Effect of Sperm Cryopreservation on the European Eel Sperm Viability and Spermatozoa Morphology

The main objective of the present work was to study the effect of cryopreservation of European eel sperm both on the sperm viability and the spermatozoa head morphology. Spermatozoa morphology was evaluated with computer-assisted morphology analysis after collection in fresh samples, after adding the freezing medium containing dimethyl sulfoxide as cryoprotectant and, finally, after the cryopreservation process and thawing. Cell viability was assessed, in both fresh and thawed samples, by Hoechst 33258 staining. Computer-assisted sperm analysis (CASA) was used to determine the percentage of motile cells and to measure motility parameters in sperm samples. A significant decrease of head perimeter (12.56%) and area (17.90%) was detected from spermatozoa in fresh to thawed samples, indicating that cells do not recover the original size after the cryopreservation process. CASA was used to measure the percentage of motile cells (51.9%) and spermatozoa motility parameters such as curvilinear, straight line and angular path velocities, as well as beating cross frequency. This technique was employed in the fresh sperm samples but proteins present at the freezing medium (L-alpha-phosphatidylcholine) made impossible to use this last technique in thawed samples. When sperm viability was assessed by Hoechst staining, a significant decrease of approximately 15% (73.10 vs 58.26%) of alive spermatozoa was registered from fresh to thawed samples. The percentage of motile cells measured by CASA in fresh samples (51.9%) was lower than the percentage of alive cells determined by Hoechst stainning, suggesting the existence of different batches of spermatozoa in different stages of development, even during the eight to tenth weeks of treatment, when the highest sperm quality was found.     

A common fold mediates vertebrate defense and bacterial attack

Proteins containing membrane attack complex/perforin (MACPF) domains play important roles in vertebrate immunity, embryonic development, and neural-cell migration. In vertebrates, the ninth component of complement and perforin form oligomeric pores that lyse bacteria and kill virus-infected cells, respectively. However, the mechanism of MACPF function is unknown. We determined the crystal structure of a bacterial MACPF protein, Plu-MACPF from Photorhabdus luminescens, to 2.0 angstrom resolution. The MACPF domain reveals structural similarity with poreforming cholesterol-dependent cytolysins (CDCs) from Gram-positive bacteria. This suggests that lytic MACPF proteins may use a CDC-like mechanism to form pores and disrupt cell membranes. Sequence similarity between bacterial and vertebrate MACPF domains suggests that the fold of the CDCs, a family of proteins important for bacterial pathogenesis, is probably used by vertebrates for defense against infection.     

Ultraviolet Emissions Observed near Venus from Mariner V

A Lyman-alpha airglow of atomic hydrogen measured in the outer atmosphere of Venus showed that atomic hydrogen is present. The variation as a function of height indicates that the temperature of the upper atmosphere of Venus is lower than that of Earth. An ultraviolet airglow of atomic oxygen was not found. An ultraviolet nightglow was observed on the dark limb.     

Effects of resident rhizobial communities and soil type on the effective nodulation of pulse legumes

Communities of resident rhizobia capable of effective nodulation of pulse crops were found to vary considerably over a range of soil environments. These populations from soils at 50 sites in Southern Australia were evaluated for nitrogen fixing effectiveness in association with Pisum sativum, Vicia faba, Lens culinaris, Vicia sativa, Cicer arietinum and Lupinus angustifolius. The values for nitrogen fixing effectiveness could be related to soil pH as determined by soil type and location. It was found that 33% of paddocks had sufficient resident populations of Rhizobium leguminosarum bv viciae for effective nodulation of faba bean, 54% for lentils, 55% for field pea and 66% for the effective nodulation of the vetch host plant. Mesorhizobium cicer populations were very low with only 7% of paddocks surveyed having sufficient resident populations for effective nodulation. Low resident rhizobial populations (<10 rhizobia g⁻¹ soil) of R. leguminosarum bv viciae and M. cicer were found in acid soil conditions. In contrast, Bradyrhizobium populations increased as soil pH decreased. Inoculation increased faba bean yields from 0.34 to 4.4 t ha⁻¹ and from 0.47 to 2.37 t ha⁻¹ for chickpeas on acid soils. On alkaline soils, where resident populations were large there was no consistent response to inoculation. Observations at experimental field sites confirmed the findings from the survey data, stressing the importance of rhizobial inoculation, especially on the acid soils in south-eastern Australia.     

Effect of temperature on somatic growth and survivorship of early post-settled green sea urchins, Strongylocentrotus droebachiensis (Müller)

A laboratory experiment was run for 171 days to assess growth and survivorship of recently settled juveniles of the green sea urchin, Strongylocentrotus droebachiensis (Müller), reared at five temperatures: 4.7±0.8, 9.0±1.1, 12.9±1.1, 16.0±1.5 and 19.7±1.3°C (mean±SD, n=7942). Individual sea urchins were housed separately in PVC pots with Nitex mesh bottoms (10 per tank and five replicate tanks per temperature treatment) and fed a combination of benthic diatoms and macroalgae (Porphyra sp.). The test diameter of each urchin was measured and survivorship recorded on a monthly basis. Mean (±SE) test diameter of all individuals at the beginning of the experiment was 2.41±0.03 mm (n=250). At the end of the experiment, mean test diameter (±SE) was significantly larger at 9.0°C (8.46±0.06 mm) and 12.9°C (8.20±0.25 mm) than at 4.7°C (7.27±0.05 mm), 16.0°C (6.72±0.17 mm) and 19.7°C (2.65±0.24 mm) and significantly larger at 4.7 and 16.0°C than at 19.7°C. When growth was expressed as a per cent increase in test diameter from the start of the experiment, however, there were no significant pair‐wise differences among 4.7, 9.0, 12.9 and 16.0°C treatments at the end of the experiment, but all these treatments were significantly greater than at 19.7°C. Mean per cent survivorship (±SE) at the end of the experiment for the various temperature treatments was 76.0±6.0%, 90.0±5.5%, 100.0±0.0%, 98.0±2.0% and 26.0±11.2% at 4.7, 9.0, 12.9, 16.0 and 19.7°C respectively. Per cent survivorship was significantly greater at 4.7, 9.0, 12.9 and 16.0°C than at 19.7°C and significantly greater at 12.9 and 16.0°C than at 4.7°C. Mean area increase of urchins per replicate tank at the end of the experiment – taking into account both test diameter growth and survivorship – was significantly larger at 9.0 and 12.9°C than at 4.7, 16.0 and 19.7°C, and significantly larger at 4.7 and 16.0°C than at 19.7°C. The results of this study suggest that young juveniles of S. droebachiensis should be reared at 9–13°C in order to optimize production for aquaculture.     

Integrating contact network structure into tuberculosis epidemiology in meerkats in South Africa: Implications for control

Empirical studies that integrate information on host contact patterns with infectious disease transmission over time are rare. The aims of this study were to determine the relative importance of intra-group social interactions in the transmission of tuberculosis (TB; Mycobacterium bovis infection) in a population of wild meerkats (Suricata suricatta) in South Africa, and to use this information to propose an evidence-based intervention strategy to manage this disease. Detailed behavioural observations of all members of eight meerkat groups (n=134 individuals) were made over 24 months from January 2006 to December 2007. Social network analysis of three types of interaction (aggression, foraging competitions and grooming) revealed social structure to be very stable over time. Clustering of interactions was positively correlated with group size for both aggression (r=0.73) and grooming interactions (r=0.71), suggesting that infections may spread locally within clusters of interacting individuals but be limited from infecting all members of large groups by an apparent threshold in connections between different clusters. Repeated biological sampling every three months of all members of one social group (n=37 meerkats) was undertaken to quantify individual changes in M. bovis infection status. These empirical data were used to construct a dynamic network model of TB transmission within a meerkat group. The results indicated that grooming (both giving and receiving) was more likely than aggression to be correlated with M. bovis transmission and that groomers were at higher risk of infection than groomees. Intervention strategies for managing TB in meerkats that focus on those individuals engaging in the highest amount of grooming are therefore proposed.