Search

Corynebacterineae is a specific suborder of Gram-positive bacteria that includes Mycobacterium tuberculosis and Corynebacterium glutamicum. The ultrastructure of the cell envelope is very atypical. It is composed of a heteropolymer of peptidoglycan and arabinogalactan (AG) covalently associated to an outer membrane. Five arabinosyltransferases are involved in the biosynthesis of AG in C. glutamicum. AftB catalyzes the transfer of Araf (arabinofuranosyl) onto the arabinan domain of the arabinogalactan to form terminal [beta](1 [right arrow] 2)-linked Araf residues. Here we show that [DELTA]aftB cells lack half of the arabinogalactan mycoloylation sites but are still able to assemble an outer membrane. In addition, we show that a [DELTA]aftB mutant grown on a rich medium has a perturbed cell envelope and sheds a significant amount of membrane fragments in the external culture medium. These fragments contain mono- and dimycolate of trehalose and PorA/H, the major porin of C. glutamicum, but lack conventional phospholipids that typify the plasma membrane, suggesting that they are derived from the atypical mycolate outer membrane of the cell envelope. This is the first report of outer membrane destabilization in the Corynebacterineae, and it suggests that a strong interaction between the mycolate outer membrane and the underlying polymer is essential for cell envelope integrity. The presence of outer membrane-derived fragments (OMFs) in the external medium of the [DELTA]aftB mutant is also a very promising tool for outer membrane characterization. Indeed, fingerprint analysis of major OMF-associated proteins has already led to the identification of 3 associated mycoloyltransferases and an unknown protein with a C-terminal hydrophobic anchoring domain reminiscent of that found for the S-layer protein PS2 of C. glutamicum. doi: 10.1128/JB.00009-10

Corynebacterineae are gram-positive bacteria that possess a true outer membrane composed of mycolic acids and other lipids. Little is known concerning the modulation of mycolic acid composition and content in response to changes in the bacterial environment, especially temperature variations. To address this question, we investigated the function of the Rv3802c gene, a gene conserved in Corynebacterineae and located within a gene cluster involved in mycolic acid biosynthesis. We showed that the Rv3802 ortholog is essential in Mycobacterium smegmatis, while its Corynebacterium glutamicum ortholog, NCgl2775, is not. We provided evidence that the NCgl2775 gene is transcriptionally induced under heat stress conditions, and while the corresponding protein has no detectable activity under normal growth conditions, the increase in its expression triggers an increase in mycolic acid biosynthesis concomitant with a decrease in phospholipid content. We demonstrated that these lipid modifications are part of a larger outer membrane remodeling that occurs in response to exposure to a moderately elevated temperature (42 [degrees]C). In addition to showing an increase in the ratio of saturated corynomycolates to unsaturated corynomycolates, our results strongly suggested that the balance between mycolic acids and phospholipids is modified inside the outer membrane following a heat challenge. Furthermore, we showed that these lipid modifications help the bacteria to protect against heat damage. The NCgl2775 protein and its orthologs thus appear to be a protein family that plays a role in the regulation of the outer membrane lipid composition of Corynebacterineae under stress conditions. We therefore propose to name this protein family the envelope lipids regulation factor (ElrF) family. doi: 10.1128/JB.01042-09

Static converters are used with increasingly high switching frequencies. Consequently, they impose increasingly severe electromagnetic interference (EMI) constraints in their environment. In order to study and to quantify the radiated perturbations, we have used a test bench for measuring the magnetic field radiated in the near zone. In this paper, we present measurements of the magnetic field radiated by the switching cell of a Buck chopper in the near field at high and low frequencies. By comparing the mappings of the magnetic field over the switching cell with the ones of a circular loop, we have deduced that the switching cell can be effectively modeled by a loop. The loop's geometric characteristics and its equivalent current flowing in have been determined from near magnetic field data. The model has been validated at high and low frequencies. Index Terms--Magnefic field measurement, near field, power electronics.

With the fast development of power electronics circuits at increasing switching frequency (over 10 MHz), the multilayered printed circuits boards (PCBs) are being used more and more in the field of power electronics. In this paper, two main computational methods are presented to simulate the dynamic behavior of power electronics interconnection systems. Our aim is to present a methodology to analyze the electromagnetic (EM) behavior of power PCB regarding parasitic effects (EM couplings) or dynamic effects (impedance): a general procedure is given to calculate EM couplings between strip conductors in multilayered configurations based on the principle of hybrid methods. Finally, we propose a new method to limit computation time based on matrix Sparsification. Index Terms--Distributed model, hybrid methods, partial element equivalent circuit (PEEC), power electronics, printed circuits boards (PCBs) modeling, thin-wire method (TWM).

The characterization of the mle locus from Leuconostoc oenos shows a 2.6-kb transcript, indicating that it may have an operon structure containing the malolactic enzyme gene mleA and malate permease gene mleP. The mle operon has one transcription start site situated 17 nucleotides upstream of the ATG translation start site for the mleA gene. An 894-bp open reading frame (RF), that transcribes divergently from the mle operon, is located upstream of the mleA gene. This ORF encodes a polypeptide belonging to the LysR-type regulatory protein family, and has a molecular mass of 34 kDa.

The genes that code for the malolactic enzyme and the malate permease in the bacterium Leuconostoc oenos are arranged in a cluster. A 324-bp DNA fragment amplified by PCR from Leuconostoc oenos was used to screen the genome bank. Of the two open reading frames, the first protein has highly conserved protein regions. The expression of the gene in Escherichia coli and Saccharomyces cerevisiae produced malolactic activity in the organisms. The second open reading frame codes a protein that has properties of a carrier protein and probably has 10 membrane-spanning segments.

Corynebacterineae is a specific suborder of Gram-positive bacteria that includes Mycobacterium tuberculosis and Corynebacterium glutamicum. The ultrastructure of the cell envelope is very atypical. It is composed of a heteropolymer of peptidoglycan and arabinogalactan (AG) covalently associated to an outer membrane. Five arabinosyltransferases are involved in the biosynthesis of AG in C. glutamicum. AftB catalyzes the transfer of Araf (arabinofuranosyl) onto the arabinan domain of the arabinogalactan to form terminal beta(1 --> 2)-linked Araf residues. Here we show that Delta aftB cells lack half of the arabinogalactan mycoloylation sites but are still able to assemble an outer membrane. In addition, we show that a Delta aftB mutant grown on a rich medium has a perturbed cell envelope and sheds a significant amount of membrane fragments in the external culture medium. These fragments contain mono- and dimycolate of trehalose and PorA/H, the major porin of C. glutamicum, but lack conventional phospholipids that typify the plasma membrane, suggesting that they are derived from the atypical mycolate outer membrane of the cell envelope. This is the first report of outer membrane destabilization in the Corynebacterineae, and it suggests that a strong interaction between the mycolate outer membrane and the underlying polymer is essential for cell envelope integrity. The presence of outer membrane-derived fragments (OMFs) in the external medium of the Delta aftB mutant is also a very promising tool for outer membrane characterization. Indeed, fingerprint analysis of major OMF-associated proteins has already led to the identification of 3 associated mycoloyltransferases and an unknown protein with a C-terminal hydrophobic anchoring domain reminiscent of that found for the S-layer protein PS2 of C. glutamicum.