Podbel’skogo, St. Petersburg, 196608 Russia, e-mail kutuzova_rs@mail.ru Acknowledgements: Authors are thankful to the All-Russia Research Institute for Agricultural Microbiology employees E.E. Andronov and A.E. Pinaev for molecular genetic studies of the enrichment cultures provided. <...> A b s t r a c t Due to advanced molecular methods of taxonomical attribution and quantification more data are recently accumulated about the activity of small forms in microbial communities. <...> A substantial part of the bacteria from soil Fe-Mn concretions is known to exist as nanoforms which mostly are viable. <...> Both among nanoforms and large bacteria there are the same phylogenetic groups. <...> Because of the role of Al (Fe, Mn)-depositing microorganism we earlier described in clay genesis it is widely spread in mineral fraction of the slag loose layer. <...> The potential of this microorganism for Al detoxication by means of ion deposition on its surface is not estimated, and the meaning of Al (Fe, Mn)-depositing microorganism in soils with high Al acidity and toxicity is to be assessed. <...> According to our data, many features of the Al (Fe, Mn)-depositing microorganism are the same as in saprophytic free-living mycoplasma-like microorganisms associated with primary bauxite formation. <...> Herein we summarize our data on Al (Fe, Mn)depositing microorganism from sod-podzolic soil and volcanic substrates of resent eruptions as initial stage of bauxite formation. <...> So far as Al-depositing microorganism earlier found by T.B. Aristovskaya was described as related to from silt and widespread in soils, our investigations of bacteria also are under considerations During cultivation of Al (Fe, Mn)-depositing microorganism the cells became smaller, so the scanning microscopy showed the ultra small forms sized 0.1-0.2 µm. <...> In the fine fractions of volcanic substrate the thready structures were found consisting of the oval bodies of 0.1-0.3 µm diameter. <...> The nanoforms were observed using electronic microscopy of silt preparation, in which the finest filaments of the colonies and surrounded bodies were much smaller than 0.2 µm. <...> An attempt to assign the taxonomic status of the Al (Fe, Mn)-depositing microorganism using elective media and PCR-analysis failed because of inadequate DNA <...>