Izolacija, biokemijske značajke i identifikacija termotolerantnih i celulolitičkih bakterija Paenibacillus lactis i Bacillus licheniformis

Research background. Cellulose is an ingredient of waste materials that can be converted to other valuable substances. This is possible provided that the polymer molecule is degraded to smaller particles and used as a carbon source by microorganisms. Because of the frequently applied methods of pretreatment of lignocellulosic materials, the cellulases derived from thermophilic microorganisms are particularly desirable. Experimental approach. We were looking for cellulolytic microorganisms able to grow at 50 °C and we described their morphological features and biochemical characteristics based on carboxymethyl cellulase (CMCase) activity and the API® ZYM system. The growth curves during incubation at 50 °C were examined using the BioLector® microbioreactor. Results and conclusions. Forty bacterial strains were isolated from fermenting hay, geothermal karst spring, hot spring and geothermal pond at 50 °C. The vast majority of the bacteria were Gram-positive and rod-shaped with the maximum growth temperature of at least 50 °C. We also demonstrated a large diversity of biochemical characteristics among the microorganisms. The CMCase activity was confirmed in 27 strains. Hydrolysis capacities were significant in bacterial strains: BBLN1, BSO6, BSO10, BSO13 and BSO14, and reached 2.74, 1.62, 1.30, 1.38 and 8.02 respectively. Rapid and stable growth was observed, among others, for BBLN1, BSO10, BSO13 and BSO14. The strains fulfilled the selection conditions and were identified based on the 16S rDNA sequences. BBLN1, BSO10, BSO13 were classified as Bacillus licheniformis, whereas BSO14 as Paenibacillus lactis. Novelty and scientific contribution. We described cellulolytic activity and biochemical characteristics of many bacteria isolated from hot environments. We are also the first to report the cellulolytic activity of thermotolerant P. lactis. Described strains can be a source of new thermostable cellulases, which are extremely desirable in various branches of circular bioeconomy.Pozadina istraživanja. Celuloza je sastojak otpadnih tvari koji se može preraditi u korisne spojeve. To je moguće ako se molekule polimera razgrade na manje čestice koje mikroorganizmi mogu iskoristiti kao izvor ugljika. Celulaze proizvedene s pomoću termofilnih mikroorganizama su naročito zanimljive zbog njihove učestale primjene u prethodnoj obradi lignoceluloznog materijala. Eksperimentalni pristup. Istražili smo celulolitičke mikroorganizme koji rastu na 50 °C te opisali njihove morfološke i biokemijske značajke na osnovi aktivnosti karboksimetil celulaze i ostalih enzima ispitanih sustavom API® ZYM. Krivulje rasta tijekom inkubacije pri 50 °C ispitane su uzgojem bakterija u mikrobioreaktoru BioLector®. Rezultati i zaključci. Četrdeset sojeva bakterija izolirano je iz fermentirane slame, geotermičkog izvora u kršu, termalnog vrela i geotermalnog jezera s temperaturom od 50 °C. Većina bakterija bile su Gram-pozitivne i štapićastog oblika, a najviša temperatura pri kojoj su rasle je iznosila najmanje 50 °C. Također smo potvrdili veliku raznolikost biokemijskih značajki među ispitanim mikroorganizmima. Aktivnost karboksimetil celulaze potvrđena je u 27 sojeva. Sojevi bakterija sa značajnim hidrolitičkim kapacitetom bili su: BBLN1 s 2,74; BSO6 s 1,62; BSO10 s 1,30; BSO13 s 1.38 i BSO14 s kapacitetom od 8,02. Sojevi BBLN1, BSO10, BSO13 i BSO14 rasli su brzo i stabilno. Ispunjavali su odabrane preduvjete pa su identificirani 16S rDNA sekvenciranjem. Sojevi BBLN1, BSO10 i BSO13 klasificirani su kao sojevi bakterije Bacillus licheniformis, dok je soj BSO14 potvrđen kao soj Paenibacillus lactis. Novina i znanstveni doprinos. Opisali smo celulolitičku aktivnost i biokemijska svojstva velikog broja bakterija izoliranih iz lokacija gdje vladaju velike vrućine. Prvi smo izvijestili o celulolitičkoj aktivnosti termotolerantne bakterije P. lactis. Opisani bi sojevi mogli biti izvor novih termički stabilnih celulaza, što je izuzetno poželjno u različitim granama cirkularne bioekonomije

Hydroelementation of diynes

This review highlights the hydroelementation reactions of conjugated and separated diynes, which depending on the process conditions, catalytic system, as well as the type of reagents, leads to the formation of various products: enynes, dienes, allenes, polymers, or cyclic compounds. The presence of two triple bonds in the diyne structure makes these compounds important reagents but selective product formation is often difficult owing to problems associated with maintaining appropriate reaction regio- and stereoselectivity. Herein we review this topic to gain knowledge on the reactivity of diynes and to systematise the range of information relating to their use in hydroelementation reactions. The review is divided according to the addition of the E–H (E = Mg, B, Al, Si, Ge, Sn, N, P, O, S, Se, Te) bond to the triple bond(s) in the diyne, as well as to the type of the reagent used, and the product formed. Not only are the hydroelementation reactions comprehensively discussed, but the synthetic potential of the obtained products is also presented. The majority of published research is included within this review, illustrating the potential as well as limitations of these processes, with the intent to showcase the power of these transformations and the obtained products in synthesis and materials chemistry

Structural studies suggest aggregation as one of the modes of action for teixobactin

Teixobactin is a new promising antibiotic that targets cell wall biosynthesis by binding to lipid II and has no detectable resistance thanks to its unique but yet not fully understood mechanism of operation. To aid in the structure-based design of teixobactin analogues with improved pharmacological properties, we present a 3D structure of native teixobactin in membrane mimetics and characterise its binding to lipid II through a combination of solution NMR and fast (90 kHz) magic angle spinning solid state NMR. In NMR titrations, we observe a pattern strongly suggesting interactions between the backbone of the C-terminal “cage” and the pyrophosphate moiety in lipid II. We find that the N-terminal part of teixobactin does not only act as a membrane anchor, as previously thought, but is actively involved in binding. Moreover, teixobactin forms a well-structured and specific complex with lipid II, where the N-terminal part of teixobactin assumes a b conformation that is highly prone to aggregation, which likely contributes to the antibiotic's high bactericidal efficiency. Overall, our study provides several new clues to teixobactin's modes of action

Substrate and Stereochemical Control of Peptidoglycan Cross-Linking by Transpeptidation by Escherichia coli PBP1B

Penicillin binding proteins (PBPs) catalyzing transpeptidation reactions that stabilize the peptidoglycan component of the bacterial cell wall are the targets of β-lactams, the most clinically successful antibiotics to date. However, PBP-transpeptidation enzymology has evaded detailed analysis, because of the historical unavailability of kinetically competent assays with physiologically relevant substrates and the previously unappreciated contribution of protein cofactors to PBP activity. By re-engineering peptidoglycan synthesis, we have constructed a continuous spectrophotometric assay for transpeptidation of native or near native peptidoglycan precursors and fragments by Escherichia coli PBP1B, allowing us to (a) identify recognition elements of transpeptidase substrates, (b) reveal a novel mechanism of stereochemical editing within peptidoglycan transpeptidation, (c) assess the impact of peptidoglycan substrates on β-lactam targeting of transpeptidation, and (d) demonstrate that both substrates have to be bound before transpeptidation occurs. The results allow characterization of high molecular weight PBPs as enzymes and not merely the targets of β-lactam acylation

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements