DNA Builds and Strengthens the Extracellular Matrix in Myxococcus xanthus Biofilms by Interacting with Exopolysaccharides

One intriguing discovery in modern microbiology is the extensive presence of extracellular DNA (eDNA) within biofilms of various bacterial species. Although several biological functions have been suggested for eDNA, including involvement in biofilm formation, the detailed mechanism of eDNA integration into biofilm architecture is still poorly understood. In the biofilms formed by Myxococcus xanthus, a Gram-negative soil bacterium with complex morphogenesis and social behaviors, DNA was found within both extracted and native extracellular matrices (ECM). Further examination revealed that these eDNA molecules formed well organized structures that were similar in appearance to the organization of exopolysaccharides (EPS) in ECM. Biochemical and image analyses confirmed that eDNA bound to and colocalized with EPS within the ECM of starvation biofilms and fruiting bodies. In addition, ECM containing eDNA exhibited greater physical strength and biological stress resistance compared to DNase I treated ECM. Taken together, these findings demonstrate that DNA interacts with EPS and strengthens biofilm structures in M. xanthus.     

Tools for high efficiency genetic manipulation of the human pathogen Penicillium marneffei

Penicillium marneffei is an opportunistic pathogen of humans and displays a temperature dependent dimorphic transition. Like many fungi, exogenous DNA introduced by DNA mediated transformation is integrated randomly into the genome resulting in inefficient gene deletion and position-specific effects. To enhance successful gene targeting, the consequences of perturbing components of the non-homologous end joining recombination pathway have been examined. The deletion of the KU70 and LIG4 orthologs, pkuA and ligD, respectively, dramatically enhanced the observed homologous recombination frequency leading to efficient gene deletion. While ΔpkuA was associated with reduced genetic stability over-time, ΔligD represents a suitable recipient strain for downstream applications and combined with a modified Gateway? system for the rapid generation of gene deletion constructs, this represents an efficient pipeline for characterizing gene function in P. marneffei.     

Molecular cooperativity of drebrin(1-300) binding and structural remodeling of f-actin

Drebrin A, an actin-binding protein, is a key regulatory element in synaptic plasticity of neuronal dendrites. Understanding how drebrin binds and remodels F-actin is important for a functional analysis of their interactions. Conventionally, molecular models for protein-protein interactions use binding parameters derived from bulk solution measurements with limited spatial resolution, and the inherent assumption of homogeneous binding sites. In the case of actin filaments, their structural and dynamic states—as well as local changes in those states—may influence their binding parameters and interaction cooperativity. Here, we probed the structural remodeling of single actin filaments and the binding cooperativity of DrebrinA_1-300 –F–actin using AFM imaging. We show direct evidence of DrebrinA_1-300-induced cooperative changes in the helical structure of F-actin and observe the binding cooperativity of drebrin to F-actin with nanometer resolution. The data confirm at the in vitro molecular level that variations in the F-actin helical structure can be modulated by cooperative binding of actin-binding proteins.     

Tunable Properties of Surface Plasmon Resonance of Metal Nanospheroid: Graphene Plasmon Interaction

Plasmonics - Graphene plasmonic resonances play a significant role for enhancing the photon absorption inside thin film solar devices. We investigate the field rising at the intersection of...