Identification of the Meiotic Division of Malarial Parasites

Zygotes of Plasmodium berghei were cultured 15–25 h in vitro to yield mature infective ookinetes. Samples taken in the first 5 h of culture were examined by electron microscopy. Meiotic figures were detected in the nuclei of the zygotes. Threadlike leptotene chromatids (chromosomes) condensed from attachment plaques on the nuclear envelope; chromatid pairing followed (zygotene), with synaptonemal complexes subsequently appearing (pachytene). These complexes persisted into metaphase but dissociated when the chromatids rapidly decondensed during anaphase. At telophase of the first meiotic division the kinetochores were retracted toward two small spindle complexes, which were found at widely separated poles in the nuclear envelope. The observations are consistent with a haploid genome of 8–10 chromosomes.     

CONFERENCE REPORT

ABSTRACT

Sperm whale Physeter macrocephalus L. clicks have been studied for nearly fifty years, during which time great efforts have been made to understand the functions and production mechanisms of this sound. Other than clicks, sperm whales may also produce low intensity sounds arranged in short sequences, named trumpets, which have been recorded occasionally in the past by few groups of researchers. Sperm whale recordings collected in the Mediterranean Sea with a towed array and digital tags were used to describe the temporal and spectral characteristics of trumpets. This sound is made of a series of repeated units, around 0.2 s long, arranged in short sequences lasting between 0.6 s to 3.5 s. Each of these units comprises an amplitude modulated tonal waveform with a complex harmonic structure, and a spectrum composed of a low frequency component at 500 Hz and a mid-frequency component at 3 kHz. The apparent source level could be estimated for one of the trumpets and was estimated to be 172 dB_pp re: 1μPa at lm with energy flux density of 147 dB re: 1μ Pa²s.     

Overview of microbial biofilms

As the success of this two-issue special section of the Journal of Industrial Microbiology attests, the study of microbial biofilms is truly burgeoning as the uniqueness and the importance of this mode of growth is increasingly recognized. Because of its universality the biofilm concept impacts virtually all of the subdivisions of Microbiology (including Medical, Dental, Agricultural, Industrial and Environmental) and these two issues incorporate contributions from authors in all of these disciplines. Some time ago we reasoned that bacteria cannot possibly be aware (sic) of their precise location, in terms of this spectrum of anthrocentric subspecialties, and that their behavior must be dictated by a standard set of phenotypic responses to environmental conditions in what must seem to them (sic) to be a continuum of very similar aquatic ecosystems. In this overview I will, therefore, stress the common features of microbial biofilms that we should bear in mind as we use this simple universal concept to seek to understand bacterial behavior in literally hundreds of aquatic ecosystems traditionally studied by dozens of subspecies of microbiologists reared in sharply different scientific and academic conventions.     

Genome-wide identification of specific oligonucleotides using artificial neural network and computational genomic analysis

Background  

Genome-wide identification of specific oligonucleotides (oligos) is a computationally-intensive task and is a requirement for designing microarray probes, primers, and siRNAs. An artificial neural network (ANN) is a machine learning technique that can effectively process complex and high noise data. Here, ANNs are applied to process the unique subsequence distribution for prediction of specific oligos.     

Acoustic behaviour and phonotaxis in the duetting ephippigerines,Steropleurus nobrei* and Steropleurus stali (Tettigoniidae)

Both sexes of the ephippigerines Steropleurus stall and S. nobrei can stridulate and produce multisyllabic calls which are described. Female stridulation is in response to the conspecific male call. In both species cither sex can perform phonotaxis on the call of the conspecific member of the opposite sex, but ignore the calls of other species. The parameters of the calls are examined with the conclusion that the only reliably distinctive feature is the modal or carrier frequency generated during stridulation. There are frequency differences between male and female calls in both species. Males only perform phonotaxis on female replies generated in response to their own call, implying that there is also some time window involved. Male phonotaxis was faster and more accurate than that of the female. Acoustic rivalry and aggression were also noted, particularly in females.     

Basolateral K channels in an insect epithelium. Channel density, conductance, and block by barium

K channels in the basolateral membrane of insect hindgut were studied using current fluctuation analysis and microelectrodes. Locust recta were mounted in Ussing-type chambers containing Cl-free saline and cyclic AMP (cAMP). A transepithelial K current was induced by raising serosal [K] under short-circuit conditions. Adding Ba to the mucosal (luminal) side under these conditions had no effect; however, serosal Ba reversibly inhibited the short-circuit current (Isc), increased transepithelial resistance (Rt), and added a Lorentzian component to power density spectra of the Isc. A nonlinear relationship between corner frequency and serosal [Ba] was observed, which suggests that the rate constant for Ba association with basolateral channels increased as [Ba] was elevated. Microelectrode experiments revealed that the basolateral membrane hyperpolarized when Ba was added: this change in membrane potential could explain the nonlinearity of the 2 pi fc vs. [Ba] relationship if external Ba sensed about three-quarters of the basolateral membrane field. Conventional microelectrodes were used to determine the correspondence between transepithelially measured current noise and basolateral membrane conductance fluctuations, and ion-sensitive microelectrodes were used to measure intracellular K activity (acK). From the relationship between the net electrochemical potential for K across the basolateral membrane and the single channel current calculated from noise analysis, we estimate that the conductance of basolateral K channels is approximately 60 pS, and that there are approximately 180 million channels per square centimeter of tissue area.