Unveiling the biodiversity of lipid species in Corynebacteria- characterization of the uncommon lipid families in C. glutamicum and pathogen C. striatum by mass spectrometry.

Uncommon lipids in biotechnologically important Corynebacterium glutamicum and pathogen Corynebacterium striatum in genus Corynebacterium are isolated and identified by linear ion-trap multiple stage mass spectrometry (LIT MSn) with high resolution mass measurement. We redefined several lipid structures that were previously mis-assigned or not defined, including cytidine diphosphate diacylglycerol (CDP-DAG), glucuronosyl diacylglycerol (GlcA-DAG), (α-d-mannopyranosyl)-(1 â†’ 4)-(α-D-glucuronyl diacyglycerol (Man-GlcA-DAG), 1-mycolyl-2-acyl-phosphatidylglycerol (MA-PG), acyl trehalose monomycolate (acyl-TMM). We also report the structures of mycolic acid, phosphatidylglycerol, phosphatidylinositol, cardiolipin, trehalose dimycolate lipids in which many isomeric structures are present. The LIT MSn approaches afford identification of the functional group, the fatty acid substituents and their regiospecificity in the molecules, revealing the biodiversities of the lipid species in two Corynebacterium strains that have played very different and important roles in human nutrition and health.

Mechanism of High-Level Daptomycin Resistance in Corynebacterium striatum.

Daptomycin, a last-line-of-defense antibiotic for treating Gram-positive infections, is experiencing clinical failure against important infectious agents, including Corynebacterium striatum The recent transition of daptomycin to generic status is projected to dramatically increase availability, use, and clinical failure. Here we confirm the genetic mechanism of high-level daptomycin resistance (HLDR; MIC = >256 µg/ml) in C. striatum, which evolved within a patient during daptomycin therapy, a phenotype recapitulated in vitro In all 8 independent cases tested, loss-of-function mutations in phosphatidylglycerol synthase (pgsA2) were necessary and sufficient for high-level daptomycin resistance. Through lipidomic and biochemical analysis, we demonstrate that daptomycin's activity is dependent on the membrane phosphatidylglycerol (PG) concentration. Until now, the verification of PG as the in vivo target of daptomycin has proven difficult since tested cell model systems were not viable without membrane PG. C. striatum becomes daptomycin resistant at a high level by removing PG from the membrane and changing the membrane composition to maintain viability. This work demonstrates that loss-of-function mutation in pgsA2 and the loss of membrane PG are necessary and sufficient to produce high-level resistance to daptomycin in C. striatumIMPORTANCE Antimicrobial resistance threatens the efficacy of antimicrobial treatment options, including last-line-of-defense drugs. Understanding how this resistance develops can help direct antimicrobial stewardship efforts and is critical to designing the next generation of antimicrobial therapies. Here we determine how Corynebacterium striatum, a skin commensal and opportunistic pathogen, evolved high-level resistance to a drug of last resort, daptomycin. Through a single mutation, this pathogen was able to remove the daptomycin's target, phosphatidylglycerol (PG), from the membrane and evade daptomycin's bactericidal activity. We found that additional compensatory changes were not necessary to support the removal of PG and replacement with phosphatidylinositol (PI). The ease with which C. striatum evolved high-level resistance is cause for alarm and highlights the importance of screening new antimicrobials against a wide range of clinical pathogens which may harbor unique capacities for resistance evolution.

Comparative transcriptomics elucidates adaptive phenol tolerance and utilization in lipid-accumulating Rhodococcus opacus PD630.

Lignin-derived (e.g. phenolic) compounds can compromise the bioconversion of lignocellulosic biomass to fuels and chemicals due to their toxicity and recalcitrance. The lipid-accumulating bacterium Rhodococcus opacus PD630 has recently emerged as a promising microbial host for lignocellulose conversion to value-added products due to its natural ability to tolerate and utilize phenolics. To gain a better understanding of its phenolic tolerance and utilization mechanisms, we adaptively evolved R. opacus over 40 passages using phenol as its sole carbon source (up to 373% growth improvement over wild-type), and extensively characterized two strains from passages 33 and 40. The two adapted strains showed higher phenol consumption rates (∼20 mg/l/h) and ∼2-fold higher lipid production from phenol than the wild-type strain. Whole-genome sequencing and comparative transcriptomics identified highly-upregulated degradation pathways and putative transporters for phenol in both adapted strains, highlighting the important linkage between mechanisms of regulated phenol uptake, utilization, and evolved tolerance. Our study shows that the R. opacus mutants are likely to use their transporters to import phenol rather than export them, suggesting a new aromatic tolerance mechanism. The identified tolerance genes and pathways are promising candidates for future metabolic engineering in R. opacus for improved lignin conversion to lipid-based products.

IQGAP1: a regulator of intracellular spacetime relativity.

Activating and inhibiting receptors of lymphocytes collect valuable information about their mikròs kósmos. This information is essential to initiate or to turn off complex signaling pathways. Irrespective of these advances, our knowledge on how these intracellular activation cascades are coordinated in a spatiotemporal manner is far from complete. Among multiple explanations, the scaffolding proteins have emerged as a critical piece of this evolutionary tangram. Among many, IQGAP1 is one of the essential scaffolding proteins that coordinate multiple signaling pathways. IQGAP1 possesses multiple protein interaction motifs to achieve its scaffolding functions. Using these domains, IQGAP1 has been shown to regulate a number of essential cellular events. This includes actin polymerization, tubulin multimerization, microtubule organizing center formation, calcium/calmodulin signaling, Pak/Raf/Mek1/2-mediated Erk1/2 activation, formation of maestrosome, E-cadherin, and CD44-mediated signaling and glycogen synthase kinase-3/adenomatous polyposis coli-mediated ß-catenin activation. In this review, we summarize the recent developments and exciting new findings of cellular functions of IQGAP1.