Team:TU Delft/Project/alkane-degradation/results/alkane hydroxylase


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(New page: ===Characterization of the alkane hydroxylase system=== ====Growth analysis==== We attempted to culture our recombinant AH-carrying ''E.coli'' K12 strains ([
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===Characterization of the alkane hydroxylase system===
===Characterization of the alkane hydroxylase system===
====Growth analysis====
====Growth analysis====

Revision as of 19:55, 27 October 2010

Characterization of the alkane hydroxylase system

Growth analysis

We attempted to culture our recombinant AH-carrying E.coli K12 strains (BBa_K398014) on 1% v/v octanol or 1% v/v dodecane. Negligible growth was observed.

Resting-cell assays

The resting cell assays were performed on our recombinant AH-carrying E.coli K12 cells (BBa_K398014). 100 micromoles of octane was added to 6 mL of growth-stalled cells (1.5 mg cell dry weight total) and incubated at 37 degrees with shaking o/n. The organic phase was extracted using EtOAc and analysed by gas chromatography.

The following are examples of typical chromatographs obtained:

Chromatograph of blank containing octane.
Chromatograph of the negative control for the resting cell assay of the alkane hydroxylase system. The negative control consisted of E.coli K12 carrying BBa_J13002 in pSB1A2.
Chromatograph of E.coli K12 strain carrying the AH system.

The peaks shown in the chromatographs belong to the following compounds:

Retention time [min] Compound
~2.2 Ethyl acetate (solvent)
~5.2 Octane (substrate)
~11.8 Undecane (internal standard, 0.1% v/v of solvent)

The surface areas of the peaks correspond to the amount of molecules present in the sample. Due to the fact that many factors play a role in establishing an equilibrium between the aqueous and organic phase once the EtOAC is added, it's general procedure to add an internal standard to the EtOAc. In our experiment we decided to use a 0.1% vol/vol of undecane in EtOAc. The ratio between the surface areas of octane and undecane can now give an indication of the amount of octane still present in the sample and be very useful for comparisons between chromatographs.

The following table contains the average ratio of the hexadecane/undecane surface areas. Strains numbers 1 and 2 are two positive colonies taken from the same plate.

Strain Ratio octane/undecane Standard deviation [%] Octane converted [umol] Protein [mg] Enzymatic activity [U/mg protein]
Blank 0.832 6.16 0.00 0.00 0.00
E.coli K12 negative control 0.821 13.3 1.34 1.51 1.23E-3
E.coli K12 strain #1 (AH-system) 0.652 14.4 21.6 1.70 1.77E-2
E.coli K12 strain #2 (AH-system) 0.439 3.96 47.0 1.46 4.49E-2

From the ratios we may conclude that the samples obtained from the E.coli strain, carrying the AH system, contain relatively less octane than the control strain. Using a two-point calibration method, where we set the ratio of 0.898 equal to the total amount of octane added (16.2 uL, 99.7 umol), we can estimate the enzymatic activity of the AH-system. We know the reaction time (12 h.) and the mg of protein for each sample (using the conversion factor 0.41g/L/OD). See the table below for details.


We've succeeded in characterizing the activity of the alkane hydroxylase system using gas chromatography. By comparing peak ratios we were able to estimate the specific enzymatic activity of the system. The lack of an octanol peak in the GC-graphs above could be caused by the octanol being trapped by the cell, and thus not showing up in the organic (EtOAc) phase. Another likely explanation is that the octanol is readily converted by an aspecific alcohol dehydrogenase native to the E.coli K12 strain. In the future we would like to perform a resting-cell assay using P. putida and determine the enzymatic activity needed to support growth. A comparison of this natural-degrader value with the biological activity we've found of 0.045 U/mg would give more information on the growth feasibility of a strain carring the AH-system BioBrick on octane. Furthermore, a study could be done on the AH-system over time to find out more information on the kinetics of the system.