Team:Bielefeld-Germany/Results/halo

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Laccase Lbh1 from Bacillus halodurans C-125

Summary

First some trials of shaking flask cultivations were made with various parameters to identify the best conditions for production of the His tagged laccase Lbh1 from Bacillus halodurans C-125 named BHAL. Due to inactivity of the enzyme in the cell lysate a purification method was established (using Ni-NTA-Histag resin). BHAL could not be detected by SDS-PAGE (theoretical molecular weight of 56 kDa) or activity test by using the BioBrick <partinfo>BBa_K863020</partinfo> and E. coli KRX as expression system. Due to this results the new BioBrick <partinfo>BBa_K863022</partinfo> was constructed and expressed E. coli Rossetta-Gami 2. With this expression system the laccase could be produced and analysed via SDS-PAGE. A small scale Ni-NTA-column was used to purify the laccase. The fractionated samples were tested regarding their activity with ABTS and showed ability in oxidizing ABTS. A scale up to 12 L with a optimized medium (HSG) and a labscale Ni-NTA-Purification were implemented to enable additional experiments to characterize BHAL.


Contents


Cultivation, Purification and SDS-PAGE

Cultivation

The first trials to produce the Lbh1 - laccase from Bacillus halodurans (named BHAL) were performed in shaking flasks with various flask designs (from 100 mL-1 to 1 L flasks, with and without baffles) and under several conditions. The varied parameters in our screening experiments were temperature (27 °C,30 °C and 37 °C), concentration of chloramphenicol (20-170 µg mL-1), induction strategy (autoinduction and manual induction with 0,1 % rhamnose) and cultivation time (6 to 24 h). Furthermore we cultivated with and without 0.25 mM CuCl2 to provide a sufficient amount of copper, which is needed for the active center of the laccase. E.coli KRX was not able to produce active BHAL under the tested conditions, therefore another chassis was chosen. For further cultivations E. coli Rosetta-Gami 2 was transformed with BBa_K863012, because of its ability to translate rare codons. BHAL was produced under the following conditions:

  • flask design: shaking flask without baffles
  • medium: LB-Medium
  • antibiotics: 60 µg mL-1 chloramphenicol and 300 µg mL-1 ampicillin
  • temperature: 37 °C
  • cultivation time: 24 h


Purification

The cells were harvested and resuspended in Ni-NTA-equilibration buffer, mechanically lysed by sonification and centrifuged. After preparing the cell paste the BHALlaccase could not be purified with the 15 mL column, because of the column was not available. For this reason a small scale purification (6 mL) of the supernatant of the lysate was performed with a 1 mL Ni-NTA-column. The elution was collected in 1 mL fractions.

SDS-PAGE

Figure 1:SDS-PAGE of purified lysate derived from a flask cultivation of E. coli Rosetta-Gami 2 carrying <partinfo>BBa_K863022</partinfo>. Lanes 2 to 7 show the flow-through, the wash and the elution fractions 1 to 4. BHAL has a molecular weight of 56 kDa and is marked with an arrow.

In figure 1 the different fractions of the purified cell lysate of E. coli Rosetta-Gami 2 with <partinfo>BBa_K863022</partinfo> are shown in a SDS-PAGE. BHAL has a molecular weight of 56 kDa. In lane 5, which corresponds to the elution fraction 2, a faint band of 56 kDa is visible. Therefore the fractions were further analysed by activity test and MALDI-TOF.


Since Regionals: 12L Fermentation of E. coli Rosetta-Gami 2 with <partinfo>BBa_K863022</partinfo>

Figure 2: Fermentation of E. coli Rosetta-Gami 2 with <partinfo>BBa_K863022</partinfo> (TTHL) in a Bioengineering NFL22. Conditions: 12 L of HSG autoinduction medium + 60 µg mL -1 chloramphenicol at 37 °C, pH 7. Agitation increased when pO2 was below 50 % and OD600 was measured each hour.

After the measurement of BHAL activity we made a scale-up and fermented E. coli Rosetta-Gami 2 with <partinfo>BBa_K863022</partinfo> in a Bioengineering NFL 22 fermenter with a total volume of 12 L. Agitation speed, pO2 and OD600 were determined as well as the glycerin concentration. The data were illustrated in Figure 2. This time HSG autodinduction medium was used to produce more biomass. Due to the change of media and to a low amount of cells for inocculation we got a long lag phase of nearly 10 hours. During this phase the glycerin concentration is approximately constant. The following cell growth caused a decrease of glycerin concentration and of pO2. After 11 hours the value fell below 50 %, so that the agitation speed increased automatically. After 21 hours the deceleration phase started and therefore the agitation speed was decreased. The maximal OD600 of 9.9 was reached after 22 hours, when the cells were entering the stationary phase. The glycerin is completely consumed. The cells were harvested at this time. It might have been better to cultivate a few hours longer.


Since Regionals: Purification of BHAL

The harvested cells were resuspended in Ni-NTA- equilibration buffer and mechanically disrupted by homogenization. The cell debris were removed by centrifugation and microfiltration via Millipore Pellicon XL 50. The supernatant of the cell lysate was concentrated with Millipore Pellicon XL 50 with 10 kDa and loaded on the Ni-NTA column (15 mL Ni-NTA resin) with a flow rate of 1 mL min-1 cm-2. Then the column was washed with 10 column volumes (CV) Ni-NTA equilibration buffer. The bound proteins were eluted by an increasing Ni-NTA elution buffer step elution from 5 % (equates to 25 mM imidazol) with a length of 80 mL, to 50 % (equates to 250 mM imidazol) with a length of 80 mL and finally to 100 % (equates to 500 mM imidazol) with a length of 90 mL. This strategy was chosen to improve the purification caused by a step by step increasing Ni-NTA-elution buffer concentration. The elution was collected in 10 mL fractions. In figure 3 only the UV-detection signal of the wash step and the elution are shown, this is because of the high UV-detection signal of the loaded samples and to simplify the illustration of the detected product peak. A typical chromatogram of purified laccases is illustrated here. The chromatogram of the BHAL elution is shown in Figure 5:

Figure 3: Chromatogram of wash and elution fractions from FLPC Ni-NTA His-tag Purification of BHAL produced by 12 L fermentation of E. coli Rosetta Gami 2 with <partinfo>BBa_K863022</partinfo>. TTHL was eluted by a concentration of 50 % (equates to 250 mM imidazol) with a maximal UV-detection signal of 123 mAU.

The chromatogram shows two distinguished peaks. The first peak was detected at a Ni-NTA-equilibration buffer concentration of 5 % (equates to 25 mM imidazol) and resulted from the elution of weakly bound proteins. Contrary to our expectations, the chromatogram shows the second distinguished peak. This peak was detected at a Ni-NTA-equilibration buffer concentration of 100 % (equates to 500 mM imidazol) and resulted from the elution of bound protein. Earlier measurements of other bacterial laccases showed that the elution of these laccases begins with a elution buffer concentration of 50 %(equates to 250 mM imidazol). One explanation of this result could be a low concentration of the produced TTHL. Consequently all elution fractions were analyzed by SDS-PAGE to detect TTHL. In the chromatogram no further peaks were detected. The following increasing UV detection signal by increasing concentration of the eltutionbuffer results from the rising imidazol concentration of the Ni-NTA elution buffer. The corresponding SDS-PAGES are shown in Figure 4.


Activity Analysis of BHAL

Initial activity tests of purified fractions

The resulting fractions of the cultivation and purification of BHAL (fraction 1 to 5) were analysed with activity tests. After rebuffering into deionized H2O and incubation with 0.4 mM CuCl2 for 2 hours, the samples were measured with 140 µL sample, 0.1 mM ABTS, 100 mM sodium acetate buffer to a final volume of 200 µL. The change in optical density was measured at 420 nm, reporting the oxidation of ABTS for 5 hours at 25°C. An increase in ABTSox can be seen (Figure 4), indicating produced BHAL laccase in each fraction. Fraction 2 shows the highest amount of ABTSox (55%) reaching saturation after 3 hours. Similar to BPUL laccase, BHAL is capable to reach saturation after 3 hours with approximately oxidizing 55% of the supplied ABTS. Therefore BHAL is going to be characterized further.

Figure 4: Activity test of BHAL fractions after purification. Reaction setup includes 140 µL fraction sample (CuCl2 incubated), 0.1 mM ABTS and 100 mM sodium actetate buffer (pH 5) to a final volume of 200 µL. Measurements were done at 25°C and over a time period of 5 hours. Each fraction shows activity, especially fraction 2, which therefore contains most BHAL laccase. (n=4)


To determine the substrate saturation with ABTS as a substrate, different concentrations of ABTS were used for activity measurements. 616 ng of BHAL laccase were used for measurements in Britton-Robinson buffer (pH 5) and ABTS concentrations ranging from 0.1 mM to 5 mM ABTS, 308 ng of BHAL laccase for measurements ranging from 5 mM to 8 mM.

Since Regionals: Initial activity tests of purified fractions

Different fractions of the purification of a new cultivation since the Regional Jamborees in Amsterdam were tested regarding their activity of the produced BHAL enzyme. Before re-buffering, the protein concentration was determined and again after re-buffering. The initial activity tests were done in Britton-Robinson buffer (pH 5) with 0.1 mM ABTS at 25 °C. The protein amount was adjusted in each sample for comparison. One distinct fraction showed the highest activity: fraction 5% 3 (Fig. 5). The contained laccase amount was calculated by assuming, that the most active fraction contains 90 % laccase. This leads to a BHAL laccase concentration 10,9 ng mL-1.

Figure 5: Activity assay of each purified fraction of the new cultivation with BHAL. Samples were re-buffered into H2O and the protein amount in each fraction has been adjusted. The measurements were done using the standard activity assay protocol over night. The first number indicates the percentage of used elution buffer, whereas the second number stands for the fraction number of this elution.

Since Regionals: BHAL pH optimum

Figure 6: Microtiter plate of the measurements for pH optimum determination. The more intensive the blue color the more ABTS got oxidized. At pH 4 and pH 5 the darkest colour has been reached.

To determine the optimal experimental setup for BHAL activity measurements the best pH has to be determined. Using Britton-Robinson buffer pHs between pH 4 and pH 9 had been adjusted. 308 ng BHAL laccase per well had been tested under these pH conditions using 7 mM ABTS. The CuCl2 incubated and therefor activated BHAL laccases showed a high activity at pH 4 and pH 5, where most of ABTS has been oxidized (compare to Fig. 6 and 7). The calculated specific enzyme activity of BHAL shows the high activity at both mentioned pHs (Fig. 8). While BHAL has an activity of ~8 U mg-1 at pH 4 and pH 5, the enzyme activity decreases at higher pHs. At a pH of 6 only 1/3 of enzyme activity can be detected compared to the activity at pH 4 and pH 5. While still active at pH 7, the BHAL laccase is not as suitable as thought for an application at a waste water treatment plant because of its high activity in acidic environments.

Figure 7: Oxidzed ABTS by BHAL laccases at different pH adjustments. The experimental setup included CuCl2 incubated BHAL laccase (308 ng), Britton Robinson buffer adjusted to the tested pHs and 5 mM ABTS. Measurements were done at 25 °C for 30 minutes. The most amount of oxidzed ABTS can be detected at pH 4 and pH 5.
Figure 8: Calculated specific enzyme activity of BHAL at different pH conditions. The highest specific enzyme activity for ABTS is under pH 4 and pH 5 conditions. The higher the pH, the less ABTS gets oxidzed.


Since Regionals: BHAL activity at different temperatures

Figure 9: Standard activity test for BHAL measured at 10°C and 25°C resulting in a decreased activity at 10°C. As a negative control the impact of 0.4 mM CuCl2 in oxidizing ABTS at 10°C and 25°C were analyzed.
Figure 10: Deriving from the obtained values of oxidized ABTS in time at 10°C and 25°C the specific enzyme activity was calculated. For the temperatures a difference of 3 U/mg could be detected.

To investigate the activity of BHAL at temperatures that will apply at a waste water treatment plant throughout the year, activity tests as described above were performed at 10°C and 25°C. The measurements were conducted for 30 minutes. The obtained results reveal a lower activity of BHAL at 10°C in comparison to 25°C (see Fig. 9). The obtained results were used to calculate the specific enzyme activity which was at 4.2 and 7.2 U/mg, respectively (see Figure 10). The negative control without BHAL laccase but 0.4 mM CuCl2 at 10°C and 25°C show a negligible oxidation of ABTS. The activity of BHAL is increased to about 60% at 10°C but never the less the observed activity at both conditions is great news for the possible application in waste water treatment plants.



Since Regionals: BHAL activity depending on different ABTS concentrations

To be able to calculate the activity in Units mg-1, measurments have to be dne under substrate saturation. This allows the comparison of Units mg-1 with other laccase activities and the literature. For this purpose ABTS concentrations ranging from 0.1 mM to 8 mM were applied in an experimental setup contain Britton-Robinson buffer (pH) and tmeperature conditions of 25 °C. For measurements with 0.1 mM to 5 mM ABTS 616 ng BHAL laccase were used (Fig. 11). Measurements with 5 mM to 8 mM ABTS only 308 ng BHAL laccase were applied (Fig. 12). Applying less then 7 mM ABTS a static increase in oxidized ABTS is given. Measurements with 8 mM ABTS show a slower increase in oxidized ABTS as with 7 mM ABTS (Fig. 12). This may be due to a substrate toxication. The most compromising ABTS concentration is 7 mM with the highest increase in oxidized ABTS. Therefor a substrate saturation is reached with 7 mM ABTS.

Figure 11: Activity assay to determine the substrate saturation with ABTS as a substrate. Measurements were done with 616 ng BHAL laccase in Britton-Robinson buffer (pH 5) at 25 °C. ABTS concentrations ranged from 0.1 mM to 5 mM.
Figure 12: Activity assay to determine the substrate saturation with ABTS as a substrate. Measurements were done with 308 ng BHAL laccase in Britton-Robinson buffer (pH 5) at 25 °C. ABTS concentrations ranged from 5 mM to 8 mM. An ABTS concentration of 7 mM was determined as substrate saturated.


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