Combination of hydrophobicity and codon usage bias determines sorting of model K+ channel protein to either mitochondria or endoplasmic reticulum.

When the K+ channel-like protein Kesv from Ectocarpus siliculosus virus 1 is heterologously expressed in mammalian cells, it is sorted to the mitochondria. This targeting can be redirected to the endoplasmic reticulum (ER) by altering the codon usage in distinct regions of the gene or by inserting a triplet of hydrophobic amino acids (AAs) into the protein's C-terminal transmembrane domain (ct-TMD). Systematic variations in the flavor of the inserted AAs and/or its codon usage show that a positive charge in the inserted AA triplet alone serves as strong signal for mitochondria sorting. In cases of neutral AA triplets, mitochondria sorting are favored by a combination of hydrophilic AAs and rarely used codons; sorting to the ER exhibits the inverse dependency. This propensity for ER sorting is particularly high when a common codon follows a rarer one in the AA triplet; mitochondria sorting in contrast is supported by codon uniformity. Since parameters like positive charge, hydrophobic AAs, and common codons are known to facilitate elongation of nascent proteins in the ribosome the data suggest a mechanism in which local changes in elongation velocity and co-translational folding in the ct-TMD influence intracellular protein sorting.

Learning the relationship between nanoscale chemical patterning and hydrophobicity.

The hydrophobicity of proteins and similar surfaces, which display chemical heterogeneity at the nanoscale, drives countless aqueous interactions and assemblies. However, predicting how surface chemical patterning influences hydrophobicity remains a challenge. Here, we address this challenge by using molecular simulations and machine learning to characterize and model the hydrophobicity of a diverse library of patterned surfaces, spanning a wide range of sizes, shapes, and chemical compositions. We find that simple models, based only on polar content, are inaccurate, whereas complex neural network models are accurate but challenging to interpret. However, by systematically incorporating chemical correlations between surface groups into our models, we are able to construct a series of minimal models of hydrophobicity, which are both accurate and interpretable. Our models highlight that the number of proximal polar groups is a key determinant of hydrophobicity and that polar neighbors enhance hydrophobicity. Although our minimal models are trained on particular patch size and shape, their interpretability enables us to generalize them to rectangular patches of all shapes and sizes. We also demonstrate how our models can be used to predict hot-spot locations with the largest marginal contributions to hydrophobicity and to design chemical patterns that have a fixed polar content but vary widely in their hydrophobicity. Our data-driven models and the principles they furnish for modulating hydrophobicity could facilitate the design of novel materials and engineered proteins with stronger interactions or enhanced solubilities.

Interaction between S4 and the phosphatase domain mediates electrochemical coupling in voltage-sensing phosphatase (VSP).

Voltage-sensing phosphatase (VSP) consists of a voltage sensor domain (VSD) and a cytoplasmic catalytic region (CCR), which is similar to phosphatase and tensin homolog (PTEN). How the VSD regulates the innate enzyme component of VSP remains unclear. Here, we took a combined approach that entailed the use of electrophysiology, fluorometry, and structural modeling to study the electrochemical coupling in Ciona intestinalis VSP. We found that two hydrophobic residues at the lowest part of S4 play an essential role in the later transition of VSD-CCR coupling. Voltage clamp fluorometry and disulfide bond locking indicated that S4 and its neighboring linker move as one helix (S4-linker helix) and approach the hydrophobic spine in the CCR, a structure located near the cell membrane and also conserved in PTEN. We propose that the hydrophobic spine operates as a hub for translating an electrical signal into a chemical one in VSP.

Contiguously hydrophobic sequences are functionally significant throughout the human exome.

Hydrophobic interactions have long been established as essential for stabilizing struc-tured proteins as well as drivers of aggregation, but the impact of hydrophobicity on thefunctional significance of sequence variants has rarely been considered in a genome-wide context. Here we test the role of hydrophobicity on functional impact across70,000 disease- and non­disease-associated single-nucleotide polymorphisms (SNPs),using enrichment of disease association as an indicator of functionality. We find thatfunctional impact is uncorrelated with hydrophobicity of the SNP itself and only weaklycorrelated with the average local hydrophobicity, but is strongly correlated with boththe size and minimum hydrophobicity of the contiguously hydrophobic sequence (or"blob") that contains the SNP. Disease association is found to vary by more than sixfoldas a function of contiguous hydrophobicity parameters, suggesting utility as a prior foridentifying causal variation. We further find signatures of differential selective constrainton hydrophobic blobs and that SNPs splitting a long hydrophobic blob or joiningtwo short hydrophobic blobs are particularly likely to be disease associated. Trends arepreserved for both aggregating and nonaggregating proteins, indicating that the role ofcontiguous hydrophobicity extends well beyond aggregation risk.

Ultrahigh Transparent Safety Film for Spectrally Selective Photo/Electrothermal Conversion via Surface-Enhanced Plasma Resonance Dynamics.

Traditional deicing methods are increasingly insufficient for modern technologies like 5G infrastructure, photovoltaic systems, nearspace aerocraft, and terrestrial observatories. To address the challenge of combining anti-icing efficiency with operational performance, an innovative, spectrally selective, photo/electrothermic, ice-phobic film was prepared through a cost-effective mist deposition method. By manipulating the diameter ratio and density of nanowires, the local density of free electrons within this film is controlled to precisely dictate the position and intensity of surface plasmon resonance to achieve spectrally selective photo/electrothermal conversion. Additionally, the synthesized hydrophobic N-Boroxine-PDMS/SiO2 layer improves thermal stability and accelerates the deicing process. It achieves rapid deicing within 86 s under photothermal conditions and 65 s with Joule heating while maintaining high optical transmittance. The film improves the operational efficiency and thermal safety of equipment while preserving aesthetics and stability, thereby underscoring its broad suitability for advanced outdoor installations in cold environments.

Bacterial nucleoid is a riddle wrapped in a mystery inside an enigma.

Bacterial chromosome, the nucleoid, is traditionally modeled as a rosette of DNA mega-loops, organized around proteinaceous central scaffold by nucleoid-associated proteins (NAPs), and mixed with the cytoplasm by transcription and translation. Electron microscopy of fixed cells confirms dispersal of the cloud-like nucleoid within the ribosome-filled cytoplasm. Here, I discuss evidence that the nucleoid in live cells forms DNA phase separate from riboprotein phase, the "riboid." I argue that the nucleoid-riboid interphase, where DNA interacts with NAPs, transcribing RNA polymerases, nascent transcripts, and ssRNA chaperones, forms the transcription zone. An active part of phase separation, transcription zone enforces segregation of the centrally positioned information phase (the nucleoid) from the surrounding action phase (the riboid), where translation happens, protein accumulates, and metabolism occurs. I speculate that HU NAP mostly tiles up the nucleoid periphery-facilitating DNA mobility but also supporting transcription in the interphase. Besides extruding plectonemically supercoiled DNA mega-loops, condensins could compact them into solenoids of uniform rings, while HU could support rigidity and rotation of these DNA rings. The two-phase cytoplasm arrangement allows the bacterial cell to organize the central dogma activities, where (from the cell center to its periphery) DNA replicates and segregates, DNA is transcribed, nascent mRNA is handed over to ribosomes, mRNA is translated into proteins, and finally, the used mRNA is recycled into nucleotides at the inner membrane. The resulting information-action conveyor, with one activity naturally leading to the next one, explains the efficiency of prokaryotic cell design-even though its main intracellular transportation mode is free diffusion.

The polar amino acid in the TatA transmembrane helix is not strictly necessary for protein function.

The twin-arginine translocation (Tat) pathway utilizes the proton-motive force to transport folded proteins across cytoplasmic membranes in bacteria and archaea, as well as across the thylakoid membrane in plants and the inner membrane in mitochondria. In most species, the minimal components required for Tat activity consist of three subunits, TatA, TatB, and TatC. Previous studies have shown that a polar amino acid is present at the N terminus of the TatA transmembrane helix (TMH) across many different species. In order to systematically assess the functional importance of this polar amino acid in the TatA TMH in Escherichia coli, we examined a complete set of 19-amino-acid substitutions. Unexpectedly, although the polar amino acid is preferred overall, our experiments suggest that it is not necessary for a functional TatA. Hydrophilicity and helix-stabilizing properties of this polar amino acid were found to be highly correlated with the Tat activity. Specifically, change in charge status of the amino acid side chain due to pH resulted in a shift in hydrophilicity, which was demonstrated to impact the Tat transport activity. Furthermore, we identified a four-residue motif at the N terminus of the TatA TMH by sequence alignment. Using a biochemical approach, we found that the N-terminal motif was functionally significant, with evidence indicating a potential role in the preference for utilizing different proton-motive force components. Taken together, these findings yield new insights into the functionality of TatA and its potential role in the Tat transport mechanism.

The role of leucine and isoleucine in tuning the hydropathy of class A GPCRs.

Leucine and Isoleucine are two amino acids that differ only by the positioning of one methyl group. This small difference can have important consequences in α-helices, as the ß-branching of Ile results in helix destabilization. We set out to investigate whether there are general trends for the occurrences of Leu and Ile residues in the structures and sequences of class A GPCRs (G protein-coupled receptors). GPCRs are integral membrane proteins in which α-helices span the plasma membrane seven times and which play a crucial role in signal transmission. We found that Leu side chains are generally more exposed at the protein surface than Ile side chains. We explored whether this difference might be attributed to different functions of the two amino acids and tested if Leu tunes the hydrophobicity of the transmembrane domain based on the Wimley-White whole-residue hydrophobicity scales. Leu content decreases the variation in hydropathy between receptors and correlates with the non-Leu receptor hydropathy. Both measures indicate that hydropathy is tuned by Leu. To test this idea further, we generated protein sequences with random amino acid compositions using a simple numerical model, in which hydropathy was tuned by adjusting the number of Leu residues. The model was able to replicate the observations made with class A GPCR sequences. We speculate that the hydropathy of transmembrane domains of class A GPCRs is tuned by Leu (and to some lesser degree by Lys and Val) to facilitate correct insertion into membranes and/or to stably anchor the receptors within membranes.

Transmembrane proteins-Different anchoring systems.

Transmembrane proteins are active in amphipathic environments. To stabilize the protein in such surrounding the exposure of hydrophobic residues on the protein surface is required. Transmembrane proteins are responsible for the transport of various molecules. Therefore, they often represent structures in the form of channels. This analysis focused on the stability and local flexibility of transmembrane proteins, particularly those related to their biological activity. Different forms of anchorage were identified using the fuzzy oil-drop model (FOD) and its modified form, FOD-M. The mainly helical as well as ß-barrel structural forms are compared with respect to the mechanism of stabilization in the cell membrane. The different anchoring system was found to stabilize protein molecules with possible local fluctuation.

Comprehensive analysis of silk proteins and gland compartments in Limnephilus lunatus, a case-making trichopteran.

Caddisfly larvae produce silk containing heavy and light fibroins, similar to the silk of Lepidoptera, for the construction of underwater structures. We analyzed the silk of Limnephilus lunatus belonging to the case-forming suborder Integripalpia. We analyzed the transcriptome, mapped the transcripts to a reference genome and identified over 80 proteins using proteomic methods, and checked the specificity of their expression. For comparison, we also analyzed the transcriptome and silk proteome of Limnephilus flavicornis. Our results show that fibroins and adhesives are produced together in the middle and posterior parts of the silk glands, while the anterior part produces enzymes and an unknown protein AT24. The number of silk proteins of L. lunatus far exceeds that of the web-spinning Plectrocnemia conspersa, a previously described species from the suborder Annulipalpia. Our results support the idea of increasing the structural complexity of silk in rigid case builders compared to trap web builders.

Regulation of Wnt distribution and function by Drosophila glypicans.

The extracellular distribution of secreted Wnt proteins is crucial for their ability to induce a response in target cells at short and long ranges to ensure proper development. Wnt proteins are evolutionarily conserved ligands that are lipid-modified, and their hydrophobic nature interferes with their solubility in the hydrophilic extracellular environment. This raises the question of how Wnt proteins spread extracellularly despite their lipid modifications, which are essential for both their secretion and function. Seminal studies on Drosophila Wingless (Wg), a prototypical Wnt, have discovered multiple mechanisms by which Wnt proteins spread. A central theme emerges from these studies: the Wnt lipid moiety is shielded from the aqueous environment, allowing the ligands to spread and remain viable for signaling. Wnt distribution in vivo is primarily facilitated by glypicans, which are cell-surface heparan sulfate proteoglycans, and recent studies have further provided mechanistic insight into how glypicans facilitate Wnt distribution. In this Review, we discuss the many diverse mechanisms of Wnt distribution, with a particular focus on glypican-mediated mechanisms.

Inorganic Oxide-Based "Hydrophobic-Hydrophilic-Hydrophobic" Separators Systems for Long-Life Zinc-Ion Batteries.

Hydrogen reduction reaction (HER) and corrosion limit the long-life cycle of zinc-ion batteries. However, hydrophilic separators are unable to prevent direct contact between water and electrodes, and hydrophobic separators have difficulty in transporting electrolytes. In this work, an inorganic oxide-based "hydrophobic-hydrophilic-hydrophobic" self-assembled separator system is proposed. The hydrophobic layer consists of a porous structure, which can isolate a large amount of free water to avoid HER and corrosion reactions, and can transport electrolyte by binding water. The middle hydrophilic layer acts as a storage layer consisting of the GF separator, storing large amounts of electrolyte for proper circulation. By using this structure separator, Zn||Zn symmetric cell achieve 2200 h stable cycle life at 5 mA cm-2 and 1mAh cm-2 and still shows a long life of 1800 h at 10 mA cm-2 and 1mAh cm-2. The assembled Zn||VO2 full cell displays high specific capacity and excellent long-term durability of 60.4% capacity retention after 1000 cycles at 2C. The assembled Zn||VO2 pouch full cell displays high specific capacity of 172.5mAh g-1 after 40 cycles at 0.5C. Changing the inorganic oxide materials, the hydrophobic-hydrophilic-hydrophobic structure of the separators still has excellent performance. This work provides a new idea for the engineering of water-based battery separators.

Hydrophobic TaOx Species Overlayer Tuning Light-Driven Methane Chlorination with Inorganic Chlorine.

Halogenated methane serves as a universal platform molecule for building high-value chemicals. Utilizing sodium chloride solution for photocatalytic methane chlorination presents an environmentally friendly method for methane conversion. However, competing reactions in gas-solid-liquid systems leads to low efficiency and selectivity in photocatalytic methane chlorination. Here, an in situ method is employed to fabricate a hydrophobic layer of TaOx species on the surface of NaTaO3. Through in-situ XPS and XANES spectra analysis, it is determined that TaOx is a coordination unsaturated species. The TaOx species transforms the surface properties from the inherent hydrophilicity of NaTaO3 to the hydrophobicity of TaOx/NaTaO3, which enhances the accessibility of CH4 for adsorption and activation, and thus promotes the methane chlorination reaction within the gas-liquid-solid three-phase system. The optimized TaOx/NaTaO3 photocatalyst has a good durability for multiple cycles of methane chlorination reactions, yielding CH3Cl at a rate of 233 µmol g-1 h-1 with a selectivity of 83%. In contrast, pure NaTaO3 exhibits almost no activity toward CH3Cl formation, instead catalyzing the over-oxidation of CH4 into CO2. Notably, the activity of the optimized TaOx/NaTaO3 photocatalyst surpasses that of reported noble metal photocatalysts. This research offers an effective strategy for enhancing the selectivity of photocatalytic methane chlorination using inorganic chlorine ions.

Hydrophobic Multilayered PEG@PAN/MXene/PVDF@SiO2 Composite Film with Excellent Thermal Management and Electromagnetic Interference Shielding for Electronic Devices.

With the rapid development of electronic industry, it's pressing to develop multifunctional electromagnetic interference (EMI) shielding materials to ensure the stable operation of electronic devices. Herein, multilayered flexible PEG@PAN/MXene (Ti3C2Tx)/PVDF@SiO2 (PMF) composite film has been constructed from the level of microstructure design via coaxial electrospinning, coating spraying, and uniaxial electrospinning strategies. Benefiting from the effective encapsulation for PEG and high conductivity of MXene coating, PEG@PAN/MXene composite film with MXene coating loading density of 0.70 mg cm-2 exhibits high thermal energy storage density of 120.77 J g-1 and great EMI shielding performance (EMI SE of 34.409 dB and SSE of 49.086 dB cm3 g-1) in X-band (8-12 GHz). Therefore, this advanced composite film can not only help electronic devices prevent the influence of electromagnetic pollution in the X-band but also play an important role in electronic device thermal management. Additionally, the deposition of nano PVDF@SiO2 fibers (289 ± 128 nm) endowed the PMF composite film with great hydrophobic properties (water contact angle of 126.5°) to ensure the stable working of hydrophilic MXene coating, thereby breaks the limitation of humid application environments. The finding paves a new way for the development of novel multifunctional EMI shielding composite films for electronic devices.

Counterintuitive Trend of Intrusion Pressure with Temperature in the Hydrophobic Cu2(tebpz) MOF.

Liquid porosimetry experiments reveal a peculiar trend of the intrusion pressure of water in hydrophobic Cu2(3,3',5,5'-tetraethyl-4,4'-bipyrazolate) MOF. At lower temperature (T) range, the intrusion pressure (Pi) increases with T. For higher T values, Pi first reaches a maximum and then decreases. This is at odds with the Young-Laplace law, which for systems showing a continuous decrease of contact angle with T predicts a corresponding reduction of the intrusion pressure. Though the Young-Laplace law is not expected to provide quantitative predictions at the subnanoscale of Cu2(tebpz) pores, the physical intuition suggests that to a reduction of their hydrophobicity corresponds a reduction of the Pi. Molecular dynamics simulations and sychrothron experiments allowed to clarify the mechanism of the peculiar trend of Pi with T. At increasing temperatures the vapor density within the MOF' pores grows significantly, bringing the corresponding partial pressure to ≈5 MPa. This pressure, which is consistent with the shift of Pi observed in liquid porosimetry, represents a threshold to be overcame before intrusion takes place. Beyond some value of temperature, the phenomenon of reduction of hydrophobicity (and water surface tension) dominated over the opposite effect of increase of vapor pressure and Pi inverts its trend with T.

Hydrophobicity Promoted Efficient Hydroxyl Radical Generation in Visible-Light-Driven Photocatalytic Oxidation.

Hydroxyl radical (•OH) with strong oxidation capability is one of the most important reactive oxygen species. The generation of •OH from superoxide radicals (•O2 -) is an important process in visible-light-driven photocatalysis, but the conversion generally suffers from slow reaction kinetics. Here, a hydrophobicity promoted efficient •OH generation in a visible-light-driven semiconductor-mediated photodegradation reaction is reported. Hydrophobic TiO2 that is synthesized by modifying the TiO2 surface with a thin polydimethylsiloxane (PDMS) layer and rhodamine B (RhB) are used as model semiconductors and dye molecules, respectively. The surface hydrophobicity resulted in the formation of a solid-liquid-air triphase interface microenvironment, which increased the local concentration of O2. In the meanwhile, the saturated adsorption quantity of RhB on hydrophobic TiO2 is improved by five-fold than that on untreated TiO2. These advantages increased the density of the conduction band photoelectrons and •O2 - generation, and stimulated the conversion of •O2 - to •OH. This consequently not only increased the kinetics of the photocatalytic reaction by an order of magnitude, but also altered the oxidation route from conventional decolorization to mineralization. This study highlights the importance of surface wettability modulation in boosting •OH generation in visible-light-driven photocatalysis.

Acidic and Alkaline pH Controlled Oxygen Reduction Reaction Pathway over Co-N4C Catalyst.

Enhanced oxygen reduction reaction (ORR) kinetics and selectivity are crucial to advance energy technologies like fuel cells and metal-air batteries. Single-atom catalysts (SACs) with M-N4/C structure have been recognized to be highly effective for ORR. However, the lack of a comprehensive understanding of the mechanistic differences in the activity under acidic and alkaline environments is limiting the full potential of the energy devices. Here, a porous SAC is synthesized where a cobalt atom is coordinated with doped nitrogen in a graphene framework (pCo-N4C). The resulting pCo-N4C catalyst demonstrates a direct 4e- ORR process and exhibits kinetics comparable to the state-of-the-art (Pt/C) catalyst. Its higher activity in an acidic electrolyte is attributed to the tuned porosity-induced hydrophobicity. However, the pCo-N4C catalyst displays a difference in ORR activity in 0.1 m HClO4 and 0.1 m KOH, with onset potentials of 0.82 V and 0.91 V versus RHE, respectively. This notable activity difference in acidic and alkaline media is due to the protonation of coordinated nitrogen, restricted proton coupled electron transfer (PCET) at the electrode/electrolyte interface. The effect of pH over the catalytic activity is further verified by Ab-initio molecular dynamics (AIMD) simulations using density functional theory (DFT) calculations.

Intelligent Reconfiguration-Promoted Cellular Internalization of Core-Shell DNA Nanoprobe Equipped with Successive Dual Stimuli-Responsive Protective Satellites for Amplification Fluorescence Imaging of Tumor Cells.

Although DNA probes have attracted increasing interest for precise tumor cell identification by imaging intracellular biomarkers, the requirement of commercial transfection reagents, limited targeting ligands, and/or non-biocompatible inorganic nanostructures has hampered the clinic translation. To circumvent these shortcomings, a reconfigurable ES-NC (Na+-dependent DNAzyme (E)-based substrate (S) cleavage core/shell DNA nanocluster (NC)) entirely from DNA strands is assembled for precise imaging of cancerous cells in a successive dual-stimuli-responsive manner. This nanoprobe is composed of a strung DNA tetrahedral satellites-based protective (DTP) shell, parallelly aligned target-responsive sensing (PTS) interlayer, and hydrophobic cholesterol-packed innermost layer (HCI core). Tetrahedral axial rotation-activated reconfiguration of DTP shell promotes the exposure of interior hydrophobic moieties, enabling cholesterol-mediated cellular internalization without auxiliary elements. Within cells, over-expressed glutathione triggers the disassembly of the DTP protective shell (first stimulus), facilitating target-stimulated signal transduction/amplification process (second stimuli). Target miRNA-21 is detected down to 10.6 fM without interference from coexisting miRNAs. Compared with transfection reagent-mediated counterpart, ES-NC displays a higher imaging ability, resists nuclease degradation, and has no detectable damage to healthy cells. The blind test demonstrates that the ES-NC is suitable for the identification of cancerous cells from healthy cells, indicating a promising tool for early diagnosis and prediction of cancer.

Protein disulfide isomerase 1 is required for RodA assembling-based conidial hydrophobicity of Aspergillus fumigatus.

The hydrophobic layer of Aspergillus conidia, composed of RodA, plays a crucial role in conidia transfer and immune evasion. It self-assembles into hydrophobic rodlets through intramolecular disulfide bonds. However, the secretory process of RodA and its regulatory elements remain unknown. Since protein disulfide isomerase (PDI) is essential for the secretion of many disulfide-bonded proteins, we investigated whether PDI is also involved in RodA secretion and assembly. By gene knockout and phenotypic analysis, we found that Pdi1, one of the four PDI-related proteins of Aspergillus fumigatus, determines the hydrophobicity and integrity of the rodlet layer of the conidia. Preservation of the thioredoxin-active domain of Pdi1 was sufficient to maintain conidial hydrophobicity, suggesting that Pdi1 mediates RodA assembly through its disulfide isomerase activity. In the absence of Pdi1, the disulfide mismatch of RodA in conidia may prevent its delivery from the inner to the outer layer of the cell wall for rodlet assembly. This was demonstrated using a strain expressing a key cysteine-mutated RodA. The dormant conidia of the Pdi1-deficient strain (Δpdi) elicited an immune response, suggesting that the defective conidia surface in the absence of Pdi1 exposes internal immunogenic sources. In conclusion, Pdi1 ensures the correct folding of RodA in the inner layer of conidia, facilitating its secretion into the outer layer of the cell wall and allowing self-assembly of the hydrophobic layer. This study has identified a regulatory element for conidia rodlet assembly.IMPORTANCEAspergillus fumigatus is the major cause of invasive aspergillosis, which is mainly transmitted by the inhalation of conidia. The spread of conidia is largely dependent on their hydrophobicity, which is primarily attributed to the self-assembly of the hydrophobic protein RodA on the cell wall. However, the mechanisms underlying RodA secretion and transport to the outermost layer of the cell wall are still unclear. Our study identified a critical role for Pdi1, a fungal protein disulfide isomerase found in regulating RodA secretion and assembly. Inhibition of Pdi1 prevents the formation of correct S-S bonds in the inner RodA, creating a barrier to RodA delivery and resulting in a defective hydrophobic layer. Our findings provided insight into the formation of the conidial hydrophobic layer and suggested potential drug targets to inhibit A. fumigatus infections by limiting conidial dispersal and altering their immune inertia.

Evaluation of Salmonella biofilm attachment and hydrophobicity characteristics on food contact surfaces.

Salmonella forms biofilms, and persist on food contact surfaces. Once a biofilm is formed cleaning and sanitation protocols may be inadequate for effective removal. This study evaluated attachment characteristics, surface properties, and structure of Salmonella biofilms on food contact surfaces commonly used in the tree-fruit industry. Multi-strain Salmonella biofilms were grown in a Centers for Disease Control and Prevention (CDC) biofilm reactor at 22 ± 2 °C and sampling was conducted at 2, 24 and 96-h. After each incubation period, coupons weregently rinsed and the remaining cells enumerated. Biofilms were analyzed with Laser Scanning Confocal Microscopy (LSCM). Hydrophobicity was evaluated by measuring the contact angles of reference liquids method using a drop tensiometer instrument. Material type and biofilm age significantly influenced attachment and biofilm hydrophobicity (P < 0.05). The strength of attachment, across all time points, was highest on nylon followed by wood and high-density polyethylene. The highest contact angle measurements were observed after 96-h of biofilm formation for each material. All the results and observations from this study contribute to a better understanding of the attachment and hydrophobicity characteristics of Salmonella and might help producers make informed decisions when selecting containers for harvesting and storing in order to minimize biofilm formation and potential for cross-contamination.