Biodiversity amongst microorganisms and its relevance

Concluding remarks from the joint IUBS/IUMS workshop on Biodiversity amongst microorganisms and its relevance held in Amsterdam on 7–8 September 1991. An international microbial ecology programme can be justified in its own right now that appropriate investigative tools have been developed. Microorganisms influence global change, and indicate global health and environmental quality. At the same time, an inventory of the world's microbial species and their properties is required, together with associated culture collections and genomes. Sampling methods need to be standardized, both for species and functions. Extreme environments are a particularly rich source of microbial genomes, and endangered habitats should be sampled as a matter of priority. Cataloguing and conserving the world's microbial biodiversity is justifiable and scientifically important.     

NEW MURID RODENTS FROM THE LATE CENOZOIC OF YUSHE BASIN, SHANXI

<正> As scientific collaborators of the Chinese-American joint project "Neogene Rocks and Faunas, Yushe Basin, Shanxi, PRC", the present authors, with William R. Downs, Northern Arizona University, sampled the Yushe microfauna in the fall of 1987 and 1988. The fossil temains were retrieved by surface collection and by wet-sieving bulk quantities of sediment.     

A potent and specific immunotoxin for tumor cells expressing disialoganglioside GD2

Summary Monoclonal antibody 14G2a (anti-GD₂) reacts with cell lines and tumor tissues of neuroectodermal origin that express disialoganglioside GD₂. mAb 14G2a was coupled to the ribosome-inactivating plant toxin gelonin with the heterobifunctional cross-linking reagentN-succinimidyl-3(2-pyridyldithio)propionate. The activity of the immunotoxin was assessed by a cell-free translation assay that confirmed the presence of active gelonin coupled to 14G2a. Data from an enzyme-linked immunosorbent assay demonstrated the specificity and immunoreactivity of the 14G2a-gelonin immunotoxin, which was identical to that of native 14G2a. Assays for complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) revealed that these functional properties of the native 14G2a antibody were also preserved in the 14G2a-gelonin immunotoxin. The gelonin-14G2a immunotoxin was directly cytotoxic to human melanoma (A375-M and AAB-527) cells and was 1000-fold more active than native gelonin in inhibiting the growth of human melanoma cells in vitro. The augmentation of tumor cell killing of 14G2a-gelonin immunotoxin was examined with several lysosomotropic compounds. Chloroquine and monensin, when combined with 14G2a-gelonin immunotoxin, augmented its cytotoxicity more than 10-fold. Biological response modifiers such as tumor necrosis factor and interferon and chemotherapeutic agents such as cisplatinum andN,N-bis(2-chloroethyl)-N-nitrosourea (carmustine) augmented the cytotoxicity of 14G2a-gelonin 4- to 5-fold. The results of these studies suggest that 14G2a-gelonin may operate directly by both cytotoxic efforts and indirectly by mediating both ADCC and CDC activity against tumor cells; thus it may prove useful in the future for therapy of human neuroectodermal tumors.Research conducted, in part, by the Clayton Foundation for Research     

Techniques for encapsulating bioactive agents into liposomes

As a prerequisite for the use of liposomes for delivery of biologically active agents, techniques are required for the efficient and rapid entrapment of such agents in liposomes. Here we review the variety of procedures available for trapping hydrophilic and hydrophobic compounds. Considerations which are addressed include factors influencing the choice of a particular liposomal system and techniques for the passive entrapment of drugs in multilamellar vesicles and unilamellar vesicles. Attention is also paid to active trapping procedures relying on the presence of (negatively) charged lipid or transmembrane ion gradients. Such gradients are particularly useful for concentrating lipophilic cationic drugs inside liposomes, allowing trapping efficiencies approaching 100%.     

Coincident plasmids and antimicrobial resistance in marine bacteria isolated from polluted and unpolluted Atlantic Ocean samples.

Sewage effluent and outfall confluence samples were collected at the Barceloneta Regional Treatment Plant in Barceloneta, Puerto Rico; outfall confluence samples at Ocean City, Md., were also collected. Samples from uncontaminated open ocean areas served as clean-water controls. Bacteria were enriched in marine broth 2216 amended with 1 microgram of one of a set of chemicals selected for study per ml: nitrobenzene, dibutyl phthalate, m-cresol, o-cresol, 4-nitroaniline, bis(tributyltin) oxide, and quinone. MICs of the chemicals were determined individually for all isolates. Bacterial isolates were evaluated for resistance to nine different antibiotics and for the presence of plasmid DNA. Treated sewage was found to contain large numbers of bacteria simultaneously possessing antibiotic resistance, chemical resistance, and multiple bands of plasmid DNA. Bacteria resistant to penicillin, erythromycin, nalidixic acid, ampicillin, m-cresol, quinone, and bis(tributyltin) oxide were detected in nearly all samples, but only sewage outfall confluence samples yielded bacterial isolates that were resistant to streptomycin. Bacteria resistant to a combination of antibiotics, including kanamycin, chloramphenicol, gentamicin, and tetracycline, were isolated only from sewage effluent samples. It is concluded that bacterial isolates derived from toxic chemical wastes more frequently contain plasmid DNA and demonstrate antimicrobial resistance than do bacterial isolates from domestic sewage-impacted waters or from uncontaminated open ocean sites.     

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 microcosm salinity and organic substrate concentration on production of Vibrio cholerae enterotoxin.

The effects of aquatic processes on production of cholera toxin by Vibrio cholerae were studied with seawater microcosms. Several salinity and organic nutrient concentrations were employed. At 10 g of organic nutrient per liter of seawater, toxin production increased as the salinity was increased. At lower organic nutrient concentrations, toxin production was markedly enhanced when the salinity was 20 and 25%. Toxin concentration increased with salinity, independent of cell concentration and toxin stability. From the results obtained in this study, it is concluded that physical and chemical parameters of the aquatic environment affect not only the physiological state of V. cholerae, but also its potential pathogenicity.     

Influence of Meloidogyne incognita on Resistant and Susceptible Sweet Potato Cultivars

Effects of several population densities ofMeloidogyne incognita on the sweet potato cultivars Centennial (susceptible) and Jasper (moderately resistant) were studied. Field plots were infested with initial levels (Pi) of 0, 10, 100, 1,000, 5,000, and 10,000 eggs and juveniles/500 cm³ soil in 1980 and 0, 100, 1,000, 2,000, 3,000, 4,000, and 5,000 in 1981. M. incognita population development trends were similar on both cultivars; however, at high Pi, more eggs and juveniles were recovered from Centennial than from Jasper. The highest Pi did not result in the highest mid-season (Pm) counts. Pi was negatively correlated with the number of marketable roots and root weight but positively correlated with total cracked roots, percentage of cracked roots, and cracking severity. Jasper tolerated higher Pi with greater yields and better root quality than Centennial. Cracking of fleshy roots occurred with both cultivars at low Pi.     

The isolation and characterization of ngm2, a mutation that affects nitrosoguanidine mutagenesis in yeast

Summary We have isolated and characterized a new mutant of Saccharomyces cerevisiae, carrying a single mutant allele that we designate ngm2-1, which is defective with respect to induced mutagenesis. This mutant was isolated by screening mutagenized clones for reduced frequencies of reversion of the his1-7 allele, induced by N-methyl-N-nitro-N-nitrosoguanidine. As judged by the reversion of his1-7 and ilv1-92, ngm2-1 mutant strains are also deficient with respect to mutability induced by methyl methane sulfonate, ethyl methane sulfonate and, at least partially, by UV. UV-induced reversion of the ochre mutation arg4-17 and the frameshift mutation his4-38 was not much affected by ngm2-1, however. Like rev3 and rev7 mutations, ngm2-1 also has little influence on the reversion of the proline missense allele, cyc1-115. Ngm2-1 mutants are only at best very slightly more sensitive to the toxicity of the four mutagens used, and homozygous diploids sporulate normally.