Solving the plastic dilemma: the fungal and bacterial biodegradability of polyurethanes.

Polyurethane (PU) is a plastic polymer which, due to its various desirable characteristics, has been applied extensively in domestic, industrial and medical fields for the past 50 years. Subsequently, an increasing amount of PU waste is generated annually. PU, like many other plastics, is highly resistant to degradation and is a substantial threat to our environment. Currently PU wastes are handled through conventional disposal techniques such as landfill, incineration and recycling. Due to the many drawbacks of these techniques, a 'greener' alternative is necessary, and biodegradation appears to be the most promising option. Biodegradation has the potential to completely mineralise plastic waste or recover the input materials and better enable recycling. There are hurdles to overcome however, primarily the efficiency of the process and the presence of waste plastics with inherently different chemical structures. This review will focus on polyurethanes and their biodegradation, outlining the difficulty of degrading different versions of the same material and strategies for achieving more efficient biodegradation.

Bactericidal activity of self-assembled palmitic and stearic fatty acid crystals on highly ordered pyrolytic graphite.

The wings of insects such as cicadas and dragonflies have been found to possess nanostructure arrays that are assembled from fatty acids. These arrays can physically interact with the bacterial cell membranes, leading to the death of the cell. Such mechanobactericidal surfaces are of significant interest, as they can kill bacteria without the need for antibacterial chemicals. Here, we report on the bactericidal effect of two of the main lipid components of the insect wing epicuticle, palmitic (C16) and stearic (C18) fatty acids. Films of these fatty acids were re-crystallised on the surface of highly ordered pyrolytic graphite. It appeared that the presence of two additional CH2 groups in the alkyl chain resulted in the formation of different surface structures. Scanning electron microscopy and atomic force microscopy showed that the palmitic acid microcrystallites were more asymmetric than those of the stearic acid, where the palmitic acid microcrystallites were observed to be an angular abutment in the scanning electron micrographs. The principal differences between the two types of long-chain saturated fatty acid crystallites were the larger density of peaks in the upper contact plane of the palmitic acid crystallites, as well as their greater proportion of asymmetrical shapes, in comparison to that of the stearic acid film. These two parameters might contribute to higher bactericidal activity on surfaces derived from palmitic acid. Both the palmitic and stearic acid crystallite surfaces displayed activity against Gram-negative, rod-shaped Pseudomonas aeruginosa and Gram-positive, spherical Staphylococcus aureus cells. These microcrystallite interfaces might be a useful tool in the fabrication of effective bactericidal nanocoatings. STATEMENT OF SIGNIFICANCE: Nanostructured cicada and dragonfly wing surfaces have been discovered to be able physically kill bacterial cells. Here, we report on the successful fabrication of bactericidal three-dimensional structures of two main lipid components of the epicuticle of insect wings, palmitic (C16) and stearic (C18) acids. After crystallisation onto highly ordered pyrolytic graphite, both the palmitic and stearic acid films displayed bactericidal activity against both Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus cells. The simplicity of the production of these microcrystallite interfaces suggests that a fabrication technique, based on solution deposition, could be an effective technique for the application of bactericidal nanocoatings.

Thalassospira australica sp. nov. isolated from sea water.

Two Gram-negative, non-pigmented, motile bacteria were isolated from a sea water sample collected at St. Kilda Beach, Port Philip Bay, Victoria, Australia. The two strains were found to grow between 4 and 40 °C, pH 5-10 and tolerate up to 10 % NaCl. A phylogenetic study, based on a 16S rRNA gene sequence analysis indicated that strains NP 3b2(T) and H 94 belong to the genus Thalassospira. The sequence similarity of the 16S rRNA gene between the two new isolates is 99.8 % and between these strains and all validly named Thalassospira species was found to be in the range of 95-99.4 %. The DNA-DNA relatedness between the two strains was found to be 80.2 %, while relatedness with other validly named species of the genus Thalassospira was between 53 and 65 %. The average nucleotide identity (ANI) and the in silico genome-to-genome distance (GGD) between the two bacteria and T. profundimaris WP0211(T), T. xiamenensis M-5(T), 'T. permensis' NBRC 106175(T) and T. lucentensis QMT2(T) was 76-82 % and 21-25 %, respectively. The results of phylogenetic and genomic analysis, together with physiological and biochemical properties, indicated that the two strains represent a new species of the genus Thalassospira. Based on these data, a new species, Thalassospira australica, is proposed with strain NP 3b2(T) (=KMM 6365(T) = JCM 31222(T)) as the type strain.

Sensitive Detection of Deliquescent Bacterial Capsules through Nanomechanical Analysis.

Encapsulated bacteria usually exhibit strong resistance to a wide range of sterilization methods, and are often virulent. Early detection of encapsulation can be crucial in microbial pathology. This work demonstrates a fast and sensitive method for the detection of encapsulated bacterial cells. Nanoindentation force measurements were used to confirm the presence of deliquescent bacterial capsules surrounding bacterial cells. Force/distance approach curves contained characteristic linear-nonlinear-linear domains, indicating cocompression of the capsular layer and cell, indentation of the capsule, and compression of the cell alone. This is a sensitive method for the detection and verification of the encapsulation status of bacterial cells. Given that this method was successful in detecting the nanomechanical properties of two different layers of cell material, i.e. distinguishing between the capsule and the remainder of the cell, further development may potentially lead to the ability to analyze even thinner cellular layers, e.g. lipid bilayers.

Bacterial patterning at the three-phase line of contact with microtextured alkanes.

Aliphatic crystallites, characteristic of the eicosane and docosane components of naturally occurring lipids, were found to form microtextures that were structured by specific interactions with ordered graphite (HOPG) used as the underlying substratum, as confirmed by scanning electron microscopy (SEM) and fast Fourier transform (FFT) analysis. Confocal scanning laser microscopy (CLSM) showed highly directed bacterial alignment for two bacterial species (spherical and rod-shaped), reflecting the preferential orientation of the crystallite-air-water interfaces to give linear and triangular bacterial patterning. The mechanisms of bacterial attachment are demonstrated in terms of the balance between effective radial adhesional forces and the capillary forces resulting from the water contact angle of the bacteria at the three-phase line (TPL) of the lipid surface. It is suggested that these microtextured surfaces, which exhibit the ability to limit bacterial adhesion to a precise patterning at the lipid TPL, could be used as a means of controlling bacterial colonization.

Ecophysiological diversity of a novel member of the genus Alteromonas, and description of Alteromonas mediterranea sp. nov.

Nine non-pigmented, motile, Gram-negative bacteria originally designated as Alteromonas macleodii deep-sea ecotypes, were isolated from seawater samples collected from four separate locations; two deep-sea sites in the Mediterranean Sea and surface water of the Aegean Sea and English Channel. The six strains studied in vitro were found to tolerate up to 20 % NaCl. The DNA-DNA relatedness between the deep-sea ecotype strains was found to be between 75 and 89 %, whilst relatedness with the validly named Alteromonas species was found to be between 31 and 69 %. The average nucleotide identity (ANI) amongst the deep-sea ecotype strains was found to be 98-100 %; the in silico genome-to-genome distance (GGD), 85-100 %; the average amino acid identity (AAI) of all conserved protein-coding genes, 95-100 %; and the strains possessed 30-32 of the Karlin's genomic signature dissimilarity. The ANI between the deep-sea ecotype strains and A. macleodii ATCC 27126(T) and Alteromonas australica H 17(T) was found to be 80.6 and 74.6 %, respectively. A significant correlation was observed between the phenotypic data obtained in vitro and data retrieved in silico from whole genome sequences. The results of a phylogenetic study that incorporated a 16S rRNA gene sequence analysis, multilocus phylogenetic analysis (MLPA) and genomic analysis, together with the physiological, biochemical and chemotaxonomic data, clearly indicated that the group of deep-sea ecotype strains represents a distinct species within the genus Alteromonas. Based on these data, a new species, Alteromonas mediterranea, is proposed. The type strain is DE(T) ( = CIP 110805(T) = LMG 28347(T) = DSM 17117(T)).

Genome Sequence of "Thalassospira australica" NP3b2T Isolated from St. Kilda Beach, Tasman Sea.

Here, we present the draft genome of "Thalassospira australica" NP3b2(T), a potential poly(ethylene terephthalate) (PET) plastic biodegrader. This genomic information will enhance information on the genetic basis of metabolic pathways for the degradation of PET plastic.

Natural insect and plant micro-/nanostructsured surfaces: an excellent selection of valuable templates with superhydrophobic and self-cleaning properties.

Insects and plants are two types of organisms that are widely separated on the evolutionary tree; for example, plants are mostly phototrophic organisms whilst insects are heterotrophic organisms. In order to cope with environmental stresses, their surfaces have developed cuticular layers that consist of highly sophisticated structures. These structures serve a number of purposes, and impart useful properties to these surfaces. These two groups of organisms are the only ones identified thus far that possess truly superhydrophobic and self-cleaning properties. These properties result from their micro- and nano-scale structures, comprised of three-dimensional wax formations. This review analyzes the surface topologies and surface chemistry of insects and plants in order to identify the features common to both organisms, with particular reference to their superhydrophobic and self-cleaning properties. This information will be valuable when determining the potential application of these surfaces in the design and manufacture of superhydrophobic and self-cleaning devices, including those that can be used in the manufacture of biomedical implants.

Marinobacter salarius sp. nov. and Marinobacter similis sp. nov., isolated from sea water.

Two non-pigmented, motile, Gram-negative marine bacteria designated R9SW1T and A3d10T were isolated from sea water samples collected from Chazhma Bay, Gulf of Peter the Great, Sea of Japan, Pacific Ocean, Russia and St. Kilda Beach, Port Phillip Bay, the Tasman Sea, Pacific Ocean, respectively. Both organisms were found to grow between 4 °C and 40 °C, between pH 6 to 9, and are moderately halophilic, tolerating up to 20% (w/v) NaCl. Both strains were found to be able to degrade Tween 40 and 80, but only strain R9SW1T was found to be able to degrade starch. The major fatty acids were characteristic for the genus Marinobacter including C16:0, C16:1ω7c, C18:1ω9c and C18:1ω7c. The G+C content of the DNA for strains R9SW1T and A3d10T were determined to be 57.1 mol% and 57.6 mol%, respectively. The two new strains share 97.6% of their 16S rRNA gene sequences, with 82.3% similarity in the average nucleotide identity (ANI), 19.8% similarity in the in silico genome-to-genome distance (GGD), 68.1% similarity in the average amino acid identity (AAI) of all conserved protein-coding genes, and 31 of the Karlin's genomic signature dissimilarity. A phylogenetic analysis showed that R9SW1T clusters with M. algicola DG893T sharing 99.40%, and A3d10T clusters with M. sediminum R65T sharing 99.53% of 16S rRNA gene sequence similarities. The results of the genomic and polyphasic taxonomic study, including genomic, genetic, phenotypic, chemotaxonomic and phylogenetic analyses based on the 16S rRNA, gyrB and rpoD gene sequence similarities, the analysis of the protein profiles generated using MALDI-TOF mass spectrometry, and DNA-DNA relatedness data, indicated that strains R9SW1T and A3d10(T) represent two novel species of the genus Marinobacter. The names Marinobacter salarius sp. nov., with the type strain R9SW1(T) ( =  LMG 27497(T)  =  JCM 19399(T)  =  CIP 110588(T)  =  KMM 7502(T)) and Marinobacter similis sp. nov., with the type strain A3d10(T) ( =  JCM 19398(T)  =  CIP 110589(T)  =  KMM 7501T), are proposed.

Draft Genome Sequences of Marinobacter similis A3d10T and Marinobacter salarius R9SW1T.

Here, we present the draft genomes of Marinobacter similis A3d10(T), a potential plastic biodegrader, and Marinobacter salarius R9SW1(T), isolated from radioactive waters. This genomic information will contribute information on the genetic basis of the metabolic pathways for the degradation of both plastic and radionuclides.

Wettability of natural superhydrophobic surfaces.

Since the description of the 'Lotus Effect' by Barthlott and Neinhuis in 1997, the existence of superhydrophobic surfaces in the natural world has become common knowledge. Superhydrophobicity is associated with a number of possible evolutionary benefits that may be bestowed upon an organism, ranging from the ease of dewetting of their surfaces and therefore prevention of encumbrance by water droplets, self-cleaning and removal of particulates and potential pathogens, and even to antimicrobial activity. The superhydrophobic properties of natural surfaces have been attributed to the presence of hierarchical microscale (>1 µm) and nanoscale (typically below 200 nm) structures on the surface, and as a result, the generation of topographical hierarchy is usually considered of high importance in the fabrication of synthetic superhydrophobic surfaces. When one surveys the breadth of data available on naturally existing superhydrophobic surfaces, however, it can be observed that topographical hierarchy is not present on all naturally superhydrophobic surfaces; in fact, the only universal feature of these surfaces is the presence of a sophisticated nanoscale structure. Additionally, several natural surfaces, e.g. those present on rose petals and gecko feet, display high water contact angles and high adhesion of droplets, due to the pinning effect. These surfaces are not truly superhydrophobic, and lack significant degrees of nanoscale roughness. Here, we discuss the phenomena of superhydrophobicity and pseudo-superhydrophobicity in nature, and present an argument that while hierarchical surface roughness may aid in the stability of the superhydrophobic effect, it is nanoscale surface architecture alone that is the true determinant of superhydrophobicity.

Three-dimensional reconstruction of surface nanoarchitecture from two-dimensional datasets.

The design of biomaterial surfaces relies heavily on the ability to accurately measure and visualize the three-dimensional surface nanoarchitecture of substrata. Here, we present a technique for producing three-dimensional surface models using displacement maps that are based on the data obtained from two-dimensional analyses. This technique is particularly useful when applied to scanning electron micrographs that have been calibrated using atomic force microscopy (AFM) roughness data. The evaluation of four different surface types, including thin titanium films, silicon wafers, polystyrene cell culture dishes and dragonfly wings confirmed that this technique is particularly effective for the visualization of conductive surfaces such as metallic titanium. The technique is particularly useful for visualizing surfaces that cannot be easily analyzed using AFM. The speed and ease with which electron micrographs can be recorded, combined with a relatively simple process for generating displacement maps, make this technique useful for the assessment of the surface topography of biomaterials.

Bactericidal activity of black silicon.

Black silicon is a synthetic nanomaterial that contains high aspect ratio nanoprotrusions on its surface, produced through a simple reactive-ion etching technique for use in photovoltaic applications. Surfaces with high aspect-ratio nanofeatures are also common in the natural world, for example, the wings of the dragonfly Diplacodes bipunctata. Here we show that the nanoprotrusions on the surfaces of both black silicon and D. bipunctata wings form hierarchical structures through the formation of clusters of adjacent nanoprotrusions. These structures generate a mechanical bactericidal effect, independent of chemical composition. Both surfaces are highly bactericidal against all tested Gram-negative and Gram-positive bacteria, and endospores, and exhibit estimated average killing rates of up to ~450,000 cells min(-1) cm(-2). This represents the first reported physical bactericidal activity of black silicon or indeed for any hydrophilic surface. This biomimetic analogue represents an excellent prospect for the development of a new generation of mechano-responsive, antibacterial nanomaterials.

Molecular organization of the nanoscale surface structures of the dragonfly Hemianax papuensis wing epicuticle.

The molecular organization of the epicuticle (the outermost layer) of insect wings is vital in the formation of the nanoscale surface patterns that are responsible for bestowing remarkable functional properties. Using a combination of spectroscopic and chromatographic techniques, including Synchrotron-sourced Fourier-transform infrared microspectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) depth profiling and gas chromatography-mass spectrometry (GCMS), we have identified the chemical components that constitute the nanoscale structures on the surface of the wings of the dragonfly, Hemianax papuensis. The major components were identified to be fatty acids, predominantly hexadecanoic acid and octadecanoic acid, and n-alkanes with even numbered carbon chains ranging from C14 to C30. The data obtained from XPS depth profiling, in conjunction with that obtained from GCMS analyses, enabled the location of particular classes of compounds to different regions within the epicuticle. Hexadecanoic acid was found to be a major component of the outer region of the epicuticle, which forms the surface nanostructures, and was also detected in deeper layers along with octadecanoic acid. Aliphatic compounds were detected throughout the epicuticle, and these appeared to form a third discrete layer that was separate from both the inner and outer epicuticles, which has never previously been reported.

High-spatial-resolution mapping of superhydrophobic cicada wing surface chemistry using infrared microspectroscopy and infrared imaging at two synchrotron beamlines.

The wings of some insects, such as cicadae, have been reported to possess a number of interesting and unusual qualities such as superhydrophobicity, anisotropic wetting and antibacterial properties. Here, the chemical composition of the wings of the Clanger cicada (Psaltoda claripennis) were characterized using infrared (IR) microspectroscopy. In addition, the data generated from two separate synchrotron IR facilities, the Australian Synchrotron Infrared Microspectroscopy beamline (AS-IRM) and the Synchrotron Radiation Center (SRC), University of Wisconsin-Madison, IRENI beamline, were analysed and compared. Characteristic peaks in the IR spectra of the wings were assigned primarily to aliphatic hydrocarbon and amide functionalities, which were considered to be an indication of the presence of waxy and proteinaceous components, respectively, in good agreement with the literature. Chemical distribution maps showed that, while the protein component was homogeneously distributed, a significant degree of heterogeneity was observed in the distribution of the waxy component, which may contribute to the self-cleaning and aerodynamic properties of the cicada wing. When comparing the data generated from the two beamlines, it was determined that the SRC IRENI beamline was capable of producing higher-spatial-resolution distribution images in a shorter time than was achievable at the AS-IRM beamline, but that spectral noise levels per pixel were considerably lower on the AS-IRM beamline, resulting in more favourable data where the detection of weak absorbances is required. The data generated by the two complementary synchrotron IR methods on the chemical composition of cicada wings will be immensely useful in understanding their unusual properties with a view to reproducing their characteristics in, for example, industry applications.

Biophysical model of bacterial cell interactions with nanopatterned cicada wing surfaces.

The nanopattern on the surface of Clanger cicada (Psaltoda claripennis) wings represents the first example of a new class of biomaterials that can kill bacteria on contact based solely on their physical surface structure. The wings provide a model for the development of novel functional surfaces that possess an increased resistance to bacterial contamination and infection. We propose a biophysical model of the interactions between bacterial cells and cicada wing surface structures, and show that mechanical properties, in particular cell rigidity, are key factors in determining bacterial resistance/sensitivity to the bactericidal nature of the wing surface. We confirmed this experimentally by decreasing the rigidity of surface-resistant strains through microwave irradiation of the cells, which renders them susceptible to the wing effects. Our findings demonstrate the potential benefits of incorporating cicada wing nanopatterns into the design of antibacterial nanomaterials.

Dual role of outer epicuticular lipids in determining the wettability of dragonfly wings.

Numerous natural surfaces possess superhydrophobicity and self-cleaning properties that would be extremely beneficial when applied in industry. Dragonfly wings are one example of such surfaces, and while their general surface structure is known, their precise chemical composition is not. Here, the epicuticular lipids of dragonfly wing membranes were characterized to investigate their significance in contributing to self-cleaning and superhydrophobic properties. After just 10s of lipid extraction using chloroform, the water contact angles exhibited by the wings decreased below the accepted threshold for superhydrophobicity (150°). Infrared spectra collected at the Australian Synchrotron contained characteristic absorption bands of amide, ester and aliphatic hydrocarbons moieties on the wing surfaces, the latter of which was decreased post-extraction with chloroform. GC-MS data analysis revealed that the epicuticular wax components were dominated by n-alkanes with even-numbered carbons, especially n-hexacosane, and palmitic acid. SEM and AFM data analysis conducted on the untreated and chloroform-extracted wing surfaces demonstrated that surface topography changed after extraction; the surface nanostructure was progressively lost with extended extraction times. The data presented here indicate that epicuticular lipids contribute not only to self-cleaning and superhydrophobic properties through their inherent hydrophobic nature, but also by forming the physical structure of the wing surface. This knowledge will be extremely valuable for reconstruction of dragonfly wing structures as a biomimetic template.

Alteromonas australica sp. nov., isolated from the Tasman Sea.

A non-pigmented, motile, Gram-negative bacterium designated H 17(T) was isolated from a seawater sample collected in Port Phillip Bay (the Tasman Sea, Pacific Ocean). The new organism displayed optimal growth between 4 and 37 °C, was found to be neutrophilic and slightly halophilic, tolerating salt water environments up to 10 % NaCl. Strain H 17(T) was found to be able to degrade starch and Tween 80 but unable to degrade gelatin or agar. Phosphatidylglycerol (27.7 %) and phosphatidylethanolamine (72.3 %) were found to be the only associated phospholipids. The major fatty acids identified are typical for the genus Alteromonas and include C16:0, C16:1ω7, C17:1ω8 and C18:1ω7. The G+C content of the DNA was found to be 43.4 mol%. A phylogenetic study, based on the 16S rRNA gene sequence analysis and Multilocus Phylogenetic Analysis, clearly indicated that strain H 17(T) belongs to the genus Alteromonas. The DNA-DNA relatedness between strain H 17(T) and the validly named Alteromonas species was between 30.7 and 46.4 mol%. Based on these results, a new species, Alteromonas australica, is proposed. The type strain is H 17(T) (= KMM 6016(T) = CIP 109921(T)).

Selective bactericidal activity of nanopatterned superhydrophobic cicada Psaltoda claripennis wing surfaces.

The nanopattern on the surface of Clanger cicada (Psaltoda claripennis) wings represents the first example of a new class of biomaterials that can kill bacteria on contact based solely on its physical surface structure. As such, they provide a model for the development of novel functional surfaces that possess an increased resistance to bacterial contamination and infection. Their effectiveness against a wide spectrum of bacteria, however, is yet to be established. Here, the bactericidal properties of the wings were tested against several bacterial species, possessing a range of combinations of morphology and cell wall type. The tested species were primarily pathogens, and included Bacillus subtilis, Branhamella catarrhalis, Escherichia coli, Planococcus maritimus, Pseudomonas aeruginosa, Pseudomonas fluorescens, and Staphylococcus aureus. The wings were found to consistently kill Gram-negative cells (i.e., B. catarrhalis, E. coli, P. aeruginosa, and P. fluorescens), while Gram-positive cells (B. subtilis, P. maritimus, and S. aureus) remained resistant. The morphology of the cells did not appear to play any role in determining cell susceptibility. The bactericidal activity of the wing was also found to be quite efficient; 6.1 ± 1.5 × 10(6) P. aeruginosa cells in suspension were inactivated per square centimeter of wing surface after 30-min incubation. These findings demonstrate the potential for the development of selective bactericidal surfaces incorporating cicada wing nanopatterns into the design.