Two-state model of Paramecium bursaria thigmotaxis.

A theoretical framework has been developed for analysis of the interaction between Paramecium bursaria and a glass surface. Adhesion to and detachment from a solid substrate were considered in the model as transitions between alternative states in cell behavior: (a) swimming, and (b) motionless (positive thigmotactic) state. According to the model and experimental data, a change in the fraction of swimming cells is described by a negative exponential course. The proposed model allows positive thigmotaxis, generally referred to in the literature simply as thigmotaxis, to be considered as the rate-constant of transition into the motionless state. This approach permits quantitative determination of thigmotaxis, and reveals its dependence on the phase of culture growth and the type of medium surrounding the cells. In the mineral maintenance solution, paramecia from the stationary phase of growth swim more slowly than those in the logarithmic phase of growth, and show enhanced thigmotaxis. However, a general relationship between thigmotaxis and swimming speed was not established.     

An increase in the influx of calcium ions into cilia induces thigmotaxis inParamecium caudatum

To understand the role of calcium ions in thigmotaxis inParamecium caudatum, the effects of caffeine, ruthenium red and lanthanum (LaCl₃) on thigmotaxis were examined. Thigmotaxis in the CNR mutant, which lacks voltage-dependent Ca²⁺-channels in the ciliary membrane, was also examined. Ruthenium red and LaCl₃ suppressed thigmotaxis inP. caudatum, while caffeine enhanced it. The CNR mutant showed hardly any thigmotaxis. It can be thought that an increase in Ca²⁺ influx and the intraciliary concentration of Ca²⁺ ions induces thigmotaxis inParamecium.     

Differential sensitivity to tributyltin of cytochrome-containing and cytochrome-deficient cells ofEscherichia coli SASX76

Summary The effect of tributyltin (TBT) chloride on the growth of cytochrome-deficient and cytochrome-containing cells ofEscherichia coli SASX76 was examined. The former cells were found to be at least 20 times more sensitive to TBT. It is proposed that the differential sensitivity of these two cell types to the biocide, TBT, may be due to a different mode of energy generation by cytochrome-deficient and cytochrome-sufficient cells. In addition to the energy state, the pH change caused by the presence and absence of cytochromes which occurred during growth also resulted in a differential sensitivity of these cells.Acknowledgments. This research was financially supported by a grant from the University Grants Commission, New Delhi, India, to APS. The authors thank the Head, Department of Botany, B.H.U. for facilities.     

Selection of biting sites on man by two malaria mosquito species

While searching for blood, female mosquitoes pass through a behavioural process involving responses to visual, physical and chemical properties of the host. Temperature and humidity are thought to dominate mosquito orientation near the host. We observed that biting of two malaria mosquito species, i.e.Anopheles atroparvus (van Thiel) andAnopheles gambiae s.s. (Giles) preferentially occurs on different body regions of a naked motionless human host. Their preference for the head and foot regions respectively correlated with particular combinations of skin temperature and eccrine sweat gland density. Subsequent modification of the host's odour profile by removing exhaled breath and washing feet results in significant changes of these preferences.     

Expression of multidrug resistance (mdr) gene(s) in primary lymphoid organs of chicken immune system during embryonic development

The presence of a multidrug resistance (MDR) related protein, P-170, in normal and pathological lymphoid cells has been described. The present report evaluates the expression of themdr 1 gene by using the reverse Polymerase Chain Reaction (PCR) on cells obtained from the thymus and bursa of chicken embryos starting from day 12 until hatching. Results show that the thymic cells are positive from day 12 to the end of the observation period. In contrast,mdr mRNA was detected in the bursa from day 14 to day 17 of embryonic life. Possible relationships between the expression ofmdr and the development of T and B lymphocytes are discussed.     

The elusive engine in <Emphasis Type="Italic">Myxococcus xanthus</Emphasis> gliding motility

Bacterial motility is essential for chemotaxis, virulence and complex social interactions leading to biofilm and fruiting body formation. Although bacterial swimming in liquids with a flagellum is well understood, little is known regarding bacterial movements across solid surfaces. Gliding motility, one such mode of locomotion, has remained largely mysterious because cells move smoothly along their long axis in the absence of any visible organelle. In this review, I discuss recent evidence that focal adhesion systems mediate gliding motility in the social bacterium Myxococcus xanthus and combine this evidence with previous work to suggest a new working hypothesis inspired from knowledge in apicomplexan parasites. I then propose experimental directions to test the model and compare it to other pre-existing models. Finally, evidence on gliding mechanisms of selected organisms are presented to ask whether some features of the model have precedents in other bacteria and whether this complex biological process could be explained by a single mechanism or involves multiple distinct mechanisms. Received 12 April 2007; received after revision 8 June 2007; accepted 27 June 2007     

Intracellular proteases from the extremely thermophilic archaebacteriumSulfolobus solfataricus

Proteolytic activities from the extremely thermoacidophilic archaebacteriumSulfolobus solfataricus were detected with the aid of synthetic substrates in a cell extract fractionated by gel filtration. Two aminopeptidases (aminopeptidase I and II), three endopeptidases (proteinase I, II and III) and one carboxypeptidase could be identified. Experiments carried out with protease inhibitors led to the identification of the exopeptidases as metalloproteases. Proteinases I and II behaved as chymotrypsin-like serine proteases, and proteinase III as a cysteine protease with a trypsin-like specificity. Molecular weight values assessed with the aid of marker proteins were as follows: aminopeptidase I, >450 kDa; aminopeptidase II, 170 kDa; carboxypeptidase, 160 kDa; proteinase I, 115 kDa; proteinase II, 32 kDa; proteinase III, 27 kDa. On incubation for 15 min they retained most of their activity up to a temperature of 90°C, with the sole exception of proteinase II, which was rapidly inactivated at 60°C. Protease content was also determined in crude extracts from cells grown in a mineral medium both to the stationary and to the exponential phase, with glucose or with yeast extract as carbon sources. No dramatic change was detected depending on the growth phase; however, carboxypeptidase level was three- to four-fold higher when yeast extract was present in the medium instead of glucose; this might suggest an involvement of this enzyme in the digestion of extracellularly available peptides.     

Retention ofB. burgdorferi pathogenicity and infectivity after multiple passages in a co-culture system

In vitro cultivation ofB. burgdorferi in BSK medium results in the loss of infectivity and pathogenicity after repeated passages. To prevent this loss, a feeder layer of tibio-tarsal joint tissue derived from newborn LEW/N rats was grown on Cytodex 3 microcarriers in ESG (formerly BSKE), a novel medium developed to support the growth of both the feeder layer andB. burgdorferi. A new pathogenic isolate (FNJ) and a high passage, non-pathogenic strain (TNJ) grew well in this co-culture system with high yields of viable organism. FNJ caused no growth inhibition or visible damage to the cells in the feeder layer. FNJ remained arthritogenic for newborn LEW/N rats after 22 passages in the co-culture system, but lost its arthritogenicity after 7 passages when cultured in BSK medium. This borrelia-mammalian tissue co-culture technique presents an experimental system to study the long term interactions ofB. burgdorferi with the infected host tissues in vitro, as well as facilitate diagnostic tests and vaccine development.This article forms New Jersey Agricultural Experiment Station paper no. D8420-19-92.     

DNG1, a Dictyostelium homologue of tumor suppressor ING1 regulates differentiation of Dictyostelium cells

dng1 is a Dictyostelium homologue of the mammalian tumor suppressor ING gene. DNG1 protein localizes in the nucleus, and has a highly conserved PHD finger domain found in chromatin-remodeling proteins. Both dng1 disruption and overexpression impaired cell proliferation. In dng1-null cells, the progression of differentiation was delayed in a cell-density-dependent manner, and many tiny aggregates were formed. Exogenously applied cAMP pulses reversed the inhibitory effect caused by dng1 disruption on the aggregation during early development, but formation of tiny aggregates was not restored. dng1-overexpressing cells acquired the ability to undergo chemotaxis to cAMP earlier and exhibited enhanced differentiation. These phenotypes were found to be coupled with altered expressions of early genes such as cAMP receptor 1 (car1) and contact site A (csA). Furthermore, disordered histone modifications were demonstrated in dng1-null cells. These results suggest a regulatory role of dng1 in the transition of cells from growth to differentiation.Received 29 December 2004; received after revision 24 May 2005; accepted 26 May 2005     

Indirect visualization of hematopoietic colony-forming stem cell (CFUs) as a possible target cell forMycoplasma arthritidis

Summary Utilizing specific rabbit antiserum againstM. arthritidis together with complement, a portion of the marrow 7-day CFUs population of CBA mice infected with live mycoplasma organisms 1 day previously was shown to be inactivated. These cells might therefore be considered as candidate target cells forM. arthritidis. 11-day CFUs were unaffected by similar treatment.     

Induction of chromosome aberrations and chlorophyll mutations in plants by methylisocyanate (MIC) gas

Summary Seeds ofSolanum surattense Burm. f. collected from areas of Bhopal (India) affected by methylisocyanate gas showed chromosome aberrations in root cells, and growth retardation and chlorophyll mutation of seedlings, the frequencies of which varied from one locality to another.     

The C4-dicarboxylate transport system ofRhizobium meliloti and its role in nitrogen fixation during symbiosis with alfalfa (Medicago sativa)

TheRhizobium meliloti C₄-dicarboxylate transport (Dct) system is essential for an effective symbiosis with alfalfa plants. C₄-dicarboxylates are the major carbon source taken up by bacteroids. Genetic analysis of Dct^– mutant strains led to the isolation of thedct carrier genedctA and the regulatory genesdctB anddctD. The carrier genedctA is regulated in free-living cells by the alternative sigma factor RpoN and the two-component regulatory system DctB/D. In addition, DctA is involved in its own regulation, possibly by interacting with DctB. In bacteroids, besides the DctB/DctD system an additional symbiotic activator is thought to be involved indctA expression. Further regulation ofdctA in the free-living state is reflected by diauxic growth of rhizobia, with succinate being the preferred carbon source. The tight coupling of C₄-dicarboxylate transport and nitrogen fixation is revealed by a reduced level of C₄-dicarboxylate transport in nitrogenase negative bacteroids.     

Osmotic adaptation of moderately halophilic methanogenic Archaeobacteria,and detection of cytosolicN,N-dimethylglycine

Methanohalophilus mahii SLP andMethanohalophilus halophilus Z-7982, two closely-related, moderately halophilic, methylotrophic methanogens, were tested for their adaptation to saline conditions. They grew in a wider range of salinities than previously reported, in a defined medium with as little as 0.1 M NaCl, and with a high as 4.0 M NaCl forM. halophilus and 4.5 M NaCl forM. mahii. Fastest growth occurred with 1.5 M NaCl forM. mahii and 1.0 M NaCl forM. halophilus. M. mahii also grew in media in which NaCl was replaced by sucrose or KCl as osmolytes up to the osmolal equivalent of 2 and 2.5 M NaCl (these media contained other sodium salts totaling about 0.1 M Na⁺). In media with either sucrose of KCl replacing NaCl,M. mahii grew fastest at osmolalities approximately equiosmolal to 1 M NaCl.M. mahii not only grew well at a wide range of osmosities, it also tolerated rapid shifts in osmolality. Cells subjected to a rapid 10-fold hypertonic shift resumed growth without a prolonged lag. When cells were subjected to a rapid 10-fold hypotonic shift, 90% of cells lysed, but the remaineder continued to swell with little further lysis during the next 45 min. Surviving cells resumed growth.Methanohalophilus strains grown in defined medium had low cytosolic Na⁺ concentrations; K⁺ concentrations were as high as 0.35 M. Organic osmotica in the cytosol include glycine betaine and larger amounts of N,N-dimethylglycine.     

Presence of benzodiazepine binding sites (receptors) and amplification thereof by imprinting inTetrahymena

Summary LiveTetrahymena cells bound³H-diazepam specifically, as demonstrated by autoradiographic evidence of displacement of about 25% of labeled diazepam in the presence of a 1000-fold amount of cold diazepam. The³H-diazepam bound to membrane preparations isolated from untreated (control) cells was not displaced by cold diazepam, whereas cells involved in primary interaction (imprinting) with diazepam showed amplification and specificity of diazepam binding in both in vivo (cell suspension) and in vitro (pellicle) systems, as well as displacement of bound label in the presence of 1000-fold cold diazepam. It appears that diazepam induced imprinting and, consequently, also the formation of specific receptors inTetrahymena.     

Selective protection of cells against X-irradiation. Isoproterenol protects only those cells that possesβ-adrenoreceptors

Summary In mixed culture of Chinese hamster fibroblatst, clone 431, and transformed murine L fibroblasts, clone B-82, isoproterenol was found to protect only 431 cells against ionizing radiation. It was shown that 431 cells, in contrast to B-82 cells, possess-adrenoreceptors, and the radioprotective effect of isoproterenol can be realized only if this agent interacts with-adrenoreceptors coupled with the cAMP system. Since malignization often causes the disappearance of-adrenergic and other hormone receptors, the combined culturing and irradiation of the cells studied can be regarded as a model of the growth of malignant cells (B-82) among normal tissue cells (431 cells) under conditions of radiation therapy. A possibility of selective protection against radiation damage of normal tissue cells, with retention of the former radiosensitivity of tumor cells, is discussed.     

Variation in regulation of aflatoxin biosynthesis among isolates ofAspergillus flavus

Two new phenotypes ofAspergillus flavus which exhibit novel patterns of aflatoxin production have been identified and characterized. In one of the new variants ofA. flavus, aflatoxin is made in the absence of carbohydrate and concomitantly with growth, without a lag period. A second variant did not produce aflatoxin in the presence or absence of carbohydrate. Chemical mutagenesis of this nonaflatoxigenic strain resulted in mutant strains which produced aflatoxin on carbohydrate-containing media. The aflatoxin production pattern observed in these mutants resembled the typical production scheme, with a lag period through log phase growth.     

The Dead Sea — alive again

In the thirteen years of quantitative studies on the microbiology of the Dead Sea from 1980 onwards three distinct periods can be discerned. Mass development of the green unicellular algaDunaliella parva (up to 8,800 cells/ml) and red archaeobacteria (2×10⁷ cells/ml) was observed in 1980, following a dilution of the upper water layers by rain floods. This bloom disappeared at the end of 1982 as a result of a complete mixing of the water column. During the period 1983–1991 the lake was holomictic, and noDunaliella cells were observed. Viable bacteria were present during this period in very low numbers. Heavy rain floods during the winter of 1991–1992 caused a new stratification as the upper five meters of the water column became diluted to 70% of their normal salinity. In this upper water layerDunaliella reappeared (up to 3×10⁴ cells/ml at the beginning of May, rapidly declining to less than 40 cells/ml at the end of July), and a bloom of red archaeobacteria (3×10⁷ cells/ml) once more imparted a red coloration to the lake.     

Morphological differentiation of the growing oocyte ofCtenomys torquatus (Rodentia,Octodontidae)

Summary The ultrastructural changes observed during the growth phase of oocytes ofCtenomys torquatus (Rodentia, Octodontidae) are reported. Interest was particularly centered on the transformation and/or distribution of the components of the endoplasmic reticulum. According to the observations made it is suggested that the endoplasmic reticulum stores some kind of material which may support early stages of development.     

Relationship of prodigiosin condensing enzyme activity to the biosynthesis of prodigiosin and its precursors inSerratia marcescens

Summary Prodigiosin condensing enzyme (PCE) activities were present inSerratia marcescens wild type 08, mutants OF, WF and 9-3-3. Their specific activities exhibited different maxima and at different times during the late log phase or the early stationary phase of cell growth. The levels of prodigiosin and its precursors also showed a significant increase at this period. The results support that prodigiosin and/or its precursors are secondary metabolites. The ubiquity of the PCE activity in mutants deficient in prodigiosin biosynthesis suggest that this particular enzyme may also be present in non-pigmented clinical isolates.