A method for the differential microscopic enumeration of Halobacterium cells

When hypersaline brines are treated with low concentrations of bile salts, such as sodium deoxycholate or sodium taurocholate, Halobacterium and related halophilic archaebacteria lyse while both halophilic eubacteria and halococci remain intact. Microscopic enumeration of bacteria before and after treatment with bile salts, thus, enables the estimation of Halobacterium population sizes in natural samples. Sodium deoxycholate was found to be superior to sodium taurocholate as at least one strain (Haloferax volcanii) resists lysis by taurocholate. Treatment with 0.003% sodium deoxycholate caused lyusis of ≈ 42% of the bacteria present in a solar saltern crystallizer pond; using the same method, it was shown that no significant population of halobacteria was present in the Dead Sea in 1988.