Bioenergetics and growth in the ctenophore <Emphasis Type="Italic">Pleurobrachia pileus</Emphasis>

Knowledge of how energetic parameters relate to fluctuating factors in the natural habitat is necessary when evaluating the role of gelatinous zooplankton in the carbon flow of coastal waters. In laboratory experiments, we assessed feeding, respiration and growth of the ctenophore, Pleurobrachia pileus, and constructed carbon budgets. Clearance rates (F, l d⁻¹) of laboratory-reared Acartia tonsa as prey increased as a function of ctenophore polar length (L, mm) as F = 0.17L ^1.9. For ctenophores larger than about 11 mm, clearance rate was depressed in containers of 30–50 l volume. Clearance rates on field-collected prey were highest on the copepod, Centropages typicus, intermediate on the cladoceran, Evadne nordmanni and low on the copepods, Acartia clausi and Temora longicornis. Specific growth rates of 8–10 mm P. pileus increased with increasing prey concentrations to a maximum of 0.09 d⁻¹ attained at prey carbon densities of 40 and 100 μg C l⁻¹ of Artemia salina and A. tonsa, respectively. Weight-specific respiration rates increased hyperbolically with prey concentration. From experiments in which growth, ingestion and respiration were measured simultaneously, a carbon budget was constructed for individuals growing at maximum rates; from the measured parameters, the assimilation efficiency and net growth efficiency were estimated to be 22 and 37%, respectively. We conclude that the predation rates of P. pileus depend on ctenophore size, prey species, prey density and experimental container volume. Because the specific growth rates, respiration, assimilation and net growth efficiencies all were affected by food availability, knowledge of the ambient prey field is critical when evaluating the role of P. pileus in the carbon flow in coastal waters.     

Multiple antibiotic susceptibility of polyphosphate kinase mutants (ppk1 and ppk2) from Pseudomonas aeruginosa PAO1 as revealed by global phenotypic analysis

Background

Pseudomonas aeruginosa is known to be a multidrug resistant opportunistic pathogen. Particularly, P. aeruginosa PAO1 polyphosphate kinase mutant (ppk1) is deficient in motility, quorum sensing, biofilm formation and virulence.

Findings

By using Phenotypic Microarrays (PM) we analyzed near 2000 phenotypes of P. aeruginosa PAO1 polyP kinase mutants (ppk1 and ppk2). We found that both ppk mutants shared most of the phenotypic changes and interestingly many of them related to susceptibility toward numerous and different type of antibiotics such as Ciprofloxacin, Chloramphenicol and Rifampicin.

Conclusions

Combining the fact that ppk1 mutants have reduced virulence and are more susceptible to antibiotics, polyP synthesis and particularly PPK1, is a good target for the design of molecules with anti-virulence and anti-persistence properties.

Electronic supplementary material

The online version of this article (doi:10.1186/s40659-015-0012-0) contains supplementary material, which is available to authorized users.     

Updating fearful memories with extinction training during reconsolidation: a human study using auditory aversive stimuli

Learning to fear danger in the environment is essential to survival, but dysregulation of the fear system is at the core of many anxiety disorders. As a consequence, a great interest has emerged in developing strategies for suppressing fear memories in maladaptive cases. Recent research has focused in the process of reconsolidation where memories become labile after being retrieved. In a behavioral manipulation, Schiller et al., (2010) reported that extinction training, administrated during memory reconsolidation, could erase fear responses. The implications of this study are crucial for the possible treatment of anxiety disorders without the administration of drugs. However, attempts to replicate this effect by other groups have been so far unsuccessful. We sought out to reproduce Schiller et al., (2010) findings in a different fear conditioning paradigm based on auditory aversive stimuli instead of electric shock. Following a within-subject design, participants were conditioned to two different sounds and skin conductance response (SCR) was recorded as a measure of fear. Our results demonstrated that only the conditioned stimulus that was reminded 10 minutes before extinction training did not reinstate a fear response after a reminder trial consisting of the presentation of the unconditioned stimuli. For the first time, we replicated Schiller et al., (2010) behavioral manipulation and extended it to an auditory fear conditioning paradigm.     

Increased urinary glucocorticoid metabolites are associated with metabolic syndrome, hypoadiponectinemia, insulin resistance and β cell dysfunction

Metabolic syndrome (MetS) may have increased cortisol (F) production caused by 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) in liver and adipose tissue and/or by HPA axis dysregulation. F is then mainly metabolized by liver reductases into inactive tetrahydrometabolites (THMs). We measured THM levels in patients with or without MetS and evaluate the correlation between THMs and anthropometric and biochemical parameters. We recruited 221 subjects, of whom 130 had MetS by ATP III. We evaluated F, cortisone (E), adipokines, glucose, insulin and lipid profiles as well as urinary (24 h) F, E and THM levels. β Cell function was estimated by the HOMA Calculator. We observed that patients with MetS showed higher levels of THMs, HOMA-IR and leptin and lower levels of adiponectin and HOMA-β but no differences in F and E in plasma or urine. THM was associated with weight (r = +0.44, p < 0.001), waist circumference (r = +0.38, p < 0.01), glycemia (r = +0.37, p < 0.01), and triglycerides (r = +0.18, p = 0.06) and negatively correlated with adiponectin (r = −0.36, p < 0.001), HOMA-β (r = −0.21, p < 0.001) and HDL (r = −0.29, p < 0.01). In a logistic regression model, THM levels were associated with hypertension, hyperglycemia and dyslipidemia. We conclude that MetS is associated with increased urinary THMs but not with F and E levels in plasma or urine. Increased levels of THM, reflecting the daily cortisol production subsequently metabolized, are correlated with hypoadiponectinemia, hypertension, dyslipidemia, insulin resistance and β cell dysfunction. A subtle increased in glucocorticoid production may further account for the phenotypic and biochemical similarities observed in central obesity and Cushing’s syndrome.     

Microencapsulation by spray drying of nitrogen-fixing bacteria associated with lupin nodules

Plant growth promoting bacteria and nitrogen-fixing bacteria (NFB) used for crop inoculation have important biotechnological potential as a sustainable fertilization tool. However, the main limitation of this technology is the low inoculum survival rate under field conditions. Microencapsulation of bacterial cells in polymer matrices provides a controlled release and greater protection against environmental conditions. In this context, the aim of this study was to isolate and characterize putative NFB associated with lupin nodules and to evaluate their microencapsulation by spray drying. For this purpose, 21 putative NFB were isolated from lupin nodules and characterized (16S rRNA genes). Microencapsulation of bacterial cells by spray drying was studied using a mixture of sodium alginate:maltodextrin at different ratios (0:15, 1:14, 2:13) and concentrations (15 and 30 % solids) as the wall material. The microcapsules were observed under scanning electron microscopy to verify their suitable morphology. Results showed the association between lupin nodules of diverse known NFB and nodule-forming bacteria belonging to Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Bacteroidetes. In microencapsulation assays, the 1:14 ratio of sodium alginate:maltodextrin (15 % solids) showed the highest cell survival rate (79 %), with a microcapsule yield of 27 % and spherical microcapsules of 5–50 µm in diameter. In conclusion, diverse putative NFB genera and nodule-forming bacteria are associated with the nodules of lupine plants grown in soils in southern Chile, and their microencapsulation by spray drying using sodium alginate:maltodextrin represents a scalable process to generate a biofertilizer as an alternative to traditional nitrogen fertilization.     

Diversity of cultivable fungi associated with Antarctic marine sponges and screening for their antimicrobial, antitumoral and antioxidant potential

The diversity of sponge-associated fungi has been poorly investigated in remote geographical areas like Antarctica. In this study, 101 phenotypically different fungal isolates were obtained from 11 sponge samples collected in King George Island, Antarctica. The analysis of ITS sequences revealed that they belong to the phylum Ascomycota. Sixty-five isolates belong to the genera Geomyces, Penicillium, Epicoccum, Pseudeurotium, Thelebolus, Cladosporium, Aspergillus, Aureobasidium, Phoma, and Trichocladium but 36 isolates could not be identified at genus level. In order to estimate the potential of these isolates as producers of interesting bioactivities, antimicrobial, antitumoral and antioxidant activities of fungal culture extracts were assayed. Around 51 % of the extracts, mainly from the genus Geomyces and non identified relatives, showed antimicrobial activity against some of the bacteria tested. On the other hand, around 42 % of the extracts showed potent antitumoral activity, Geomyces sp. having the best performance. Finally, the potential of the isolated fungi as producers of antioxidant activity seems to be moderate. Our results suggest that fungi associated with Antarctic sponges, particularly Geomyces, would be valuable sources of antimicrobial and antitumoral compounds. To our knowledge, this is the first report describing the biodiversity and the metabolic potential of fungi associated with Antarctic marine sponges.     

Der Vogelzug

Ohne Zusammenfassung     

Paraheliotropism can protect water-stressed bean (Phaseolus vulgaris L.) plants against photoinhibition

In order to estimate the importance of leaf movements on photosynthesis in well-watered and water-stressed field grown bean cultivars (Arroz Tuscola (AT), Orfeo INIA (OI), Bayos Titan (BT), and Hallados Dorado (HD)), CO2 assimilation, leaf temperature, and capacity for the maximum quantum yield recovery, measured as Fv/Fm, were assessed. Leaf water potential was lower in water-stressed compared to control plants throughout the day. Water status determined a decrease in the CO2 assimilation and stomatal conductance as light intensity and temperature increased up to maximal intensities at midday. Both parameters were lower in stressed compared to control plants. Even though high light intensity and water-stress induced stomatal closure is regarded as a photoinhibitory condition, the recovery of variable to maximal fluorescence (Fv/Fm) after 30min of darkness was nearly constant in both water regimes. In fact, higher values were observed in OI and AT when under stress. Photochemical and non-photochemical fluorescence quenching resulted in minor changes during the day and were similar between watered and stressed plants. It is concluded that paraheliotropism, present in the four bean cultivars, efficiently protects stressed plants from photoinhibition in the field and helps maintain leaf temperatures far below the ambient temperatures, however, it may also be responsible for low CO2 assimilation rates in watered plants.     

Restricted responsiveness to noise interference in two anurans from the southern temperate forest

Animals adopt different strategies to communicate by means of sound in noisy environments such that some species increase, while others decrease their vocal activity in the presence of interference. Anuran amphibians from diverse latitudes exhibit both kinds of responses. Recent studies have shown that males of Batrachyla taeniata and Batrachyla antartandica from the temperate austral forest do not call in response to the presentation of advertisement calls of sympatric congeneric species. In contrast, Batrachyla leptopus responds to these signals in a similar way as to conspecific calls. The responsiveness of B. taeniata to natural abiotic interference has also been tested and found that noises of such sources produce strong increases in vocal activity. To assess the diversity in responsiveness to acoustic intrusion in this group, we exposed males of B. leptopus and B. antartandica to prolonged pre‐recorded natural abiotic noises of wind, creek, rain, and to a band‐pass noise centered at 2,000 Hz, at 67 dB Sound Pressure Level (SPL). The subjects did not increase their vocal activity significantly when exposed to these sounds and to band‐pass noise at increasing intensities (55–79 dB SPL). These results contrast with the increase in vocal activity observed previously in B. taeniata to continuous abiotic noise and point to the existence of diverse strategies to confront acoustic intrusion among related species. The lack of vocal activation observed also contrasts with the responsiveness of B. leptopus to heterospecific signals, but parallels the lack of response to such sounds in B. antartandica. Furthermore, the results obtained contrast with the responsiveness of these species to synthetic prolonged sounds observed in previous studies, suggesting that the modes of responses to acoustic intrusion may depend on previous experience, rather than having a species‐specific nature.