluctuation of OD600 was minimized at 37°C, whereas at 30°C, the Relative Fluorescence Unit (RFU) remained at its peak value.

Fig. 4：RFU and RFU/OD600 under the growth curve of E. coli BL21(DE)3 harboring PET29a-Pj23100-BS2. (A) is incubated at 20℃; (B) is incubated at 30℃. (C) is incubated at 37℃.

Contribution of Ulink-SZ 2024 team

(1) Overview

Since T7 promoter is a promoter that needs to be induced by IPTG, and IPTG is expensive and contains slightly toxic, we designed a pET-P(BAD)-BS2 plasmid that only needs non-toxic arabinose to induce, and determined whether the pET-P(BAD)-BS2 plasmid could work normally in Escherichia coli by detecting the fluorescence expression intensity of fluorescent protein Bs2.

(2) Experiment Results

1.Plasmid construction

Recombinant plasmid pET29a-Bs2 (containing T7 promoter) was used as template, and Bs2-BAB-For and Bs2-BAB-Rev were used as primers to amplify Bs2 target gene (436bp). And pET-PBAD was used as template to amplified the arabinose-induced promoter. BAB-gj-For and BAB-gj-Rev were primer linearized vectors (5070bp) and linked to target genes by one-step cloning.

Fig. 1：pET-PBad-BS2

2.Fluorescence intensity detection

Our results showed that Escherichia coli BL21(DE)3 harboring pET-PBAD-BS2 achieved efficient expression of Bs2 gene with higher RFU of 428.52, 719.85 and 772.77 under OD600 of 0.8, 1, and 1.2, respectively, compared with the control (251.17, 267.38, 273.85).

Fig.2 Comparison of RFU of Escherichia coli strain BL21 transfected with recombinant plasmid pET-PBAD-Bs2 and that transfected with pET-PBAD empty vector. RFU: Relative fluorescence unit; BS2: Escherichia coli BL21(DE)3 harboring pET-P(BAD)-BS2; BL21: Escherichia coli BL21(DE)3 harboring pET-PBAD.

3.Excitation maximum and emission peak

In order to expand its application in facultative anaerobic bacteria, we used facultative anaerobic Escherichia coli strain BL21(DE)3 as expression cell to express Bs2 protein. After 48 hours of culture, the optimal excitation wavelength and the emission wavelength was detected (Fig.3). The Ex Wavelength in nm (Em: 520) indicates that there is one peak value of excite wavelength and it is 400 nm. The Em Wavelength in nm (Ex: 400 nm) shows excluding the impact of three peaks value of excite wavelength, the emission wavelength is around 525 nm.

Fig. 3 Excitation maximum and emission peak (RFU: Relative fluorescence unit).

4. The expression of Bs2 protein in facultative anaerobic bacteria

According to the measured excitation/emission wavelength, we measured the change of unit fluorescence intensity of E. coli BL21(DE)3 introduced with pET-P(BAD)-BS2 plasmid by controlling the culture temperature and time. After entering the logarithmic growth phase (OD600~0.5), 10 mM arabinose was added to E. coli BL21(DE)3 harboring pET-P(BAD)-BS2 plasmid to induce Bs2 gene expression. OD600 and fluorescence intensity were measured every 1 h, and OD600 and fluorescence intensity were measured every 2 h after entering the stable phase. The unit fluorescence intensity of Bs2 in E. coli BL21(DE)3 was determined (Fig 4). (A)-(C) indicates that OD600 has the minimal fluctuation at 30℃. Besides, at 30℃, RFU maintained the highest than the other two.

Fig. 4 RFU and RFU/OD600 under the growth curve of E. coli harboring pET-P(BAD)-BS2 plasmid. (A) is incubated at 20℃; (B) is incubated at 30℃. (C) is incubated at 37℃.