Seasonal succession of a microphagotroph community in a small pond during litter decomposition

Temporal dynamics of a lentic microphagotroph community were studied during leaf litter decomposition from December to May. Small plastic vessels containing leaf litter were placed on a pond bottom. They were sampled periodically to collect microphagotrophs. Three abiotic factors and abundance of two food items were also measured to analyze the autogenic and allogenic phenomena during a microphagotroph succession. Three behavior types were recognized in dominant taxa: a free-swimming type, a vagile (creeps on substratum, sometimes swims) type, and a voluntarily fixed type. Dominant taxa changed from the free-swimming to the vagile type up to mid-March, and the reverse change occurred from mid-April. Principal component analysis (PCA) indicated four factors affecting the dynamics of the community: water temperature as a seasonal factor, detritus volume on the litter surface as a habitat factor, and densities of bacteria and small flagellates as food factors. Taxa replacement appeared to occur through two mechanisms. (1) Dominance of small holotrichs, a free-swimming type, was brought about by a high bacterial density caused by seasonal events, i.e., leaf fall in December and detritus formation by litter feeders in mid-April. This is an allogenic aspect of community dynamics. (2) The free-swimming type was replaced by the vagile one during the period with high taxa diversity. This replacement occurred through intertaxa competition for scarce food and/or selective predation by larger microphagotrophs. It is an autogenic process within the community.     

Biology of mammary fat pad in fetal mouse: capacity to support development of various fetal epithelia in vivo

Epithelia from the lobular part of submandibular salivary gland, glandular stomach, intestine and colon of 14-day C3H/HeN fetuses, and from pituitary gland and pancreas of 12-day fetuses were recombined with 14-day mammary fat pad precursor tissue and syngrafted under the kidney capsule. The normal organogenetic development typical of the epithelium occurred. The same epithelia taken from earlier stage fetuses did not develop normally. Thus, 14-day fetal mouse mammary fat pad precursor tissue has the capacity to support normal organogenesis of various fetal epithelia of developmentally advanced stages. This supportive capacity is decreased in the fat pad precursor tissue of 17- to 18-day fetal mice and is entirely lost postnatally.     

Cloning and expression of a novel rat GABAA receptor

Two full-length cDNA clones encoding alpha- and beta-subunits of a GABAA receptor have been isolated from a rat cerebral cortex cDNA library. The mature alpha-subunit protein consists of 428 amino acids with a calculated Mr of 48,680. This protein is highly homologous (approximately 99% amino acid identity) with the bovine brain alpha 1-subunit receptor [(1988) Nature 335, 76-79]. The mature rat beta-subunit receptor is a 448 amino acid polypeptide and shares approximately 80% amino acid identity with the previously characterized bovine GABAA receptor beta-subunit [(1987) Nature 328, 221-227]. Co-expression of the cloned DNA in Xenopus oocytes produces a functional receptor and ion channel with pharmacological characteristics of a GABAA receptor. GABAA alpha- and beta-subunit mRNA is detectable in the cortex, cerebellum and hippocampus.     

Structural and functional analysis of a polyoma-related mammalian plasmid (L factor): the enhancer activity and plasmid establishment.

L factor is a unique plasmid DNA which was originally discovered in a subclone (B822) of mouse L cells at a high copy number (more than 5,000 copies/cell). The presence of L factor caused no detectable abnormalities to the plasmid-bearing cells. We determined the total DNA sequence of the L factor I (and a part of L factor II) and compared it with that of polyoma DNA. Both DNA are common to the general construction of DNA frames such as early, late and noncoding regions, suggesting the two to be closely related. On the other hand, the L factor DNA sequences differ substantially from that of polyoma in the DNA sequences corresponding to the polyoma large T antigen, capsid proteins and a portion of the enhancer region. In order to investigate the mechanism of plasmid establishment of L factor, we compared the enhancer activity, capacity of DNA replication and efficiency of plasmid establishment of L factor with those of polyoma. The results indicate that L factor enhancer activity and DNA replication capacity were considerably lower than those of polyoma, suggesting that these altered (lowered) activities associated with L factor contribute to the plasmidal establishment and stable maintenance of L factor.     

Molecular cloning and expression ofThiobacillus ferrooxidans chromosomal ribulose bisphosphate carboxylase genes inEscherichia coli

The genes coding ford-ribulose-1,5-bisphosphate carboxylase (RuBPCase) from an iron-oxidizing bacterium,Thiobacillus ferrooxidans, were cloned into anEscherichia coli plasmid, pUC18. The recombinant plasmid, termed pTR11, contained a 4.0-kb PstI fragment including the entire coding regions for both large and small subunits of RuBPCase.Escherichia coli carrying pTR11 did not show any CO₂-fixing activity. However, a derivative plasmid with an appropriate deletion, which was placed under the control of atac promoter, conferred ribulose bisphosphate-dependent CO₂-fixing activity on the host cell. Analysis of gel-filtration chromatography of the RuBPCase synthesized inE. coli revealed that it had a hexadecameric form like the native enzyme ofT. ferrooxidans.     

Correlation of Transmitter Release with Membrane Properties of the Presynaptic Fiber of the Squid Giant Synapse

Depolarization of the presynaptic terminal by current produced a postsynaptic potential (PSP) which increased with increasing presynaptic polarization and then reached a plateau. Iontophoretic injection of tetraethylammonium ions (TEA) into the presynaptic axon near the terminal produced a prolonged presynaptic spike. The resulting PSP is increased in size and its time course closely followed that of the presynaptic spike. The presynaptic fiber no longer exhibited rectification and strong depolarizations revealed that the PSP reached a maximum with about 110 mv depolarization. Further depolarization produced a decrease in PSP amplitude and finally transmission was blocked. However, a PSP then always appeared on withdrawal of the depolarizing current. Under the conditions of these experiments, the PSP could be considered a direct measure of transmitter release. Bathing the TEA-injected synapse with concentrations of tetrodotoxin (TTX) sufficient to block spike activity in both pre- and postsynaptic axons did not greatly modify postsynaptic electrogenesis. However, doubling TTX concentration reversibly blocked PSP. Thus the permeability changes to Na and K accompanying the spike do not appear necessary for transmitter release. Some other processes related to the level of presynaptic polarization must be involved to explain the data. The inhibition of transmitter release by strong depolarizations appears to be related to Ca action. A membrane Ca current may also be necessary for normal transmitter release.     

Comparison of axonemal proteins from two kinds of Tetrahymena. I. Different characteristics of dyneins in heat stability

Tetrahymena thermophila could still swim after incubation of the cell body at 40°C for 30 min, whereas Tetrahymena pyriformis did not show any motility after the treatment. Turbidity measurements revealed that axonemes of T. pyriformis lost ATP-dependent sliding activity by the heat treatment, whereas those of T. thermophilia still had the activity under the same conditions. In connection with this difference in susceptibility to high temperature, the biochemical characteristics of dyneins were compared between the two species of Tetrahymena. Axonemal dyneins from the two species had significant vanadate-sensitive ATPase activity even after the heat treatment. Native gel electrophoresis and the following two-dimensional electrophoresis showed that the outer arm dynein of T. thermophilia is more stable in maintaining native configuration than that of T. pyriformis against the heat treatment, although both treated dyneins keep three (α, β and γ) subunits. Analysis by peptide mapping demonstrated that β- and γ-subunits of the outer arm dynein are considerably different in amino acid sequences between the two species. These results imply that dynein of T. thermophilia changed their amino acid sequences and biochemical characteristics to adapt to high temperature.     

Molecular genetics of Thiobacillus ferrooxidans.

Thiobacillus ferrooxidans is a gram-negative, highly acidophilic (pH 1.5 to 2.0), autotrophic bacterium that obtains its energy through the oxidation of ferrous iron or reduced inorganic sulfur compounds. It is usually dominant in the mixed bacterial populations that are used industrially for the extraction of metals such as copper and uranium from their ores. More recently, these bacterial consortia have been used for the biooxidation of refractory gold-bearing arsenopyrite ores prior to the recovery of gold by cyanidation. The commercial use of T. ferrooxidans has led to an increasing interest in the genetics and molecular biology of the bacterium. Initial investigations were aimed at determining whether the unique physiology and specialized habitat of T. ferrooxidans had been accompanied by a high degree of genetic drift from other gram-negative bacteria. Early genetic studies were comparative in nature and concerned the isolation of genes such as nifHDK, glnA, and recA, which are widespread among bacteria. From a molecular biology viewpoint, T. ferrooxidans appears to be a typical member of the proteobacteria. In most instances, cloned gene promoters and protein products have been functional in Escherichia coli. Although T. ferrooxidans has proved difficult to transform with DNA, research on indigenous plasmids and the isolation of the T. ferrooxidans merA gene have resulted in the development of a low-efficiency electroporation system for one strain of T. ferrooxidans. The most recent studies have focused on the molecular genetics of the pathways associated with nitrogen metabolism, carbon dioxide fixation, and components of the energy-producing mechanisms.