ISSN 1022-7954, Russian Journal of Genetics, 2007, Vol. 43, No. 7, pp. 736–741. © Pleiades Publishing, Inc., 2007.
Original Russian Text © S.G. Botina, O.V. Piksasova, Yu.D. Tsygankov, V.V. Sukhodolets, 2007, published in Genetika, 2007, Vol. 43, No. 7, pp. 891–897 .
At present it is well established that in bacterial pop-
ulation divergence is determined by horizontal transfer
and integration of alien genes into the genome . At
the same time the mechanisms of bacterial genetic
exchange, which are responsible for the species integ-
rity in the macroevolution, are less known. Intraspecies
genetic variability is reﬂected at the physiological level
and in the genome structure in remote ecological com-
munities from various ecological niches. Investigation
of this variability is important for characterizing of the
species as a taxon. In this respect the comparison of
both phenotypic and genotypic properties of
communities, which were devel-
oped in various natural environments and widely used
for fermentation in industrial and domestic production
of dairy products. Therefore, the usage of various DNA
typing techniques permitting to distinguish bacterial
strains and to study intraspecies variability of
Previously, we have performed exact species identi-
ﬁcation of thermophilic
strains, which we examined in this study, by identiﬁca-
tion of their physiological and biochemical characteris-
tics and the analysis of 16S rRNA nucleotide sequences
. All the strains have high homology of about 100%
by nucleotide sequences of 16S rRNA gene of refer-
ence strains of
ATCC19258, the number of deposited sequences
AY687382, AY188354, and the sequences of this strain
deposited by us and others into the NCBI database .
At present we used RFLP analysis of genomic DNA
in the studies of intraspecies differences in
strains, namely variability in their genome size.
Genomic restriction method followed by pulse-gel
electrophoresis (PFGE) is considered to be highly a
efﬁcient approach of molecular typing of bacteria for
their identiﬁcation at the strain level [3, 4], ranking sec-
ond after complete genome sequencing.
Thus, the purpose of this work was to compare nat-
ural isolates of
by size and similarity of
restriction ﬁngerprints and genome size as well as to
determine their relative divergence from each other and
reference strain ATCC19258.
MATERIALS AND METHODS
strains isolated by us from various diary products
(yogurt, sour cream, cheese, cottage cheese, sour milk)
from different districts of Russia, Italy, Croatia, Slova-
kia, and France were used in this study. These strains
were BC201, BC216, BC221, BC223, BC231, BC233,
BC236, BC247, BC250, BC257, BC259, BC310,
BC311, BC313, BC314, BC316, BC317, BC322,
BC323, BC324, BC329, BC332, BC337, and BC338.
We also used two strains, B7637 and ATCC19258,
from the All-Union Collection of Industrial Microor-
ganisms (State Research Institute of Genetics and
Selection of Industrial Microorganisms). The detailed
information about examined strains was presented pre-
Media and culture conditions.
Bacterial strains were
isolated and cultured on a solid M21 medium . Agar
plates were incubated at 42
C for 48 h.
Sample preparation for genomic DNA pulse-gel
was done as described previously .
Endonuclease digestion was carried out using conven-
tional protocols  involving restriction endonucleases
Comparative Analysis of Genome Sizes
S. G. Botina, O. V. Piksasova, Yu. D. Tsygankov, and V. V. Sukhodolets
State Research Institute of Genetics and Selection of Industrial Microorganisms (GosNIIGenetika),
Moscow, 113545 Russia; e-mail: firstname.lastname@example.org
Received October 12, 2006
isolates were analyzed using pulse-ﬁeld gel electrophore-
sis (PFGE) and gene restriction proﬁle analysis techniques. 16S rRNA gene sequences of the isolates were
almost 100% homologous. However, genomic ﬁngerprinting analysis has shown variability in both genome size
and restriction fragments length. The genomes varied from 1417 to 2075 kb resulting in the difference between
marginal genome sizes in about 600 kb. The results are indicative of
genetic polymorphism, the origin of which requires further investigation.