2.4. Production of a basic cell lysate
Using the reporter assays as indicators, a basic method for lysate
production comprising only the most necessary processing steps
was established (experiments 1e3, Fig. 1). This method was
modified (Table A.1) to test the influence of single experimental
parameters on enzymatic activities, which were assessed using the
target analyte assay.
Ultrasonication (physical disruption) was applied as a standard
method for the disruption of microbial cells from activated sludge.
Cell lysiswas performed with a sonication microtip (Bandelin MS73
connected to ultrasonic transducer HD3100) at 10 mm immersion
depth in 50 mL tubes filled with 25 mL of concentrated sludge
(~19 gTSS L1 in HN-buffer). Sonicationwas applied to the ice cooled
samples with a power density of 1 W/mL for 10 min (net) in intervals
of 15 s with 15 s breaks to avoid sample heating.
Cell debris was removed by centrifugation for 20 min at
14,000 rpm, 4 C (Sigma 3K30, rotor 19776-H) and the supernatant,
i.e. the crude cell lysate, was then filtered through 0.2 mm syringe
filters (Whatman 25 mm GD/X polyethersulfone (PES) membrane
with glass microfiber prefilter) to remove residual cells or cell
debris. The resulting cell-free lysate (in HN-buffer) was kept on ice
at all times and analyzed the same day.