10Whether or not the micro swimmer Caenorhabditis elegans senses and respond to gravity is 11 unknown. We find that C. elegans aligns its swimming direction with that of the gravity vector 12 (positive gravitaxis). When placed in an aqueous solution that is denser than the animals, they 13 still orient downwards, indicating that non-uniform mass distribution and/or hydrodynamic 14 effects are not responsible for animal's downward orientation. Paralyzed worms and worms 15 with globally disrupted sensory cilia do not change orientation as they settle in solution, 16indicating that gravitaxis is an active behavior that requires gravisensation. Other types of 17 sensory driven orientation behaviors cannot explain our observed downward orientation. Like 18 other neural behaviors, the ability to respond to gravity declines with age. Our study establishes 19 gravitaxis in the micro swimmer C. elegans and suggests that C. elegans can be used as a 20genetically tractable system to study molecular and neural mechanisms of gravity sensing and 21 orientation. 22 23 24 2 Significance Statement 25Understanding how animals respond to gravity is not only of fundamental scientific interest, 26 but has clinical relevance, given the prevalence of postural instability in aged individuals. 27Determining whether C. elegans responds to gravity is important for mechanistic studies of 28 gravity sensing in an experimentally tractable animal, for a better understanding of nematode 29 ecology and evolution, and for studying biological effects of microgravity. Our experiments, 30which indicate that C. elegans senses and responds to gravity, set the stage for mechanistic 31 studies on molecular mechanisms of gravity sensing. 32When ≥ 1 and ≥ 3, over 73% and 95% of the animals are oriented, respectively, at a polar 131 angle > 90 o . We compute the concentration parameter for our data by fitting the cumulative 132 distribution function (cdf) associated with equation 2 (SI-section S4) to the experimental one. 133When the animal is at depth d = 4 mm beneath the surface ~ 0.2 (nearly uniform distribution). 134As the animal's depth increases (the animal has more time to align with the direction of gravity), 135 the skewness of the KDE and the magnitude of increase as well For the well-fed WT animals 136 increases at the approximate rate of 0.07 per mm of depth until it asymptotes to ~ 4.3 at ~60 137 mm, and approximately retains this value at depths exceeding 60 mm. KDEs at depths 120 mm 138 < d < 200 mm nearly overlap (SI -Section S5). The inset in Fig. 3 depicts the concentration 139 parameter as a function of the animal's depth (d, mm) beneath the liquid surface. The data is funded by the Ministry of Education of Taiwan, Global Networking Talent 3.0 Plan (GNT3.0),
Rapid and sensitive detection of infectious bacteria is in all-time high demand to prevent the further spread of the infection and allow early medical intervention. In this study, we use rotational diffusometry (RD), a natural phenomenon characterized by Janus particles, to detect pathogens like Escherichia coli by performing amplification of specific genes. This biosensing method is used to measure the change in viscosity of the fluid in the presence and absence of DNA in the solution by capturing images of modified microbeads at 10 Hz by a CCD camera followed by cross-correlation algorithm analysis. Using rotational diffusometry, we have achieved E. coli detection with 50 pg/μL DNA with a measurement time of 30 s and a sample volume of 2 μL. This sensitivity was achieved with 30 thermal cycles for three different amplicons, viz., 84, 147, and 246 bp. Meanwhile, in the case of 10 and 20 thermal cycles, the detection sensitivity was achieved with 0.1 and 1 ng/μL DNA concentrations for a 246 bp amplicon. Compared with conventional PCR, this technique appears to improve the detection time, thereby reaching a turnaround time of less than 60 min. Other studies showed a successful identification of DNA amplification up to 10 thermal cycles with different sizes of amplicons. The effect of DNA concentration, amplicon size, and the number of thermal cycles on the detection of E. coli was examined in detail and represented in the form of three maps. These maps show the clear difference and the advantages of RD method in comparison with conventional PCR. This unconventional and rapid biosensing method can be used further for downstream application of nucleic acid amplification-based pathogen detection and early disease control.
Background Gravity plays an important role in most life forms on Earth. Yet, a complete molecular understanding of sensing and responding to gravity is lacking. While there are anatomical differences among animals, there is a remarkable conservation across phylogeny at the molecular level. Caenorhabditis elegans is suitable for gene discovery approaches that may help identify molecular mechanisms of gravity sensing. It is unknown whether C. elegans can sense the direction of gravity. Results In aqueous solutions, motile C. elegans nematodes align their swimming direction with the gravity vector direction while immobile worms do not. The worms orient downward regardless of whether they are suspended in a solution less dense (downward sedimentation) or denser (upward sedimentation) than themselves. Gravitaxis is minimally affected by the animals’ gait but requires sensory cilia and dopamine neurotransmission, as well as motility; it does not require genes that function in the body touch response. Conclusions Gravitaxis is not mediated by passive forces such as non-uniform mass distribution or hydrodynamic effects. Rather, it is mediated by active neural processes that involve sensory cilia and dopamine. C. elegans provides a genetically tractable system to study molecular and neural mechanisms of gravity sensing.
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