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From 2013.igem.org

Contents 1 02-09 - 08-09-13 1.1 Optimizing Growth Conditions of D.acidovorans and Evaluation of Endogenous Background Gold Precipitation 1.1.1 On Agar Plate following ON Incubation at 30°C 1.1.2 Result

02-09 - 08-09-13

Optimizing Growth Conditions of D.acidovorans and Evaluation of Endogenous Background Gold Precipitation

In order to optimize plates for cultivation of D.acidovorans as well as to evaluate of endogenous capability of possible target strains, capability of D.acidovorans and E. coli DH10ß and BL21 DE3 grown on LB and ACM plates was tested.

On Agar Plate following ON Incubation at 30°C

• On agar plates, D.acidovorans, E.coli DH10ß, and Bl21 were plated from liquid culture and grown ON at 30 °C.
• The following day, 1.6 ml soft agar (0.5%) was mixed with goldchloride [100 g/l] as follows:

Final goldchloride concentration [mM]	Volume goldchloride stock [µl]
5	27
10	54.4
20	108.8

Agar plate	Goldchloride [mM]	H2O	D.acidovorans	DH10ß	BL21 DE3
ACM	0	no reaction	no reaction	no reaction	no reaction
ACM	5	postponed weak coloring ON	weak coloring after 2 min	weak coloring after 2 min	weak coloring after 2 min
ACM	10	postponed dark coloring ON	strong coloring after 2 min	strong coloring after 2 min	strong coloring after 2 min
ACM	20	postponed dark coloring ON	strong coloring after 2 min	strong coloring after 2 min	strong coloring after 2 min
LB	0	no reaction	no reaction	no reaction	no reaction
LB	5	no reaction	no reaction	no reaction	no reaction
LB	10	no reaction	no reaction	no reaction	no reaction
LB	20	no reaction	no reaction	no reaction	no reaction

Result

Evaluation of Bacteria regarding Background Gold Precipitation on Agar Plate following ON Incubation at 30°C

ACM plate before incubation with gold chloride containing soft agar.

ACM plate after incubation with gold chloride containing soft agar counter-clockwise beginning from top left in concentrations of 0 mM, 5 mM, 10 mM, 20 mM.

All bacteria showed strong and immediate purple-black coloring indicating gold precipitation depending on gold chloride concentration. Regarding the precipitation of gold, there does not seem to be a significant advantage of D.acidivorans. In contrast to the paper from Johnston et al., we only grew them ON at 30°C rather than for 3 days. We will repeat the experiment using 3 day incubation time and also evaluate gold precipitation on additional media as well as by additional bacteria.