Selection of an Isolate of the Insect Pathogenic Fungus Metarhizium anisopliae Virulent to the Lettuce Root Aphid, Pemphigus bursarius

The virulence of hyphomycete entomopathogenic fungi was measured in laboratory bioassays against the lettuce root aphid, Pemphigus bursarius, a serious pest of field lettuce grown in the UK. Of 25 isolates of fungi examined, only one isolate, Metarhizium anisopliae 391.93, killed lettuce root aphids consistently. This fungus was isolated originally from the closely related saltmarsh aphid, P. trehernei. The median lethal concentration of conidia at 10 days post6- 1 inoculation estimated from five independent bioassays was 2.45 × 10⁶ conidia ml^-1. The fungus had no significant effect on the mean number of offspring/aphid produced, but it sporulated 6 profusely on host cadavers, producing approximately 4 × 10⁶ conidia/cadaver 14 days after treatment, and diseased aphids died attached to plant roots. It thus has the potential to spread through densely packed colonies of P. bursarius feeding on the roots of susceptible or partially resistant plants.     

Laboratory investigations on the potential of entomopathogenic fungi for biocontrol of Helicoverpa armigera (Lepidoptera: Noctuidae) larvae and pupae

The susceptibility of third instar Helicoverpa armigera to seven strains of three entomopathogenic fungal species, i.e. Metarhizium anisopliae, Beauveria bassiana and Paecilomyces fumosoroseus, was tested under laboratory conditions using the larval immersion method. High efficacies ranging from 68 to 100% corrected mortality were recorded with more profound effects in treatments with B. bassiana and P. fumosoroseus strains. The median lethal concentration (LC₅₀) for L3 was 6.0×10⁵ in M. anisopliae 79, 1.5×10⁵ in B. bassiana 124 and 4.2×10⁴ in P. fumosoroseus 14. These three strains were further used to characterize the age-dependent mortality of different larval stages (L2-L5) and the effect against pupae of H. armigera. Larval stages did not differ in their mortality but differed i in median lethal time, with shorter values recorded in the second instar. Tested fungi also caused a high reduction between 74.4 and 100% in the emergence of pupae using the soil inoculation method and the pupal immersion technique. All three fungal species, especially P. fumosoroseus, have a high potential for biocontrol of H. armigera larvae and also as a soil treatment targeting the pupae.     

Media and Fermentation Processes for the Rapid Production of High Concentrations of Stable Blastospores of the Bioinsecticidal Fungus Paecilomyces fumosoroseus

In shake flask and fermentor studies, various media components and culture inocula were tested to improve P. fumosoroseus spore production rates, yield and stability. To evaluate inoculum potential and inoculum scale-up for fermentor studies, conidia and liquid culture-produced spores of various strains of P. fumosoroseus were compared as inoculum. Inoculation of liquid cultures with blastospores at concentrations of at least 1×10⁶ spores mL^-1 resulted in the rapid production of high concentrations of blastospores (∼1×10⁹ spores mL^-1, 48 h fermentation time) for all strains tested. The rapid germination rate of blastospores (90% after 6 h incubation) compared to conidia (>90% after 16 h incubation) and the use of higher inoculum rates reduced the fermentation time from 96 to 48 h for maximal spore yields. A comparison of various complex nitrogen sources showed that liquid media supplemented with acid hydrolyzed casein or yeast extract supported the production of high concentrations of blastospores that were significantly more desiccation-tolerant (79-82% survival after drying) when compared to blastospores produced in media supplemented with other nitrogen sources (12-50% survival after drying). For rapid spore production, requirements for trace metals and vitamin supplementation were dependent on the type of hydrolyzed casein used in the medium. Fermentor studies with two strains of P. fumosoroseus showed that high concentrations (1.3-1.8×10⁹ spores mL^-1) of desiccation-tolerant blastospores could be produced in 48-h fermentations. These studies have demonstrated that the infective spores of various strains of the fungal bioinsecticide Paecilomyces fumosoroseus can be rapidly produced using deep-tank, liquid culture fermentation techniques.     

Non-Susceptibility of Earthworm Eisenia fetida to the Rhabditid Nematode Phasmarhabditis hermaphrodita, a Biocontrol Agent of Slugs

The rhabditid nematode Phasmarhabditis hermaphrodita is a lethal parasite for slugs that is sold commercially in Europe under the trade name Nemaslug™. We evaluated the effects of P. hermaphrodita on the earthworm Eisenia fetida (Savigny). Adults of E. fetida were exposed in one-liter glass beakers to P. hermaphrodita at three concentrations (1×, 10× and 50× of the field recommended rate of 3×10⁹ billion nematodes/ha) during a 14-day period in an artificial soil substrate. The average body weight, burrowing behavior, mortality and other clinical signals of the earthworms were recorded at 0, 7, and 14 days after exposure to the treatments. In addition, injured earthworms (posterior ends removed) were exposed to the 10× field recommended rate of the commercial formulation. Neither intact nor injured E. fetida showed susceptibility to the slug-parasitic nematode P. hermaphrodita during the 14 days of exposure even at concentrations 10 and 50 times higher than the label dose. However, the worms in the attenuated control (autoclaved formulation) had higher mortality and lost less weight compared to the other treatments. Under the conditions of the test, we conclude that the use of the commercially available strain of P. hermaphrodita is safe to E. fetida.     

Microbial characterization during composting of municipal solid waste

This study investigates the prevailing physico-chemical conditions and microbial community; mesophilic bacteria, yeasts and filamentous fungi, bacterial spores, Salmonella and Shigella as well as faecal indicator bacteria: total coliforms, faecal coliforms and faecal Streptococci, present in a compost of municipal solid waste. Investigations were conducted in a semi-industrial pilot plant using a moderate aeration during the composting process. Our results showed that: (i) auto-sterilization induced by relatively high temperatures (60–55°C) caused a significant change in bacterial communities. For instance, Escherichia coli and faecal Streptococci populations decreased, respectively, from 2×10⁷ to 3.1×10³ and 10⁷ to 1.5×10³ cells/g waste dry weight (WDW); yeasts and filamentous fungi decreased from 4.5×10⁶ to 2.6×10³ cells/g WDW and mesophilic bacteria were reduced from 5.8×10⁹ to 1.8×10⁷ bacteria/g WDW. On the other hand, the number of bacterial spores increased at the beginning of the composting process, but after the third week their number decreased notably; (ii) Salmonella disappeared completely from compost by the 25th day as soon as the temperature reached 60°C; and (iii) the bacterial population increased gradually during the cooling phase. While Staphylococci seemed to be the dominant bacteria during the mesophilic phase and at the beginning of the thermophilic phase, bacilli predominated during the remainder of the composting cycle. The appearance of gram-negative rods (opportunistic pathogens) during the cooling phase may represent a serious risk for the sanitary quality of the finished product intended for agronomic reuse. Compost sonication for about 3 min induced the inactivation of delicate bacteria, in particular gram-negatives. By contrast, gram-positive bacteria, especially micrococcus, spores of bacilli, and fungal propagules survived, and reached high concentrations in the compost.     

Effects of environmental factors, age and genotype on sperm production and semen quality in Bos indicus and Bos taurus AI bulls in Brazil

The effects of ambient temperature and humidity, month, age and genotype on sperm production and semen quality in AI bulls in Brazil were evaluated. Data from two consecutive years were analyzed separately. Seven Bos indicus and 11 Bos taurus bulls from one artificial insemination (AI) center were evaluated in Year 1 and 24 B. indicus and 16 B. taurus bulls from three AI centers were evaluated in Year 2. Ambient temperature and humidity did not significantly affect sperm production and semen quality, probably because there was little variation in these variables. Month accounted for less than 2% of the variation in sperm production and semen quality. Increased bull age was associated with decreased sperm motility (P<0.10) and increased minor sperm defects (P<0.001) in Year 1. B. indicus bulls had greater (P<0.005) sperm concentration than B. taurus bulls in both years (1.7×10⁹/ml versus 1.2×10⁹/ml in Year 1 and 1.6×10⁹/ml versus 1.2×10⁹/ml in Year 2, respectively). Ejaculate volume was not significantly affected by genotype in Year 1 (6.6 ml versus 6.9 ml in B. indicus and B. taurus bulls, respectively), but B. indicus bulls had greater (P<0.05) total (11.4×10⁹ versus 8.2×10⁹) and viable (6.7×10⁹ versus 4.9×10⁹) numbers of spermatozoa in the ejaculate than B. taurus bulls. In Year 2, B. taurus bulls had greater (P<0.05) ejaculate volume than B. indicus bulls (8.2 ml versus 6.7 ml, respectively) and total and viable number of spermatozoa in the ejaculate were not significantly different between genotypes (10.3×10⁹ versus 9.1×10⁹ and 6.1×10⁹ versus 5.4×10⁹ in B. indicus and B. taurus bulls, respectively). Sperm motility was not significantly affected by genotype (mean, 59%). In Year 1, B. indicus bulls tended (P<0.10) to have more major sperm defects and had more (P<0.05) total sperm defects than B. taurus bulls (11.8% versus 8.7% and 13.6% versus 10.0%, respectively). In Year 2, B. indicus bulls tended (P<0.10) to have more total sperm defects than B. taurus bulls (16.2% versus 13.3%, respectively). In conclusion, neither ambient temperature and humidity nor month (season) significantly affected sperm production and semen quality. B. indicus bulls had significantly greater sperm concentration and B. taurus bulls had significantly fewer morphologically defective spermatozoa.     

Structure of 7S seed globulin from Phaseolus vulgaris L. in solution

The structure of the 7S globulin from Phaseoulus vulgaris L in dilatue solutions has been studied by small angle X-ray scattering (SAXS), by quasi-elastic light scattering (Q ELS), by circular dichroism spectroscopy (c.d.), and by precise density measurements. The molar mass, the radius of gyration, the volume, the maximum dimension and the diffusion coefficient were determined as M = 1.45 × 10⁵ g mol⁻¹, R_G = 4.05 nm, V = 300- nm³, L = 13.0 nm and D_20,w⁰ = 4.5 × 10⁻⁷ cm² s⁻¹, respectively. The molecule has an asymmetrical shape with the dimensions 12.5 × 12.5 × 3.75 nm. The secondary structure of the 7S globulin is characterized by a small portion of -helical structure (14%) and a marked content of β-structure (18%).     

Effects of Pseudomonas chlororaphis on Pythium aphanidermatum and Root Rot in Peppers Grown in Small-scale Hydroponic Troughs

The ability of Pseudomonas (Ps.) chlororaphis isolate Tx-1 to suppress Pythium aphanidermatum and control root rot was investigated in sweet peppers grown in small-scale hydroponic trough units with recirculating nutrient solution. The agent was introduced to the nutrient solution 3 days after the peppers were inoculated with P. aphanidermatum, or 4 days before and 3 days after inoculation, or 4 days before and 3 and 10 days after. Controls either received no agent or pathogen, or the agent only (applied once, 4 days before the time of pathogen inoculations), or the pathogen only. The experiment was conducted in a greenhouse with repetitions beginning in January, March, and May. Severity of root browning associated with P. aphanidermatum, in the absence of Ps. chlororaphis, increased in the first, second and third repetitions, respectively, to 74% at 21 days, 28% at 21 days, and 68% at 11 days. In treatments with one, two, or three applications of Ps. chlororaphis, respectively, areas under root browning progress curves were reduced by 18-48%, 50-73%, and 62-79% compared to the pathogen controls, and recovery incidence of the pathogen from roots at 21 days after inoculation was reduced by 14-47%, 62-82%, and 60-89%. Roots not inoculated with P. aphanidermatum were whitish and not colonized by the pathogen. Density of Ps. chlororaphis in treated plants was usually 2×10³-1.2×10⁵ cfu g^-1 fresh roots. The Ps. chlororaphis treatments almost invariably prevented reductions in plant height, leaf area, fresh mass and dry mass of the shoots and of the roots, and root volume associated with P. aphanidermatum and root browning. It is concluded that Ps. chlororaphis Tx-1 strongly antagonized P. aphanidermatum in the pepper roots and that the agent has considerable potential for controlling root rot and maintaining productivity in commercial hydroponic peppers.     

Field application of an insect virus in the Mekong Delta: Effects of a Vietnamese nucleopolyhedrovirus on Spodoptera litura (Lepidoptera: Noctuidae) and its parasitic natural enemies

A new Vietnamese isolate of Spodoptera litura nucleopolyhedrovirus (NPV) was applied in local soybean fields, and the effect of its application on S. litura larvae was examined. The virus was propagated in vivo and a crude extract was prepared for spraying at high and low doses (1.7×10⁸ and 3.3×10⁷ occlusion bodies/m², respectively). The percentage of larvae infected with NPV increased from 22.2% on the day before NPV application (Day 0) to 50.8% (Day 6) in the high dose treatment plot, and from 7.9% (Day 0) to 35.7% (Day 6) in the low-dose plot. Microsporidium sp. was observed as another major pathogen of S. litura larvae. Three dominant parasitic natural enemies were found in S. litura larvae: Microplitis manilae (Braconidae), Chelonus sp. (Braconidae), and Peribaea orbata (Tachinidae). The fate of parasitoids developing within virus- and Microsporidium- infected hosts differed between these three parasitoids; more Chelonus sp. emerging from infected hosts died during their larval stage before spinning cocoons, or failed to reach adult eclosion, than did P. orbata. This suggests that the impact of virus application on the survival of parasitoids varies from species to species.     

Biological Control and Use of Adjuvants against Multiple Seeded Cocklebur (Xanthium strumarium) in Comparison with Several Other Cocklebur Types

Common cocklebur has several biotypes including multiple seeded cocklebur (MSC), NCC-TX, and NCC-MS. Alternaria helianthi applied at 2.5×10⁴ conidia mL^-1 in a 50% micro-emulsion of unrefined corn oil (MESUCO) or 0.2% Silwet L 77 caused 60-75% mortality on NCC-TX and MSC. Increasing the conidial concentration to 5×10⁴ mL^-1 increased mortality to 100% on MSC and NCC-TX, and 75% on NCC-MS. At 10×10⁴ conidia mL^-1, A. helianthi caused 100% mortality in all three biotypes. No mortality occurred in any biotype at inoculation rates of 2.5 and 5×10⁴ conidia mL^-1 when applied in water. Increasing the dew period from 0 to 12 h increased mortality from 0 to 100% on all three biotypes at a rate of 2.5×10⁴ conidia mL^-1 in Silwet and MESUCO. MSC appears to be the most sensitive biotype.     

Production of a Mixed Inoculum of Fusarium oxysporum Fo47 and Pseudomonas fluorescens C7 to Control Fusarium Diseases

Strains of non-pathogenic Fusarium oxysporum and Pseudomonas fluorescens are effective biocontrol agents against Fusarium diseases. Use of strain Fo47 of F. oxysporum in combination with strain C7 of P. fluorescens improves disease control in comparison to application of Fo47 alone. To develop a product based on a combination of these two strains, it would be beneficial to produce and formulate both organisms together. When an irradiated peat was inoculated with these strains either alone or in combination, they grew actively and reached similar maximum population densities irrespective of the initial inoculum concentration (1×10³ and 1×10⁶ g^-1 of peat) and mode of inoculation. These populations survived well with only a slight decrease in population densities after 11 months storage at 25°C. A bioassay was performed to evaluate peat and microbial suspension inocula of C7 and Fo47 alone or in combination against the flax pathogen, F. oxysporum f. sp. lini. Biocontrol activity of the peat-produced inocula was as effective as the suspensions. There was no dose-response relationship for C7, and when C7 was used as a mixed inoculum with Fo47, the biocontrol activity was always greater than that provided by Fo47 alone. This process could be used to produce an effective mixed inoculum with a shelf life of one year or more.     

Effect of reaction temperature and reaction time on the preparation of low-molecular-weight chitosan using phosphoric acid

Low-molecular-weight chitosan were prepared using 85% phosphoric acid at different reaction temperatures and reaction time. At room temperature, the viscosity average-molecular weights (M_v) of chitosan decreased to 7.1×10⁴ from 21.4×10⁴ after 35 days treatment. The degradation rate decreased with increasing hydrolysis time. The yields of chitosan also continuously decreased from 68.4 to 40.2% after 35 days. At 40, 60 and 80 °C, the molecular weight decreased to 3.70×10⁴, 3.50×10⁴ and 2.00×10⁴ on 8 h hydrolysis, respectively. The yields of chitosan remain at a high level compared with that at room temperature and were 86.5, 71.4 and 61.3% at 40, 60 and 80 °C treatment, respectively. The different reaction time gave chitosan with different molecular weights. At 60 °C, the molecular weight of products decreased to 7.40×10⁴ from 21.4×10⁴ within 4 h, then decreased slowly to 1.90×10⁴ in 15 h. It was also found that the water-solubility of chitosan increased as the molecular weight decreased. Results show the changes in yields and molecular weight of chitooligomers were strongly dependent on the reaction temperature and reaction time.     

The solution molecular weight and shape of the bacterial exopolysaccharides amylovoran and stewartan

Amylovoran, the acidic exopolysaccharide (EPS) of Erwinia amylovora, and stewartan, the capsular EPS of E. stewartii, were characterized by analytical ultracentrifugation and by size exclusion chromatography connected to dual detection of light scattering and mass. The average molecular weights of amylovoran and stewartan were determined as 1.0×10⁶ and 1.7×10⁶ Da, with polydispersity values (M_w/M_n) of 1.5 and 1.4, respectively. Based on the sugar composition and their molecular weight, both exopolysaccharides consist of approximately 1000 repeating units per molecule, this suggests a similar mechanism for chain length determination during biosynthesis of EPS in both organisms.     

Plant regeneration from mesophyll protoplasts of Solanum commersonii dun

Somatic fusion of Solanum commersonii, a frost tolerant wild potato species not crossable with Solanum tuberosum, relies on the possibility to isolate and culture protoplasts. This study was conducted to determine whether protoplasts could be isolated and plants regenerated in three S. commersonii accessions. Shoot cultures for protoplast isolation were maintained on Murashige and Skoog medium. Mesophyll protoplasts were isolated and cultured using a protocol originally described for S. tuberosum with some modifications. Differences were evident among the three accessions for protoplast yield, plating efficiency and regeneration frequency. Protoplast yield ranged from 3.0 to 8.5 × 10⁶ protoplasts per g of fresh tissue. At 1–2 × 10⁴ protoplasts ml⁻¹, which was the optimal plating density, 10–20% of plated protoplasts gave multicellular colonies. Regeneration of shoots was observed in two accessions only, the maximum regeneration frequency being 66%. In one of these accessions the reduction of sucrose concentration in regeneration media improved the regeneration frequency from 14 to 35%. About three hundred plants were rooted in vitro and successfully transferred to soil.     

Augmentation of Soil with Sporangia of Actinoplanes spp. for Biological Control of Pythium Damping-off

A method was developed for applying strains of Actinoplanes spp. that are hyper-parasites of oospores of Pythium ultimum to soil for reducing Pythium damping-off of plants. The method is based on the augmentation of soil with sporangia of a strain of Actinoplanes spp. borne on clay granules. In vitro sporulation of strains K30, W57, W257 and 25844 was: (1) greater for most strains on dilute Czapek-Dox agar than on four other agar media; (2) inhibited by continuous exposure to fluorescent light of intensity 4-150 μEm^-2s^-1, but not by exposure to 1 μEm^-2s^-1 or darkness; (3) greater at 20-307deg;C than at 10°C;and (4) greater at pH 6-7 than at pH 5 or 8. On solid carriers treated with dilute Czapek-Dox broth (pH 7) and incubated in the dark at 30°C for 3 weeks, strains sporulated poorly or not at all on vermiculite, perlite and rice hulls, but sporulated abundantly (10⁷-10⁹ colony-forming units (CFU) g^-1 of granules) on montmorillonite clay granules. When strains 25844, W57 and W257 were applied as granules (4 10⁷ - 4 × 10⁸ CFU g^-1) at 5% (w/w) to field plots infested with 750-1000 oospores of P. ultimum g^-1 of soil, only strain 25844 consistently increased emergence and reduced root rot of table beets 8- 1 at 24-28 days after planting compared with controls. Strain 25844 (10⁸ CFU g^-1 of granules) at 1% (w/w) also increased the emergence of bush beans at 28 days after planting in P. ultimum-infested plots, but lower rates were ineffective. The inoculum viability of strain 25844 on clay granules declined 100-fold during 2 months of storage at 5-35°C, but thereafter remained stable for another 4 months. Strain 25844 on 6-month-old granules retained a high degree of hyper-parasitic activity toward oospores of P. ultimum. Augmentation of field soil with sporangia of Actinoplanes spp. is a valid approach to the biological control of pythium damping-off.     

Catalysis of plastocyanin electron self-exchange by redox-inert multivalent cations

Electron self-exchange in solutions of the ‘blue’ copper protein plastocyanin is catalysed by the redox-inert multivalent cations Mg²⁺ or Co(NH₃)³⁺₆. Measurements of specific ¹H-NMR line broadening with 50% reduced solutions in the presence of these cations show that electron exchange proceeds through encounters of cation-protein complexes which dissociate at high ionic strength. In the presence of 8mM (5 equivalents/total protein) Co(NH₃)³⁺₆, with 10 mM cacodylate (pH^*6.0) as background electrolyte, the bimolecular rate constant at 25°C is 7 × 10⁴ M⁻¹·s⁻¹. For comparison, the ‘electrostatically screened’ rate constant measured in 0.1 M KCl in the absence of added multivalent cations is ˜ 4 × 10³ M¹·s⁻¹.

Plastocyanin Electron self-exchange NMR Protein-protein interaction Multivalent cation Blue copper protein     

One-electron reduction of selenomethionine oxide

Experimental evidence is provided that selenomethionine oxide (MetSeO) is more readily reducible than its sulfur analogue, methionine sulfoxide (MetSO). Pulse radiolysis experiments reveal an efficient reaction of MetSeO with one-electron reductants, such as e^-_aq (k = 1.2 × 10¹⁰M^-1s^-1), CO^·-₂ (k = 5.9 × 10⁸ M^-1s^-1) and (CH₃)₂) C^·OH (k = 3.5 × 10⁷M^-1s^-1), forming an intermediate selenium-nitrogen coupled zwitterionic radical with the positive charge at an intramolecularly formed Se_∴ N 2σ/1σ* three-electron bond, which is characterized by an optical absorption with λ_max at 375 nm, and a half-life of about 70 μs. The same transient is generated upon HO^· radical-induced one-electron oxidation of selenomethionine (MetSe). This radical thus constitutes the redox intermediate between the two oxidation states, MetSeO and MetSe. Time-resolved optical data further indicate sulfur-selenium interactions between the Se_∴ N transient and GSH. The Se_∴ N transient appears to play a key role in the reduction of selenomethionine oxide by glutathione.     

DNA-biding of IQ, Me-IQ and Me-IQx, strong mutagens found in broiled foods

Non-covalent DNA-binding has been studied of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (Me-IQ) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (Me-IQx), strong mutagens found in broiled foods. These mutagens are intercalated into DNA, as found by ultraviolet absorption gel electrophoresis. The binding of IQ is stronger with GC pairs than AT pairs in DNA. The binding constants with calf thymus DNA are 1.6 × 10⁶ (Me-IQ), 0.9 × 10⁶ (IQ) and 0.7 × 10⁶ M⁻¹ (Me-IQx) at pH 6.0. This order of DNA affinity agrees with the order of mutagenicity towards Salmonella typhimurium TA98.     

不同无机碳源对粉核油球藻生长的影响

研究了2种无机碳源对粉核油球藻(Pinguiococcus pyrenoidosus CCMP2078)生长的影响。结果表明,适量添加NaHCO₃和通CO₂对P.pyrenoidosus CCMP2078的生长均有促进作用,NaHCO₃的添加方式对该藻的生长具有显著差异。一次性添加和分批添加NaHCO₃的优化浓度分别为5mmoL·L^-1和20mmoL·L^-1,后者对数生长末期的细胞密度、干重和比生长速率均最高,分别为8.93×10⁶cells·mL^-1,0.247g·L^-1和0.225dL^-1。通入CO₂的体积分数为0.5%时,最有利于藻细胞的生长,对数生长末期的细胞密度、干重和比生长率分别为3.83×10⁷cells·mL^-1、0.42g·L^-1和0.212d^-1。     

The effect of hydroxyl radicals on the rheological performance of hylan and hyaluronan

Shear flow, dynamic oscillation and extensional viscosity measurements were used to compare the rheological performance of several hylan samples (M_v 1.6, 3.2, 3.7, 4.7 and 5.6×10⁶) and hyaluronan (M_v 1.4 and 1.8×10⁶) before and after hydroxyl radicals (√OH) induced degradation. It was found that the higher molecular weight cross-linked structure of hylan was more resistant to degradation than hyaluronan and that this superior stability was reflected in various rheological parameters. The √OH degradation of the initial hylan and hyaluronan samples produced a range of polysaccharides based on hylan and hyaluronan with molecular weight covering a range from 0.5–5.6×10⁶. The rheological parameters associated with the polysaccharides could then also be studied. Zero shear values of the complex viscosity (η*), dynamic viscosity (η′) and shear viscosity (η) were calculated using the method of Morris¹ and shown to approach the same value at zero shear or frequency. An adaptation of the method of Gibbs et al.² gave a ‘master curve’ for the storage and loss modulus of hyaluronan and hylan, which encompasses a 10-fold molecular weight and a 5-fold concentration variation. In all instances for hylan, the storage modulus predominates over the loss modulus, whereas for hyaluronan, the reverse is true, demonstrating the greater elasticity of hylan throughout the whole experimental range of molecular weights and concentrations.