Multiple Bacteriocin Production by Leuconostoc mesenteroidesTA33a and Other Leuconostoc/Weissella Strains

Leuconostoc (Lc.) mesenteroides TA33a produced three bacteriocins with different inhibitory activity spectra. Bacteriocins were purified by adsorption/desorption from producer cells and reverse phase high-performance liquid chromatography. Leucocin C-TA33a, a novel bacteriocin with a predicted molecular mass of 4598 Da, inhibited Listeria and other lactic acid bacteria (LAB). Leucocin B-TA33a has a predicted molecular mass of 3466 Da, with activity against Leuconostoc/Weissella (W.) strains, and appears similar to mesenterocin 52B and dextranicin 24, while leucocin A-TA33a, which also inhibited Listeria and other LAB strains, is identical to leucocin A-UAL 187. A survey of other known bacteriocin-producing Leuconostoc/Weissella strains for the presence of the three different bacteriocins revealed that production of leucocin A-, B- and C-type bacteriocins was widespread. Lc. carnosum LA54a, W. paramesenteroides LA7a, and Lc. gelidum UAL 187-22 produced all three bacteriocins, whereas W. paramesenteroides OX and Lc. carnosum TA11a produced only leucocin A- and B-type bacteriocins. Received: 11 April 1997 / Accepted: 10 June 1997     

Guaraná (Paullinia cupana) as a commercial crop in Brazilian Amazonia

Guaraná (Paullinia cupana) is a woody vine or sprawling shrub native to the central Amazon Basin. The seeds are commercially produced on some 6,000 ha in the state of Amazonas near Manaus. The principal article of commerce is an amber-colored, carbonated soft drink. It is also widely used as a high caffeine stimulant and in local medicines. The plant is monoecious and is damaged by a number of diseases, the most severe being anthracnose. Prospects are excellent for greatly expanded international markets.     

Suppression of the rotifer Polyarthra remata by the omnivorous copepod Tropocyclops extensus: predation or competition

Indirect evidence from observations in the field suggested thata common and often abundant cyclopoid copepod, Tropocyclopsextensus, despite its small size (0.5 mm) and largely algaldiet, is an important predator of the rotifer Polyarthra remata.Laboratory experiments showed that copepodids and adults, butnot nauplii, markedly suppressed the population growth of thisrotifer. The suppression could be attributed entirely to predation,rather than to exploitative competition for shared food resourcesor to interference. Mortality rates predicted from a separatefeeding-rate experiment weresufficient to account for the declinein population size observed in the Tropocyclops treatment ofculture experiments. Also, monitoring the availability of cryptomonadfood in treatments with and without Tropocyclops throughoutthese experiments showed that cryptomonad densities always remainedhigh and were just as high or significantly higher in the copepodtreatments. Furthermore, direct videographic observations ofP. remata from cultures with and without Tropocyclops demonstratedno significant differences in swimming velocity, tendency todeviate from a straight-line path, or frequency and length ofspontaneous escape responses. Per capita ingestion rates ofT. extensus on P. remata varied from 2 to 8 day^-1, were significantlyhigher for adult females than adult males or copepodids V, andincreased significantly with rotifer density. A tendency ofcopepods to have higher ingestion rates on young than adultrotifers was not significant. Copepods cultured since birthwith cryptomonads and P. remata ate significantly fewer rotifersthan those cultured only with cryptomonads; this may be explainedby a more sated condition of the former and provided no evidencefor the idea that previous experience with this rotifer mightincrease predation efficiency. The results show that T. extensusin natural communities has the potential to deplete naturalpopulations of susceptible rotifer prey. Accordingly, it mayshift the species structure of rotifer assemblages in favourof resistant species, and provide selection pressure for avoidanceresponses.     

The presence of chlorophyll b and the estimation of phaeopigments in marine phytoplankton

A reverse-phase h.p.l.c. technique was used to estimate theconcentration of chlorophyll b in phytoplankton cultures, fecalpellets of Calanus pacificus, and suspended paniculate matterfrom the Central North Pacific, Oregon coastal waters, and DabobBay (a temperate fjord in Puget Sound, WA, USA). The purposewas to assess the distribution of this pigment in the euphoticzone and its effect on the fluorometnc estimation of phaeopigments.Analyses of natural waters confirm high chlorophyll b concentrations(median mass ratio of b:a > 0.3) at the depth of the chlorophylla maximum in tropical waters while values for temperate planktonare relatively low (median mass ratio of chl b:a = 0.05) andpatchy. Zooplankton fecal pellets showed a significant enrichmentin chlorophyll b, suggesting grazing as a mechanism to explainhigh concentrations of this pigment at the bottom of the euphoticzone. It is estimated that the presence of chlorophyll b couldcause an average overestimation of phaeopigment concentrationby the fluorometnc technique of 38% between 0 and 200 m in theCentral North Pacific. This effect is more pronounced at thelayer of chlorophyll b maximum (120–140 m). ¹Present address: Marine Biology Research Division, A-002, ScrippsInstitution of Oceanography, La Jolla, CA 92093, USA     

Pertussis Toxin Attenuates D2 Inhibition and Enhances D1 Stimulation of Adenylate Cyclase by Dopamine in Rat Striatum

The response of adenylate cyclase to GTP and to dopamine (DA) was investigated in synaptic plasma membranes isolated from rat striatum injected with pertussis toxin, which inactivates the inhibitory guanine nucleotide-binding regulatory protein (Ni) of adenylate cyclase. Pertussis toxin treatment reverted the inhibitory effects on the enzyme activity elicited by micromolar concentrations of GTP and reduced by 50% the DA inhibition of cyclase activity via D2 receptors. The toxin treatment enhanced the net stimulation of enzyme activity by DA in the presence of micromolar concentrations of GTP. However, the stimulatory effect of the selective D1 receptor agonist SKF 38393 was not significantly affected. The data indicate that Ni mediates D2 inhibition of striatal adenylate cyclase and participates in the modulation of D1 stimulation of the enzyme activity by DA.     

Hydrolysis of sunflower oil by means of hydrophobic membrane with lipolytic activity

Polytetrafluoroethylene (PTFE) membranes of different porosity were used for lipase from Rhizopus immobilization. The immobilized enzyme applied to sunflower oil hydrolysis achieved the activity of 1228 U/m² of the membrane area and the half-life time was calculated to be 7 days.     

Expression of HOX homeogenes in human neuroblastoma cell culture lines

Mammalian genes containing a class-I homeobox (HOX genes) are highly expressed in the embryonic nervous system. As a first step towards the molecular analysis of the role these genes play in neural cells, we studied the expression of four human HOX genes in five neuroblastoma (NB) cell lines - SK-N-BE, CHP-134, IMR-32, SK-N-SH and LAN-1 - during the process of differentiation induced by treatment with retinoic acid (RA). The four genes, HOX1D, 2F, 3E and 4B, located at corresponding positions in the four HOX loci, share a high degree of sequence similarity with the Drosophila Deformed homeotic gene and constitute a homology group, group 10. One of these genes, HOX1D, is not expressed in the cells used, whereas the other three are highly expressed in untreated and RA-induced NB cells, even though the expression pattern in the various lines is slightly different for the three genes. Our analysis reveals a complex and specific expression pattern in these lines, paving the way to an identification of different NB-cell populations by means of specific HOX gene expression schemes. On the other hand, in every line studied, morphological maturation toward a neuronal differentiated phenotype appears to be associated with increased HOX gene expression.     

The cytotaxonomy ofEmilia spp. (Asteraceae: Senecioneae) occurring in Brazil

Analysis of several populations in a large part of the distribution area of the genusEmilia in Brazil has revealed only two species: the diploidE. sonchifolia and the tetraploidE. fosbergii. The more widely reportedE. coccinea was not found. They show a karyotype constancy in morphology and chromosome number (2n = 10 and 2n = 20, respectively), C-banding pattern and number of secondary constrictions. Some indications were found thatE. fosbergii may be an allopolyploid and that its ancestors had different genome sizes.     

Tricyclic Imipramine Modification of the Circadian Rhythms of Hypothalamic Serotonin, its Precursors and Acid Catabolite in Individually Housed Rats

Circadian rhythms of serotonin (5HT), its precursors tryptophan (TP) and 5-hydroxy-tryptophan (5HTP) and its acid catabolite 5-hydroxy-indoleacetic acid (5HIAA), were determined in the hypothalamus of control rats and rats which had been treated continuously with subcutaneous imipramine (10 mg/kg/day) for 2 weeks.

Rats were individually housed and entrained to LD12:12. Controls showed the 5HT and TP peaks in the light and dark periods respectively, as reported in the literature, but no inverted correlation (antiphase) between SHT and 5HIAA rhythms.

Imipramine significantly modified circadian rhythm characteristics: the 5HT acrophase was advanced, that of TP and 5HIAA was delayed. Imipramine also significantly increased hypothalamic SHT and TP concentrations.     

Suitability of a rapid gas chromatographic method for total mesophilic bacteria and coliform enumeration in hamburgers

An instrumental method for the rapid determination of total mesophilic bacteria and total coliforms in hamburgers is described. The two procedures are based on the gas chromatographic determination of metabolic CO₂ in equilibrium in the head space of sealed vials containing suitable media and inoculated with aliquots of the sample under examination. Both procedures proved to be suitable for quality control of meat products, being highly sensitive, reproducible, simple and rapid. Good correlation coefficients were obtained with plate counting for microbial concentrations ranging between 10¹ and 10⁸.