Eppendorf MixMate – Resuspension of bacteria
pellets in deepwell plates (96- and 384-well)
and micro test tubes
Caroline Osterhoff1, Philip Müller2 and Lars Borrmann1
Eppendorf AG, Hamburg, Germany; 2Eppendorf Instrumente GmbH, Hamburg, Germany
MixMate has been specially developed to mix small volumes in plates (up to 384 wells) and micro test tubes (up
to 2.0 ml). Its application range extends from the mixing of liquid sample material to the resuspension of solid cell
pellets – an important step in molecular biology research (e.g., in the context of nucleic acid isolation and protein
The goal of this work was to examine the performance of MixMate in the resuspension of bacteria pellets in
various plate and tube formats. The experiments show that Eppendorf MixMate can dissolve bacteria pellets in
both 384- and 96-well deepwell plates (DWP), as well as in 1.5 ml and 2.0 ml micro test tubes, in less than 1 min
– without any wetting of the tube lids. The results show that, in general, all experimental preparations could be
entirely resuspended with a single setting (1 min, 2,000 rpm) with MixMate.
As an integral component of methods such as the
isolation of plasmid DNA or recombinant proteins, the
resuspension of bacteria pellets is one of the most
common applications in molecular biology. Complete
dissolving of the pellet is, therefore, an important
prerequisite for obtaining the optimal yield from the
molecules being isolated. However, the resuspension of
pellets has often proved to be laborious and time-
consuming: for example, in some cases tubes must be
individually vortexed, and it is also difficult for some
mixers to dissolve the compact bacteria pellets. Some
mixers cause wetting of the tube lid because of
uncontrolled mixing movements, thus resulting in an
increased risk of contamination. Lastly, many plate mixers
are not even capable of resuspending bacteria pellets in
96- and 384-well plates.
With MixMate, in contrast, its 2DMix-Control technology
and tube holders can quickly mix both 96- and 384-well plates (Fig. 1) as well as micro test tubes (1) – without any
wetting of the lid or risk of cross-contamination (2). To more
precisely examine MixMate’s ability to resuspend bacteria
pellets bacteria cultures were pelleted in both 96- and 384-
well deepwell plates, as well as in both 1.5 ml and 2.0 ml
micro test tubes, and then resuspended in buffer.
Materials and Methods
150 ml of LB medium (Roth, Karlsruhe, Germany) was
inoculated with an E.coli K12 bacteria strain (DH5a) and
cultivated overnight under agitation at 37 °C. In accordance
with the entries given in table 1, the bacteria suspension
was divided among the various plate and tube formats
and then pelleted in either Eppendorf® Centrifuge Model
5417 C (for micro test tubes) or Model 5804 R with
rotor A-2-DWP (for deepwell plates). The centrifugation
parameters (Tab. 1) corresponded to the standard values
described in the literature. After disposing of the
supernatant, resuspension buffer (50 mM Tris-HCl
(pH 8.0), 10 mM EDTA) was added to the bacteria pellets
(100 µl in 1.5 and 2.0 ml micro test tubes; 150 µl for 96-well DWP; 30 µl for 384-well DWP). Deepwell plates
were subsequently inserted directly into MixMate’s
universal holder; the micro test tubes were positioned and
mixed with the help of the 1.5/2.0 ml tube holder. A visual
inspection of the pellet was carried out after 15 s, 30 s,
45 s, 1 min, 2 min and 5 min.
Along with MixMate, Eppendorf Thermomixer comfort
(Thermomixer R in the U.S.) with 1.5 ml, 2.0 ml and MTP
exchangeable thermoblocks as well as a competitor plate
shaker (Competitor A, see also reference 1) were tested.
Unless specified otherwise, the experiments were carried
out at their maximum mixing speeds.
Results and discussion
These experiments show that MixMate resuspends
bacteria pellets quickly – and without any wetting of the
tube lids. The mixing result is independent of the type of
vessel used, and the pellets were dissolved in less than
1 min in 1.5/2.0 ml micro test tubes and 96/384-well
deepwell plates (Tab. 1). Results show that all experimental
preparations could be entirely resuspended with a single
setting (1 min, 2,000 rpm) using Eppendorf MixMate.
When using MixMate’s touch vortex function (3,500 rpm
mixing frequency), pellets could be entirely resuspended in
1.5/2.0 ml micro test tubes in 10–20 s (results not shown),
but there is a risk of lid wetting (and, thus, risk of
contamination). It is important to note, however, that
MixMate’s tube holders enable the simultaneous mixing of
24 tubes, which easily compensates any time advantage
through manual vortexing.
The Eppendorf Thermomixer comfort (Thermomixer R in
the U.S.) also demonstrated excellent suitability for the
resuspension of bacteria pellets in 1.5/2.0 ml micro test
tubes and in 96-well deepwell plates; however, it was
primarily developed for the temperature control of samples
over long incubation times and therefore takes somewhat
longer to completely dissolve pellet. In comparison to
MixMate, this device is not particularly suited for
resuspension in 384-well plates.
- Osterhoff C, Mueller P, Borrmann L. Comparison of mixing performance in 96- and 384-well plates of Eppendorf MixMate and competitor devices. Eppendorf Application Note 130, 2006.
- Osterhoff C, Mueller P, Borrmann L. Eppendorf MixMate – Experimental evidence of controlled mixing, using a PCR-based chessboard assay. Eppendorf Application Note 129, 2006.
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