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ArgR and AhrC Are Both Required for Regulation of Arginine Metabolism in Lactococcus lactis. Rasmus Larsen, 2004.The DNA binding proteins ArgR and AhrC are essential for regulation of arginine metabolism in Escherichia coli and Bacillus subtilis, respectively . A unique property of these regulators is that they form hexameric protein complexes, mediating repressionof arginine biosynthetic pathways as well as activation of arginine catabolic pathways . The gltS-argE operon of Lactococcus lactis encodes a putative glutamate or arginine transport protein and acetylornithine deacetylase, which catalyzes an important stepin the arginine biosynthesis pathway . By random integrationknockout screening we found that derepression mutants had ISS1 integrations in, among others, argR and ahrC . Single as well as double regulator deletion mutants were constructed from Lactococcus lactis subsp . cremoris MG1363 . The three arginine biosynthetic operons argCJDBF, argGH, and gltS-argE were shown to be repressedby the products of argR and ahrC . Furthermore, the argininecatabolic arcABD1C1C2TD2 operon was activated by the productof ahrC but not by that of argR . Expression from the promoterof the argCJDBF operon reached similar levels in the singlemutants and in the double mutant, suggesting that the regulatorsare interdependent and not able to complement each other . Atthe same time they also appear to have different functions,as only AhrC is involved in activation of arginine catabolism.This is the first study where two homologous arginine regulatorsare shown to be involved in arginine regulation in a prokaryote,representing an unusual mechanism of regulation. Fur Is Involved in Manganese-Dependent Regulation of mntA (sitA) Expression in Sinorhizobium meliloti. Raúl Platero, 2004.Fur is a transcriptional regulator involved in iron-dependent control of gene expression in many bacteria . In this work we analyzed the phenotype of a fur mutant in Sinorhizobium meliloti, an  -proteobacterium that fixes N2 in association with host plants . We demonstrated that some functions involved in high-affinity iron transport, siderophore production, and iron-regulated outer membrane protein expression respond to iron in a Fur-independent manner . However, manganese-dependent expression of the MntABCD manganese transport system was lost in a fur strain as discerned by constitutive expression of a mntA::gfp fusion reporter gene in the mutant . Thus, Fur directly or indirectly regulates a manganese-dependent function . The data indicate a novel function for a bacterial Fur protein in mediating manganese-dependent regulation of gene expression .
Propane Monooxygenase and NAD+-Dependent Secondary Alcohol Dehydrogenase in Propane Metabolism by Gordonia sp . Strain TY-5. Tetsuya Kotani, 2003.A new isolate, Gordonia sp . strain TY-5, is capable of growth on propane and n-alkanes with C13 to C22 carbon chains as the sole source of carbon . In whole-cell reactions, significant propane oxidation to 2-propanol was detected . A gene cluster designated prmABCD, which encodes the components of a putative dinuclear-iron-containing multicomponent monooxygenase, including the large and small subunits of the hydroxylase, an NADH-dependent acceptor oxidoreductase, and a coupling protein, was cloned and sequenced . A mutant with prmB disrupted (prmB::Kanr) lost the ability to grow on propane, and Northern blot analysis revealed that polycistronic transcription of the prm genes was induced during its growth on propane . These results indicate that the prmABCD gene products play an essential role in propane oxidation by the bacterium . Downstream of the prm genes, an open reading frame (adh1) encoding an NAD+-dependent secondary alcohol dehydrogenase was identified, and the protein was purified and characterized . The Northern blot analysis results and growth properties of a disrupted mutant (adh1::Kanr) indicate that Adh1 plays a major role in propane metabolism . Two additional NAD+-dependent secondary alcohol dehydrogenases (Adh2 and Adh3) were also found to be involved in 2-propanol oxidation. On the basis of these results, we conclude that Gordonia sp. strain TY-5 oxidizes propane by monooxygenase-mediated subterminal oxidation via 2-propanol .
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