Microbial precipitation of manganese by bacteria and fungi from desert rock and rock varnish

Abstract Precipitation of manganese by fungi and chemoorganotrophic bacteria isolated from desert rock was quantitatively shown to be dependent on increasing NaCl concentrations in vitro. Many fungi were able to precipitate Mn(IV) under conditions suggested to be similar to those found on desert rock. However, Mn(IV) precipitation in bacterial cultures took place mostly at pH values above 8. Our results lend farther support to the hypothesis on the microbial genesis and stabilization of rock varnish and the patination of ancient petroglyphs.