POTENTIAL RAPID BIOASSAY FOR ALIMET® USING A METHIONINE ESCHERICHIA COLI AUXOTROPH

A potential rapid bioassay for methionine hydroxy analog (MHA) feed additive (ALIMET®) was examined using a methionine auxotroph E. coli strain. Bacterial cells were grown in minimal media containing a concentration range of 0 to 26.8 μM of either L-methionine or MHA as ALIMET®. Increasing either methionine or MHA concentration increased the growth rate of the methionine auxotroph. The estimated substrate affinities for methionine compared to MHA were not significantly different (P > 0.13) and the maximum growth rate estimates were also similar (P > 0.34). Methionine and MHA standard curves yielded linear responses (R²= 0.96) to increasing concentrations of the respective substrate. Based on these results it appears that the E. coli methionine auxotroph would have potential utility for further development of a rapid bioassay of ALIMET®.     

A karyological study of Asphodelus L. (Asphodelaceae) from the Western Mediterranean

The following aspects of Asphodelus karyology are analysed: base number, polyploidy, chromosome size, chromosome morphology, satellited chromosomes, structural heteromorphism, karyotype asymmetry and karyotype evolution. The base number 0 ×= 14 is common to all species except for A. refractus , which has the derived ×= 13. Three ploidy levels occur, often in the same species; diploid, tetraploid and hexaploid, with 2n = 28, 56 and 84. Chromosomes are generally small to medium-small, with the occasional presence of medium-large chromosomes. The most frequent chromosome types are metacentric of type m and submetacentric. Metacentric chromosomes of type M occur only in sections. Verineopsis, Verinea and Plagiasphodelus ; subtelocentric chromosomes occur only in sections Asphodelus and Plagiasphodelus. There is a wide variability in relation to the number of satellited chromosomes, relative to ploidy level. There are usually two to four in diploids, four to eight in tetraploids and usually six, exceptionally up to 12, in the hexaploid. Satellites are present on the shortest arm, exceptionally on the longest arm. There is a high degree of structural heteromorphism in practically all the species which affects satellited and non satellited chromosomes. Karyotype asymmetry is generally of type 2B. Inter-and intra-chromosomal differences are estimated by the A1 and A2 indexes. Both indices vary in the karyotype evolution of the genus, with a decrease of A1 and an increase of A2. The role of polyploidy, hybridization, asymmetry and decrease of chromosome size in the evolution of Asphodelus is discussed.     

Food resource matching by foraging tits Parus spp. during spring-summer in a Mediterranean mixed forest; evidence for an ideal free distribution

We analysed whether patterns of microhabitat use by Blue Tits Parus caeruleus , Great Tits Parus major and Crested Tits Parus cristatus inhabiting a mixed forest consistently matched the patterns of food availability experienced by foraging birds during spring-summer. The use of five microhabitats by each bird species (the foliage of three tree species, shrubs and ground) and the availability of food in trees during the prebreeding, breeding and post-breeding periods of the birds' annual cycle were measured. All three tit species foraged mainly in the outer part of tree canopies (small branches and leaves or needles). Tit distributions between tree species matched food resource distributions irrespective of overall food resource levels, which varied four-fold between the study periods, and tit species. Tits also exploited secondary microhabitats (shrubs and ground) in periods of low food availability; Blue Tits tended to use shrubs, whereas Great and Crested Tits foraged on the ground. Between-trees distributions fitted that expected from an ideal free distribution, suggesting that food availability and intraspecific exploitative competition were the main factors governing tree use by tits. In contrast, patterns of use of secondary microhabitats (shrubs and ground) seemed to indicate a role for the species-specific morphological configurations of each tit species since Blue Tits are better adapted to hang and tended to forage in shubs, whereas Great and Crested Tits are better adapted to feed on horizontal surfaces and tended to forage on the ground. No evidence of interspecific interactions was observed. Overall, the results pointed to an independent exploitation of Mediterranean mixed forest by each bird species, food availability and food accessibility being the main factors affecting microhabitat use by foraging tits.     

Factors Controlling the Abundance and Size Distribution of the Phototrophic Ciliate Myrionecta rubra in Open Waters of the North Atlantic

ABSTRACT. Myrionecta rubra, a ubiquitous planktonic ciliate, has received much attention due to its wide distribution, occurrence as a red tide organism, and unusual cryptophyte endosymbiont. Although well studied in coastal waters, M. rubra is poorly examined in the open ocean. In the Irminger Basin, North Atlantic, the abundance of M. rubra was 0–5 cells/ml, which is low compared with that found in coastal areas. Distinct patchiness (100 km) was revealed by geostatistical analysis. Multiple regression indicated there was little relationship between M. rubra abundance and a number of environmental factors, with the exception of temperature and phytoplankton biomass, which influenced abundance in the spring. We also improve on studies that indicate distinct size classes of M. rubra; we statistically recognise four significantly distinct width classes (5–16, 12–23, 18–27, 21–33 μm), which decrease in abundance with increasing size. A multinomial logistic regression revealed the main variable correlated with this size distribution was ambient nitrate concentration. Finally, we propose a hypothesis for the distribution of sizes, involving nutrients, feeding, and dividing of the endosymbiont.