A. Kaminskayaa, V. Pushkarevaa, M. Moisenovichb, T. Stepanovaa,
N. Volkovaa, J. Romanovaa, V. Litvina, A. Gintsburga, and S. Ermolaevaa
a Gamaleya Research Institute of Epidemiology and Microbiology, Moscow, Russia
b Moscow State University, Vorob’evy gory, Moscow, Russia
e-mail: sveta@ermolaeva.msk.su
Abstract—Biofilm formation is an important part of the bacterial life cycle. Biofilms provide bacterial resis-
tance to external stresses and protozoan grazing. Biofilm formation by the wild type of B. cenocepacia strain
370 in the presence of the free-living ciliate Tetrahymena pyriformis was studied. T. pyriformis grazed on plank-
tonic bacteria and reduced the planktonic bacterial subpopulation while it noticeably stimulated biofilm forma-
tion. When cultivated alone, T. pyriformis did not form visible biofilms. Confocal laser scanning microscopy
was used to demonstrate the inclusion and further destruction of protozoan cells within the biofilms formed by
the bacteria. The destruction of protozoan cells was accompanied by the exit of bacteria from vacuoles and
intracytoplasmic multiplication; changes in the form of protozoan cells; the demolition of internal structures;
and the visual exit of the cytoplasmic content from destructing cells. Microcolonies of a characteristic round
shape were revealed in the biofilms formed by B. cenocepacia in the presence of T. pyriformis. These structures
were absent in the biofilms formed by B. cenocepacia alone. Insertion of protozoan cells within biofilms seems
to be a driving force that promotes biofilm proliferation and influences their structure. The mortality of proto-
zoan cells in the biofilms caused a decrease in the T. pyriformis population under conditions advantageous to
B. cenocepacia biofilm formation. The mutant B. cenocepacia strain Bcb-1, which is unable to form biofilms,
was isolated by plasposon mutagenesis. In contrast to the parental strain, the cocultivation with Bcb-1 bacteria
improved the growth of T. pyriformis. A mutation was mapped in the ompR gene.
Keywords: biofilms; ecology of pathogens Burkholderia; Tetrahymena
DOI:10.3103/S0891416807040088
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