Volume 29, Issue 2
June 2004, pages 129-207
pp 143-152 Perspectives
pp 153-161 Articles
Potassium deficiency enhanced the synthesis of fifteen proteins in the nitrogen-fixing cyanobacterium Anabaena torulosa and of nine proteins in Escherichia coli. These were termed potassium deficiency-induced proteins or PDPs and constitute hitherto unknown potassium deficiency–induced stimulons. Potassium deficiency also enhanced the synthesis of certain osmotic stress-induced proteins. Addition of K+ repressed the synthesis of a majority of the osmotic stress-induced proteins and of PDPs in these bacteria. These proteins contrast with the dinitrogenase reductase of A. torulosa and the glycine betaine-binding protein of E. coli, both of which were osmo-induced to a higher level in potassium-supplemented conditions. The data demonstrate the occurrence of novel potassium deficiency-induced stimulons and a wider role of K+ in regulation of gene expression and stress responses in bacteria.
pp 163-167 Articles
Electrochemical and scanning tunnelling microscopy (STM) studies have been carried out to investigate the suitability of the hexapeptide KCTCCA as a facilitator for bioelectrochemistry. The stable, quasi-reversible electrochemical response of cytochrome 𝑏562 on a KCTCCA modified gold electrode and the high degree of surface coverage of KCTCCA on gold (111), as observed by STM, indicate applicability of the molecule as an electrochemical facilitator.
pp 169-177 Articles
The aim of this work was to investigate the possibility of conducting a continuous aerobic bioprocess in a horizontal rotating tubular bioreactor (HRTB). Aerobic oxidation of acetate by the action of a mixed microbial culture was chosen as a model process. The microbial culture was not only grown in a suspension but also in the form of a biofilm on the interior surface of HRTB. Efficiency of the bioprocess was monitored by determination of the acetate concentration and chemical oxygen demand (COD). While acetate inlet concentration and feeding rate influenced efficiency of acetate oxidation, the bioreactor rotation speed did not influence the bioprocess dynamics significantly. Gradients of acetate concentration and pH along HRTB were more pronounced at lower feeding rates. Volumetric load of acetate was proved to be the most significant parameter. High volumetric loads (above 2 g acetate l–1 h–1) gave poor acetate oxidation efficiency (only 17 to 50%). When the volumetric load was in the range of 0.60–1.75 g acetate l–1 h–1, acetate oxidation efficiency was 50–75%. At lower volumetric loads (0.14–0.58 g acetate l–1 h–1), complete acetate consumption was achieved. On the basis of the obtained results, it can be concluded that HRTB is suitable for conducting aerobic continuous bioprocesses.
pp 179-187 Articles
Both hypotonic exposure (185 mOsmol/l) and infusion of glutamine plus glycine (2 mmol/l each) along with the isotonic medium caused a significant increase of 14CO2 production from [1-14C]glucose by 110 and 70%, respectively, from the basal level of 18.4 ± 1.2 nmol/g liver/min from the perfused liver of Clarias batrachus. Conversely, hypertonic exposure (345 mOsmol/l) caused significant decrease of 14CO2 production from [1-14C]glucose by 34%. 14CO2 production from [6-14C]glucose was largely unaffected by anisotonicity. The steady-state release of oxidized glutathione (GSSG) into bile was 1.18 ± 0.09 nmol/g liver/min, which was reduced significantly by 36% and 34%, respectively, during hypotonic exposure and amino acid-induced cell swelling, and increased by 34% during hypertonic exposure. The effects of anisotonicity on 14CO2 production from [1-14C]glucose and biliary GSSG release were also observed in the presence of t-butylhydroperoxide (50 𝜇mol/l). The oxidative stress-induced cell injury, caused due to infusion of t-butylhydroperoxide, was measured as the amount of lactate dehydrogenase (LDH) leakage into the effluent from the perfused liver; this was found to be affected by anisotonicity. Hypotonic exposure caused significant decrease of LDH release and hypertonic exposure caused significant increase of LDH release from the perfused liver. The data suggest that hypotonically-induced as well as amino acid-induced cell swelling stimulates flux through the pentose-phosphate pathway and decreases loss of GSSG under condition of mild oxidative stress; hypotonically swollen cells are less prone to hydroperoxide-induced LDH release than hypertonically shrunken cells, thus suggesting that cell swelling may exert beneficial effects during early stages of oxidative cell injury probably due to swelling-induced alterations in hepatic metabolism.
pp 189-200 Articles
The distribution of acetylcholinesterase (AChE) in the central vocal control nuclei of the zebra finch was studied using enzyme histochemistry. AChE fibres and cells are intensely labelled in the forebrain nucleus area X, strongly labelled in high vocal centre (HVC) perikarya, and moderately to lightly labelled in the somata and neuropil of vocal control nuclei robust nucleus of arcopallium (RA), medial magnocellular nucleus of the anterior nidopallium (MMAN) and lateral magnocellular nucleus of the anterior nidopallium (LMAN). The identified sites of cholinergic and/or cholinoceptive neurons are similar to the cholinergic presence in vocal control regions of other songbirds such as the song sparrow, starling and another genus of the zebra finch (Poephila guttata), and to a certain extent in parallel vocal control regions in vocalizing birds such as the budgerigar. AChE presence in the vocal control system suggests innervation by either afferent projecting cholinergic systems and/or local circuit cholinergic neurons. Co-occurrence with choline acetyltransferase (ChAT) indicates efferent cholinergic projections. The cholinergic presence in parts of the zebra finch vocal control system, such as the area X, that is also intricately wired with parts of the basal ganglia, the descending fibre tracts and brain stem nuclei could underlie this circuitry’s involvement in sensory processing and motor control of song.
pp 201-207 Articles
The ability of bronze frog Rana temporalis tadpoles (pure or mixed parental lines) to assess the profitability of food habitats and distribute themselves accordingly was tested experimentally using a rectangular choice tank with a non-continuous input design. Food (boiled spinach) was placed at two opposite ends of the choice tank in a desired ratio (1 : 1, 1 : 2 or 1 : 4) to create habitat A and B. The tadpoles in Gosner stage 28–33, pre-starved for 24 h, were introduced in an open ended mesh cylinder placed in the center of the choice tank, held for 4 min (for acclimation) and then released to allow free movement and habitat selection. The number of tadpoles foraging at each habitat was recorded at 10, 15, 20, 25 and 30 min time intervals. The actual suitability, 𝑆𝑖 (the food available in a habitat after colonization of tadpoles) of each habitat was obtained from the equation 𝑆𝑖 = 𝐵𝑖 - 𝑓𝑖 (𝑑𝑖) where 𝐵𝑖 is basic suitability (amount of food provided at each habitat before release of tadpoles), 𝑓𝑖 is the rate of depletion of food (lowering effect) with introduction of each tadpole, and 𝑑𝑖 is the density of tadpoles in habitat 𝑖. The expected number of tadpoles at each habitat was derived from the actual suitability. With no food in the choice tank, movement of the tadpoles in the test arena was random indicating no bias towards any end of the choice tank or the procedure. In tests with a 1 : 1 food ratio, the observed ratio of tadpoles (11.71 : 12.28) was comparable with the expected 12 : 12 ratio. The observed number of tadpoles in the habitats with a 1 : 2 food ratio was 8.71 : 15.29 and 7.87 : 16.13 for pure and mixed parental lines respectively. In both cases, the observed ratios were close to the expected values (7 : 17). Likewise, in experiments with a 1 : 4 food ratio, the observed number of tadpoles in the two habitats (10.78 : 37.22) did not differ significantly from the expected ratio of 7 : 41. In all tests, the number of R. temporalis tadpoles matched ideally with habitat profitability (undermatching index 𝐾 ≅ 1). The study shows that tadpoles of the bronze frog exhibit an ideal free distribution while foraging regardless of whether they are siblings or non-siblings in a group, which correlates well with their group living strategy in nature.
Volume 42 | Issue 4