Dynamics of biofilm detachment in biofilm airlift suspension reactors

The dynamic change in the overall detachment rate of spherical biofilms in a biofilm airlift suspension reactor was measured after a downshift of the substrate loading rate to zero while all other conditions remained constant. In contrast to the expectations, the overall detachment rate decreased rapidly to a nearly stable level. Correlations available from literature were not able to describe this phenomenon. Concepts were formulated which can describe the observations from this study. Research under dynamic conditions and careful monitoring of the biofilm surface area and biofilm morphology are necessary to elucidate and discriminate biofilm detachment mechanisms. (c) 1995 John Wiley & Sons, Inc.     

The Sandfish＇s Skin： Morphology, Chemistry and Reconstruction

The sandfish is a lizard having the remarkable ability to move in desert sand in a swimming-like fashion. The most outstanding adaptations to this mode of life are the low friction behaviour and the extensive abrasion resistance of the sandfish skin against sand, outperforming even steel. We investigated the topography, the composition and the mechanical properties of sandfish scales. These consist of glycosylated keratins with high amount of sulphur but no hard inorganic material, such as silicates or lime. Remarkably, atomic force microscopy shows an almost complete absence of attractive forces between the scale surface and a silicon tip, suggesting that this is responsible for the unusual tribological properties. The unusual glycosylation of the keratins was found to be absolutely necessary for the described phenomenon. The scales were dissolved and reconstituted on a polymer surface resulting in properties similar to the original scale. Thus, we provide a pathway towards exploitation of the reconstituted scale material for future engineering applications.     

The Sandfish's Skin:Morphology,Chemistry and Reconstruction

The sandfish is a lizard having the remarkable ability to move in desert sand in a swimming-like fashion. The most out-standing adaptations to this mode of life are the low friction behaviour and the extensive abrasion resistance of the sandfish skin against sand, outperforming even steel. We investigated the topography, the composition and the mechanical properties of sandfish scales. These consist of glycosylated keratins with high amount of sulphur but no hard inorganic material, such as silicates or lime. Remarkably, atomic force microscopy shows an almost complete absence of attractive forces between the scale surface and a silicon tip, suggesting that this is responsible for the unusual tribological properties. The unusual glycosylation of the keratins was found to be absolutely necessary for the described phenomenon. The scales were dissolved and reconstituted on a polymer surface resulting in properties similar to the original scale. Thus, we provide a pathway towards exploitation of the reconstituted scale material for future engineering applications.     

Localization of tabersonine 16-hydroxylase and 16-OH tabersonine-16-O-methyltransferase to leaf epidermal cells defines them as a major site of precursor biosynthesis in the vindoline pathway in Catharanthus roseus

The Madagascar periwinkle (Catharanthus roseus) produces the well known and remarkably complex anticancer dimeric alkaloids vinblastine and vincristine, which are derived by the coupling of vindoline and catharanthine monomers. Recent data from in situ RNA hybridization and immunolocalization suggest that combinatorial cell factories within the leaf are involved in vindoline biosynthesis. In this study, the cell types responsible for vindoline biosynthesis were identified by laser-capture microdissection/RNA isolation/RT-PCR to show that geraniol hydroxylase, secologanin synthase, tryptophan decarboxylase, strictosidine synthase, strictosidine ss-glucosidase and tabersonine 16-hydroxylase can be detected preferentially in epidermal cells. A new and complementary application of the carborundum abrasion (CA) technique was developed to obtain epidermis-enriched leaf extracts that can be used to measure alkaloid metabolite levels, enzyme activities and gene expression. The CA technique showed that tabersonine and 16-methoxytabersonine, together with 16-hydroxytabersonine-16-O-methyltransferase, are found predominantly in Catharanthus leaf epidermis, in contrast to vindoline, catharanthine and later enzymatic steps in vindoline biosynthesis. The results show that leaf epidermal cells are biosynthetically competent to produce tryptamine and secologanin precursors that are converted via many enzymatic transformations to make 16-methoxytabersonine. This alkaloid or its 2,3 dihydro-derivative is then transported to cells (mesophyll/idioblast/laticifer) within Catharanthus leaves to complete the last three or four enzymatic transformations to make vindoline.     

猫儿山铁杉相邻植株冠层机械磨损对枝叶性状的影响

机械磨损是邻体植物冠层接壤区域的重要生态过程之一, 对枝叶生理和形态特征具有重要影响。但是, 当前非常缺乏邻体植物冠层机械磨损对枝叶功能性状影响特征和权衡机制的深入研究。该研究以广西猫儿山的铁杉(Tsuga chinensis)为对象, 通过比较邻体冠层间机械磨损区优势枝、劣势枝与非机械磨损区的叶面积、叶长、叶宽、叶厚、比叶面积、叶干物质含量、叶干质量、末端枝含水率和枝直径的差异, 分析枝叶功能性状在机械磨损影响下的变异和权衡关系。结果显示: 机械磨损显著影响邻体冠层叶干物质含量、比叶面积和叶干质量。具体而言, 机械磨损区优势枝叶干物质含量显著大于劣势枝和非机械磨损区, 优势枝比叶面积显著低于劣势枝和非机械磨损区, 劣势枝叶干质量显著低于优势枝和非机械磨损区。其次, 机械磨损对枝叶性状关系的影响格局不同。叶面积-叶长在机械磨损区优势枝、劣势枝和非机械磨损区间表现出一致的正向关系; 叶面积-叶宽、叶面积-叶干质量、叶宽-叶厚、叶厚-末端枝直径和叶长-叶宽仅在机械磨损区优势枝显著正相关; 叶面积-末端枝直径和末端枝直径-末端枝含水率仅在劣势枝显著负相关; 叶干物质含量-叶厚仅在劣势枝显著正相关。其余性状关系在机械磨损区优势枝、劣势枝和非机械磨损区均不显著。以上结果表明, 森林植物邻体间的冠层机械磨损可显著改变枝叶功能性状的权衡关系。     

Quantifying Abrasion of Stable Substrata in Streams: A New Disturbance Index for Epilithic Biota

Abrasion is a significant disturbing force to which the streambed epilithic biota is exposed during high flow periods. However, abrasion of biota in the field has not been measured, and effects of abrasion on biota are usually inferred. We describe a method that quantifies abrasion of a standardised substrate in the field. This provides an index of the level of abrasion to which flora and fauna are exposed. The method uses autoclaved lightweight aerated concrete (ALC) blocks that are fixed in place on the streambed and subsequently abraded. Two methods were used to quantify abrasion: the change in mass of the block from before to after deployment, and the reduction in cross-sectional area of the corners of the blocks as measured by image analysis. We performed preliminary trials in the laboratory to quantify the amount of work required to remove mass from the blocks. These measurements confirmed that ALC was a consistent substrate with regards to the amount of work required to remove a given mass. The technique was field-tested during a year-long survey at six sites in the Acheron valley, south-eastern Australia. Blocks were deployed for approximately 2 months at a time at each of six sites. The method was able to distinguish average differences in abrasion between trials and sites, but neither of these factors was constant. The variability of abrasion within sites was also high. Results show that the technique in its current form can be used to provide an index of the amount of abrasion to which the epilithic biota is exposed in streams and rivers. An assessment of the strengths and weaknesses of the technique is provided, and suggestions made for further improvements and research.     

Scanning electron microscopic examination of calcium alginate beads immobilizing growing mycelia of Aspergillus phoenicus

Calcium alginate beads inoculated with conidia of Aspergillus phoenicus have been incubated in various culture vessels for 120 h. Scanning electron microscopy revealed that the degree of agitation was a factor in surface stability of the beads. Highly significant was the successful restriction of mycelial growth to the subsurface, a condition required if the full advantages of immobilized fungi are to be realized.     

Resistance against spider mites in cotton induced by mechanical abrasion

Mechanical abrasion of cotyledons induced resistance to spider mites (Tetranychus urticae Koch) in cotton plants in four of six replicates. Mite population grwoth was reduced on plants that had either been abraded or had been previously exposed to mite feeding, compared to undamaged controls. Populations of mites were not different for plants that were abraded and for those that had been exposed previously to mites. In two of the six replicates, mite populations were not different for abraded, previously exposed and control plants. In these two replicates, densities of mites were greater than in the four replicates in which abrasion and previous exposure were effective, although the reasons for this discrepancy are not known.Induction of resistance by mechanical abrasion indicates that the response is not caused only by some factor specific to mites but can be caused by general wounding.

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Résumé L'abrasion mécanique des cotylédons a induit la résistance aux acariens (Tetranychus urticae) sur des pieds de coton dans 4 répétitions sur 6. La croissance des populations d'acariens sur plantes abrasées ou précédemment exposées à l'alimentation des acariens, était plus faible que celle des témoins. Les populations d'acariens sur plantes abrasées et sur plantes exposées précédemment aux acariens ne différaient pas. Dans 2 des 6 lots, les populations d'acariens ne différaient pas sur plantes abrasées, précédemment exposées ou témoin. Dans ces 2 lots, les densités d'acariens étainet plus élevées que dans les 4 autres, où l'abrasion et l'exposition antérieure étaient efficaces, bien ce que les raisons de cette discordance soient inconnues. L'induction de la résistance par une abrasion mécanique montre que la réaction n'est pas provoquée seulement par quelque facteur spécifique pour les acariens, mais par une réponse générale aux blessures.

     

Determination of biomass detachment rate coefficients in anaerobic fluidized-bed-GAC reactors

In this study a simple analytical technique that determines the active biomass in a sample capable of degrading specific substrates anaerobically was developed and used to measure first-order detachment rate coefficients of acetate and phenol utilizing organisms. Different detachment rate coefficients were measured for the two microbial populations. A general relationship between the detachment rate coefficients and biomass accumulation was developed. The detachment rate coefficient was found to increase sharply after a certain biomass accumulation until it reaches a maximum, after which it decreases continuously with increasing biomass until it levels off at a constant value independent of biomass. Detachment rate coefficients measured in different reactors, operating at different conditions with respect to loading, biological SRT, and attachment media particle size, were in close agreement with each other after being normalized to the shear stress and daily methane production rate per unit biofilm area.