Thermotaxis in Chlamydomonas is brought about by membrane excitation and controlled by redox conditions

Snow algae exhibit diverse motile behaviors and thermal responses

Snow algal blooms influence snow and glacier melt dynamics, yet the mechanisms involved in community assemblage, development, and dispersal are not well understood. While microbial swimming behavior contributes significantly to the productivity and organization of aquatic and terrestrial microbiomes, the potential impact of algal cell motility in melting snow on the formation of visible, large-scale surface bloom patterns is largely unknown. Here, using video tracking and phototaxis experiments of unique isolates, we evaluated the motility of diverse snow algal taxa from green, red, and golden colored snow blooms in response to light and thermal gradients. We show that many species are efficient cryophilic microswimmers with speed thermal optima below 10°C although taxa with cryotolerant swimming traits were also identified. The significant motility of snow algae at low temperatures, a result of specialized adaptations, supports the importance of active movement in the life histories of algae inhabiting snow meltwater. However, diversity in swimming performance and behavior reveal a range of evolutionary outcomes and sensitivity of motile life stages to dynamic environments.IMPORTANCESwimming motility is a fundamental mechanism that controls the assembly, structure, and productivity of microbiomes across diverse environments and is highly sensitive to temperature. Especially, the role of cell swimming activity in algal bloom formation at the very low temperatures of snowmelt has been hypothesized, but not studied. By examining the movement patterns of snow algae and modeling the thermal response curves of swimming speed, the data reveal the key role of active cell movement that may have further important impacts on the microbial ecology and melt rates of snow and ice in polar and alpine regions.

COP5/HKR1 changes ciliary beat pattern and biases cell steering during chemotaxis in Chlamydomonas reinhardtii

This study investigates the control of ciliary beat patterns during ammonium chemotaxis in the model ciliate microalga Chlamydomonas reinhardtii. Screening the chemotaxis response of mutant strains with ciliary defects revealed that a strain lacking CAV2, the alpha subunit of the voltage-gated calcium channel, is deficient in ammonium chemotaxis. CAV2 regulates the switching of the ciliary beat pattern from the asymmetric to the symmetric waveform. Strains lacking COP5/HKR1 (chlamyopsin 5/histidine kinase rhodopsin 1) are also deficient in ammonium chemotaxis. Conversely, strains defective in phototaxis perform ammonium chemotaxis normally. Cell motility analysis revealed wild-type cells reduce the incidences of switching the ciliary beat pattern from the asymmetric to symmetric waveform when swimming up the ammonium gradient. In contrast, the COP5/HKR1 disrupted strain does not bias ciliary beat pattern switching in the gradient. This finding reveals that COP5/HKR1 plays a critical role in Chlamydomonas chemotaxis signaling transduction, similarly to animal chemotaxis. On the other hand, ciliary beat pattern switching induces randomized directional changes, analogous to run-and-tumble chemotaxis of bacteria and archaea. This study reveals that Chlamydomonas signaling transduction is similar to the eukaryotic mechanism, yet the cellular locomotion follows the bacteria and archaea mechanism.

Temperature-dependent augmentation of ciliary motility by the TRP2 channel in Chlamydomonas reinhardtii

Temperature is a critical factor for living organisms. Many microorganisms migrate toward preferable temperatures, and this behavior is called thermotaxis. In this study, the molecular and physiological bases for thermotaxis are examined in Chlamydomonas reinhardtii. A mutant with knockout of a transient receptor potential (TRP) channel, trp2-3, showed defective thermotaxis. The swimming velocity and ciliary beat frequency of wild-type Chlamydomonas increase with temperature; however, this temperature-dependent enhancement of motility was almost absent in the trp2-3 mutant. Wild-type Chlamydomonas showed negative thermotaxis, but mutants deficient in the outer or inner dynein arm showed positive thermotaxis and a defect in temperature-dependent increase in swimming velocity, suggesting involvement of both dynein arms in thermotaxis.

Effects of season and water quality on community structure of planktonic eukaryotes in the Chaohu Lake Basin

Introduction

Analyzing the correlation between planktonic eukaryotic communities (PECs) and aquatic physicochemical parameters (APPs) provides important references for predicting the impact of climate change and human activities on aquatic ecosystems.

Methods

To assess the influence of seasons and APPs on PEC structures in lakes and rivers, we utilized high-throughput sequencing of the 18S rRNA gene to analyze PEC structures in a lake and seven rivers in the Chaohu Lake Basin and analyzed their correlations with APPs.

Results

Our results revealed that PEC structure was significantly affected by season, with the highest α-diversity observed in summer. Furthermore, we identified several APPs, including water temperature, conductivity, dissolved oxygen, pH, phosphate, total phosphorus, trophic level index (TLI), nitrate, ammonia nitrogen, and total nitrogen, that significantly influenced PEC structures. Specifically, we found that Stephanodiscus hantzschii, Simocephalus serrulatus, Cryptomonas sp. CCAC_0109, Pedospumella encystans, Actinochloris sphaerica, Chlamydomonas angulosa, Gonyostomum semen, Skeletonema potamos, Chlamydomonas klinobasis, Pedospumella sp., and Neochlorosarcina negevensis were significantly correlated to TLI, while Limnoithona tetraspina, Theileria sp., and Pseudophyllomitus vesiculosus were significantly correlated to the water quality index (WQI). However, our random forest regression analysis using the top 100 species was unable to accurately predict the WQI and TLI.

Discussion

These results provide valuable data for evaluating the impact of APPs on PEC and for protecting water resource in the Chaohu Lake Basin.

Thermotaxis in an apolar, non-neuronal animal

Neuronal circuits are hallmarks of complex decision-making processes in the animal world. How animals without neurons process information and respond to environmental cues promises a new window into studying precursors of neuronal control and origin of the nervous system as we know it today. Robust decision making in animals, such as in chemotaxis or thermotaxis, often requires internal symmetry breaking (such as anterior-posterior (AP) axis) provided naturally by a given body plan of an animal. Here we report the discovery of robust thermotaxis behaviour in Trichoplax adhaerens, an early-divergent, enigmatic animal with no anterior-posterior symmetry breaking (apolar) and no known neurons or muscles. We present a quantitative and robust behavioural response assay in Placozoa, which presents an apolar flat geometry. By exposing T. adhaerens to a thermal gradient under a long-term imaging set-up, we observe robust thermotaxis that occurs over timescale of hours, independent of any circadian rhythms. We quantify that T. adhaerens can detect thermal gradients of at least 0.1°C cm-1. Positive thermotaxis is observed for a range of baseline temperatures from 17°C to 22.5°C, and distributions of momentary speeds for both thermotaxis and control conditions are well described by single exponential fits. Interestingly, the organism does not maintain a fixed orientation while performing thermotaxis. Using natural diversity in size of adult organisms (100 µm to a few millimetres), we find no apparent size-dependence in thermotaxis behaviour across an order of magnitude of organism size. Several transient receptor potential (TRP) family homologues have been previously reported to be conserved in metazoans, including in T. adhaerens. We discover naringenin, a known TRPM3 antagonist, inhibits thermotaxis in T. adhaerens. The discovery of robust thermotaxis in T. adhaerens provides a tractable handle to interrogate information processing in a brainless animal. Understanding how divergent marine animals process thermal cues is also critical due to rapid temperature rise in our oceans.

Colloidal Active Matter Mimics the Behavior of Biological Microorganisms-An Overview

This article provides a review of the recent development of biomimicking behaviors in active colloids. While the behavior of biological microswimmers is undoubtedly influenced by physics, it is frequently guided and manipulated by active sensing processes. Understanding the respective influences of the surrounding environment can help to engineering the desired response also in artificial swimmers. More often than not, the achievement of biomimicking behavior requires the understanding of both biological and artificial microswimmers swimming mechanisms and the parameters inducing mechanosensory responses. The comparison of both classes of microswimmers provides with analogies in their dependence on fuels, interaction with boundaries and stimuli induced motion, or taxis.

High-throughput identification of novel heat tolerance genes via genome-wide pooled mutant screens in the model green alga Chlamydomonas reinhardtii

Different high temperatures adversely affect crop and algal yields with various responses in photosynthetic cells. The list of genes required for thermotolerance remains elusive. Additionally, it is unclear how carbon source availability affects heat responses in plants and algae. We utilized the insertional, indexed, genome-saturating mutant library of the unicellular, eukaryotic green alga Chlamydomonas reinhardtii to perform genome-wide, quantitative, pooled screens under moderate (35°C) or acute (40°C) high temperatures with or without organic carbon sources. We identified heat-sensitive mutants based on quantitative growth rates and identified putative heat tolerance genes (HTGs). By triangulating HTGs with heat-induced transcripts or proteins in wildtype cultures and MapMan functional annotations, we presented a high/medium-confidence list of 933 Chlamydomonas genes with putative roles in heat tolerance. Triangulated HTGs include those with known thermotolerance roles and novel genes with little or no functional annotation. About 50% of these high-confidence HTGs in Chlamydomonas have orthologs in green lineage organisms, including crop species. Arabidopsis thaliana mutants deficient in the ortholog of a high-confidence Chlamydomonas HTG were also heat sensitive. This work expands our knowledge of heat responses in photosynthetic cells and provides engineering targets to improve thermotolerance in algae and crops.

Wide-field fluorescent nanodiamond spin measurements toward real-time large-area intracellular thermometry

Measuring optically detected magnetic resonance (ODMR) of diamond nitrogen vacancy centers significantly depends on the photon detectors used. We study camera-based wide-field ODMR measurements to examine the performance in thermometry by comparing the results to those of the confocal-based ODMR detection. We show that the temperature sensitivity of the camera-based measurements can be as high as that of the confocal detection and that possible artifacts of the ODMR shift are produced owing to the complexity of the camera-based measurements. Although measurements from wide-field ODMR of nanodiamonds in living cells can provide temperature precisions consistent with those of confocal detection, the technique requires the integration of rapid ODMR measurement protocols for better precisions. Our results can aid the development of camera-based real-time large-area spin-based thermometry of living cells.

Transgenic Chlamydomonas Expressing Human Transient Receptor Potential Ankyrin 1 (TRPA1) Channels to Assess the Effect of Agonists and Antagonists

Transient receptor potential ankyrin 1 (TRPA1) channel is an ion channel whose gating is controlled by agonists, such as allyl isothiocyanate (AITC), and temperature. Since TRPA1 is associated with various disease symptoms and chemotherapeutic side effects, it is a frequent target of drug development. To facilitate the screening of TRPA1 agonists and antagonists, this study aimed to develop a simple bioassay for TRPA1 activity. To this end, transgenic Chlamydomonas reinhardtii expressing human TRPA1 was constructed. The transformants exhibited positive phototaxis at high temperatures (≥20°C) but negative phototaxis at low temperatures (≤15°C); wild-type cells showed positive phototaxis at all temperatures examined. In the transgenic cells, negative phototaxis was inhibited by TRPA1 antagonists, such as HC030031, A-967079, and AP18, at low temperatures. Negative phototaxis was induced by TRPA1 agonists, such as icilin and AITC, at high temperatures. The effects of these agonists were blocked by TRPA1 antagonists. In wild-type cells, none of these substances had any effects on phototaxis. These results indicate that the action of TRPA1 agonists and antagonists can be readily assessed using the behavior of C. reinhardtii expressing human TRPA1 as an assessment tool.

Structure of the thermo-sensitive TRP channel TRP1 from the alga Chlamydomonas reinhardtii

Algae produce the largest amount of oxygen on earth and are invaluable for human nutrition and biomedicine, as well as for the chemical industry, energy production and agriculture. The mechanisms by which algae can detect and respond to changes in their environments can rely on membrane receptors, including TRP ion channels. Here we present a 3.5-Å resolution cryo-EM structure of the transient receptor potential (TRP) channel crTRP1 from the alga Chlamydomonas reinhardtii that opens in response to increased temperature and is positively regulated by the membrane lipid PIP₂. The structure of crTRP1 significantly deviates from the structures of other TRP channels and has a unique 2-fold symmetrical rose-shape architecture with elbow domains and ankyrin repeat domains submerged and dipping into the membrane, respectively. Our study provides a structure of a TRP channel from a micro-organism and a structural framework for better understanding algae biology and TRP channel evolution.