Interferometry with Bose-Einstein condensates in microgravity.

Atom interferometers covering macroscopic domains of space-time are a spectacular manifestation of the wave nature of matter. Because of their unique coherence properties, Bose-Einstein condensates are ideal sources for an atom interferometer in extended free fall. In this Letter we report on the realization of an asymmetric Mach-Zehnder interferometer operated with a Bose-Einstein condensate in microgravity. The resulting interference pattern is similar to the one in the far field of a double slit and shows a linear scaling with the time the wave packets expand. We employ delta-kick cooling in order to enhance the signal and extend our atom interferometer. Our experiments demonstrate the high potential of interferometers operated with quantum gases for probing the fundamental concepts of quantum mechanics and general relativity.

Phase-locking of two self-seeded tapered amplifier lasers.

We report on the phase-locking of two diode lasers based on self-seeded tapered amplifiers. In these lasers, a reduction of linewidth is achieved using narrow-band high-transmission interference filters for frequency selection. The lasers combine a compact design with a Lorentzian linewidth below 200 kHz at an output power of 300 mW for a wavelength of 780 nm. We characterize the phase noise of the phase-locked laser system and study its potential for coherent beam-splitting in atom interferometers.

Gauss sum factorization with cold atoms.

We report the first implementation of a Gauss sum factorization algorithm by an internal state Ramsey interferometer using cold atoms. A sequence of appropriately designed light pulses interacts with an ensemble of cold rubidium atoms. The final population in the involved atomic levels determines a Gauss sum. With this technique we factor the number N=263193.

The dhb operon of Bacillus subtilis encodes the biosynthetic template for the catecholic siderophore 2,3-dihydroxybenzoate-glycine-threonine trimeric ester bacillibactin.

Bacillus subtilis was reported to produce the catecholic siderophore itoic acid (2,3-dihydroxybenzoate (DHB)-glycine) in response to iron deprivation. However, by inspecting the DNA sequences of the genes dhbE, dhbB, and dhbF as annotated by the B. subtilis genome project to encode the synthetase complex for the siderophore assembly, various sequence errors within the dhbF gene were predicted and confirmed by re-sequencing. According to the corrected sequence, dhbF encodes a dimodular instead of a monomodular nonribosomal peptide synthetase. We have heterologously expressed, purified, and assayed the substrate selectivity of the recombinant proteins DhbB, DhbE, and DhbF. DhbE, a stand-alone adenylation domain of 59.9 kDa, activates, in an ATP-dependent reaction, DHB, which is subsequently transferred to the free thiol group of the cofactor phosphopantetheine of the bifunctional isochorismate lyase/aryl carrier protein DhbB. The third synthetase, DhbF, is a dimodular nonribosomal peptide synthetase of 264 kDa that specifically adenylates threonine and, to a lesser extent, glycine and that covalently loads both amino acids onto their corresponding peptidyl carrier domains. To functionally link the dhb gene cluster to siderophore synthesis, we have disrupted the dhbF gene. Comparative mass spectrometric analysis of culture extracts from both the wild type and the dhbF mutant led to the identification of a mass peak at m/z 881 ([M-H](1-)) that corresponds to a cyclic trimeric ester of DHB-glycine-threonine.

Characterization of the relA/spoT gene from Bacillus stearothermophilus.

By use of degenerate primers, we amplified a fragment of a relA/spoT homologous gene from Bacillus stearothermophilus. Chromosomal walking enabled us to sequence the entire gene and its flanking regions. The primary sequence of the gene product is 78% identical to the RelA/SpoT homologue of Bacillus subtilis and both gene loci share a similar genetic organization. The B. stearothermophilus rel gene was analyzed in vivo by heterologous expression in the B. subtilis relA deletion strain TW30, and is shown to complement the growth defects of TW30. The recombinant RelBst protein was detected by Western immunoanalysis, and synthesizes guanosine-3'-diphosphate-5'-(tri)diphosphate ((p)ppGpp) after amino acid stress and carbon starvation. These in vivo data, the genetic organization, and the primary structure compared to other RelA/SpoT homologues provide circumstantial evidence that the identified gene encodes the only (p)ppGpp synthetase in B. stearothermophilus presumed to serve also as (p)ppGpp hydrolase.

A family of cold shock proteins in Bacillus subtilis is essential for cellular growth and for efficient protein synthesis at optimal and low temperatures.

Like other bacteria, Bacillus subtilis possesses a family of homologous small acidic proteins (CspB, CspC and CspD, identity >70%) that are strongly induced in response to cold shock. We show that deletion of cspC or cspD genes did not result in a detectable phenotype; in contrast, csp double mutants exhibited severe reduction in cellular growth at 15 degrees C as well as at 37 degrees C, including impairment of survival during the stationary phase. Two-dimensional gel analysis showed that protein synthesis was deregulated in csp double mutants and that the loss of one or two CSPs led to an increase in the synthesis of the remaining CSP(s) at 37 degrees C and after cold shock, suggesting that CSPs down-regulate production of members from this protein family. A cspB/C/D triple mutant (64BCDbt) could only be generated in the presence of cspB in trans on a plasmid that was not lost, in spite of lack of antibiotic pressure, indicating that a minimum of one csp gene is essential for viability of B. subtilis. After cold shock, synthesis of CspB in 64BCDbt was drastically lower than in wild-type cells accompanied by cessation in growth and strong reduction in general protein synthesis. As CspB, CspC and CspD are shown to bind to RNA in a co-operative and interactive manner, CSPs are suggested to function as RNA chaperones facilitating the initiation of translation under optimal and low temperatures.

Cloning and characterization of a relA/spoT homologue from Bacillus subtilis.

A PCR-amplified DNA fragment of the relA gene from genomic Bacillus subtilis DNA was used to isolate the entire relA/spoT homologue and two adjacent open reading frames (ORFs) from a lambda ZAP Express library. The relA gene, which encodes a protein of 734 amino acid residues (aa), is flanked by an ORF (170aa) that shares high similarity to adenine phosphoribosyltransferase genes (apt), and downstream by an ORF (131 aa) of unknown function. This genetic organization is similar to that in Streptomyces coelicolor A3(2) and Streptococcus equismilis H46A. relA shows significant similarity to the Escherichia coli relA and spoT genes, which are responsible for the synthesis and degradation of the highly phosphorylated guanosine nucleotides (p)ppGpp, triggering the stringent response. Deletion of the relA gene generated a (p)ppGpp0 phenotype that demonstrated its essential role in the response to amino acid deprivation and resulted in impaired/lowered induction of proteins involved in stress response as well as amino acid biosynthesis, as judged by two-dimensional gel electrophoresis. The same effects of impaired induction of some sigmaB-independent proteins could also be shown in a sigB/relA double mutant, supporting the role of relA in derepression/induction of catabolic and anabolic genes during stringent response.