Worm Breeder's Gazette 11(1): 64

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Notes on Galvanotaxis

Bob Klein, Stuart Kim and Barbara Meyer

As a joke, Stuart and I decided to put worms in an electric field.  
We did this by placing worms on an agarose mini-gel (0.3% in 1X M9 
salts) with the running buffer just touching the sides of the gel.  
Interestingly, when we turned the power on, the worms rapidly moved 
toward the cathode.  As a result of these observations, we have been 
following up this behavior in order to determine if it can tell us 
anything about worm biology.
Galvanotaxis shows two distinct phases.  The first occurs at 
relatively low voltage (~0.07 V/mm in M9 salts) and consists of 
animals moving somewhat haphazardly toward the cathode in a manner 
similar to that seen in chemotaxis assays.  As the voltage increases, 
the response gets stronger until a new type of behavior is seen.  At 
approximately 0.4 V/mm (in M9 salts) the worms move toward the cathode 
in a much more directed manner.  They very quickly decide on the 
direction in which they are going and, once decided, rarely stop or 
change directions.  Although the worms move in a straight line at the 
higher voltage, they do not move directly toward the cathode.  Rather, 
worms initially placed in a single spot will move out of that spot in 
two streams, each of which makes an approximately 45  angle with a 
line between the initial spot and the cathode.  An animal traveling 
along one of these angles will generally (but not always) have its 
ventral side closer to the cathode.  Occasionally a worm will flip 
onto its other side causing it to change its angle of movement such 
that it now moves at an angle that is flipped relative to its starting 
angle (i.e.  it makes a V-shaped pattern).  The exact angle that a 
group of worms adopts is somewhat variable and appears to depend on 
the agarose concentration.
Adult and L4 hermaphrodites as well as males show the strongest 
response.  However, male worms tend to get distracted and make slower 
progress toward the cathode.  L3 and L2 hermaphrodites show weaker 
responses in that younger animals spend a greater proportion of their 
time moving in a direction other than toward the cathode.  L1 animals 
show little if any response to an electric field.  Finally, dauer 
larvae tend to galvanotax fairly strongly over short periods of time.  
However, they often can be seen going in a direction other than toward 
the cathode.
In order to determine if galvanotaxis might be a tractable genetic 
behavior, we have checked (and are continuing to check) existing 
mutations for the ability to galvanotax.  These include a large number 
of unc, daf, che, lin, mec, and osm mutations.  To date only three 
mutations appear to be defective (to varying extents) in galvanotaxis; 
lin-32(u282), 33), and n1754, a mutation isolated 
by L.  Bloom as defective in thermal avoidance and also found to be 
chemotaxis deficient.  All three of these mutations are quite 
pleiotropic in their defects and clearly are not specific for 
One possible explanation for this behavior could be that the worms 
are responding to a heat or salt gradient set up over time by the 
electric field.  We do not believe this to be true for two reasons: (1)
the response starts as soon as the power is turned on and stops 
immediately after the power is turned off, and (2) two mutations, 
n1937 and n1938, isolated by C.  Bargmann as being completely 
chemotaxis deficient, are wild type for galvanotaxis.  Therefore, it 
is likely that at least some components of galvanotaxis are distinct 
from chemotaxis.
In order to find mutations that are specific for galvanotaxis, we 
have begun a mutant screen for animals that do not respond to an 
electric field.  To date we have screened approximately 3000 haploid 
genomes without finding any galvanotaxis mutations.  In order to try 
to increase the number of worms we can screen as well as make the 
assay easier to set up, we have adapted the assay to 9 cm tissue 
culture plates.