While H. volcanii is often noted for its unique gene transfer
system [56], the mechanism and genes underpinning this
phenomenon remain largely uncharacterized [57,94]. Here
we report that mating occurs within biofilms at the
same frequency as in earlier reports (Figure 5), consistent
with the known cell-contact-dependent nature of
the mechanism. Mating was discovered and has been
routinely observed in the laboratory by several groups by
co-precipitating cells or co-filtering them on nitrocellulose
filters [56–58,94,95]. These experimental methods for
bringing cells together in close proximity can be thought
of as proxies for naturally formed biofilms