Worm Breeder's Gazette 11(5): 69

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.

Social Behavior in bor-1 Mutants Depends on Bacterial Smell

M. Wayne Davis and Leon Avery

Figure 1

bor-1 was first defined by Randy Cassada (1987 worm meeting: 162) as 
a gene controlling bordering behavior in the wild strain RC301.  
Subsequently we induced two alleles in N2 by EMS mutagenesis.  bor-1 
worms crawl almost exclusively along the border of a lawn of bacteria. 
In addition, they clump together in congregations of 10 to 50 or more.
Many wild isolates show these behaviors, suggesting that in some 
environments this behavior has a selective advantage.
The effect of different shapes of bacterial lawns on the bordering 
behavior gives some evidence of the cause of the effect.  On a ring of 
bacteria the worms clump on the outer border, and on a Z shape they 
clump at the vertices.  This indicates a long range (>1cm) effect to 
which bor-1 worms respond.
To determine if the bor-1 phenotypes require the amphid channel 
cilia, an osm-3; utant was constructed.  osm-
3 is required for normal structure and function of the channel cilia (
Dev Biol 117: 456), which in turn are required for many responses to 
nonvolatile chemicals (e.g.  chemotaxis, WBG 10(2): 42).  The double 
mutant showed an actual increase in clumping, and no noticeable change 
in bordering behavior.  The channel cilia are therefore not required 
for clumping or bordering, suggesting the behaviors aren't mediated by 
non-volatile chemicals.
These results suggested bor-1 worms might be responding to volatile 
chemicals, perhaps the smell of the bacteria.  Indeed, when bor-1 
worms were grown on streptomycin-killed E.  coli, they no longer 
clumped (see figure).  Even more striking, when bor-1 worms on killed 
bacteria were exposed to the smell of live bacteria (which were placed 
in the lid of the petri plate), clumping was restored.  None of these 
treatments make wild-type worms clump.
These results implicate the smell of the bacteria in the bordering 
and clumping behavior.  The distribution of worms on different shapes 
of lawns is consistent with the worms seeking the lowest concentration 
of odor while remaining in the lawn.  The clumping is consistent with 
this mechanism if the odor is lower near another worm and even lower 
near a clump of worms (perhaps because the worms destroy the smell).  
Further experiments are needed to determine the chemistry, neural 
circuitry, and molecular basis of this effect.
[See Figure 1]

Figure 1