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1.  In vitro communities derived from oral and gut microbial floras inhibit the growth of bacteria of foreign origins 
Microbial ecology  2010;60(3):665-676.
The gastrointestinal (GI) tract is home to trillions of microbes. Within the same GI tract substantial differences in the bacterial species that inhabit the oral cavity and intestinal tract have been noted. While the influence of host environments and nutritional availability in shaping different microbial communities is widely accepted, we hypothesize that the existing microbial flora also plays a role in selecting the bacterial species that are being integrated into the community. In this study, we used cultivable microbial communities isolated from different parts of the GI tract of mice (oral cavity and intestines) as a model system to examine this hypothesis. Microbes from these two areas were harvested and cultured using the same nutritional conditions, which led to two distinct microbial communities, each with about 20 different species as revealed by PCR-DGGE analysis. In vitro community competition assays showed that the two microbial floras exhibited antagonistic interactions towards each other. More interestingly, all the original isolates tested and their closely related species displayed striking community preferences: they persisted when introduced into the bacterial community of the same origin, while their viable count declined more than 3 orders of magnitude after 4 days of coincubation with the microbial flora of foreign origin. These results suggest that an existing microbial community might impose a selective pressure on incoming foreign bacterial species independent of host selection. The observed inter-flora interactions could contribute to the protective effect of established microbial communities against the integration of foreign bacteria to maintain the stability of the existing communities.
doi:10.1007/s00248-010-9711-9
PMCID: PMC2954289  PMID: 20625712
2.  In Vitro Communities Derived from Oral and Gut Microbial Floras Inhibit the Growth of Bacteria of Foreign Origins 
Microbial Ecology  2010;60(3):665-676.
The gastrointestinal (GI) tract is home to trillions of microbes. Within the same GI tract, substantial differences in the bacterial species that inhabit the oral cavity and intestinal tract have been noted. While the influence of host environments and nutritional availability in shaping different microbial communities is widely accepted, we hypothesize that the existing microbial flora also plays a role in selecting the bacterial species that are being integrated into the community. In this study, we used cultivable microbial communities isolated from different parts of the GI tract of mice (oral cavity and intestines) as a model system to examine this hypothesis. Microbes from these two areas were harvested and cultured using the same nutritional conditions, which led to two distinct microbial communities, each with about 20 different species as revealed by PCR-based denaturing gradient gel electrophoresis analysis. In vitro community competition assays showed that the two microbial floras exhibited antagonistic interactions toward each other. More interestingly, all the original isolates tested and their closely related species displayed striking community preferences: They persisted when introduced into the bacterial community of the same origin, while their viable count declined more than three orders of magnitude after 4 days of coincubation with the microbial flora of foreign origin. These results suggest that an existing microbial community might impose a selective pressure on incoming foreign bacterial species independent of host selection. The observed inter-flora interactions could contribute to the protective effect of established microbial communities against the integration of foreign bacteria to maintain the stability of the existing communities.
Electronic supplementary material
The online version of this article (doi:10.1007/s00248-010-9711-9) contains supplementary material, which is available to authorized users.
doi:10.1007/s00248-010-9711-9
PMCID: PMC2954289  PMID: 20625712
3.  Horizontal Transfer of Iturin A Operon, itu, to Bacillus subtilis 168 and Conversion into an Iturin A Producer 
Antimicrobial Agents and Chemotherapy  2005;49(11):4641-4648.
Iturin A and its derivatives are lipopeptide antibiotics produced by Bacillus subtilis and several closely related bacteria. Three iturin group operons (i.e., iturin A, mycosubtilin, and bacillomycin D) of those antibiotic-producing strains have been cloned and sequenced thus far, strongly implying the horizontal transfer of these operons. To examine the nature of such horizontal transfer in terms of antibiotic production, a 42-kb region of the B. subtilis RB14 genome, which contains a complete 38-kb iturin A operon, was transferred via competent cell transformation to the genome of a non-iturin A producer, B. subtilis 168, using a method based on double-crossover homologous recombination with two short landing pad sequences (LPSs) in the genome. The recombinant was positively selected by confirming the elimination of the cI repressor gene, which was localized between the two LPSs and substituted by the transferred segment. The iturin A operon-transferred strain 168 was then converted into an iturin A producer by the introduction of an sfp gene, which encodes 4′-phosphopantetheinyl transferase and is mutated in strain 168. By inserting the pleiotropic regulator degQ, the productivity of iturin A increased sevenfold and was restored to about half that of the donor strain RB14, without the transfer of additional genes, such as regulatory or self-resistance genes.
doi:10.1128/AAC.49.11.4641-4648.2005
PMCID: PMC1280175  PMID: 16251307
4.  The Genes degQ, pps, and lpa-8 (sfp) Are Responsible for Conversion of Bacillus subtilis 168 to Plipastatin Production 
Bacillus subtilis YB8 produces the lipopeptide antibiotic plipastatin. B. subtilis MI113, which is a derivative of strain 168, was converted into a new plipastatin producer, strain 406, by competence transformation with the chromosomal DNA of YB8. Transposon mini-Tn10 insertional mutagenesis was applied to strain 406, which revealed that lpa-8 (sfp) (encoding 4′-phosphopantetheinyl transferase) and the pps operon (located between 167 and 171°) are essential for plipastatin production. The pps operon was previously suggested to encode putative peptide synthetases (A. Tognoni, E. Franchi, C. Magistrelli, E. Colombo, P. Cosmina, and G. Grandi, Microbiology 141:645–648, 1995) and was thought to be the fengycin operon (V. Tosato, A. M. Albertini, M. Zotti, S. Sonda, and C. V. Bruschi, Microbiology 143:3443–3450, 1997). We claim that the pps operon is the pli operon, encoding plipastatin synthetase. By using a new high-performance liquid chromatography system, we revealed that strain 168 expressing only lpa-8 can also produce plipastatin, although the yield is very low. However, the introduction of the pleiotropic regulator degQ of strain YB8 into strain 168 expressing lpa-8 resulted in a 10-fold increase in the production of plipastatin.
PMCID: PMC89444  PMID: 10471562

Results 1-4 (4)