Original Sex

Bacteria normally multiply by sexless fission-they simply split in two. Still, scientists believe that some kinds of bacteria occasionally manage a kind of sexual mating. It is almost impossible to catch them in the act, though, because they have no special sex organs, and often when they cling together it is not for love. But at least one kind of microscopic bug has a sex life with a difference. Professors Pavel Nemec and Vojtech Bystricky of the Slovak Polytechnical University in Bratislava report that the Caulobacter, a harmless bacterium found in soil, possesses a multi-purpose organ that it often uses for a primitive kind of conjugation.

A caulobacter, say Drs. Nemec and Bystricky, is a sausagelike object with a long stalk protruding from one end.

Sometimes a caulobacter attaches the end of its stalk to the body wall of a bacterium of another species and feeds by sucking out the victim's protoplasm.

But often two caulobacters put the ends of their stalks together and cling for a long time while spherical grains in their stalk tips gradually fuse together.

Nemec and Bystricky believe that when two caulobacters cling together in this manner they are, in effect, mating -exchanging genetic material through their stalks. If the conjugating caulobacters belong to strains with different hereditary endowment, both may be improved by the swap. This is the great advantage of sexuality for any form of life; it permits faster evolution.

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