Biosynthesis of mycobacterial arabinogalactan: identification of a novel (13)arabinofuranosyltransferase

The cell wall mycolyl-arabinogalactan-peptidoglycan complex is essential in mycobacterial species, such as Mycobacterium tuberculosis and is the target of several anti-tubercular drugs. For instance, ethambutol targets arabinogalactan biosynthesis through inhibition of the arabinofuranosyltransferases Mt-EmbA and Mt-EmbB. A bioinformatics approach identified putative integral membrane proteins, MSMEG2785 in Mycobacterium smegmatis, Rv2673 in Mycobacterium tuberculosis and NCgl1822 in Corynebacterium glutamicum, with 10 predicted transmembrane domains and a glycosyltransferase motif (DDX), features that are common to the GT-C superfamily of glycosyltransferases. Deletion of M. smegmatis MSMEG2785 resulted in altered growth and glycosyl linkage analysis revealed the absence of AG (13)-linked arabinofuranosyl (Araf) residues. Complementation of the M. smegmatis deletion mutant was fully restored to a wild type phenotype by MSMEG2785 and Rv2673, and as a result, we have now termed this previously uncharacterized open reading frame, arabinofuranosyltransferase C (aftC). Enzyme assays using the sugar donor -D-arabinofuranosyl-1-monophosphoryldecaprenol (DPA) and a newly synthesized linear (15)-linked Ara5 neoglycolipid acceptor together with chemical identification of products formed, clearly identified AftC as a branching (13) arabinofuranosyltransferase. This newly discovered glycosyltransferase sheds further light on the complexities of Mycobacterium cell wall biosynthesis, such as in M. tuberculosis and related species and represents a potential new drug target

Domain size effects on the dynamics of a charge density wave in 1T-TaS2

Recent experiments have shown that the high temperature incommensurate (I) charge density wave (CDW) phase of 1T-TaS2 can be photoinduced from the lower temperature, nearly commensurate (NC) CDW state. Here we report a time-resolved x-ray diffraction study of the growth process of the photoinduced I-CDW domains. The layered nature of the material results in a marked anisotropy in the size of the photoinduced domains of the I-phase. These are found to grow self-similarly, their shape remaining unchanged throughout the growth process. The photoinduced dynamics of the newly formed I-CDW phase was probed at various stages of the growth process using a double pump scheme, where a first pump creates I-CDW domains and a second pump excites the newly formed I-CDW state. We observe larger magnitudes of the coherently excited I-CDW amplitude mode in smaller domains, which suggests that the incommensurate lattice distortion is less stable for smaller domain sizes.Comment: 8 pages, 8 figure

Unexpected population distribution in a microbial mat community: Sulfate-reducing bacteria localized to the highly oxic chemocline in contrast to a eukaryotic preference for anoxia

The distribution and abundance of sulfate-reducing bacteria (SRB) and eukaryotes within the upper 4 mm of a hypersaline cyanobacterial mat community were characterized at high resolution with group-specific hybridization probes to quantify 16S rRNA extracted from 100-mu m depth intervals. This revealed a preferential localization of SRB within the region defined by the oxygen chemocline. Among the different groups of SRB quantified, including members of the provisional families "Desulfovibrionaceae" and "Desulfobacteriaceae," Desulfonema-like populations dominated and accounted for up to 30% of total rRNA extracted from certain depth intervals of the chemocline. These data suggest that recognized genera of SRB are not necessarily restricted by high levels of oxygen in this mat community and the possibility of significant sulfur cycling within the chemocline. In marked contrast, eukaryotic populations in this community demonstrated a preference for regions of anoxia

Improving lipid recovery from Scenedesmus wet biomass by surfactant-assisted disruption

Citation: Lai, Y. S., De Francesco, F., Aguinaga, A., Parameswaran, P., & Rittmann, B. E. (2016). Improving lipid recovery from Scenedesmus wet biomass by surfactant-assisted disruption. Green Chemistry, 18(5), 1319-1326. doi:10.1039/c5gc02159fMicroalgae-derived lipids are good sources of biofuel, but extracting them involves high cost, energy expenditure, and environmental risk. Surfactant treatment to disrupt Scenedesmus biomass was evaluated as a means to make solvent extraction more efficient. Surfactant treatment increased the recovery of fatty acid methyl ester (FAME) by as much as 16-fold vs. untreated biomass using isopropanol extraction, and nearly 100% FAME recovery was possible without any Folch solvent, which is toxic and expensive. Surfactant treatment caused cell disruption and morphological changes to the cell membrane, as documented by transmission electron microscopy and flow cytometry. Surfactant treatment made it possible to extract wet biomass at room temperature, which avoids the expense and energy cost associated with heating and drying of biomass during the extraction process. The best FAME recovery was obtained from high-lipid biomass treated with Myristyltrimethylammonium bromide (MTAB)- and 3-(decyldimethylammonio)-propanesulfonate inner salt (3_DAPS)-surfactants using a mixed solvent (hexane : isopropanol = 1 : 1, v/v) vortexed for just 1 min; this was as much as 160-fold higher than untreated biomass. The critical micelle concentration of the surfactants played a major role in dictating extraction performance, but the growth stage of the biomass had an even larger impact on how well the surfactants disrupted the cells and improved lipid extraction. Surfactant treatment had minimal impact on extracted-FAME profiles and, consequently, fuel-feedstock quality. This work shows that surfactant treatment is a promising strategy for more efficient, sustainable, and economical extraction of fuel feedstock from microalgae

Coordination-driven magnetic-to-nonmagnetic transition in manganese doped silicon clusters

The interaction of a single manganese impurity with silicon is analyzed in a combined experimental and theoretical study of the electronic, magnetic, and structural properties of manganese-doped silicon clusters. The structural transition from exohedral to endohedral doping coincides with a quenching of high-spin states. For all geometric structures investigated, we find a similar dependence of the magnetic moment on the manganese coordination number and nearest neighbor distance. This observation can be generalized to manganese point defects in bulk silicon, whose magnetic moments fall within the observed magnetic-to-nonmagnetic transition, and which therefore react very sensitively to changes in the local geometry. The results indicate that high spin states in manganese-doped silicon could be stabilized by an appropriate lattice expansion

Watching the birth of a charge density wave order: diffraction study on nanometer-and picosecond-scales

Femtosecond time-resolved X-ray diffraction is used to study a photo-induced phase transition between two charge density wave (CDW) states in 1T-TaS$_2$, namely the nearly commensurate (NC) and the incommensurate (I) CDW states. Structural modulations associated with the NC-CDW order are found to disappear within 400 fs. The photo-induced I-CDW phase then develops through a nucleation/growth process which ends 100 ps after laser excitation. We demonstrate that the newly formed I-CDW phase is fragmented into several nanometric domains that are growing through a coarsening process. The coarsening dynamics is found to follow the universal Lifshitz-Allen-Cahn growth law, which describes the ordering kinetics in systems exhibiting a non-conservative order parameter.Comment: 6 pages, 5 figure

Archaea and Bacteria Acclimate to High Total Ammonia in a Methanogenic Reactor Treating Swine Waste

Citation: Esquivel-Elizondo, S., Parameswaran, P., Delgado, A. G., Maldonado, J., Rittmann, B. E., & Krajmalnik-Brown, R. (2016). Archaea and Bacteria Acclimate to High Total Ammonia in a Methanogenic Reactor Treating Swine Waste. Archaea-an International Microbiological Journal, 10. doi:10.1155/2016/4089684Inhibition by ammonium at concentrations above 1000mgN/L is known to harm the methanogenesis phase of anaerobic digestion. We anaerobically digested swine waste and achieved steady state COD-removal efficiency of around 52% with no fatty-acid or H-2 accumulation. As the anaerobic microbial community adapted to the gradual increase of total ammonia-N (NH3 -N) from 890 +/- 295 to 2040 +/- 30 mg/L, the Bacterial and Archaeal communities became less diverse. Phylotypes most closely related to hydrogenotrophic Methanoculleus (36.4%) and Methanobrevibacter (11.6%), along with acetoclastic Methanosaeta (29.3%), became the most abundant Archaeal sequences during acclimation. This was accompanied by a sharp increase in the relative abundances of phylotypes most closely related to acetogens and fatty-acid producers (Clostridium, Coprococcus, and Sphaerochaeta) and syntrophic fatty-acid Bacteria (Syntrophomonas, Clostridium, Clostridiaceae species, and Cloacamonaceae species) that have metabolic capabilities for butyrate and propionate fermentation, as well as for reverse acetogenesis. Our results provide evidence countering a prevailing theory that acetoclastic methanogens are selectively inhibited when the total ammonia-N concentration is greater than similar to 1000 mgN/L. Instead, acetoclastic and hydrogenotrophic methanogens coexisted in the presence of total ammonia-N of similar to 2000 mgN/L by establishing syntrophic relationships with fatty-acid fermenters, as well as homoacetogens able to carry out forward and reverse acetogenesis

Ultrafast relaxation dynamics of the antiferrodistortive phase in Ca doped SrTiO3

The ultrafast dynamics of the octahedral rotation in Ca:SrTiO3 is studied by time resolved x-ray diffraction after photo excitation over the band gap. By monitoring the diffraction intensity of a superlattice reflection that is directly related to the structural order parameter of the soft-mode driven antiferrodistortive phase in Ca:SrTiO3, we observe a ultrafast relaxation on a 0.2 ps timescale of the rotation of the oxygen octahedron, which is found to be independent of the initial temperaure despite large changes in the corresponding soft-mode frequency. A further, much smaller reduction on a slower picosecond timescale is attributed to thermal effects. Time-dependent density-functional-theory calculations show that the fast response can be ascribed to an ultrafast displacive modification of the soft-mode potential towards the normal state, induced by holes created in the oxygen 2p states