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We have shown previously that Caulobacter crescentus grows on maltodextrins which are actively transported across the outer membrane by the MalA protein. Evidence for energy-coupled transport was obtained by deletion of the exbB exbD genes which abolished transport. However, removal of the TonB protein, which together with the ExbB ExbD proteins is predicted to form an energy-coupling device between the cytoplasmic membrane and the outer membrane, left transport unaffected. Here we identify an additional tonB gene encoded by the cc2334a ORF, which when deleted abolished maltose transport. MalA contains a TonB box that reads EEVVlT and is predicted to interact with TonB. Replacement of valine number 15 in the TonB box by proline abolished maltose transport. Maltose was transported across the cytoplasmic membrane by the MalY protein (CC2283). Maltose transport was induced by maltose and repressed by the Mall protein (CC2284). In addition to MatA, MalY and Mall, the mal locus encodes two predicted cytoplasmic [alpha]-amylases (CC2285 and CC2286) and a periplasmic glucoamylase (CC2282). The TonB dependence together with the previously described ExbB ExbD dependence demonstrates energy-coupled maltose transport across the outer membrane. MalY is involved in maltose transport across the cytoplasmic membrane by a presumably ion-coupled mechanism.

The colicin G producer Escherichia coli CA46, the colicin H producer E. coli CA58 and E. coli Nissle 1917 (DSM 6601) were shown to produce microcin H47 and the newly described microcin M. Both microcins were exported like colicin V by an RND-type export system, including TolC. The gene cluster encoding microcins H47 and M in strains CA46 and CA58 is nearly identical to that in strain DSM 6601, except that two additional genes are included. A Fur box identified in front of the microcin-encoding genes explained the observed iron regulation of microcin production. The catecholate siderophore receptors Fiu, Cir and FepA from E. coli and IroN, Cir and FepA from Salmonella were identified as receptors for microcins M, H47 and E492. Iron takes up the glucose-containing catecholate siderophore salmochelin, whose synthesis is encoded in the iro gene cluster found in Salmonella and certain, often uropathogenic, E. coli strains. A gene in this iro cluster, iroB, which encodes a putative glycosyltransferase, was also found in the microcin H47/M and microcin E492 gene clusters. These microcins could aid the producing strain in competing against enterobacteria that utilize catecholate siderophores.

A letter to the editor is presented concerning the article "Zero-phonon lines of nitrogen-cluster states in GaNx As1−x: H identified by time-resolved photoluminescence," from the April 8, 2008 issue.

The article reports on TonB-dependent maltose transport by Caulobacter crescentus. It identifies an additional tonB gene encoded by the cc2334a ORF, which when deleted abolished maltose transport. According to the article, evidence for energy-coupled transport was obtained by deletion of the exbB exbD genes which abolished transport. It is said that TonB dependence, together with the ExbB ExbD dependence demonstrates energy-coupled maltose transport across the outer membrane. It is further said that MalY is involved in maltose transport across the cytoplasmic membrane by a presumably ion-coupled mechanism.

The nanosecond dynamics of near-infrared semiconductor disk lasers is investigated experimentally and theoretically. Lasing and photoluminescence following barrier pumping are analyzed. Their spectral and temporal features such as luminescence overshoot and clamping, delay of lasing onset, and redshift of the emission are explained by a rate equation model taking into account the microscopic gain and luminescence. [ABSTRACT FROM AUTHOR]

We measured time-resolved photoluminescence on as-grown, annealed, as well as annealed and hydrogenated (Ga0.7In0.3)(N0.006As0.994)/GaAs quantum-well structures. The postgrowth treatment changes not only the photoluminescence decay time but also the intensity of photoluminescence directly after excitation. This initial luminescence intensity is determined by a competition between relaxation of electrons into nitrogen related potential fluctuations in the conduction band and their capture by deep traps. In contrast, the decay of the photoluminescence is mainly determined by the competition between radiative and nonradiative recombination, which are both influenced by localization. Annealing decreases localization effects and nonradiative recombination. Hydrogenation also reduces localization effects but increases nonradiative recombination. [ABSTRACT FROM AUTHOR]