Chemoreception in Caenorhabditis elegans

Bacteria and bacterial metabolites stimulate feeding, defecation, egg laying. A pheromone regulates entry into the dauer stage (sounds a little like quorum-sensing in bacteria). Other pheromones mediate mating. Chemotaxis is and important behavior in enabling nematodes to locate food sources.

Nematodes are exposed to liquid and airborne chemicals at the air-water interface in soil. Water soluble attractants are detected by Caenorhabditis elegans at Ámolar concs, volatile molecules at picomolar levels. Water-soluble signals may be used for short-range chemotaxis and volatiles for longer-range detection of food (important concept, I think**). Many attractants are metobolic products of bacteria.

C. elegans can discriminate between related chemicals. At least five classes of water-soluble attractants and seven classes of volatile attractants have been defined. Different classes of molecules are probably recognized by different receptor proteins.

Repellants include specific water-soluble molecules, acids, high osmotic compounds. All are toxic and cause paralysis or death. Other toxic chemicals are not avoided by the nematode.

Attractants

Water-soluble

Volatile

Na+, K+, Li+, Ca++, Mg++

alcohols

Cl-, SO4-, NO3-, Br-, I-

ketones

aAMP, cGMP

diketones

Biotin

esters

Lysine, histidine, cysteine, serotonin

pyrazines

Basic pH

thiazoles

 

aldehydes

 

aromatics

 

ethers

   

Repellants

Water-soluble

Volatile

High osmotic strength

heptanol, octanol, nonanol

Acid pH

nonanone

Cu ions

benzaldehyde

Sodium dodecyl sulfate

2,4,5-trimethylthiazole

D-tryptophan

ethyl heptanoate

   

 

 

from: Bargmann, C.I. and I Mori. 1997. Chemotaxis and thermotaxis. Chap 25 in D.L. Riddle, T. Blumenthal, B.J. Meyer and J.R. Priess (eds). C. elegans II.

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