Bubble-Induced Cave Collapse

Conventional wisdom among cave divers is that submerged caves in aquifers, such as in Florida or the Yucatan, are unstable due to their ever-growing size from limestone dissolution in water. Cave divers occasionally noted partial cave collapses occurring while they were in the cave, attributing this to their unintentional (and frowned upon) physical contact with the cave walls or the aforementioned “natural” instability of the cave. Here, we suggest that these cave collapses do not necessarily result from cave instability or contacts with walls, but rather from divers bubbles rising to the ceiling and reducing the buoyancy acting on isolated ceiling rocks. Using familiar theories for the strength of flat and arched (un-cracked) beams, we first show that the flat ceiling of a submerged limestone cave can have a horizontal expanse of 63 meters. This is much broader than that of most submerged Florida caves (~ 10 m). Similarly, we show that an arched cave roof can have a still larger expanse of 240 meters, again implying that Florida caves are structurally stable. Using familiar bubble dynamics, fluid dynamics of bubble-induced flows, and accustomed diving practices, we show that a group of 1-3 divers submerged below a loosely connected ceiling rock will quickly trigger it to fall causing a “collapse”. We then present a set of qualitative laboratory experiments illustrating such a collapse in a circular laboratory cave (i.e., a cave with a circular cross section), with concave and convex ceilings. In these experiments, a metal ball represented the rock (attached to the cave ceiling with a magnet), and the bubbles were produced using a syringe located at the cave floor.     

Outer membrane proteins of Pseudomonas

In this review, we describe the outer membrane proteins of Pseudomonas aeruginosa and related strains from the Pseudomonas fluorescens rRNA homology group of the Pseudomonadaceae, with emphasis on the physiological function and biochemical characteristics of these proteins. The use of opr (for outer membrane protein) is proposed as the genetic designation for the P. aeruginosa outer membrane proteins and letters are assigned, in conjunction with this designation, to known outer membrane proteins. Proteins whose primary functions involve pore formation, transport of specific substrates, cell structure determination and membrane stabilization are discussed. The conservation of selected proteins in the above Pseudomonas species is also examined.     

Turnover of cell surface-bound capsular polysaccharide in Staphylococcus aureus

The capsular polysaccharide (CPS) of Staphylococcus aureus strain Smith was labelled by growth of bacteria in the presence of radioactive N-acetylglucosamine and was separated from labelled cell wall components by affinity chromatography on wheat germ agglutinin following dissolution of the cells by lysostaphin. The products were partially characterised chemically and immunochemically. Similar labelled components were found in the culture fluid during growth. In a pulse-chase experiment, cell-bound CPS was released continuously into the culture fluid at the same rate as cell wall turnover and there was no evidence of direct excretion of CPS.     

Characterization of two surface-localized antigenic sites on porin protein F of Pseudomonas aeruginosa

A rapid colony immunoblot screening procedure was used to demonstrate the surface localization of porin protein F on bacterial colonies of Pseudomonas aeruginosa. By this method, we demonstrated that protein F was accessible to four different specific monoclonal antibodies in a wide variety of both mucoid and nonmucoid P. aeruginosa strains. Controls were performed to demonstrate that, using this procedure, only surface-exposed epitopes bound monoclonal antibodies and that nonspecific binding of monoclonal antibodies either to cells lacking protein F or to mucoid exopolysaccharide did not occur. Monoclonal antibodies MA4-4, MA2-10, and MA4-10, specific for protein F, also interacted with colonies of Pseudomonas putida and Pseudomonas syringae, whereas the protein F specific monoclonal antibody MA5-8 interacted only with P. aeruginosa strains. Using the above-named monoclonal antibodies, we investigated the antigenic structure of protein F. Monoclonal antibodies MA4-4, MA2-10, and MA4-10 bound to 29-31 kilodalton proteolytic fragments produced after papain or trypsin digestion of purified protein F or of protein F in outer membranes or intact cells. Antibody MA5-8 did not interact with proteolytically digested protein F but did interact with two of the six fragments produced after partial cyanogen bromide cleavage of protein F. Antibodies MA4-4, MA2-10, and MA4-10 did not interact with protein F after reduction of its internal disulphide bonds with 2-mercaptoethanol; in contrast, the reactivity of MA5-8 was unaffected. This data suggests that there are at least two distinct highly conserved surface epitopes on porin protein F.     

EMBRYONIC GENETIC LOAD IN THE HIGHBUSH BLUEBERRY,VACCINIUM CORYMBOSUM (ERICACEAE)

Hand-pollinations of 28 autotetraploid V. corymbosum accessions from a single population resulted in lower self- than outcross seed set. Fertility varied widely, ranging from clones that were effectively female sterile to individuals with high seed yields in both matings. Self- and outcross fertility were highly correlated. A genetic load model was invoked to explain these phenomena. Reduced self-fertility was attributed to homozygosity for sublethal mutations at loci controlling embryo development, or to loss of heterotic interactions at these loci. Near zero cross-fertility in some clones may be evidence of partially dominant mutational load. Estimates of the number of lethal equivalents per zygote carried by individuals in this population ranged from 2.2 to 20.4, with a mean of 9.6. Embryonic genetic load at the individual level was significantly correlated with heterozygosity at nine enzyme loci. Low pollen viability and reduced receptivity to pollen from any source were also noted in the low fertility genotypes. It is suggested that gametic, gametophytic, and embryonic development are symptomatic of the amount of genetic load carried by individuals.     

Neutron activation analysis of bulk and selected trace elements in bones using a low flux SLOWPOKE reactor

The mineral phase of bone is a reservoir for some biologically important ions and is the place where some toxic elements are also stored. For these reasons it is important to measure accurately and nondestructively the chemical content of bone, with respect to its main elements (Ca, P, Mg, Na) and its trace elements. We have analyzed different types of human bone by instrumental neutron activation analysis (INAA), using a SLOWPOKE reactor. We have compared our results with inductively coupled plasma emission spectroscopy (ICPES), and we have determined the limits of detection and sensitivity for the various elements, especially some biologically or toxicologically significant trace elements. Finally, we have given two examples of the use of INAA in following the penetration of an element (F) with time into bone and in characterizing nondestructively the mineral content of bone biopsies of a rare pathological condition (osteopetrosis).     

Metal ion size selectivity in ligands with groups containing the neutral oxygen donor atom. A crystallographic and thermodynamic study

The coordinating properties of open-chain ligands containing alcoholic or ethereal oxygen donors are examined. Addition of oxygen donors usually leads to complex stabilisation for large metal ions (Pb²⁺, Cd²⁺) and to less favourable effects on complex stability for small metal ions (Cu²⁺, Ni²⁺). The formation constants of these metal ions with the set of ligands RN(CH₂CHOH·CH₃)₂ where R is ---H, ---CH₂CHOH·CH₃, ---CH₂CH₂OCH₃, ---CH₂CH₂OCH₂CH₂OH, and ---CH₂---CHOCH₂CH₂CH₂ are reported. The largest stabilisation for each case where R is an O-donor group relative to R = H occurs for Pb²⁺, the largest metal ion, while Cu²⁺, the smallest metal ion, shows the smallest stabilisation. The crystal structure of [Ni(HOCH₂CH₂NHCH₂CH₂NH₂)₂] (NO₃)₂ is reported. The space group is P , with cell constants a = 13.098(3), b = 8.737(4), and c = 7.746(3) Å, β = 112.66(3), β = 90.65(3), and γ = 85.03(2), and Z = 2. Disorder of the nitrate anions hindered refinement, with the result that a final conventional R factor of 0.0903 was achieved. The Ni---N bond lengths average 2.06(1) (secondary nitrogen) and 2.10(2) (primary nitrogen). The Ni---O bond lengths are rather long, averaging 2.15(1) Å, which is used to support the idea that the steric effects are responsible for destabilising the complexes of small metal ions such as Ni(11) when neutral oxygen donors are present.     

Isolation of the outer membrane and characterization of the major outer membrane protein from Spirochaeta aurantia.

The outer membrane of Spirochaeta aurantia was isolated after cells were extracted with sodium lauryl sarcosinate and was subsequently purified by differential centrifugation and KBr isopycnic gradient centrifugation. The purified outer membrane was obtained in the form of carotenoid-containing vesicles. Four protein species with apparent molecular weights of 26,000 (26K), 36.5K, 41K, and 48.5K were readily observed as components of the vesicles. The 36.5K protein was the major polypeptide and constituted approximately 90% of the outer membrane protein observed on sodium dodecyl sulfate-polyacrylamide gels. Under mild denaturing conditions the 36.5K major protein exhibited an apparent molecular weight of approximately 90,000. This, together with the results of protein cross-linking studies, indicates that the 36.5K polypeptide has an oligomeric conformation in the native state. Reconstitution of solubilized S. aurantia outer membrane into lipid bilayer membranes revealed the presence of a porin, presumably the 36.5K protein, with an estimated channel diameter of 2.3 nm based on the measured single channel conductance of 7.7 nS in 1 M KCl.     

Interleukin 2 receptors are expressed by alveolar macrophages during pulmonary sarcoidosis and are inducible by lymphokine treatment of normal human lung macrophages, blood monocytes, and monocyte cell lines

Expression of receptors for IL 2 was believed initially to be restricted to T cells after their activation by IL 1 and antigen. However, recently IL 2 receptors (IL 2R) were demonstrated on activated B cells by using an anti-IL 2R monoclonal antibody (anti-Tac). In this study, we examined the capacity of cultured human alveolar macrophages, blood monocytes, and myelomonocytic (HL-60) or monoblast (U937) cell lines to bind three different anti-IL 2R monoclonal antibodies before or after stimulation with the monocyte-activating agents IFN-gamma, LPS, phorbol ester, or lymphokine-containing conditioned medium. For each of the four cell populations examined, resting unstimulated cells bound little or no anti-IL 2R antibody, as shown independently by quantitative cell binding assay and by immunoperoxidase labeling. By contrast, incubation with recombinant IFN-gamma, conditioned medium, or to a lesser extent, native or recombinant IL 2 itself, resulted in a significant enhancement of anti-IL 2 receptor monoclonal antibody binding by all four populations, whereas LPS, PMA, or IL 1 had no effect. In addition, membrane binding of anti-Tac antibody, similar to that seen after stimulation of normal lung macrophages with IFN-gamma, was detected by using macrophages obtained by bronchoalveolar lavage of five patients with active pulmonary sarcoidosis. These findings are consistent with the expression of a functional IL 2R on activated cells of the monocyte lineage, since anti-Tac binding to IFN-gamma-treated HL-60 cells was inhibited by addition of excess IL-2; specific binding of anti-IL 2 monoclonal antibodies was detected in the presence of exogenous IL 2; and a 50 to 55 kD molecule was immunoprecipitated from both activated lung macrophages and T lymphoblasts by using anti-Tac antibody. We conclude that human mononuclear phagocytes can be induced by lymphokines to express IL 2R, and that such IL 2R+ macrophages can be detected in vivo during inflammation.     

Properties of the superoxide-generating oxidase of B-lymphocyte cell lines. Determination of Michaelis parameters.

The capacity of three B-lymphocyte cell lines to generate superoxide (O2.-) was examined. The Burkitt lymphoma lines P.3HR-1 and Jijoye gave no response to phorbol 12-myristate 13-acetate (PMA) at 100 ng/ml but produced up to 0.35 nmol of O2.-/min per mg of protein when stimulated with 5 micrograms of PMA/ml; the cell line RPMI 1788 produced Nitro Blue Tetrazolium-positive responses to low PMA concentrations and approx. 0.4 nmol of O2.-/min per mg of protein at 5 micrograms of PMA/ml. Each cell line contained approx. 10 pmol of low-potential cytochrome b (cytochrome b-245)/mg of protein. Homogenates of PMA-activated cells gave 10-20-fold greater rates of O2.- produced per mg of protein. The Km for NADPH varied between approx. 250 microM for P3.HR-1 and RPMI 1788 cell lines and 30.5 +/- 6.5 microM for the Jijoye cell line; the Km values for NADH were higher. Determination of intracellular NADPH concentration showed that this might limit the rate of O2.- production since in each cell line it was at or below the Km concentration.