Phenyllactic acid

    Phenylllisted acid (PLA)[1], also known as 3-phenyllactic acid or β-PLA, whose system called 2-hydroxy-3-phenylpropanoic acid. Phenyllactic acid (PLA) is widely found in cheese, honey and other foods, and it is not toxic for human and animal cells [2]. And it is a very stable and important natural small molecule organic acid, whose molecular formula is C9H10O3[2].
    There are two isomers of phenyllactic acid is D- phenyllactic acid(D-PLA) and L- phenyllactic acid(L-PLA), while D- phenyllactic acid (D-PLA) has higher antibacterial activity.

Fig.1 Chemical structure of PLA

Fig.2 Natural growth of Staphylococcus epidermidis with an initial OD=1

Application

    PLA has high safety and is non-toxic for human and animal cells. As a new natural antibacterial substance and preservative, it can inhibit a series of gram-negative, gram-positive bacteria and fungi.
And as a clinical hemostatic drug, PLA can be used to prevent platelet aggregation and coronary artery expansion. In addition, phenyllactic acid can also be used as a skin protectant to prevent dry skin.

Methods

  We followed this protocol to do the Interlab Study.
  When we completed three of the calibration measurements, performing the cell measurements. Used the same plates, volumes and settings that we used in calibration protocol. We transformed E.coli DH5α competent cells with the 8 plasmids and picked 2 colonies from each of plates into 5 mL LB medium + Chloramphenicol. After culturing the cells overnight at 37°C and 220 rpm, we used plate reader to measure the Abs600 and fluorescence of samples at 0, 6 hours.

Result

Calibration
Calibration 1: OD600 reference point

Calibration 2: Particle Standard Curve

Cell measurement

Analyse

  A standard curve in a linear relationship can be obtained by calibration experiments.
By comparing and analyzing the fluorescence values and Absorbance value of the different test devices at 0 and 6 hours, we can draw the following conclusions: the negative control and the positive control showed significant differences in the 6h fluorescence measurement results. Among the six different test equipment, Device 4 has the strongest fluorescence, while Device 3 has the lowest fluorescence. Compared with the relation between absorbance and fluorescence value, we can't get the relationship, and we need to improve on the control variables during the experiment.

Discussion

    During the experiment, we encountered two problems.
  1. In the cell measurement experiment, we need to dilute the cultures further to a target Abs600 of 0.02, but there are errors with in the actual operation, can not be accurately diluted to 0.02. So we hope that the protocol can provide acceptable error range.
  2. In the second calibration, the particle standard curve log graph is not a straight line. We guess that it is due to pipetting error or the time to add the sample is too long.

Reference

1.Beal J, Haddock-Angelli T, Gershater M, de Mora K, Lizarazo M, Hollenhorst J, et al. (2016) Reproducibility of Fluorescent Expression from Engineered Biological Constructs in E. coli. PLoS ONE 11(3): e0150182.
2.https://2018.igem.org/Measurement/InterLab
3.http://parts.igem.org/Part:BBa_J61002