16S ribosomal RNA sequence analysis for determination of phylogenetic relationship among methylotrophs.

16S ribosomal RNAs (rRNA) of 12 methylotrophic bacteria have been almost completely sequenced to establish their phylogenetic relationships. Methylotrophs that are physiologically related are phylogenetically diverse and are scattered among the purple eubacteria (class Proteobacteria). Group I methylotrophs can be classified in the beta- and the gamma-subdivisions and group II methylotrophs in the alpha-subdivision of the purple eubacteria, respectively. Pink-pigmented facultative and non-pigmented obligate group II methylotrophs form two distinctly separate branches within the alpha-subdivision. The secondary structures of the 16S rRNA sequences of 'Methylocystis parvus' strain OBBP, 'Methylosinus trichosporium' strain OB3b, 'Methylosporovibrio methanica' strain 81Z and Hyphomicrobium sp. strain DM2 are similar, and these non-pigmented obligate group II methylotrophs form one tight cluster in the alpha-subdivision. The pink-pigmented facultative methylotrophs, Methylobacterium extorquens strain AM1, Methylobacterium sp. strain DM4 and Methylobacterium organophilum strain XX form another cluster within the alpha-subdivision. Although similar in phenotypic characteristics, Methylobacterium organophilum strain XX and Methylobacterium extorquens strain AM1 are clearly distinguishable by their 16S rRNA sequences. The group I methylotrophs, Methylophilus methylotrophus strain AS1 and methylotrophic species DM11, which do not utilize methane, are similar in 16S rRNA sequence to bacteria in the beta-subdivision. The methane-utilizing, obligate group I methanotrophs, Methylococcus capsulatus strain BATH and Methylomonas methanica, are placed in the gamma-subdivision. The results demonstrate that it is possible to distinguish and classify the methylotrophic bacteria using 16S rRNA sequence analysis.     

Comparison of fungicidal properties of non-thermal plasma produced by corona discharge and dielectric barrier discharge

The inactivation of four micromycete species by action of non-thermal plasma was followed. Two sources of plasma were compared, namely, positive corona discharge and dielectric barrier discharge. The corona discharge appeared as suitable for fungal spore inactivation in water suspension, whereas the barrier discharge inactivated spores on the surface of cultivation agar. Cladosporium sphaerospermum was the most sensitive, being inactivated within 10 min of exposure to plasma, whereas Aspergillus oryzae displayed decrease in viable cell count only, the complete inactivation was not achieved even after 40 min of exposure. Intermediate sensitivity was found for Alternaria sp. and Byssochlamys nivea. The significant delay of growth was observed for all fungi after exposure to sublethal dose of plasma, but we failed to express this effect quantitatively.     

Possible risk posed by drift of the insect growth regulator pyriproxyfen to the rare dung beetle Circellium bacchus (F.) in a national park

Aerial drift of the juvenile hormone analogue (JHA), pyriproxyfen (Nemesis 100 ec®), used to control red scale on citrus on farms close to the Addo Elephant National Park in South Africa, was suspected of causing a decline in a population of the rare dung beetle species Circellium bacchus (F.) in the Park. The effect of pyriproxyfen on fertility and egg viability, as well as larval, pupal and callow adult development of C. bacchus was studied in a laboratory assay. Adult beetles, soil surface and the initial dung supply were exposed to pyriproxyfen applied as a spray at 10 times less than the concentration used commercially to simulate spray drift. Exposure of adult beetles to pyriproxyfen did not affect egg production or the viability of eggs, nor did the compound have adverse effects on immature development, indicating that pyriproxyfen is unlikely to be the cause of the observed population depression of C. bacchus.     

Megafaunal influences on tree recruitment in African equatorial forests

The forests of central Africa are distinct from counterpart forests in Amazonia by having fewer trees ≥ 10 cm dbh ha^?1, especially small trees < 20 cm dbh, and in having sapling cohorts with less diversity than canopy trees. We tested four hypotheses to investigate whether herbivory, in particular, browsing by forest elephants, could be a factor in these differences. We found that the density of small saplings and diversity of large saplings were inversely associated with local density of elephants. We then tested the hypothesis that steep slopes might serve as refugia from elephant foraging, but found that elephants routinely forage on slopes with an inclination of less than ca 30 deg. Nevertheless, the diversity of small trees (≥ 10 cm, < 20 cm dbh) was higher on slopes than on paired level‐ground sites. The incidence of break scars on saplings ≥ 2 cm dbh and < 6 cm dbh was greater (107/100 stems) on level ground than on slopes (77/100 stems), although high variability precluded statistical significance. After correcting for background breakage not caused by elephants, an estimated 71% of breaks on level ground and 43% of breaks on slopes were attributable to elephants. Liana loads borne by trees at different sites were highly variable and unrelated to slope. Apparently, disturbances are more critical to liana development than herbivory. Elephants, along with other large mammals such as gorillas, duikers, red river hogs and rodents, appear to act as powerful filters on the tree recruitment process in African forests that still retain intact megafaunal communities.     

Regulation of rat liver 4-hydroxy-2-ketoglutarate aldolase

The possibility is examined that 4-hydroxy-2-ketoglutarate aldolase (4-hydroxy-2-ketoglutarate glyoxylatelyase, EC 4.1.3.16), the last step in hydroxyproline catabolism is regulated by intermediates of gluconeogenesis. Inhibition of isolated 4-hydoxy-2-ketoglutarate aldolase was examined using dual inhibition studies. It was found that the enzyme exhibits synergistic inhibition by oxaloacetate and pyruvate, but only when the substrate concentration is low. At substrate concentrations approaching saturation, the inhibition by the oxaloacetate and pyruvate becomes additive. These results are discussed in terms of possible control of the use of carbon from hydroxyproline breakdown in glucose production.     

Impact of Embryonopsis halticella eaton larvae (Lepidoptera: Yponomeutidae) feeding in Marion Island tussock grassland

Summary Embryonopsis halticella is a brachypterous moth endemic to the Kerguelen Province of sub-Antarctic islands. Its larvae are strictly host-specific grass-borers of the tussock grass Poa cookii, and are the major herbivores on Marion Island. Monthly sampling over one year (1984) on Marion Island showed that E. halticella larvae reach a biomass of 0.222 g m^-2 (dry mass) in P. cookii grassland in summer. In feeding experiments conducted in the laboratory on Marion Island, larvae consumed 0.3 X their own live mass in leaf material daily. Extrapolated consumption rates in the field range from 1 kg ha^-1 month^-1 in winter to 18 kg ha^-1 month^-1 (dry mass) in summer. Total annual consumption, based on leaf feeding only, amounts to 86 kg ha^-1 (dry mass). Significant shifts in diet from foliage to seeds occur during spring, and larvae also consume their own frass and exuviae. It is calculated that E. halticella larvae remove 2.5% of the annual production of Poa cookii in Marion Island tussock grassland.     

Kinetics of amide proton exchange in helical peptides of varying chain lengths. Interpretation by the Lifson-Roig equation.

The kinetics of amide proton exchange (1H----2H) have been measured by proton nuclear magnetic resonance spectroscopy for a set of helical peptides with the generic formula Ac-(AAKAA)m Y-NH2 and with chain lengths varying from 6 to 51 residues. The integrated intensity of the amide resonances has been measured as a function of time in 2H2O at pH* 2.50. Exchange kinetics for these peptides can be modeled by applying the Lifson-Roig treatment for the helix-to-coil transition. The Lifson-Roig equation is used to compute the probability that each residue is helical, as defined by its backbone (phi, psi) angles. A recursion formula then is used to find the probability that the backbone amide proton of each residue is hydrogen bonded. The peptide helix can be treated as a homopolymer, and direct exchange from the helix can be neglected. The expression for the exchange kinetics contains only three unknown parameters: the rate constant for exchange of a non-hydrogen-bonded (random coil) backbone amide proton and the nucleation (v2) and propagation (w) parameters of the Lifson-Roig theory. The fit of the exchange curves to these three parameters is very good, and the values for v2 and w agree with those derived from circular dichroism studies of the thermally-induced unfolding of related peptides [Scholtz, J.M., Qian, H., York, E.J., Stewart, J.M., & Baldwin, R.L. (1991) Biopolymers (in press]).