New insights into survival strategies of tardigrades Møbjerg, Nadja; Neves, Ricardo Cardoso
Comparative biochemistry and physiology. Part A, Molecular & integrative physiology,
April 2021, 2021-Apr, 2021-04-00, Volume:
254
Journal Article
Peer reviewed
Open access
Life is set within a narrow frame of physicochemical factors, yet, some species have adapted to conditions far beyond these constraints. Nature appears to have evolved two principal strategies for ...living organisms to cope with hostile conditions. One way is to remain active, retaining metabolism through adaptations that enable the organism to match the physiological requirements of environmental change. The other is to enter a state of dormancy with metabolic suppression. One form of metabolic suppression, known as cryptobiosis, is a widespread state across life kingdoms, in which metabolism comes to a reversible standstill. Among animals, nematodes, rotifers and tardigrades, comprise species that have the ability to enter cryptobiosis at all stages of their life cycle. Tardigrades are microscopic cosmopolitan metazoans found in permanent and temporal aquatic environments. They are renowned for their ability to tolerate extreme stress and are particularly resistant after having entered a cryptobiotic state known as a “tun”. As new molecular tools allow for a more detailed investigation into their enigmatic adaptations, tardigrades are gaining increasing attention. In this graphical review, we provide an outline of survival strategies found among tardigrades and we summarize current knowledge of the adaptive mechanisms that underlie their unique tolerance to extreme or changing environments
Abstract
To thrive in harsh environments, tardigrades have evolved the ability to enter the quiescent state of cryptobiosis, often characterized by transition into a so-called ‘tun’. Here, we ...investigate osmobiosis, a substate of cryptobiosis induced by rising osmolyte concentrations. We follow the behaviour and morphology of Ramazzottius varieornatus during transfer from freshwater conditions into 3 Osmol/kg sucrose solution. The tardigrades easily survive the extreme change in external osmolality. During gradual exposure, they initiate tun formation at 0.2 Osmol/kg, with most specimens fully contracted into a tun at 0.5 Osmol/kg. The first transcriptomic profiling of osmobiotic tuns in comparison to active tardigrades reveals a modest shift, with 16% of the 3322 differentially expressed transcripts having a |log2 fold change| > 1. A gene ontology enrichment analysis shows enrichment within protein homeostasis and neurohormonal signalling, with a ubiquitin-conjugating enzyme and neurotransmitter receptor transcripts being down- and upregulated, respectively. A putative Hsp70 is upregulated, whereas transcripts related to eutardigrade-specific proteins, antioxidant defence and DNA repair show minor fold changes. Among putative membrane transporters, a monocarboxylate and two amino acid transporters are downregulated. Our findings are in agreement with previous studies in Ramazzottius indicating that cryptobiosis and tun formation involve no change or modest change in transcription.
Tardigrades are renowned for their ability to enter the extremotolerant state of latent life known as cryptobiosis. While it is widely accepted that cryptobiosis can be induced by freezing ...(cryobiosis) and by desiccation (anhydrobiosis), the latter involving formation of a so-called tun, the exact mechanisms underlying the state—as well as the significance of other cryptobiosis inducing factors—remain ambiguous. Here, we focus on osmotic and chemical stress tolerance in the marine tidal tardigrade
Echiniscoides sigismundi
. We show that
E. sigismundi
enters the tun state following exposure to saturated seawater and upon exposure to locality seawater containing the mitochondrial uncoupler DNP. The latter experiments provide evidence of osmobiosis and chemobiosis, i.e., cryptobiosis induced by high levels of osmolytes and toxicants, respectively. A small decrease in survival was observed following simultaneous exposure to DNP and saturated seawater indicating that the tardigrades may not be entirely ametabolic while in the osmobiotic tun. The tardigrades easily handle exposure to ultrapure water, but hypo-osmotic shock impairs tun formation and when exposed to ultrapure water the tardigrades do not tolerate DNP, indicating that tolerance towards dilute solutions involves energy-consuming processes. We discuss our data in relation to earlier and more contemporary studies on cryptobiosis and we argue that osmobiosis should be defined as a state of cryptobiosis induced by high external osmotic pressure. Our investigation supports the hypothesis that the mechanisms underlying osmobiosis and anhydrobiosis are overlapping and that osmobiosis likely represents the evolutionary forerunner of cryptobiosis forms that involve body water deprivation.
During lautering, a filtration process in beer production, an inhomogeneous filter cake composed of different horizontal layers is formed. Fine particles settle slower than coarse particles and form ...a layer on top of the cake. Due to its low permeability, the fine layer acts as a stamp on the compressible bottom layer, thus resulting in cake compression and reduced flow rate (stamp effect). A method to prove the stamp effect and investigate its impact on the filtration was developed. The structure of the cake was preserved by freezing, which enabled sampling from different layers at different filtration times. An optical porosity determination (surface roughness) was established to study the compression. A predominant impact of the stamp effect compared with a less pronounced skin effect was shown. To avoid the stamp effect during filtration, a filtration technique was developed, which includes the removal of fines from the filter cake.
•Fine particles form a layer on top of the cake during filtration in the lauter tun.•Optical measurement of the cake porosity via the surface roughness was established.•The top layer acts as a stamp (stamp effect) and compresses the bottom layer.•A filtration technique to remove the fine particles before filtration was developed.
When NB-IoT is used to monitor UAVs, developers need to access a UAV via SSH (Secure Shell). However, NB-IoT services are sometimes behind symmetric NAT, and NB-IoT modules can only be controlled by ...specific AT commands, rendering existing NAT traversal software not applicable. This letter proposes NB-SSH, which provides remote SSH service to UAVs that are behind symmetric NAT. NB-SSH has two variants, in one of which the client side does not need to install any software, and in the other the UAV appears to the client as a neighbor. We implement both variants and evaluate them in a real-world environment.
The book explores the world of Chinese manuscripts from ninth-tenth century Dunhuang, an oasis city along the Silk Roads. It centres around four groups of manuscripts and argues for the existence of ...a unique local culture combining Chinese and Central Asian elements. The book makes a contribution to the study of cultural and linguistic interaction along the Silk Roads at the end of the first millennium CE.
The novel TUN-type aluminoborosilicate zeolite (denoted as Al, B-TUN), which consists of a three-dimensional pore system with 10-ring, has been hydrothermally synthesized for the first time and ...implied in cracking reaction. The mother gel composition including aluminum, boron, organic structure-directing agent and sodium were intensively studied and optimized. We found for the first time that the incorporation of B together with Al T-sites into the TUN framework led to the control of acidic properties including the number, strength and distribution of acid sites. The n-hexane cracking over different catalysts show that the Al, B-TUN zeolites have a longer catalyst duration and a higher P/E ratio (propylene/ethylene selectivity) than Al-TUN. Moreover, the comparison between TUN, MFI and *BEA-type zeolites indicates that TUN-type zeolite has a preference for propylene production. The relationship between acidic properties and carking behaviors were discussed and supported by the constraint index (CI) value measurement.
Display omitted
•The TUN-type aluminoborosilicate zeolites (Al, B-TUN) were successfully synthesized and the acidic properties have been modified by B incorporation.•The effect of B incorporation on the catalytic performance of Al, B-TUN were studied and compared with ZSM-5 and Beta in n-hexane cracking.•Constrain index (CI) measurements were performed to clarify the different distributions and steric constraints effect of the acid sites.
Researches on high coherence light sources always pursue fast tuning speed, linear tunability and persistence of narrow linewidths at different tuning channels. Fortunately, acousto-optical ...interaction (AOI) can be employed in the fast management of the lasing wavelength. Herein, we propose a fast tunable narrow-linewidth fiber laser assisted by the acoustically-induced polarization selection in dispersion compensation fiber (DCF). The lasing wavelength is determined by the acoustically-induced band-pass grating in DCF. The large dispersion slope of the DCF suppresses the bandwidth of the TM 01 peak to be less than 1 nm. The acousto-optic-controlled polarization conversion effectively restrains the acousto-optic frequency shift. With side longitudinal mode suppressions induced by the combintion of the self-injection feedback and saturable absorption filtering, the output laser successfully achieves the narrow-linewdith operation and owns a low relative intensity noise floor of −135 dB/Hz. By controlling the acoustic-wave frequency, the laser can be linearly tuned with a large wavelength range (over 20 nm, linear fitting R 2 reaches 0.99781), and the laser linewidths remain about ∼2 kHz in different tuning channels. The laser tuning dynamics under the acousto-optical controlling are experimentally revealed, and the lasing tuning response time is ∼800 μs.
PDF
