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Divergent structure of the ComQXPA quorum-sensing components: molecular basis of strain-specific communication mechanism in Bacillus subtilis (2000)

Tran, Lam-Son Phan ; Nagai, Toshiro ; Itoh, Yoshifumi

Oxford, UK : Blackwell Science Ltd

Molecular microbiology 37 (2000), S. 0

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ISSN: 1365-2958

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Medicine

Notes: In Bacillus subtilis, the ComQXPA quorum-sensing system controls cell density-dependent phenotypes such as the production of degradative enzymes and antibiotics and the development of genetic competence. Bacillus subtilis (natto) NAF12, a mutant defective in poly-γ-glutamate (γ-PGA) production, was derived from B. subtilis (natto) NAF4 by Tn917-LTV1 insertional mutagenesis. Determination of the mutant DNA sequences flanking the Tn917-LTV1 insert revealed that the insertion had inactivated comP in this mutant, indicating that γ-PGA synthesis in B. subtilis (natto) is under the control of the ComP–ComA signal transduction system. A comparison of the amino acid sequences revealed striking variation in the primary structures of ComQ (44% identity), ComX (26%) and the sensor domain of ComP (36%) between B. subtilis (natto) NAF4 and B. subtilis 168. In contrast, the amino acid and nucleotide sequences of the kinase domains of ComP and of the ComA response regulator share 95% and 100% identity respectively. The comP genes of NAF4 and 168 restored the impaired competence of B. subtilis BD1658 (comP::cat) and γ-PGA production of B. subtilis (natto) NAF12 (comP::Tn917-LTV1) to only 15% of the level achieved by the respective parent comP genes. However, when introduced together with the cognate comQ and comX genes, the comP genes restored the relevant defect of the heterologous comP mutants nearly to wild-type levels. Analogous to the comCDE system of Streptococcus strains and the agrBCDE system of Staphylococcus aureus, the concerted variation in the comQXP genes appears to establish specific intercellular communication between B. subtilis strains sharing the same pheromone system.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2958.2000.02069.x

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The development of a FACS-based strategy for the isolation of Shigella flexneri mutants that are deficient in intercellular spread (2000)

Rathman, Michelle ; Jouirhi, Noureddine ; Allaoui, Abdelmounaaïm ; [et al.]

Oxford, UK : Blackwell Science Ltd

Molecular microbiology 35 (2000), S. 0

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ISSN: 1365-2958

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Medicine

Notes: In the disease course of bacillary dysentery, pathogenic Shigella flexneri invade colonic epithelial cells and spread both within and between host cells. The ability to spread intercellularly allows the organism to infect an entire epithelial layer without significant contact with the extracellular milieu. Using fluorescence activated cell sorter (FACS)-based technology, we developed a rapid and powerful selection strategy for the isolation of S. flexneri mutants that are unable to spread from cell to cell. The majority of mutants identified using this strategy harbour mutations that affect the structure of their lipopolysaccharide or the ability of the bacteria to move intracellularly via actin-based motility; both factors have previously been shown to be essential for cell-to-cell spread. However, using a modified strategy that eliminated both of these types of mutants, we identified several mutants that provide us with evidence that bacterial proteins of the type III secretion system, which are essential for bacterial entry into host cells, also play a role in cell-to-cell spread.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01770.x

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Dominant sources of dietary carbon and nitrogen for shrimp reared in extensive rice-shrimp ponds (2004)

Burford, Michele A ; Preston, Nigel P ; Minh, Truong Hoang ; [et al.]

Oxford, UK : Blackwell Science Ltd

Aquaculture research 35 (2004), S. 0

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ISSN: 1365-2109

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Stable isotope analysis was used to determine the sources of dietary nitrogen (N) and carbon (C) for shrimp during the rearing phase in extensive rice-shrimp ponds in My Xuyen and Gia Rai districts, Vietnam. Farm-made feed was added as a food source in shrimp ponds in My Xuyen district, and based on stable isotope analyses, was generally a poor dietary source. The commercial formulated feed used in Gia Rai also appeared to contribute little directly to the nutritional needs of the shrimp. In contrast, the natural biota in all ponds appeared to contribute substantially. In particular, biota from beam trawls and benthic organic matter were the most likely sources of nutrition in My Xuyen ponds, while benthic organic matter was the main source in Gia Rai ponds. δ15N ratios in the natural biota in My Xuyen farms decreased over the growing season, suggesting increased N fixation in the case of the benthic organic matter reaching values as low as 1‰. This suggests N-limitation in the ponds and that natural biota become increasingly dependent on N fixed by algae and/or other microorganisms. There is the potential to promote the growth of the plankton and hence, the other natural biota, by the judicious addition of fertilizer.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2109.2004.01012.x

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RovA is autoregulated and antagonizes H-NS-mediated silencing of invasin and rovA expression in Yersinia pseudotuberculosis (2004)

Heroven, Ann Kathrin ; Nagel, Geraldine ; Tran, Hien J. ; [et al.]

Oxford, UK : Blackwell Science Ltd

Molecular microbiology 53 (2004), S. 0

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ISSN: 1365-2958

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Medicine

Notes: The transcriptional activator RovA of Yersinia pseudotuberculosis, a member of the SlyA/Hor family, activates its own expression and that of the virulence factor invasin in response to moderate growth temperature, but not at 37°C. In this work, we analysed the mechanism of RovA-dependent transcription of the rovA and inv genes. We found that rovA is transcribed by two different promoters. Sequences located upstream and downstream of the promoters were involved in rovA autoregulation and interacted specifically with the RovA protein. To define the nucleotides recognized by the RovA protein, we determined the RovA binding sites in the rovA and the inv regulatory region and revealed related AT-rich sequence motifs at diverse positions relative to the transcriptional start sites. We also showed that rovA and the RovA-dependent inv gene were both subject to silencing by the nucleoid-associated H-NS protein of Y. pseudotuberculosis. The binding sites of the H-NS and RovA proteins in the rovA and inv regulatory sequences were superimposed, and the presence of the RovA protein alleviated H-NS-mediated repression of the rovA and inv promoter. Moreover, loss of H-NS function led to a significant increase in rovA and inv transcription nearly independently of RovA, indicating that RovA acts mainly as an antirepressor. We therefore hypothesize that the transcription level of RovA-dependent genes reflects the outcome of the RovA/H-NS competition and the rovA autoregulatory mechanism.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2958.2004.04162.x

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5

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SpoIVB-mediated cleavage of SpoIVFA could provide the intercellular signal to activate processing of Pro-σK in Bacillus subtilis (2003)

Dong, Tran C. ; Cutting, Simon M.

Oxford, UK : Blackwell Science Ltd

Molecular microbiology 49 (2003), S. 0

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ISSN: 1365-2958

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Medicine

Notes: SpoIVB is the critical determinant for intercompartmental signalling of pro-σK processing during sporulation in Bacillus subtilis. We show here that the SpoIVB serine peptidase can cleave the SpoIVFA protein, which is one component of the pro-σK processing complex. SpoIVFA has been shown elsewhere (Rudner, D.Z., and Losick, R., 2002, Genes Dev 16: 1007–1018) to tether BofA and SpoIVFB in a membrane-embedded heteroligomeric complex in which BofA directly inhibits the activity of SpoIVFB. Cleavage of SpoIVFA would provide the necessary signal to dissolve this complex and release BofA-mediated inhibition on the zinc metalloprotease, SpoIVFB, that is responsible for cleaving pro-σK to its mature form. We also show that the SpoIVB PDZ domain is required for self-recognition and trans cleavage of SpoIVB and is probably also used to target an internal motif within the C-terminal region of SpoIVFA exposed in the space between the inner and outer forespore membranes. This work reveals the mechanism of intercompartmental signalling and provides a unified model as to how σK-directed gene expression in the mother cell is co-ordinated with events in the forespore chamber.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2958.2003.03651.x

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Detection, identification and significance of phytoplasmas in grasses in northern Australia (2003)

Blanche, K. R. ; Tran-Nguyen, L. T. T. ; Gibb, K. S.

Oxford, UK : Blackwell Science Ltd

Plant pathology 52 (2003), S. 0

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ISSN: 1365-3059

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Sugarcane yields have been severely reduced by white leaf and grassy shoot phytoplasma diseases in many parts of Asia. Australian sugarcane crops are not known to be affected by these diseases, but plant pathogenic phytoplasmas found in other introduced and native grasses in northern Australia could pose a serious threat to the Australian sugarcane industry. To further evaluate this threat, leaves from plants of 20 grass species, with and without symptoms, were collected during field surveys in northern Australia and tested to determine whether phytoplasmas were present and whether symptoms were reliable indicators of phytoplasma presence. Molecular tools were used to detect and characterize phytoplasmas. Four different phytoplasmas were found in seven grass species known to grow near healthy sugarcane crops. All the phytoplasmas were closely related to sugarcane white leaf phytoplasma (SCWL), one of the phytoplasmas that causes disease in sugarcane in Asia. Four of the host plant species and two of the phytoplasmas were new records. The relationship between symptoms and phytoplasma presence was poor. Because some plants with symptoms tested negative for phytoplasmas, a series of surveys was carried out in which flowers, leaves, roots and stems of two known host plant species, Whiteochloa cymbiformis and Sorghum stipoideum, were tested separately on nine occasions during two wet seasons. This was done to investigate the distribution of phytoplasmas within plants over time. Results showed that spatial and temporal variation of phytoplasmas occurred in these two host plant species. Hence, evaluation of disease distribution within a region requires repeated testing of all plant parts from plants without symptoms, as well as those with symptoms. To date, there is no report of a vector capable of transmitting to Australian sugarcane the phytoplasmas found in grasses in this study. If one is present, or occurs in the future, then native and introduced grasses could constitute a large reservoir of phytoplasma for vectors to draw on. This work provides an early warning for the sugarcane industry that the potential for infection exists.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-3059.2003.00871.x

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Diversity of phytoplasmas in northern Australian sugarcane and other grasses (2000)

Tran-Nguyen, L. ; Blanche, K. R. ; Egan, B. ; [et al.]

Oxford, UK : Blackwell Science Ltd

Plant pathology 49 (2000), S. 0

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ISSN: 1365-3059

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Plant pathogenic phytoplasmas found in grasses in northern Australia have the potential to adversely affect sugarcane production. To begin assessment of this threat, the number of grass species with phytoplasmas, the identity of those phytoplasmas, and their relationship with disease symptoms were determined. Sugarcane with and without symptoms of yellow leaf syndrome was included in the surveys. Molecular methods were used to detect and characterize phytoplasmas in grass species exhibiting symptoms typical of phytoplasma disease. Sugarcane samples were from the Ord River Irrigation Area, Western Australia, and Samford, Queensland. Samples of other grasses were from Wyndham, Kununurra and Broome, Western Australia, and Darwin, Northern Territory. Our survey identified four new phytoplasma host species and confirmed four known previously. Counting phytoplasmas, phytoplasma variants, and mixtures of phytoplasmas and variants, these eight host species had 33 different infections. Two phytoplasmas were new, cenchrus bunchy shoot which is related to Candidatus phytoplasma australiense, and sorghum bunchy shoot which is not closely related to any described phytoplasma. Twenty-five phytoplasma isolates were detected in sugarcane. Of these, tomato big bud phytoplasma was the most common. In most cases no clear association between phytoplasmas and symptoms could be determined. None of the phytoplasmas in Australian sugarcane, but two in other grasses, were closely related to phytoplasmas associated with white leaf and grassy shoot diseases in Asian sugarcane. This study demonstrates that diversity of phytoplasmas and grass host species in northern Australia is greater than previously thought, and that symptoms alone are not always reliable indicators of phytoplasma presence or absence. It provides the groundwork to improve future field surveys, and for initiation of transmission trials to determine whether insect vectors capable of transmitting phytoplasmas from native grasses to sugarcane are present in the region.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-3059.2000.00498.x

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