Freezing and thawing in Antarctica: characterization of antifreeze protein (AFP) producing microorganisms isolated from King George Island, Antarctica

Antarctic temperature variations and long periods of freezing shaped the evolution of microorganisms with unique survival mechanisms. These resilient organisms exhibit several adaptations for life in extreme cold. In such ecosystems, microorganisms endure the absence of liquid water and exhibit resistance to freezing by producing water-binding molecules such as antifreeze proteins (AFP). AFPs modify the ice structure, lower the freezing point, and inhibit recrystallization. The objective of this study was to select and identify microorganisms isolated from different Antarctic ecosystems based on their resistance to temperatures below 0 °C. Furthermore, the study sought to characterize these microorganisms regarding their potential antifreeze adaptive mechanisms. Samples of soil, moss, permafrost, and marine sediment were collected on King George Island, located in the South Shetland archipelago, Antarctica. Bacteria and yeasts were isolated and subjected to freezing-resistance and ice recrystallization inhibition (IR) tests. A total of 215 microorganisms were isolated, out of which 118 were molecularly identified through molecular analysis using the 16S rRNA and ITS regions. Furthermore, our study identified 24 freezing-resistant isolates, including two yeasts and 22 bacteria. A total of 131 protein extracts were subjected to the IR test, revealing 14 isolates positive for AFP production. Finally, four isolates showed both freeze-resistance and IR activity (Arthrobacter sp. BGS04, Pseudomonas sp. BGS05, Cryobacterium sp. P64, and Acinetobacter sp. M1_25C). This study emphasizes the diversity of Antarctic microorganisms with the ability to tolerate freezing conditions. These microorganisms warrant further investigation to conduct a comprehensive analysis of their antifreeze capabilities, with the goal of exploring their potential for future biotechnological applications.

Establishment and cryptic transmission of Zika virus in Brazil and the Americas

Transmission of Zika virus (ZIKV) in the Americas was first confirmed in May 2015 in northeast Brazil. Brazil has had the highest number of reported ZIKV cases worldwide (more than 200,000 by 24 December 2016) and the most cases associated with microcephaly and other birth defects (2,366 confirmed by 31 December 2016). Since the initial detection of ZIKV in Brazil, more than 45 countries in the Americas have reported local ZIKV transmission, with 24 of these reporting severe ZIKV-associated disease. However, the origin and epidemic history of ZIKV in Brazil and the Americas remain poorly understood, despite the value of this information for interpreting observed trends in reported microcephaly. Here we address this issue by generating 54 complete or partial ZIKV genomes, mostly from Brazil, and reporting data generated by a mobile genomics laboratory that travelled across northeast Brazil in 2016. One sequence represents the earliest confirmed ZIKV infection in Brazil. Analyses of viral genomes with ecological and epidemiological data yield an estimate that ZIKV was present in northeast Brazil by February 2014 and is likely to have disseminated from there, nationally and internationally, before the first detection of ZIKV in the Americas. Estimated dates for the international spread of ZIKV from Brazil indicate the duration of pre-detection cryptic transmission in recipient regions. The role of northeast Brazil in the establishment of ZIKV in the Americas is further supported by geographic analysis of ZIKV transmission potential and by estimates of the basic reproduction number of the virus.

Investigation of complexity of the instruction manuals for electrical coffeepots

BACKGROUND

Electrical coffeepots are commonly used in professional and residential environments. Their instruction manuals are related to issues that involve the user's safety and ability to operate the machine correctly. To provide the best product performance to the user, one must indicate or inform the correct usability, to turn the interaction easier.

OBJECTIVE

This research proposes to investigate the instruction manuals of the electrical coffeepots.

METHODS

Four coffee pot instruction manuals were analyzed in relation to the complexity through the heuristic evaluation. For that, eight experts of the Graphic Design were chosen to answer twenty four questions with the aim of analyzing: images; texts; layout development; information and warnings.

RESULTS

This study shows the results of the 04 (four) items analyzed: a) images; b) texts; c) layout development; d) information and warnings, together with the suggestions of improvements for each manual.

CONCLUSIONS

It is believed that the methodological procedures for the application of the heuristic evaluation have facilitated the diagnosis of fragilities and barriers that the users find during the interaction with electrical coffeepot manuals.

Tensile strength of human dentin as a function of tubule orientation and density

PURPOSE

This study investigated the ultimate tensile strength (UTS) of human dentin as a function of tubule orientation and density.

MATERIALS AND METHODS

Slabs of dentin (ca 0.7 mm thick) were obtained from human third molars by either transversally or longitudinally sectioning the crowns with an Isomet saw. The slabs were gently trimmed to reduce the central area of the coronal dentin to a cross-sectional area of approximately 0.5 mm2. The longitudinally sectioned slabs were either trimmed from the mesial and distal sides or from the occlusal and pulpal aspects to permit the tensile load to be applied either parallel or perpendicular to the tubule orientation. The transversally sectioned specimens were obtained at several distances from the pulp and were used to evaluate the effects of tubule density. The trimmed specimens were tested in tension on a Kratos testing machine at 0.5 mm/min. After failure, the UTS of each was calculated and expressed in MPa. The fractured ends of the transversally sectioned specimens were viewed under SEM to calculate the number of tubules per mm2 at the site of fracture, and its relation with the UTS was investigated by regression analysis.

RESULTS

The UTS of dentin is higher when the load is applied perpendicular to the tubule orientation (80 +/- 13 MPa) than when applied parallel to tubule orientation (58 +/- 11 MPa, p < 0.05). There was a tendency for dentin to be weaker as the number of tubules at the site of fracture increased, although this relationship was not statistically significant (R2 = 0.051, p > 0.05).

CONCLUSION

The UTS of dentin is dependent on the tubule direction. Dentin tends to be weaker as the number of tubules per area increases.

The microtensile bond test: a review

PURPOSE

The purpose of this review is to describe all of the various modifications of the microtensile bond test in one paper, so that investigators can select the modification that best suits their needs.

METHODS

The essence of the microtensile test is the division of resin-bonded teeth into slabs between 0.5 and 1.0 mm thick that are then trimmed in such a manner that tensile force will be concentrated on the bonded interface during testing. Among the many advantages of the technique are that each tooth produces multiple specimens. Further, there is no need for a matrix to limit the bonded surface area, since the area is determined by the dimensions of the trimmed specimens.

RESULTS

The various modifications of the microtensile test have been used to measure differences in regional bond strength across occlusal dentin, down the external surface of teeth from crown through roots, down the internal surface of root canals from cervical to apical thirds, as well as to compare normal vs caries-affected occlusal dentin and normal vs sclerotic cervical dentin. The technique is ideal for evaluating the long-term durability of resin-hard-tissue bonds.

CONCLUSION

The microtensile test methods offer versatility that cannot be achieved by conventional methods. It is more labor-intensive than conventional testing, but holds great potential for providing insight into the strength of adhesion of restorative materials to clinically relevant sites and substrates.

Effects of prism orientation on tensile strength of enamel

PURPOSE

This study tested the hypothesis that the tensile strength of enamel varies according to prismatic orientation.

MATERIALS AND METHODS

Eight extracted, caries-free human third molars were thoroughly cleaned with pumice and water. The entire enamel surface was conditioned with 37% phosphoric acid for 30 s, air dried, and bonded with Single Bond adhesive system. Several layers of composite (Z-100) were incrementally applied to the crown to build up a "cube-like" resin structure approximately 5 mm thick covering the entire crown of the teeth. The teeth were stored for 24 h in water at 37 degrees C, and then the crown was serially, vertically sectioned in a mesio-distal direction to obtain several slices approximately 0.7 mm thick. The slices were sectioned into halves, and each half was gently trimmed from both sides with a diamond bur to reduce the cross-sectional area to a "neck" located in enamel, either on the external slope or functional slope of the cusps. The specimens were trimmed to permit testing of enamel with its prisms either oriented parallel (PL) or perpendicular (PD) to the applied load. The trimmed specimens were glued to the fixtures of a Vitrodyne tester and stressed in tension at 0.5 mm/min. SEM images were taken from the fractured surfaces to examine the site of failure and confirm the prism orientation.

RESULTS

Mean tensile strength of enamel was 24.7 +/- 9.6 MPa (n = 22) for PL and 11.4 +/- 6.3 MPa (n = 22) for PD oriented enamel prisms (t value = -5.45, p < 0.05). There was no significant difference between specimens originating from different slopes of the cusps (p > 0.05).

CONCLUSION

The results showed that tensile strength of enamel is dependent on the prismatic orientation.