Chloramphenicol inhibition of Pythium ultimum and Rhodotorula glutinis

Summary The growth of Rhodotorula glutinis is inhibited by both D-threo chloramphenicol and an L-threo isomer of chloramphenicol (lacking the dichloroacetyl group), causing an increase in the mean generation time, in a variety of media, approximately proportional to the concentration of antibiotic. The antibiotic is not removed from the growth medium in any quantity during this inhibition of growth. The oxygen uptakes of normal and chloramphenicol-grown cells of R. glutinis are similar when expressed on a dry weight basis. The oxygen uptake of normal and L-threo isomer-grown cells is strongly inhibited by antimycin A, whereas D-threo chloramphenicol-grown cells are unaffected. There was no evidence to suggest that any uncoupling of phosphorylation occurred with either isomer. Pythium ultimum mycelium also showed similar oxygen uptakes per unit dry weight whether grown in the presence or absence of D-threo chloramphenicol. The D-threo chloramphenicol-grown mycelium was also insensitive to antimycin A in contrast to the normal mycelium which was strongly inhibited. P. ultimum grows slowly in the presence of 100 g/ml D-threo chloramphenicol in a glucose salts medium, but is completely inhibited by a similar concentration in a glycerol salts medium. The L-threo isomer does not inhibit the growth of P. ultimum.The mitochondria of Rhodotorula glutinis show a progressive disorganization when grown in the presence of increasing concentrations of D-threo chloramphenicol up to 1000 g/ml. There is an associated over synthesis of cell wall material in the higher concentrations of the antibiotic. The L-threo isomer produces no obvious fine structural abnormalities even at concentrations of 1000 g/ml.     

MITOSIS,CYTOKINESIS, AND COLONY FORMATION IN THE GREEN ALGA SORASTRUM1

Synchronous mitotic divisions produce multi-nucleate cells of Sorastrum. Perinuclear envelopes of endoplasmic reticulum and a virtually intact nuclear envelope enclose mitotic nuclei. Cytoplasmic cleavage, which shirts before the last round of Synchronous mitoses, gives rise to uninucleate fragments which differentiate to form zoospores. These zoospores are released into a spherical vesicle, presumably derived from the inner layer of the parental cell wall, in which they swarm actively before aggregating as a spherical colony. The roughly conical shaped zoospores apparently adhere laterally before withdrawing their flagella and extending horns and a stipe, which, following wall deposition, interconnects the cells at the center of the colony. The probable role of the microtubules, which underlie the plasmalemma of aggregating cells, in determining the shape of both the cells and the colony itself is discussed.     

Lomasomes and plasmalemmasomes in fungi

Summary Electron microscope observations of fungal hyphae and yeast-like cells, using conventional fixation methods and freeze-etching, demonstrate that plasmalemmasomes are not fixation artifacts. The small invaginations of the plasmalemma observed in aldehyde-fixed preparations are also present in frozen-etched samples. The morphology of plasmalemmasomes in the species examined is variable and ranges from vesicles or tubules within the plasmalemma invagination to parallel arrays of membrane lamellae. Plasmalemmasomes thus appear to be primarily excess plasma membrane that has accumulated, perforce, endocellularly. Lomasomes, in contrast, appear to be accumulations of ejected material between the plasmalemma and cell wall that have become sequestered by the deposition of wall material.     

Classification of macroinvertebrate communities across drainage basins in Victoria, Australia: consequences of sampling on a broad spatial scale for predictive modelling

1. Spatial scale may influence the interpretation of environmental gradients that underlie classification and ordination analyses of lotic macroinvertebrate communities. This could have important consequences for the spatial scale over which predictive models derived from these multivariate analyses can be applied. 2. Macroinvertebrate community data (identified to genus or species) from edge and main-channel habitats were obtained for sites on rivers from 25 of the 29 drainage basins in Victoria. Trends in community similarity were analysed by carrying out separate multivariate analyses on data from the edge habitats (199 sites) and the main-channel habitats (163 sites). 3. Hierarchical classification (UPGMA) showed that the edge data could be placed into 11 site groups and the main-channel data into 12 site groups. 4. Ordination analysis (hybrid multidimensional scaling) showed no sharp disjunctions between site groups in either habitat; overlap was frequent. Correlation of the ordination patterns with environmental variables showed that edge communities varied longitudinally within a drainage basin and from the east to the west of Victoria. These two trends were superimposed on one another to form a single gradient on the ordination. The taxon richness of edge communities was also related to the species richness of macrophytes at a site. Main-channel communities also displayed a longitudinal and a geographic gradient, but these two gradients were uncorrelated on the ordination. 5. Community similarity only weakly reflected geographic proximity in either habitat. A preliminary subdivision of Victoria into a series of biogeographic regions did not match the pattern of distribution of site groups for the edge habitat, illustrating the difficulties of applying to lotic communities a priori regionalizations based on terrestrial features of the landscape. 6. The longitudinal gradients in the two data sets were commonly observed in data gathered at smaller spatial scales in Victoria. The other gradients (geographic, macrophyte), however, were either not consistently repeated or not evident at smaller spatial scales. At small spatial scales (i.e. within a single drainage basin) gradients were related to variables that varied over restricted ranges, e.g. mean particle size of the substratum. 7. Species richness was very variable when plotted against river slope or distance of site from source; both of these are measures of position on the longitudinal gradients. In contrast to suggestions in the literature, species richness did not show a unimodal trend on these gradients, or any other trend. 8. Environmental gradients (apart from longitudinal gradients) that underlie predictive models of macroinvertebrate distribution are reflections of the spatial scale on which the model has been constructed and cannot be extrapolated to different scales. Models must be suited to the spatial scale over which predictions are required.     

Complete primary structure of the chicken alpha1(V) collagen chain.

Chicken alpha1(V) collagen cDNAs have been cloned by a variety of methods and positively identified. We present here the entire translated sequence of the chick polypeptide and compare selected regions to other collagen chains in the type V/XI family.     

Microbial rhamnolipid production: a critical re-evaluation of published data and suggested future publication criteria

High production cost and potential pathogenicity of Pseudomonas aeruginosa, commonly used for rhamnolipid synthesis, have led to extensive research for safer producing strains and cost-effective production methods. This has resulted in numerous research publications claiming new non-pathogenic producing strains and novel production techniques many of which are unfortunately without proper characterisation of product and/or producing strain/s. Genes responsible for rhamnolipid production have only been confirmed in P. aeruginosa, Burkholderia thailandensis and Burkholderia pseudomallei. Comparing yields in different publications is also generally unreliable especially when different methodologies were used for rhamnolipid quantification. After reviewing the literature in this area, we strongly feel that numerous research outputs have insufficient evidence to support claims of rhamnolipid-producing strains and/or yields. We therefore recommend that standards should be set for reporting new rhamnolipid-producing strains and production yields. These should include (1) molecular and bioinformatic tools to fully characterise new microbial isolates and confirm the presence of the rhamnolipid rhl genes for all bacterial strains, (2) using gravimetric methods to quantify crude yields and (3) use of a calibrated method (high-performance liquid chromatography or ultra-performance liquid chromatography) for absolute quantitative yield determination.     

Birds in the matrix: the role of agriculture in avian conservation in the Taita Hills,Kenya

Agricultural conversion of tropical forests is a major driver of biodiversity loss. Slowing rates of deforestation is a conservation priority, but it is also useful to consider how species diversity is retained across the agricultural matrix. Here, we assess how bird diversity varies in relation to land use in the Taita Hills, Kenya. We used point counts to survey birds along a land‐use gradient that included primary forest, secondary vegetation, agroforest, timber plantation and cropland. We found that the agricultural matrix supports an abundant and diverse bird community with high levels of species turnover, but that forest specialists are confined predominantly to primary forest, with the matrix dominated by forest visitors. Ordination analyses showed that representation of forest specialists decreases with distance from primary forest. With the exception of forest generalists, bird abundance and diversity are lowest in timber plantations. Contrary to expectation, we found feeding guilds at similar abundances in all land‐use types. We conclude that whilst the agricultural matrix, and agroforest in particular, makes a strong contribution to observed bird diversity at the landscape scale, intact primary forest is essential for maintaining this diversity, especially amongst species of conservation concern.