Bacteria Pattern Spontaneously on Periodic Nanostructure Arrays

Surface-associated bacteria typically form self-organizing communities called biofilms. Spatial segregation is important for various bacterial processes associated with cellular and community development. Here, we demonstrate bacterial ordering and oriented attachment on the single-cell level induced by nanometer-scale periodic surface features. These surfaces cause spontaneous and distinct patterning phases, depending on their periodicity, which is observed for several strains, both gram positive and negative. This patterning is a general phenomenon that can control natural biofilm organization.Chemistry and Chemical BiologyEngineering and Applied Science

Enhanced thermoelectric performance of a chalcopyrite compound CuIn3Se5-xTex (x=0~0.5) through crystal structure engineering

In this work the chalcopyrite CuIn3Se5−xTex (x = 0~0.5) with space group through isoelectronic substitution of Te for Se have been prepared, and the crystal structure dilation has been observed with increasing Te content. This substitution allows the anion position displacement ∆u = 0.25-u to be zero at x ≈ 0.15. However, the material at x = 0.1 (∆u = 0.15 × 10−3), which is the critical Te content, presents the best thermoelectric (TE) performance with dimensionless figure of merit ZT = 0.4 at 930 K. As x value increases from 0.1, the quality factor B, which informs about how large a ZT can be expected for any given material, decreases, and the TE performance degrades gradually due to the reduction in nH and enhancement in κL. Combining with the ZTs from several chalcopyrite compounds, it is believable that the best thermoelectric performance can be achieved at a certain ∆u value (∆u ≠ 0) for a specific space group if their crystal structures can be engineered

Roadmap on emerging concepts in the physical biology of bacterial biofilms: from surface sensing to community formation

Bacterial biofilms are communities of bacteria that exist as aggregates that can adhere to surfaces or be free-standing. This complex, social mode of cellular organization is fundamental to the physiology of microbes and often exhibits surprising behavior. Bacterial biofilms are more than the sum of their parts: single-cell behavior has a complex relation to collective community behavior, in a manner perhaps cognate to the complex relation between atomic physics and condensed matter physics. Biofilm microbiology is a relatively young field by biology standards, but it has already attracted intense attention from physicists. Sometimes, this attention takes the form of seeing biofilms as inspiration for new physics. In this roadmap, we highlight the work of those who have taken the opposite strategy: we highlight the work of physicists and physical scientists who use physics to engage fundamental concepts in bacterial biofilm microbiology, including adhesion, sensing, motility, signaling, memory, energy flow, community formation and cooperativity. These contributions are juxtaposed with microbiologists who have made recent important discoveries on bacterial biofilms using state-of-the-art physical methods. The contributions to this roadmap exemplify how well physics and biology can be combined to achieve a new synthesis, rather than just a division of labor

Metabolic fingerprinting of bacteria by fluorescence lifetime imaging microscopy.

Bacterial populations exhibit a range of metabolic states influenced by their environment, intra- and interspecies interactions. The identification of bacterial metabolic states and transitions between them in their native environment promises to elucidate community behavior and stochastic processes, such as antibiotic resistance acquisition. In this work, we employ two-photon fluorescence lifetime imaging microscopy (FLIM) to create a metabolic fingerprint of individual bacteria and populations. FLIM of autofluorescent reduced nicotinamide adenine dinucleotide (phosphate), NAD(P)H, has been previously exploited for label-free metabolic imaging of mammalian cells. However, NAD(P)H FLIM has not been established as a metabolic proxy in bacteria. Applying the phasor approach, we create FLIM-phasor maps of Escherichia coli, Salmonella enterica serovar Typhimurium, Pseudomonas aeruginosa, Bacillus subtilis, and Staphylococcus epidermidis at the single cell and population levels. The bacterial phasor is sensitive to environmental conditions such as antibiotic exposure and growth phase, suggesting that observed shifts in the phasor are representative of metabolic changes within the cells. The FLIM-phasor approach represents a powerful, non-invasive imaging technique to study bacterial metabolism in situ and could provide unique insights into bacterial community behavior, pathology and antibiotic resistance with sub-cellular resolution

Metabolic fingerprinting of bacteria by fluorescence lifetime imaging microscopy.

Bacterial populations exhibit a range of metabolic states influenced by their environment, intra- and interspecies interactions. The identification of bacterial metabolic states and transitions between them in their native environment promises to elucidate community behavior and stochastic processes, such as antibiotic resistance acquisition. In this work, we employ two-photon fluorescence lifetime imaging microscopy (FLIM) to create a metabolic fingerprint of individual bacteria and populations. FLIM of autofluorescent reduced nicotinamide adenine dinucleotide (phosphate), NAD(P)H, has been previously exploited for label-free metabolic imaging of mammalian cells. However, NAD(P)H FLIM has not been established as a metabolic proxy in bacteria. Applying the phasor approach, we create FLIM-phasor maps of Escherichia coli, Salmonella enterica serovar Typhimurium, Pseudomonas aeruginosa, Bacillus subtilis, and Staphylococcus epidermidis at the single cell and population levels. The bacterial phasor is sensitive to environmental conditions such as antibiotic exposure and growth phase, suggesting that observed shifts in the phasor are representative of metabolic changes within the cells. The FLIM-phasor approach represents a powerful, non-invasive imaging technique to study bacterial metabolism in situ and could provide unique insights into bacterial community behavior, pathology and antibiotic resistance with sub-cellular resolution

The Phe-Ile Zipper: A Specific Interaction Motif Drives Antiparallel Coiled-Coil Hexamer Formation

Coiled coils are a robust motif for exploring amino acid interactions, generating unique supramolecular structures, and expanding the functional properties of biological materials. A recently discovered antiparallel coiled-coil hexamer (ACC-Hex, peptide <b>1</b>) exhibits a unique interaction in which Phe and Ile residues from adjacent α-helices interact to form a Phe-Ile zipper within the hydrophobic core. Analysis of the X-ray crystallographic structure of ACC-Hex suggests that the stability of the six-helix bundle relies on specific interactions between the Phe and Ile residues. The Phe-Ile zipper is unprecedented and represents a powerful tool for utilizing the Phe-Ile interactions to direct supramolecular assembly. To further probe and understand the limits of the Phe-Ile zipper, we designed peptide sequences with natural and unnatural amino acids placed at the Phe and Ile residue positions. Using size exclusion chromatography and small-angle X-ray scattering, we found that the proper assembly of ACC-Hex from monomers is sensitive to subtle changes in side chain steric bulk and hydrophobicity introduced by mutations at the Phe and Ile residue positions. Of the sequence variants that formed ACC-Hex, mutations in the hydrophobic core significantly affected the stability of the hexamer, from a Δ<i>G</i>_u^w of 2–8 kcal mol^–1. Additional sequences were designed to further probe and enhance the stability of the ACC-Hex system by maximizing salt bridging between the solvent-exposed residues. Finally, we expanded on the generality of the Phe-Ile zipper, creating a unique sequence that forms an antiparallel hexamer that is topologically similar to ACC-Hex but atomistically unique

X‑ray Crystallographic Structure and Solution Behavior of an Antiparallel Coiled-Coil Hexamer Formed by <i>de Novo</i> Peptides

The self-assembly of peptides and proteins into higher-ordered structures is encoded in the amino acid sequence of each peptide or protein. Understanding the relationship among the amino acid sequence, the assembly dynamics, and the structure of well-defined peptide oligomers expands the synthetic toolbox for these structures. Here, we present the X-ray crystallographic structure and solution behavior of <i>de novo</i> peptides that form antiparallel coiled-coil hexamers (ACC-Hex) by an interaction motif neither found in nature nor predicted by existing peptide design software. The 1.70 Å X-ray crystallographic structure of peptide <b>1a</b> shows six α-helices associating in an antiparallel arrangement around a central axis comprising hydrophobic and aromatic residues. Size-exclusion chromatography studies suggest that peptides <b>1</b> form stable oligomers in solution, and circular dichroism experiments show that peptides <b>1</b> are stable to relatively high temperatures. Small-angle X-ray scattering studies of the solution behavior of peptide <b>1a</b> indicate an equilibrium of dimers, hexamers, and larger aggregates in solution. The structures presented here represent a new motif of biomolecular self-assembly not previously observed for <i>de novo</i> peptides and suggest supramolecular design principles for material scaffolds based on coiled-coil motifs containing aromatic residues

Single crystalline mesoporous silicon nanowires Nano Lett.

. In addition, they can also serve as drug or gene delivery matrix because of their good bio-compatibilit