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Archives of Microbiology (v.193, #3)
Horizontal gene transfer amongst probiotic lactic acid bacteria and other intestinal microbiota: what are the possibilities? A review by Carol A. van Reenen; Leon M. T. Dicks (pp. 157-168).
Probiotics are live cultures, usually lactic acid bacteria, which are ingested to promote a healthy gastrointestinal tract. These organisms require certain traits to survive and compete in this niche, but these traits may be transferred to other microbiota in the gastrointestinal tract (GIT). Similarly, virulence factors from pathogens may be acquired by probiotic strains. Bacteria have developed a plethora of methods to transfer genetic material between strains, species and genera. In this review, the possible factors that may be exchanged and the methods of exchange are discussed.
Keywords: Probiotics; Intestinal microbiota; Gene transfer
Paenibacillus polymyxa JB05-01-1 and its perspectives for food conservation and medical applications by Karim Naghmouchi; Lyn Paterson; Bob Forster; Tim McAllister; Sam Ohene-Adjei; Djamel Drider; Ron Teather; John Baah (pp. 169-177).
The aim of this study was to isolate a novel bacterial strain with strong and broad spectrum antibacterial activity from a livestock feed prebiotic supplement. A novel strain, termed Paenibacillus polymyxa JB05-01-1, was isolated using traditional microbiological methods and identified on the basis of its phenotypic and biochemical properties as well as its 16S rRNA gene sequence. This strain was able to inhibit growth of gram-negative bacteria including Escherichia coli RR1, Pseudomonas fluorescens R73, Pantoea agglomerans BC1, Butyrivibrio fibrisolvens OR85, and Fibrobacter succinogenes. The above antagonism against the aforementioned bacteria was attributed to production of an antimicrobial substance(s) termed “JB05-01-1.” Its production was optimal during the stationary phase. JB05-01-1 has a molecular weight of 2.5 KDa, its mode of action is bactericidal, and the divalent cations, Ca2+ and Mn2+, reduced its lethality. The antibacterial activity was heat-stable and was effective at a pH range of 2–9. Enzymes like trypsin, α-chymotrypsin, and proteinase K have abolished the antibacterial activity of JB05-01-1 indicating a proteinaceous motif. This type of naturally occurring bacteria and inhibitory substance(s) could represent an additional value in livestock feed supplements. The natural presence of antibacterial activity indicates an opportunity to decrease the addition of antibiotics.
Keywords: Antibacterial substance(s); Antagonism; Escherichia coli ; gram-negative bacteria; Paenibacillus polymyxa JB05-01-1
Arginine-dependent acid-resistance pathway in Shigella boydii by Kelvin Goh; Darren Chua; Brian Beck; Marian L. McKee; Arvind A. Bhagwat (pp. 179-185).
Ability to survive the low pH of the human stomach is considered be an important virulent determinant. It was suggested that the unique acid tolerance of Shigella boydii 18 CDPH, the strain implicated in a 1998 outbreak, may have played an important role in surviving the acidic food (bean salad). The strain was capable of inducing arginine-dependent acid-resistance (ADAR) pathway. This pathway was assumed to be absent in Shigella sp. Here, we have examined occurrence and efficacy of ADAR pathway in 21 S. boydii strains obtained from the American Type Culture Collection (ATCC) along with strains of S. flexneri (n = 7), S. sonnei (n = 4), and S. dysenteriae (n = 2). The eight S. boydii strains were able to induce ADAR to survive the acid challenge at pH 2.0; additional 8 strains could tolerate acid challenge at pH 2.5 but not at pH 2.0. The remaining five S. boydii strains were not able to induce ADAR pathway and could not survive acid challenge even at pH 2.5. ADAR pathway also appears to be present in all four Shigella sp. Shigella ADAR pathway was induced when cells were grown under partial oxygen pressure while its expression in E. coli required mere fermentative growth on glucose.
Keywords: Microbial food safety; Acid resistance; Traveler’s diarrhea
Characterization of the tyrosine recombinase MrpA encoded by the Streptomyces coelicolor A3(2) plasmid SCP2* by Lydia Warth; Iris Haug; Josef Altenbuchner (pp. 187-200).
MrpA is the multimer resolution protein of the Streptomyces coelicolor A3(2) plasmid SCP2*. Previously, MrpA was found to significantly increase the stability of SCP2*-derived plasmids in Streptomyces lividans. The present report gives a functional characterization of MrpA. A sequence alignment revealed that MrpA shares highly conserved residues with members of the tyrosine recombinase family. After overexpression and Strep-tag purification, a DNase I footprint analysis and a gel mobility shift assay allowed for the identification of the 36-bp MrpA binding site mrpS. The mrpS site shows the configuration typical for tyrosine recombinases and contains two MrpA binding sites. The activity of MrpA was explored in vivo in E. coli cells and in vitro using purified MrpA. Depending on the position and orientation of the mrpS sites, three activities were detected: integration, resolution, and inversion. No accessory sites or proteins were required. Substitution of the conserved tyrosine (Y354F) by site-directed mutagenesis resulted in a complete loss of recombination activity but it still allowed the binding of MrpA to mrpS. The results define MrpA as a new site-specific tyrosine recombinase that acts with mrpS. In addition, we suggest that Y354 provides the nucleophile for DNA cleavage during recombination.
Keywords: Plasmid SCP2*; Tyrosine recombinase; Site-specific recombination; Multimer resolution
Cloning and molecular analysis of a mannitol operon of phosphoenolpyruvate-dependent phosphotransferase (PTS) type from Vibrio cholerae O395 by Sanath Kumar; Kenneth P. Smith; Jody L. Floyd; Manuel F. Varela (pp. 201-208).
A putative mannitol operon of the phosphoenolpyruvate phosphotransferase (PTS) type was cloned from Vibrio cholerae O395, and its activity was studied in Escherichia coli. The 3.9-kb operon comprising three genes is organized as mtlADR. Based on the sequence analysis, these were identified as genes encoding a putative mannitol-specific enzyme IICBA (EIIMtl) component (MtlA), a mannitol-1-phosphate dehydrogenase (MtlD), and a mannitol operon repressor (MtlR). The transport of [3H]mannitol by the cloned mannitol operon in E. coli was 13.8 ± 1.4 nmol/min/mg protein. The insertional inactivation of EIIMtl abolished mannitol and sorbitol transport in V. cholerae O395. Comparison of the mannitol utilization apparatus of V. cholerae with those of Gram-negative and Gram-positive bacteria suggests highly conserved nature of the system. MtlA and MtlD exhibit 75% similarity with corresponding sequences of E. coli mannitol operon genes, while MtlR has 63% similarity with MtlR of E. coli. The cloning of V. cholerae mannitol utilization system in an E. coli background will help in elucidating the functional properties of this operon.
Keywords: Mannitol; Vibrio cholerae O395; PTS; IIMtl ; MtlD
Two putative histidine kinases are required for cyst formation in Rhodospirillum Centenum by Neena Din; Charles J. Shoemaker; Kent L. Akin; Christopher Frederick; Terry H. Bird (pp. 209-222).
The photosynthetic bacterium, Rhodospirillum centenum, has a flexible life cycle that permits it to survive starvation as dormant cyst cells. Previous studies have identified some of the key regulators for encystment and demonstrated that the control of development is intricate. This complexity may arise from the need to integrate several environmental signals to mediate a switch from one mode of energy metabolism to another and to ensure that a transition to dormancy is initiated only when necessary. We searched for additional regulators of development by screening for encystment deficient strains after subjecting wild type R. centenum to mini-Tn5 mutagenesis. Analysis of “hypo-cyst” strains led to the identification of two genes that encode putative hybrid histidine kinases (cyd1 and cyd2). Cells with deletions of either gene fail to form cysts under conditions that normally induce development. Furthermore, the deletion strains exhibit altered swarming behavior suggesting that Cyd1 and Cyd2 affect behaviors utilized when the organism is attached to a substrate.
Keywords: Signal transduction; Hybrid histidine kinase; Bacterial development; Encystment
Survival of Francisella tularensis Type A in brackish-water by Zenda Lea Berrada; Sam R. Telford III (pp. 223-226).
Martha’s Vineyard (MV), Massachusetts has been the location of two outbreaks of pneumonic tularemia; landscaping activities have been associated with risk, suggesting environmental inhalation exposure. We determined whether salinity or other components of brackish-water present in a location with endemic tularemia may prolong survival of F. tularensis. In addition, we demonstrate for the first time that F. tularensis Type A appears similar to Type B with respect to environmental stability. The results of this study suggest an explanation for why MV is the site of pneumonic tularemia transmission as opposed to sites in the southcentral USA, where tularemia is more commonly reported: Bacteria may be more prone to surviving in salt-influenced soil or moisture in the island setting.
Keywords: Tularemia; Environmental stability; Microcosm; Type A; Martha’s Vineyard
Pseudomonas aeruginosa aerobic fatty acid desaturase DesB is important for virulence factor production by Herbert P. Schweizer; Kyoung-Hee Choi (pp. 227-234).
Unsaturated fatty acids (UFAs) play a pivotal role in maintaining a functional cellular membrane in response to changes in environmental factors. Unlike in other gram-negative bacteria, in Pseudomonas aeruginosa, UFA synthesis is governed by 2 pathways: (1) the anaerobic FabAB-mediated pathway and (2) the aerobic inducible DesA/DesB desaturase pathway. Although fatty acids are functional constituents of several known virulence factors, the roles of Pseudomonas aeruginosa fatty acid synthesis enzymes in virulence factor production and pathogenesis have not yet been examined. Previous studies have shown that the mycobacterial DesA1 and DesA3 proteins are required for full virulence. Therefore, we assessed the effect, if any, of mutations affecting the various UFA synthesis enzymes on virulence factor production. Testing of individual mutations or combinations of mutations revealed that desB mutants were severely deficient in the production of proteolytic enzymes, pyocyanin, and rhamnolipid. In addition, the desB mutants showed impaired swarming and twitching motilities and reduced virulence in the Caenorhabditis elegans infection model. Taken together, these results demonstrate that DesB is not only a fatty acid desaturase but also a factor required for full virulence in Pseudomonas aeruginosa. DesB may thus constitute a novel drug target.
Keywords: Pseudomonas aeruginosa ; DesB; Desaturase; Virulence factor