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The RNA-Binding Protein Hfq of Listeria monocytogenes: Role in Stress Tolerance and Virulence. Janne K. Christiansen, 2004.In gram-negative bacteria, the RNA-binding protein Hfq has emerged as an important regulatory factor in a variety of physiological processes, including stress resistance and virulence . In Escherichia coli, Hfq modulates the stability or the translation of mRNAs and interacts with numerous small regulatory RNAs . Here, we studied the role of Hfq in the stress tolerance and virulence of the gram-positive food-borne human pathogen Listeria monocytogenes . We present evidence that Hfq is involved in the ability of L . monocytogenes to tolerate osmotic and ethanol stress and contributes to long-term survival under amino acid-limiting conditions . However, Hfq is not required for resistance to acid and oxidative stress . Transcription of hfq is induced under various stress conditions, including osmotic and ethanol stress and at the entry into the stationary growth phase, thus supporting the view that Hfq is important for the growth and survival of L . monocytogenes in harsh environments . The stress-inducible transcription of hfq depends on the alternative sigma factor  B,
which controls the expression of numerous stress- and
virulence-associated genes in L . monocytogenes. Infection
studies showed that Hfq contributes to pathogenesis in mice, yet
plays no role in the infection of cultured cell lines . This study
provides, for the first time, information on the role of Hfq in the
stress tolerance and virulence of a gram-positive pathogen .
Degradation of Estrogens by Rhodococcus zopfii and Rhodococcus equi Isolates from Activated Sludge in Wastewater Treatment Plants. Takeshi Yoshimoto, 2004.We have isolated four strains of Rhodococcus which specifically degrade estrogens by using enrichment culture of activated sludge from wastewater treatment plants . Strain Y 50158, identified as Rhodococcus zopfii, completely and rapidly degraded 100 mg of 17ß-estradiol, estrone, estriol, and ethinyl estradiol/liter, as demonstrated by thin-layer chromatography and gas chromatography-mass spectrometry analyses . Strains Y 50155, Y 50156, and Y 50157, identified as Rhodococcus equi, showed degradation activities comparable with that of Y 50158 . Using the random amplified polymorphism DNA fingerprinting test, these three strains were confirmed to have been derived from different sources . R . zopfii Y 50158, which showed the highest activity among these four strains, revealed that the strain selectively degraded 17ß-estradiol during jar fermentation, even when glucose was used as a readily utilizable carbon source in the culture medium . Measurement of estrogenic activities with human breast cancer-derived MVLN cells showed that these four strains each degraded 100 mg of 17ß-estradiol/liter to 1/100 of the specific activity level after 24 h . It is thus suggested that these strains degrade 17ß-estradiol into substances without estrogenic activity . SipY Is the Streptomyces lividans Type I Signal Peptidase Exerting a Major Effect on Protein Secretion. Arantxa Palacín, 2002.Most bacteria contain one type I signal peptidase (SPase) for cleavage of signal peptides from secreted proteins . The developmental complex bacterium Streptomyces lividans has the ability to produce and secrete a significant amount of proteins and has four different type I signal peptidases genes (sipW, sipX, sipY, and sipZ) unusually clustered in its chromosome . Functional analysis of the four SPases was carried out by phenotypical and molecular characterization of the different individual sip mutants . None of the sip genes seemed to be essential for bacterial growth . Analysis of total extracellular proteins indicated that SipY is likely to be the major S . lividans SPase, since the sipY mutant strain is highly deficient in overall protein secretion and extracellular protease production, showing a delayed sporulation phenotype when cultured in solid medium .
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