29-04 - 05-05-13

Reproduction of Johnsson et al. Paper

Aim

Reproduction of Johnsson et al. paper: Precipitating gold with D.acidovorans on agar plate, in culture, the medium of the culture and possibly purified delftibactin.

Preparations

• Obtain D. acidovorans from DSMZ
• Prapare ACM medium as described
• Prepare ACM agar plates

Gold Precipitation on ACM Plates

• Culture D. acidovorans for 3 days on agar plates at 30°C
• Overlay agar plates with 0.2% HAuCl₄ in 0.5 % soft agarose

Result

ACM agar plate with D. acidovorans (left) overlaid with 0.2% HAuCl4 in 0.5% agarose

ACM agar plate with D. acidovorans (left) overlaid with 0.2% HAuCl4 in 0.5% agarose

• Gold precipitation on ACM agar plate worked even better than described in paper

Gold Precipitation in D. acidovorans Supernatants

• Culture D. acidovorans for 3 days in ACM plates
• Centrifuge bacteria in liquid culture (10 min 6,000 rpm)
• Add 0.2% HAuCl₄ to supernatant and medium control

Result

D. acidovorans Supernatant (top) and ACM negative control (bottom) with (left to right) 600µl, 400µl, 200µl, 100µl, 50µl, 0µl 0.2% HAuCl4. Far right: top: uncentrifuged solution culture with 600µl 0.2% HAuCl4, bottom: ACM with 600µl HAuCl4

The supernatant/ medium with gold was centrifuged after 2 h reaction time. left to right: supernatant with 600µl 0.2% HAuCl4, ACM with 600µl 0.2% HAuCl4, supernatant with 400µl 0.2% HAuCl4, ACM with 400µl 0.2% HAuCl4, supernatant with 200µl 0.2% HAuCl4, ACM with 200µl 0.2% HAuCl4

• Gold precipitation with D. acidovorans supernatant worked well

Gold Precipitation in D. acidovorans Supernatants at different Gold Chloride Concentrations

• Culture D. acidovorans for 3 days in ACM plates
• Centrifuge bacteria in liquid culture (10 min 6,000 rpm)
• Add HAuCl₄ to supernatant and medium control

Result

Sequences of movie showing gold precipitation in D. acidovorans supernatant using gold concentrations ranging from 0 to 2.55 µg/ml

• Gold precipitation with supernatant worked at very low concentration Gold
• Gold precipitation with unpurified culture worked as well

13-05 - 19-05-13

Gold Recovery from Electronic Waste

As test experiment, pins from an old CPU processor chip were dissolved.

Fig.0 Old motherboard from which we will recycle gold.

Step 1: Pins were mechanically removed and collected in a flask.

Fig.1.1 CPU from which pins will be removed.

Fig.1.2 Removed pins.

Step 2: Flask was put onto heating plate and covered in concentrated HCl.

Fig.2 Pins covered in HCl.

Step 3: HNO₃ was carefully added to the pins and heated.

Fig.3 Evolution NO2 gas.

Step 4: After several minutes of moderate heating, pins dissolved completely. The solution turned green.

Fig.4 Green solution of dissolved pins.

Step 5: The solution was carefully neutralized to pH ~6 in a step-wise manner using first 5 M, later 0.5 M NaOH.
Step 6: This led to precipitation of copper salts, indicated by the milky green coloring.

Fig.6 Milky solution following neutralization.

Step 7: In order to remove the precipitates, the solution was filtered using a buechner funnel and sterile filtrated (0.2 µm).

Fig.7.1 Filtering solution to remove precipitates.

Fig.7.2 Sterile filtering.

Fig.7.3 Filters used for sterile filteration.

Step 8: The final yellow-green gold containing solution was collected in a volumetric flask.

Fig.8Final gold containing solution.

Precipitation of Gold from Electronic Waste

Protocol

In order to evaluate optimial cultivation temperature of D. acidovorans, glycerol stock was streaked on ACM plates and incubated at RT, 30°C and 37°C ON. The next day, plates were covered with 200 µl 0.5% soft agar supplemented with 27 µl "dissolved electronic waste" solution.

Result

D. acidovorans showed intermediate, postponed purple-black coloring upon addition of "dissolved electronic waste" soft agar. Strongest coloring was observed on plates incubated at room temperature and 30°C. Delftibactin expression seems to be significantly decreased in D. acidovorans cultivated at 37°C. Reduced coloring further indicates lower gold ion concentration in the solution recovered compared to th ecommercially availible gold chloride solution [100 g/l]
We could therefore prove capability of D. acidovorans to specifically recover solid gold from dissolved electronic waste.

Fig.9.1 "Dissolved electronic waste" and D. acidovorans.

Fig.9.2 ACM plates prior to addition of gold chloride solution.

Fig.9.3 ACM plates covered with gold chloride solution T= 0:00 h.

Left plate: RT, upper plate: 30°C, lower right plate: 37°C

Fig.9.4 ACM plates covered with gold chloride solution T= 0:30 h.

Fig.9.5 ACM plates covered with gold chloride solution T= 1:00 h.

Fig.9.6 ACM plates covered with gold chloride solution T= 1:30 h.

05-08 - 11-08-13

Melting Gold Nanoparticles to Solid Gold

Step 1: Cultivation of D. acidovorans
200 ml ACM medium were inocculated with recently obtained D. acidovorans SPH-1 from glycerol stock and incubated at 30°C for 3 days.

Step 2: Precipitation of Gold Nanoparticles

• D. acidovorans culture in ACM was divided in 50 ml aliquots and centrifuges at 3,750 rpm for 30 min.
• Supernatant was transferred to fresh tube.
• 300 µl gold chloride stock solution [µg/ml] was added to D. acidovorans supernatant, suspention mixed and incubated at RT for 20 min.

Fig.2.1 Supernatant of D. acidovorans.

Fig.2.2 Precipitated gold nanoparticles in D. acidovorans supernatant.

Step 3: Aggregation of gold nanoparticles.

Fig.3 Gold nanoparticle solution on melting pot.

Step 4: Melting gold nanoparticles to solid gold.

Fig.4.1 Heating aggregated gold nanoparticles in melting pot.	Fig.4.2 Heating aggregated gold nanoparticles in melting pot upside down.	Fig.4.3 Remaining solid gold in melting pot.	Fig.4.3 Sparkling gold appearing in the melting pot.
Fig.4.4 Final recovered solid gold collected in tube.

Alternatively, we also performed the protocol described above in a 2 ml tube.

Fig.5 Solid gold recovered from nanoparticles in 2 ml tube.

09-09 - 15-09-13

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

In order to optimize plates, growth time and incubation temperature of D.acidovorans as well as to evaluate of endogenous capability of possible target strains, various growth conditions and bacteria were tested.

On Agar Plate following 3 Day Incubation at 30°C

• Media was chelex treated, agar added and autoclaved, before plates were poured.
• On agar plates, D.acidovorans, E.coli DH10ß, Bl21 DE3, and BL21 pLys as well as MG1655 and Bacillus subtilus were plated from liquid culture and grown for three days at 30 °C.
• 14.4 ml soft agar (0.5%) was mixed with gold chloride [100 g/l] as follows and 200 µl per quarter plate added:

Result

Gold precipitation on ACM plates incubated for 3 days at 30°C

Fig.1.1 Gold precipitation on ACM plates incubated for 3 days at 30°C: prior to addition of soft agar.	Fig.1.2 Gold precipitation on ACM plates incubated for 3 days at 30°C: T= 0:00.	Fig.1.3 Gold precipitation on ACM plates incubated for 3 days at 30°C: T= 0:20.	Fig.1.4 Gold precipitation on ACM plates incubated for 3 days at 30°C: T= 0:50.
Fig.1.5 Gold precipitation on ACM plates incubated for 3 days at 30°C: T= 1:00.	Fig.1.6 Gold precipitation on ACM plates incubated for 3 days at 30°C: T= 2:00.	Fig.1.7 Gold precipitation on ACM plates incubated for 3 days at 30°C: T= 3:00.

Gold precipitation on LB plates incubated for 3 days at 30°C

Fig.2.1 Gold precipitation on LB plates incubated for 3 days at 30°C: T= 0:00.	Fig.2.2 Gold precipitation on LB plates incubated for 3 days at 30°C: T= 0:10.	Fig.2.3 Gold precipitation on LB plates incubated for 3 days at 30°C: T= 0:20.	Fig.2.4 Gold precipitation on LB plates incubated for 3 days at 30°C: T= 0:50.
Fig.2.5 Gold precipitation on LB plates incubated for 3 days at 30°C: T= 2:00.

Gold precipitation on M9 plates incubated for 3 days at 30°C

Fig.3.1 Gold precipitation on M9 plates incubated for 3 days at 30°C: T= 0:00.	Fig.3.2 Gold precipitation on M9 plates incubated for 3 days at 30°C: T= 0:10.	Fig.3.3 Gold precipitation on M9 plates incubated for 3 days at 30°C: T= 0:20.	Fig.3.4 Gold precipitation on M9 plates incubated for 3 days at 30°C: T= 0:50.
Fig.3.5 Gold precipitation on M9 plates incubated for 3 days at 30°C: T= 2:00.

Unfortunately, the streaked E.coli DH10ß were contaminated (obvious only on LB plates) and can threfore not be analyzed.
On ACM plates following 30°C incubation, D.acidovorans, B.circulans, E.coli BL21 DE3 as well as the negative control next to D.acidovorans, but not the one on plate B, showed immediate purple-black coloring indicating formation of gold nanoparticles at 5 mM gold chloride. At 2.5 mM, D.acidovorans and the neighbouring negative control as well as B.circulans showed some coloring. E.coli BL21 pLys and MG1655 only showed minor coloring at 5 mM. At lower concentrations, no gold precipitation was observed.

=> E.coli BL21 pLys and MG1655 are promissing candidates for expression since they show the least background activity.

=> Optimal gold chloride concentration lies between 2.5 and 5 mM.

=> Delftibactin can diffuse through agar.

On LB plates following 30°C incubation, none of the tested bacteria showed any reaction.

=> LB is not suitable for expression of NRPs.

=> What is missing in LB that does not allow metall precipitating activity?

On M9 plates following 30°C incubation (which were mistakenly autoclaved after addition of glucose), D.acidovorans hardly grew. At 5 mM and 2.5 mM gold chloride, there is heavy background activity on the negative controls. Additionally, B.circulans shows strong - D.acidovorans minor formation of nanoparticles.

=> M9 is not suitable for gold precipitation experiments.

On Agar Plate following 3 Day Incubation at RT

• Media was chelex treated, agar added and autoclaved, before plates were poured.
• On agar plates, D.acidovorans, E.coli DH10ß, Bl21 DE3, and BL21 pLys as well as MG1655 and Bacillus subtilus were plated from liquid culture and grown for three days at RT.
• 14.4 ml soft agar (0.5%) was mixed with gold chloride [100 g/l] as follows and 200 µl per quarter plate added:

Result

Gold precipitation on ACM plates incubated for 3 days at RT

Fig.4.1 Gold precipitation on ACM plates incubated for 3 days at RT: T= 0:00.

Fig.4.2 Gold precipitation on ACM plates incubated for 3 days at RT: T= 0:10.

Fig.4.3 Gold precipitation on ACM plates incubated for 3 days at RT: T= 0:20.

Fig.4.4 Gold precipitation on ACM plates incubated for 3 days at RT: T= 1:00.

Gold precipitation on LB plates incubated for 3 days at RT

Fig.5.1 Gold precipitation on LB plates incubated for 3 days at RT: T= 0:00.

Fig.5.2 Gold precipitation on LB plates incubated for 3 days at RT: T= 0:10.

Fig.5.3 Gold precipitation on LB plates incubated for 3 days at RT: T= 0:20.

Fig.5.4 Gold precipitation on LB plates incubated for 3 days at RT: T= 1:00.

Gold precipitation on M9 plates incubated for 3 days at RT

Fig.6.1 Gold precipitation on M9 plates incubated for 3 days at RT: T= 0:00.

Fig.6.2 Gold precipitation on M9 plates incubated for 3 days at RT: T= 0:10.

Fig.6.3 Gold precipitation on M9 plates incubated for 3 days at RT: T= 0:20.

Fig.6.4 Gold precipitation on M9 plates incubated for 3 days at RT: T= 1:00.

On ACM plates following RT incubation, D.acidovorans and the neighbouring negative control, B.circulans and E.coli MG1655 show minor immediate coloring at 5 mM. At lower concentrations, no activity can be observed.

=> There is less Delftibactin expression in D.acidovorans at lower temperatures.

=> E.coli BL21 pLys remains a promissing candidate for expression since they show the least background activity.

On LB plates following RT incubation, there is again nothing to see.

On M9 plates following RT incubation, there is again high background at negative controls as well as intermediate coloring for D.acidovorans and B.circulans.
We will therefore analyze gold precipitation capacities of supernatants of D.acidovorans, E.coli DH10ß, BL21 DE3, BL21 pLys and MG1655 in ACM liquid medium following 48 and 72 h.

In ACM Medium following 2 Day Incubation at 30°C

• In 5 ml ACM medium, D.acidovorans, E.coli DH10ß, Bl21 DE3, and BL21 pLys as well as MG1655 and pure medium were inocculated and grown for two days at 30°C.
• 1 ml supernatant was mixed with gold chloride [100 g/l] as follows:

Result

Following addition of gold chloride solution, E.coli DH10ß, Bl21 DE3, and BL21 pLys showed rapid purple-black coloring indicating gold nanoparticle formation. They exceed the capacity of D.acidovorans, which showed gold precipitation slightly faster than E.coli MG1655. The ACM did not show any background activity.
We will extend the incubation time of the cultures further to evaluate differences, possibly due to accumulation of Delftibactin in the medium.

Evaluation of Bacteria regarding Background Gold Precipitation in ACM liquid Medium following 2 day Incubation at 30°C

Fig.1.1 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans and 6 µl gold chloride stock solution in lid.	Fig.1.2 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans prior to mixing.	Fig.1.3 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 0:00 s. Particles on to bottom are undissolved gold chloride.	Fig.1.4 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 30 s.
Fig.1.5 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 1:00 min.	Fig.1.6 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 2:00 min.	Fig.1.7 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 3:00 min.	Fig.1.8 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 4:00 min.
Fig.1.9 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 5:00 min.

In ACM Medium following 3 day Incubation at 30°C

• In 5 ml ACM medium, D.acidovorans, E.coli DH10ß, Bl21 DE3, and BL21 pLys as well as MG1655 were inocculated and grown for three days at 30°C.
• 1 ml supernatant was mixed with gold chloride [100 g/l] as follows:

Result

Again, E. coli DH10ß, Bl21 DE3, and BL21 pLys showed rapid purple-black coloring exceeding the capacity of D.acidovorans and E. coli MG1655. These results are highly inconclusive and the experiment has to be repeated.

Evaluation of Bacteria regarding Background Gold Precipitation in ACM liquid Medium following 3 day Incubation at 30°C

Fig.1.1 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans and 6 µl gold chloride stock solution in lid.	Fig.1.2 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans prior to mixing.	Fig.1.3 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 0:00 min. Particles on to bottom are undissolved gold chloride.	Fig.1.4 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 1:00 min.
Fig.1.5 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 2:00 min.	Fig.1.6 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 5:00 min.	Fig.1.7 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 6:00 min.	Fig.1.8 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 7:00 min.
Fig.1.9 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 10:00 min.	Fig.1.10 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 13:00 min.	Fig.1.11 From left: 1 ml ACM medium, supernatants of E.coli DH10ß, MG1655, Bl21 pLys and BL21 DE3 as well as D.acidovorans: T= 15:00 min.

Purification of Delftibactin

Purification

• Grew 1 L of D. acidovorans SPH1 for 24h in ACM media at 30°C. (2x 500 mL ACM 15 mL about 3 days old D. acidovorans culture in ACM)
• Centrifugation of culture at 3750 rpm for 30 min
• Retrieved supernatant
• Added 20 g/L HP-20
• Stirred at RT for 2 h
• Filtration with Buchner funnel to retain HP-20
• Washed with 400 ml dddH₂O
• Elution with 400 ml Methanol
• Evaporated methanol with rotary evaporator
• Resuspended in 2 ml 50 methanol : 50 ddH₂O

Testing Purified Delftibactin

Different intermediate products were tested for their ability to precipitate gold. For this, 3 µl of AuCl₃ (100g/l) were added to 500 µl solution. The outcome is presented in the following table.