Yeast cell attachment: a tool modulating wall composition and resistance to 5-bromo-6-azauracil

The attachment of Candida utilis, Kluyveromyces lactis, and Saccharomyces cerevisiae cells stimulates an increase in the content of cell wall polysaccharides and mannoproteins, accompanied by increased resistance to the inhibitory effect of 5-bromo-6-azauracil. The covalent attachment of viable yeasts was accomplished (via dialdehyde-amino spacers) by reaction of aldehyde groups of the carrier with reactive amino groups in accessible cell surface proteins. The employed technique enables the optimization of yeast sources of β-1,3-, β-1,6- glucans, mannan, and mannoprotein. The modulatory effect of the cell attachment is discussed.     

Asymmetric swimming pattern of Vibrio alginolyticus cells with single polar flagella

The swimming pattern of bacteria with single polar flagella has usually been described as "run and reverse". We observed the swimming traces of monotrichously flagellated Vibrio alginolyticus cells and examined the relationship between the swimming pattern and the sense of progress. Swimming in regions other than a solid surface was confirmed to be linear run and reverse. Near a solid surface, the traces consisted of "run and arc"; the cells were found to curve sharply during backward swimming, while they progressed linearly during forward swimming. The "run and arc" swimming pattern may play an important role in the chemotaxis strategy of marine bacteria at solid surfaces.     

Slow Onset Inhibition of Bacterial ��-Ketoacyl-acyl Carrier Protein Synthases by Thiolactomycin

Thiolactomycin (TLM), a natural product thiolactone antibiotic produced by species of Nocardia and Streptomyces, is an inhibitor of the β-ketoacyl-acyl carrier protein synthase (KAS) enzymes in the bacterial fatty acid synthase pathway. Using enzyme kinetics and direct binding studies, TLM has been shown to bind preferentially to the acyl-enzyme intermediates of the KASI and KASII enzymes from Mycobacterium tuberculosis and Escherichia coli. These studies, which utilized acyl-enzyme mimics in which the active site cysteine was replaced by a glutamine, also revealed that TLM is a slow onset inhibitor of the KASI enzymes KasA and ecFabB but not of the KASII enzymes KasB and ecFabF. The differential affinity of TLM for the acyl-KAS enzymes is proposed to result from structural change involving the movement of helices α5 and α6 that prepare the enzyme to bind malonyl-AcpM or TLM and that is initiated by formation of hydrogen bonds between the acyl-enzyme thioester and the oxyanion hole. The finding that TLM is a slow onset inhibitor of ecFabB supports the proposal that the long residence time of TLM on the ecFabB homologues in Serratia marcescens and Klebsiella pneumonia is an important factor for the in vivo antibacterial activity of TLM against these two organisms despite the fact that the in vitro MIC values are only 100–200 μg/ml. The mechanistic data on the interaction of TLM with KasA will provide an important foundation for the rational development of high affinity KasA inhibitors based on the thiolactone skeleton.     

L’Observatoire hommes–milieux international Tessékéré (OHMi) : un outil de recherche pour étudier la complexité des écosystèmes arides du Sahel

In the Sahelian zone, the drought phenomenon, combined with anthropic factors (monoculture, bush fires, defect or deficit of manure, overgrazing, etc.), has seriously affected ecological great balances, involving a degradation of the natural resources as well as a fall in agricultural productions, pointing to a process of desertification. To face these challenges, in the course of the 8th ordinary session of the conference of the Heads of States of the African Union held in January 2007 in Addis Ababa (Ethiopia), 11 countries adopted the Panafrican project called the Green Great Wall (GGW). The total objective of the GGW is to contribute i) to the fight against the desert's advance, ii) to the development of the Saharan-Sahelian zones toward a durable management of the natural resources, and iii) to the fight against poverty. It deals with the construction of a set of zones of afforestation crossing the whole African continent in the long term (7000 km of which are in the west). Even if some decisions in the launching phase the GGW must be taken quickly, one cannot do without investment in interdisciplinary research. In particular, associating fundamental research and applied research will allow us to ensure the success in the medium and long term of such a large-scale reforestation project. Research segmented in compartmentalized knowledge fields needed to get adequate tools, among which OHMi Tessékéré, initiated by INNEE (Centre national de la recherche scientifique [CNRS]), in partnership with UCAD, constitutes an example. This suitable scientific tool, capable of action flexibility, of self-financing capacity, anchored in civil society, ready to implement a pragmatic and local interdisciplinarity founded currently on the concept of socio-ecological system (SES), is the one we chose to conduct our studies on the Ferlo arid ecosystems.     

Norditerpenoid alkaloids from the roots of Aconitum heterophyllum Wall with antibacterial activity

Two new aconitine-type norditerpenoid alkaloids 6-dehydroacetylsepaconitine (1) and 13-hydroxylappaconitine (2), along with three known norditerpenoid alkaloids lycoctonine, delphatine and lappaconitine were isolated from the roots of the Aconitum heterophyllum Wall. These compounds exhibited significant antibacterial activity. The structure of compound 1 and 2 were deduced on the basis of their spectral data.     

北柴胡不定根系生物转化合成皂苷研究

通过在北柴胡不定根系培养体系中添加目的产物柴胡皂苷的前体物质和生物合成促进物质以及进行高糖渗透胁迫试验,探讨了利用不定根系生产柴胡皂苷的条件和方法。结果表明,在1/2 MS培养基中添加硫酸镁、硝酸钾、丙酮酸钠以及高糖渗透胁迫均有利于柴胡皂苷的合成。1/2 MS培养基+硫酸镁0.37 g/L+硝酸钾5.7 g/L+丙酮酸钠2.0 mmol/L+蔗糖50 g/L是最适合柴胡皂苷转化合成的培养基,此条件下使柴胡皂苷的含量提高了9.74倍。     

Structural and Biochemical Analyses of Mycobacterium tuberculosis N-Acetylmuramyl-l-alanine Amidase Rv3717 Point to a Role in Peptidoglycan Fragment Recycling

Peptidoglycan hydrolases are key enzymes in bacterial cell wall homeostasis. Understanding the substrate specificity and biochemical activity of peptidoglycan hydrolases in Mycobacterium tuberculosis is of special interest as it can aid in the development of new cell wall targeting therapeutics. In this study, we report biochemical and structural characterization of the mycobacterial N-acetylmuramyl-l-alanine amidase, Rv3717. The crystal structure of Rv3717 in complex with a dipeptide product shows that, compared with previously characterized peptidoglycan amidases, the enzyme contains an extra disulfide-bonded β-hairpin adjacent to the active site. The structure of two intermediates in assembly reveal that Zn²⁺ binding rearranges active site residues, and disulfide formation promotes folding of the β-hairpin. Although Zn²⁺ is required for hydrolysis of muramyl dipeptide, disulfide oxidation is not required for activity on this substrate. The orientation of the product in the active site suggests a role for a conserved glutamate (Glu-200) in catalysis; mutation of this residue abolishes activity. The product binds at the head of a closed tunnel, and the enzyme showed no activity on polymerized peptidoglycan. These results point to a potential role for Rv3717 in peptidoglycan fragment recycling.