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Nitric Oxide Generated from Isoniazid Activation by KatG: Source of Nitric Oxide and Activity against Mycobacterium tuberculosis. Graham S. Timmins, 2004.Isonicotinic acid hydrazide (INH) is a frontline antituberculosis agent . Once taken up by Mycobacterium tuberculosis, INH requires activation by the catalase-peroxidase KatG, converting INH from its prodrug form into a range of bactericidal reactive species . Here we used 15N-labeled INH together with electron paramagnetic resonance spin trapping techniques to demonstrate that nitric oxide (NO·) is generated from oxidation at the hydrazide nitrogens during the activation of INH by M . tuberculosis KatG . We also observed that a specific scavenger of NO· provided protection against the antimycobacterial activity of INH in bacterial culture . No significant increases in mycobacterial protein nitration were detected, suggesting that NO· and not peroxynitrite, a nitrating metabolite of NO·, is involved in antimycobacterial action . In conclusion, INH-derived NO· has biological activity, which directly contributes to the antimycobacterial action of INH . Choline Starvation Induces the Gene licD2 in Streptococcus pneumoniae. Bhushan V. Desai, 2003.Mutant strains of Streptococcus pneumoniae were constructed to monitor the regulation of three dispersed genes known or predicted to act in choline metabolism . One gene (licD2) was regulated in response to choline deprivation over a 30-fold range . The other two (SP1860 and licC) responded little if at all to the same challenge . Slr2013 Is a Novel Protein Regulating Functional Assembly of Photosystem II in Synechocystis sp . Strain PCC 6803. Galyna I. Kufryk, 2003.The Synechocystis sp . strain PCC 6803, which has a T192H mutation in the D2 protein of photosystem II, is an obligate photoheterotroph due to the lack of assembled photosystem II complexes . A secondary mutant, Rg2, has been selected that retains the T192H mutation but is able to grow photoautotrophically . Restoration of photoautotrophic growth in this mutant was caused by early termination at position 294 in the Slr2013 protein . The T192H mutant with truncated Slr2013 forms fully functional photosystem II reaction centers that differ from wild-type reaction centers only by a 30% higher rate of charge recombination between the primary electron acceptor, QA-, and the donor side and by a reduced stability of the oxidized form of the redox-active Tyr residue, YD, in the D2 protein . This suggests that the T192H mutation itself did not directly affect electron transfer components, but rather affected protein folding and/or stable assembly of photosystem II, and that Slr2013 is involved in the folding of the D2 protein and the assembly of photosystem II . Besides participation in photosystem II assembly, Slr2013 plays a critical role in the cell, because the corresponding gene cannot be deleted completely under conditions in which photosystem II is dispensable . Truncation of Slr2013 by itself does not affect photosynthetic activity of Synechocystis sp . strain PCC 6803 . Slr2013 is annotated in CyanoBase as a hypothetical protein and shares a DUF58 family signature with other hypothetical proteins of unknown function . Genes for close homologues of Slr2013 are found in other cyanobacteria (Nostoc punctiforme, Anabaena sp . strain PCC 7120, and Thermosynechococcus elongatus BP-1), and apparent orthologs of this protein are found in Eubacteria and Archaea, but not in eukaryotes . We suggest that Slr2013 regulates functional assembly of photosystem II and has at least one other important function in the cell . Effects of Current Velocity on the Nascent Architecture of Stream Microbial Biofilms. Tom J. Battin, 2003.Current velocity affected the architecture and dynamics of natural, multiphyla, and cross-trophic level biofilms from a forested piedmont stream . We monitored the development and activity of biofilms in streamside flumes operated under two flow regimes (slow [0.065 m s-1] and fast [0.23 m s-1]) by combined confocal laser scanning microscopy with cryosectioning to observe biofilm structure and composition . Biofilm growth started as bacterial microcolonies embedded in extracellular polymeric substances and transformed into ripple-like structures and ultimately conspicuous quasihexagonal networks . These structures were particularly pronounced in biofilms grown under slow current velocities and were characterized by the prominence of pennate diatoms oriented along their long axes to form the hexagons . Microstructural heterogeneity was dynamic, and biofilms that developed under slower velocities were thicker and had larger surface sinuosity and higher areal densities than their counterparts exposed to higher velocities . Surface sinuosity and biofilm fragmentation increased with thickness, and these changes likely reduced resistance to the mass transfer of solutes from the water column into the biofilms . Nevertheless, estimates of dissolved organic carbon uptake and microbial growth suggested that internal cycling of carbon was more important in thick biofilms grown in slow flow conditions . High-pressure liquid chromatography-pulsed amperometric detection analyses of exopolysaccharides documented a temporal shift in monosaccharide composition as the glucose levels decreased and the levels of rhamnose, galactose, mannose, xylose, and arabinose increased . We attribute this change in chemical composition to the accumulation of diatoms and increased incorporation of detrital particles in mature biofilms .
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