Examination of Genetic Relatedness of Marine Synechococcus spp. by Using Restriction Fragment Length Polymorphisms

The relatedness of several marine Synechococcus spp. was estimated by DNA hybridization. Strains isolated from various geographical locations and representing a diversity of DNA base compositions and phycobiliprotein profiles were compared by restriction fragment length polymorphisms for a number of genes. DNAs from two marine red algae and a cryptomonad alga (which exhibit a phycobiliprotein composition similar to that of the marine Synechococcus spp.) and Synechococcus strain PCC6301 (Anacystis nidulans) were also included in the comparison. Strains WH8008, WH8018, and WH7805 were shown to be very similar to one another, as were strains WH7802 and WH7803. Strains WH8110 and WH5701 were clearly unrelated to any of the other strains, and no marine Synechococcus isolate showed any similarity to the freshwater Synechococcus strain PCC6301 or the eucaryotic algae. The method is relatively straightforward and sensitive and uses a variety of basic molecular biology techniques. Its utility in ascertaining the genetic relatedness and diversity of marine Synechococcus spp. and possible extension to field studies are discussed.     

Rhizobium trifolii 0403 Is Capable of Growth in the Absence of Combined Nitrogen

Rhizobium trifolii 0403 was treated with 16.6 mM succinate and other nutrients and thereby induced to grow in nitrogen-free medium. The organism grew microaerophilically on either semisolid or liquid medium, fixing atmospheric nitrogen to meet metabolic needs. Nitrogen fixation was measured via ¹⁵N incorporation (18% ¹⁵N enrichment in 1.5 doublings) and acetylene reduction. Nitrogen-fixing cells had a K_m for acetylene of 0.07 atm (ca. 7.09 kPa), required about 3% oxygen for optimum growth in liquid medium, and showed a maximal specific activity of 5 nmol of acetylene reduced per min per mg of protein at 0.04 atm (ca. 4.05 kPa) of acetylene. The doubling time on N-free liquid medium ranged from 1 to 5 days, depending on oxygen tension, with an optimum temperature for growth of about 30°C. Nodulation of white clover by the cultures showing in vitro nitrogenase activity indicates that at least part of the population maintained identity with wild-type strain 0403.     

Effects of plant spinescence on large mammalian herbivores

Summary Plant thorns and spines had these effects on the feeding behaviour of the three species of browsing ungulate that we studied, kudu, impala and domestic goats: (i) bite sizes were restricted, in most cases to single leaves or leaf clusters; (ii) hooked thorns retarded biting rates; (iii) the acceptability of those plant species offering small leaf size in conjunction with prickles was lower, at least for the kudus, than those of other palatable plant species; (iv) the inhibitory effect of prickles on feeding was much less for the smaller impalas and goats than for the larger kudus; (v) from certain hook-thorned species the kudus bit off shoot ends despite their prickles; (vi) for certain straight-thorned species the kudus compensated partially for the slow eating rates obtained by extending their feeding durations per encounter. Most spinescent species were similar in their acceptability to the ungulates to unarmed palatable species, despite higher crude protein contents in their foliage than the latter. Such structural features furthermore reduce the tissue losses incurred by plants per encounter by a large ungulate herbivore, by restricting the eating rates that the animals obtain. In this way prickles function to restrict foliage losses to large herbivores below the levels that might otherwise occur.     

Spontaneous cell shedding by tumor cells in monolayer culture

Summary Sarcoma 180 monolayers spontaneously shed single cells and small multicellular aggregates into the surrounding medium to produce a dual population of floating and substratum-attached cells. Shedding was a motility-associated event that occurred when cells attempted to migrate over one another. It resulted from a combination of cell shape change and active motility, which increased sensitivity to fluid shear dislodgement by reducing a cell's surface area of adhesive contact and increasing strain tension at its adhesive contact points. Shedding occurred at all phases of the cell cycle. Extracellular matrix but not conditioned medium enhanced the floating subpopulation by slowing the kinetics of rattachment to plastic and cellular substrata. Although sarcoma 180 cells are anchorage independent in the sense that they grow readily in single cell suspension, they nevertheless exhibited anchorage modulation of their cell cycle. Short periods in suspension produced a mild G₁ accumulation, whereas longer periods of anchorage deprivation led to a mild G₂ accumulation which appeared to result from an interference with cytokinesis. This work was supported by grants from the Medical Research Council of Canada, The National Cancer Institute of Canada, the Alberta Heritage Savings and Trust Fund for Applied Cancer Research, and the Alberta Heritage Fund for Medical Research.     

Effect of Metal-Rich Sewage Sludge Application on the Bacterial Communities of Grasslands

The effect of long-term application of heavy metal-laden sewage sludge on the total heterotrophic aerobic and the cadmium-resistant soil bacterial communities was studied. Gram-positive bacteria were completely absent from resistant communities. These findings suggest that this group is highly susceptible to Cd. Shannon's diversity indices estimated for total communities did not reveal negative effects on the communities that developed in the presence of sludge. However, Cd-resistant communities isolated from long-term sludge-amended soils were more diverse than the resistant communities from a control sample, suggesting that adaptation to Cd as a stressor had occurred in the presence of sludge constituents. This higher diversity was attributed to Cd resistance in pseudomonads and gram-negative fermenters. Resistance did not develop by dissemination of Cd resistance plasmids, because these were rarely detected in the genomes of resistant strains.     

Phylogenetic Survey of Proteins Related to Synapsin I and Biochemical Analysis of Four Such Proteins from Fish Brain

A phylogenetic survey of proteins immunologically related to Synapsin I, a major synaptic vesicle-associated phosphoprotein in mammals was carried out. Proteins antigenically related to Synapsin I were found by use of radioimmunoassay and other radioimmunochemical techniques in the nervous systems of several vertebrate and invertebrate species, which included birds, reptiles, amphibians, fish, echinoderms, arthropods, and mollusks. Four proteins present in fish brain, antigenically related to Synapsin I, were further studied and found to resemble mammalian Synapsin I in several respects. Like Synapsin I, the fish proteins were present in high amounts in nervous tissue, were enriched in synaptosomal fractions of brain where they were substrates for endogenous protein kinases, were acid extractable, and were sensitive to digestion by collagenase. In addition, two-dimensional peptide-mapping analysis revealed some homology between major phosphopeptide fragments of Synapsin I and the fish proteins. The results indicate that proteins related to Synapsin I are wide-spread in the animal kingdom.     

Thyroidectomy results in termination of photorefractoriness in starlings (Sturnus vulgaris) kept in long daylengths

Four groups of 10 male starlings were transferred from short daylengths (8 h light/day) to long daylengths (18 h light/day), which caused the tests to develop rapidly to maximum size and then to decrease to minimal size as birds became photorefractory. Birds were surgically thyroidectomized at 8, 16 or 28 weeks. A fourth group was left intact. Testicular volume and plasma FSH and prolactin concentrations were measured. After 42 weeks all birds were castrated and plasma FSH was measured during the next 6 weeks. Testicular growth began in all thyroidectomized birds between 4 and 8 weeks after thyroidectomy. By 42 weeks, the testes of all thyroidectomized birds were large, whereas those of intact birds were still of minimal size. Plasma FSH concentrations remained low in all birds and plasma prolactin values, originally elevated by long daylengths, decreased at a similar rate in thyroidectomized and intact birds. After castration at 42 weeks, plasma FSH values increased rapidly in all thyroidectomized birds but remained low in non-thyroidectomized birds. The results demonstrate that thyroidectomy of photorefractory starlings does not induce immediate testicular growth but may initiate a process which eventually terminates photorefractoriness in a way similar to that caused by return to short daylengths.     

The structure of the cytochrome a3-CuB site of mammalian cytochrome c oxidase as probed by MCD and EPR spectroscopy

The nature of the complexes formed between cytochrome c oxidase and the three inhibitory ligands N3-, CN-, and S2- have been investigated by a combination of MCD and EPR spectroscopy. CN- forms a linear bridge between the Fe III a3 and CuB II, suggesting that the distance between these centers in the oxidized enzyme is between 5 and 5.25 A. This distance is too short to permit N3- to form a linear bridge and the evidence suggests this to be bent. In contrast S2- or SH- is unable to form any bridge and it seems likely that two SH- ions are bound by the bimetallic site, one to Fe III a3 and the other to CuB I. The significance of the a3-CuB distance in terms of oxygen binding and reduction is discussed.     

Class I and class II restriction pattern polymorphisms associated with independently derived RT1 haplotypes in inbred rats

This communication reports the DNA level identification of class I and class II sequences associated with 20 RT1 haplotypes which have been assigned previously to eight RT1 groups. Sixteen to 22 bands in genomic blots hybridized with the mouse pH-2III class I cDNA probe. Only the three RT1 ^khaplotypes associated with identical class I restriction fragment patterns. Differences in restriction bands between putatively identical RT1 haplotypes were either less than or equal to 6%, or greater than 50%, suggesting a relatively high level of recombination between serologically identified RT1.A genes and the majority of class I sequences. Restriction fragment patterns associated with three RT1 ^uhaplotypes differed by less than 6%. However, intra-RT1 ^a,intra-RT1 ^b,and intra-RT1 ^lrestriction fragment differences were between 50 and 64%. In specific cases, different RT1 haplotypes associated with identical class I restriction patterns, e.g., RT1 ^m(MNR) and RT1 ^d(MR); higher resolution confirmed the difference (two bands) between RT1 ^mand RT1 ^d.Results of hybridization with the human DC₁ probe confirmed that the AVN RT1 ^aand NSD RT1 ^bhaplotypes were generated by recombinations within the vicinity of the RT1.B : RT1.D regions. These results demonstrate that a previous classification of RT1 haplotypes was incomplete and did not include the majority of class I and class II sequences which distinguish RT1 haplotypes.