DIGESTION SURVIVAL OF ALGAE: SOME ECOLOGICAL COMPARISIONS BETWEEN FREE SPORES AND PROPAGULES IN FECAL PELLETS1

Benthic algae survive passage through the digestive tract of different types of grazers, either regenerating new tissues or releasing protoplasts and swarmers which act as accessory means of reproduction to generate new individuals. The ecological importance of this phenomenon is evaluated here by studying spores and fecal pellets. Alga fragments egested alive inside fecal pellets have some ecological advantages over free propagules. In intertidal habitats, the sticky nature of the pellets permits attachment to the substratum while protecting the contained algae from desiccation. In subtidal habitats, the pellets sink 8–22 times faster than the fastest sinking algal propagule. Quantification of swarmers and protoplasts released from algal fragments in the fecal pellets indicates densities of about 217 germlings·cm^?2 and values of 300–700 propagules per pellet. Extrapolation of these results to field conditions based on number of grazers and pellets suggest production figures varying from 0.5–3.5 × 10⁵to 1.3–1.5 × 10⁶ propagules·m^?2·12 h^?1. These values are within known density ranges of settling spores in the field. The ecological significance of the phenomenon may be especially important at seasons when the density of grazers increases and the normal reproductive activity of the algae being consumed decreases.     

The ability of rufous hummingbirds Selasphorus rufus to dilute and concentrate urine

Most terrestrial animals face the challenge of having to conserve water in a desiccating environment. Not surprisingly, the ability to produce concentrated urine has been relatively well studied in birds. Nectar-feeding birds are unusual among terrestrial animals in that they often ingest and excrete prodigious water volumes to obtain adequate energy. Thus, they confront the unusual challenge of having to conserve electrolytes. The diluting abilities of birds and the renal mechanisms that may correlate with them have been relatively neglected. To elucidate diluting and concentrating abilities in nectar-feeding birds, we fed rufous hummingbirds Selasphorus rufus an electrolyte-free nectar and a nectar containing a range of NaCl concentrations. Hummingbirds had a spectacular (and possibly unique) diluting ability: when fed on electrolyte-free food they produced excreta containing less than 0.5 mM l⁻¹ each of sodium and potassium. Hummingbirds also had a poor concentrating ability, retaining sodium and chloride when their food (0.632 M l⁻¹ sucrose) contained more than 35 mM l⁻¹ of NaCl. The kidneys of hummingbirds do not appear to be suited for concentrating urine, and possibly contain structural features that give them a unique diluting ability compared with those of birds that do not feed on nectar.     

Increase in the proportion of metabolically active bacteria along gradients of enrichment in freshwater and marine plankton: implications for estimates of bacterial growth and production rates

It is generally recognized that a fraction of all bacterioplanktoncells enumerated using conventional epifluorescence techniquesis neither growing, dividing nor metabolically active, but thevariation in the proportion of active cells among aquatic systemsis not well understood. Here, we hypothesize that the proportionof metabolically active cells increases systematically alonggradients of enrichment, and to test this hypothesis the numberand proportion of metabolically active planktonic bacteria wereinvestigated during the summer in a set of 24 temperate lakes,which span a considerable range in productivity. The tetrazoliumsalt 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) was usedas an indicator of cells with an active electron transport system.The total number of bacteria ranged from 1.88x10⁶ to 7.70x10⁶ml^–1, whereas the number of active cells was more variableand ranged from 0.37x10⁶ to 2.18x10⁶ ml^–1 in the studylakes. The proportion of metabolically active cells ranged from15 to 33%, and tended to increase with nutrient and chlorophyllconcentrations, but not with dissolved organic carbon (DOC).Data on the number of total and active bacteria culled fromthe literature for marine, estuarine and freshwater systemsshow that the trends we measured in lakes are valid for pelagicsystems in general. Over a broad range of aquatic systems, thetotal number of bacteria varied by three orders of magnitude,whereas the number of active bacteria varied by four ordersof magnitude as system productivity increased. The proportionof active cells increased from ultraoligotrophic openocean areas(<5%) to highly productive estuaries (>50%). Our resultssuggest that in most aquatic systems there is a pool of rapidlygrowmg cells, embedded in a usually larger matrix of inactivebacteria, and that the relative size of the active and inactivepools varies systematically among bacterial populations alonggradients of enrichment.     

Ehrlich cell plasma membrane redox system is modulated through signal transduction pathways involvingcGMP and Ca2+ as second messengers

Ehrlich cell plasma membrane ferricyanide reductase activity increased in the presence of mastoparan, a generic activator of G proteins, using either whole cells or isolated plasma membrane fractions. Agents that increase intracellularcAMP also increased the rate of ferricyanide reduction by Ehrlich cells. For the first time, evidence is shown on a modulation of plasma membrane redox system bycGMP. In fact, permeant analogs ofcGMP, dibutyrylcGMP, and 8-bromo-cGMP increased the rate of ferricyanide reduction by the Ehrlich cell plasma membrane redox system. Furthermore, specific inhibition ofcGMP-phosphodiesterases by dipyridamole was also accompanied by an enhancement in the rate of ferricyanide reduction. On the other hand, treatments expected to increase cytoplasmic Ca²⁺ concentrations were accompanied by a remarkable stimulation of the reductase activity. Taking all these data together, it seems that the Ehrlich cell plasma membrane redox system is under a multiple and complex regulation by different signal transduction pathways involving G proteins, cyclic nucleotides, and Ca²⁺ ions.     

Preferential recognition of hepatitis B nucleocapsid antigens by Th1 or Th2 cells is epitope and major histocompatibility complex dependent.

Regulatory T-helper (Th) cells have been categorized into two functional subsets, Th1 and Th2 cells, which produce distinct lymphokines. In general, Th1 cells mediate cellular immune responses and Th2 cells mediate humoral immunity. Recent serological studies suggest that the Th1-Th2 balance may be relevant in acute and chronic hepatitis B virus (HBV) infections. The purpose of this study was to determine the potential of the nucleocapsid antigens (Ags) (hepatitis B core and e Ags [HBc/eAg]) of HBV to preferentially elicit either a Th1 or a Th2 dominant response. For this purpose, H-2 congenic B10.S and B10 mice were immunized with HBc/eAg, and Ag-specific T-cell proliferative responses, T-cell helper function, and T-cell cytokine production were analyzed. The results indicated that B10.S mice preferentially develop a Th1-like response whereas B10 mice preferentially develop a Th2-like response after immunization with HBc/eAg. Furthermore, the preferential Th1 and Th2 response patterns were reproduced when 12-residue peptides representing the dominant HBc/eAg-specific T-cell sites for B10.S (peptide 120-131) and B10 (peptide 129-140) mice were used as immunogens. Therefore, the combination of the T-cell site recognized and the major histocompatibility complex restricting element can in large part determine the Th phenotype of the HBc/eAg-specific T-cell response. Other factors that influenced Th phenotype were the presence of exogenous cytokines, Ag structure, and tissue distribution.     

Establishment and characterization of photosynthetic hairy root cultures of Datura stramonium

Twelve different lines of Datura stramonium (normal and hairy) root cultures were subjected to conditions which induce photoautotrophy. Two of the hairy root lines responded to induction, showing clearly a diminished growth rate when compared to heterotrophic cultures, an increase in chlorophyll, a net O₂ evolution, CO₂ fixation, and de novo synthesis of the ribulose 1,5 biphosphate carboxylase enzyme. A time course of growth and tropane alkaloid levels in the tissue and medium, revealed a correlation between the development of the photosynthetic apparatus and the increase in scopolamine. Although normal cultures did not grow photosynthetically, they showed some greening response under the first step of the induction. The correlation between development of photosynthesis and increase in scopolamine synthesis were corroborated with normal root cultures. This experimental model is used for the basic study of the regulatory enzymes involved in the biosynthesis of tropane alkaloids, as well as for the study of their mechanisms of transport.     

Ionic iridium-gold and rhodium-gold perfluorobenzenethiolato binuclear complexes: syntheses and solution behavior

By reacting [(C₅Me₅)M(SR_F)₂] (forM = Ir, Rf = C₆F₅ (1a) or C₆F₄H-p (1b); for M = Rh, Rf = C₆F₅ (2a) or C₆F₄H-p (2a)) in toluene with Na[AuCl₄], ionic binuclear compounds with the general formula [(C₅Me₅)M(μ-SR_F)₂AuCl₂]Cl for M = Ir, R = C₆F₅ (3a) or C₆F₄H-p (3a); for M = Rh, R_F = C₆F₅ (4a) or C₆F₄H-p (4b) can be obtained, together with small amounts of [(C₅Me₅)₂Rh₂(μ-SR_F)(μ-Cl)₂]Cl (R_F = C₆F₅ (5a) or C₆F₄H-p (5b)) as by-products when 2a and 2b were used.     

In vitro recognition of the replication origin of pLS1 and of plasmids of the pLS1 family by the RepB initiator protein.

Rolling-circle replication of plasmid pLS1 is initiated by the plasmid-encoded RepB protein, which has nicking-closing (site-specific DNA strand transferase) enzymatic activity. The leading-strand origin of pLS1 contains two regions, (i) the RepB-binding site, constituted by three directly repeated sequences (iterons or the bind region), and (ii) the sequence where RepB introduces the nick to initiate replication (the nic region). A series of plasmids, belonging to the pLS1 family, show features similar to those of pLS1 and have DNA sequences homologous to the pLS1 nic region. In addition, they all share homologies at the level of their Rep proteins. However, the bind regions of these plasmids are, in general, not conserved. We tested the substrate specificity of purified RepB of pLS1. The RepB protein has a temperature-dependent nicking-closing action on supercoiled pLS1, as well as on recombinant plasmid DNAs harboring the pLS1 nic region. The DNA strand transferase activity of pLS1-encoded RepB was also assayed on two plasmids of the pLS1 family, namely, pE194 and pFX2. DNAs from both plasmids were relaxed by RepB, provided they had a proper degree of supercoiling; i.e., it was necessary to modulate the supercoiling of pE194 DNA to achieve RepB-mediated DNA relaxation. Single-stranded oligonucleotides containing the nic regions of various plasmids belonging to the pLS1 family, including those of pE194 and pFX2, were substrates for RepB. In vitro, the RepB protein does not need to bind to the iterons for its nicking-closing activity.     

Lignin and manganese peroxidase activity in extracts from straw solid substrate fermentations

Manganese and lignin peroxidase (MnP, LiP) activities were measured in straw extracts from cultures of Phanerochaete chrysosporium. Out of six MnP substrates, the MBTH/DMAB (3-methyl-2-benzothiazolinone hydrazone/3-(dimethylamino)benzoic acid), gave the highest MnP activity. Detection of LiP activity as veratryl alcohol oxidation was inhibited by phenols in the straw culture extracts. Appropriate levels of veratryl alcohol and peroxide (4 mM and 0.4 mM, respectively), and a restricted sample volume (not larger than 10%) were necessary to detect activity.