Part:BBa_K1748010

MtrCAB

This composite part has parts BBa_K1748000 (MtrA), BBa_K1748001 (MtrB) and BBa_K1748003 (MtrC). These have been combined with promoters and ribosomal binding sites for expression of all three genes.

Characterisation of MtrCAB construct

To test the MtrCAB construct we built we ran 6 microbial fuels cells alongside each other to compare electrical output. The setup and composition of the microbial fuel cells can be found in the lab book on the Westminster 2015 lab book. 

The 6 MFC's that we setup contained the following:

1. MtrA

2. MtrC

3. MtrCAB

4. MFe 408 (positive control)

5. MFe 444 (positive control)

6. Negative control

Figure 1: Polarisation curves in order to determine the internal resistance of MFCs for MtrA, MtrC and MtrCAB cytochromes. The positive control-408 had the highest current production, followed by MtrCAB, then positive control-444. MtrA was the least productive of the MFCs measured.

 

Figure 2: The comparison of MFC performance during the lag phase of E.coli growth. As shown 408-positive control and 444-Positive Control gave maximum power density of 98±4mWm-2 and 67±3mWm-2 respectively. MtrCAB modified Top10 E. coli gave 89±2mWm-2; MtrC gave 70±3mWm-2 while MtrA gave 42±3mWm-2. The result of the control produced insignificantly maximum power generation of 0.98mWm-2.

 

Figure 3: The voltage-time profile showed that MFCs utilising the 408-positive control generated the highest voltage at the day 3 under 1000Ω resistor.  Overtime MtrCAB demonstrated that it was almost as effective at electron transfer as the positive control 408 . MtrCAB demonstrated that it was sustainable over time as would be expected for microorganisms in a MFC.

 

Table 1. Comparison of substrate degradation and electron recovery at 8 days of investigation for investigation of recombinant E. coli on electron transfer processes.              

 

                                                  Control    MtrA     MtrC      408     444     MtrCAB                             

          Parameter

COD degradation (%)                30±2       40±3      28±2      33±3    30±2      25±1                                                           

Coulombic efficiency (%)          2±0.4        8±1     14±2      14±1    12±2      17±1          

Table 1 showed the percentage substrate consumed as COD(chemical oxygen demand) with amount of electron recovery on day 8 of the investigation. The MtrA gave the highest COD degradation of 40±3. However, with regard to coulombic efficiency (CE) MtrCAB gave more CE of 17±1 than other tests. 

 

Result and Discussion:

The result showed in Figure 1 explains the performance of MFCS on the relationship of voltage as a function of current.  When no current is produced all the systems had the maximum voltage production because no electron is flowing initially. However, as current is being generated voltage begins to drop and explains the ability of each recombinant systems to maintain voltage production as function of current production. The graph shows that 408-positive control, followed closely by MtrCAB were more efficient than other system on current production. The voltage dropped as the current increased. The differences in the curves reflect the internal resistance of the MFCs which can be calculated from the slopes.

 

The result in Figure 2 shows the power density that can be obtained from the systems. This showed that power production by the recombinants MFCs is a function of their current production. As current production increases, power production increases up to a point that we get the maximum power generation. At this point, which is different across the tests, represents the performance of each of the system on power generation. The maximum point on each curve indicates the maximum power density that can be obtained. The 408-positive control produced the maximum power density ² which is closely followed by MtrCAB , while other recombinant systems produced variable results that were all less than the two systems mentioned. The maximum power increases up to the maximum power density point then the power production begins to drop as current increase. This shows how much each cell tolerates in terms of electricity production.

The result showed percentage of substrate consumed and the fraction of the substrate consumed utilised for electricity production in this case the CE. Hence, little substrate was consumed by MtrCAB and suggested to be more effective on electron transfer than the other recombinant systems. On the other hand, MtrA suggested to be very effective in bioremediation.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  INCOMPATIBLE WITH RFC[12]

  Illegal NheI site found at 29
  
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal NgoMIV site found at 2163
  Illegal NgoMIV site found at 3128
  
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal BsaI site found at 12
  Illegal BsaI.rc site found at 5259