Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots

Microorganisms move in challenging environments by periodic changes in body shape. In contrast, current artificial microrobots cannot actively deform, exhibiting at best passive bending under external fields. Here, by taking advantage of the wireless, scalable and spatiotemporally selective capabilities that light allows, we show that soft microrobots consisting of photoactive liquid-crystal elastomers can be driven by structured monochromatic light to perform sophisticated biomimetic motions. We realize continuum yet selectively addressable artificial microswimmers that generate travelling-wave motions to self-propel without external forces or torques, as well as microrobots capable of versatile locomotion behaviours on demand. Both theoretical predictions and experimental results confirm that multiple gaits, mimicking either symplectic or antiplectic metachrony of ciliate protozoa, can be achieved with single microswimmers. The principle of using structured light can be extended to other applications that require microscale actuation with sophisticated spatiotemporal coordination for advanced microrobotic technologies.

PROBIOTICS: GROWTH-PROMOTING FACTORS PRODUCED BY MICROORGANISMS

Several species of protozoa, during their logarithmic phases of growth, produce substances that prolong the logarithmic phase in other species. The effect is not as striking as the inhibition of growth caused by antibiotics, but a consistent 50-percent increase in growth has been obtained with Tetrahymena pyriformis in response to a factor produced by Colpidium campylum.

Macronuclear duplication in the ciliated protozoan Euplotes

The ribbon-like macronucleus of Euplotes eurystomus pinches in half amitotically at each cell division. Several hours before the actual division two lightly staining duplication bands (reorganization bands) appear at the ends of the nucleus and approach each other slowly, finally meeting near the middle. Distal to the bands, that is, in regions through which the bands have already passed, the concentration of DNA (Feulgen) and "histone" (alkaline fast green) is greater than in the central zone. These facts suggest the hypothesis that DNA-histone synthesis takes place in a sequential fashion starting at the tips of the nucleus and proceeding to the middle. That this hypothesis is correct is shown by autoradiographic and photometric observations. Tritium-labelled thymidine is incorporated only in a limited region immediately distal to the bands. The average amount of Feulgen dye bound by the nucleus rises as the duplication bands approach each other, and is double the presynthesis value by the time the bands meet. A similar rise in the alkaline fast green dye is seen in duplicating nuclei, although no completely post-synthesis values were obtained in this study. The quantitative data are consistent with the assumption that the macronucleus contains a number of DNA-histone "units," presumably chromosomes, each of which duplicates once and only once.

Fine structure and function in Stentor polymorphous

The fine structure of the ciliate Stentor has been studied by means of the electron microscope and the results have been correlated with observations made on the living organism by means of light microscopy; special reference has been made to structural features which may be responsible for contraction and extension in Stentor. Descriptions have been given of the structure of the macronucleus, the vacuolated cytoplasm, mitochondria and the pellicle; a detailed study has also been made of the adoral membranelles. About 250 membranelles encircle the peristomal cap and each is composed of 3 rows of cilia, with 20 to 25 cilia in each row; a fibrillar root system connected with the membranelles depends into the endoplasm for about 20 micro and each is essentially in the shape of a fan, the terminal ends of each root bifurcating to connect to neighbouring roots. The membranelles thus form a cohesive unit and this morphological arrangement may have a bearing on the motion and coordination of the whole system. Two structural features extending throughout the length of the animal have been identified per cortical stripe in the body wall of Stentor; first, km fibres lying just beneath the pellicle are composed of stacks of fibrillar sheets and are identical with the birefringent fibres observed in the living animal. The individual fibrils of the sheets are in turn connected to the kinetosomes of the body cilia; thus the km fibres are homologous to kinetodesmata. Secondly, M bands lie beneath the km fibres and form an interconnected system in contact with the surrounding vacuolated cytoplasm; the thickness of the M bands is greatest at the base of a contracted animal. The contractile and extensile properties of these organelles have been discussed in the light of experimental results and theoretical considerations.

The fine structure of cortical components of Paramecium multimicronucleatum

The electron microscope was used to study the structure and three dimensional relationships of the components of the body cortex in thin sections of Paramecium multimicronucleatum. Micrographs of sections show that the cortex is covered externally by two closely apposed membranes (together approximately 250 A thick) constituting the pellicle. Beneath the pellicle the surface of the animal is molded into ridges that form a polygonal ridgework with depressed centers. It is these ridges that give the surface of the organism its characteristic configuration and correspond to the outer fibrillar system of the light microscope image. The outer ends of the trichocysts with their hood-shaped caps are located in the centers of the anterior and posterior ridges of each polygon. The cilia extend singly from the depressed centers of the surface polygons. Each cilium shows two axial filaments with 9 peripheral and parallel filaments embedded in a matrix and the whole surrouned by a thin ciliary membrane. The 9 peripheral filaments are double and these are evenly spaced in a circle around the central pair. The ciliary membrane is continuous with the outer member of the pellicular membrane, whereas the plasma membrane is continuous with the inner member of the pellicular membrane. At the level of the plasma membrane the proximal end of the cilium is continuous with its tube-shaped basal body or kinetosome. The peripheral filaments of the cilium, together with the material of cortical matrix which tends to condense around them, form the sheath of the basal body. The kinetodesma connecting the ciliary kinetosomes (inner fibrillar system of the light microscopist) is composed of a number of discrete fibrils which overlap in a shingle-like fashion. Each striated kinetosomal fibril originates from a ciliary kinetosome and runs parallel to other kinetosomal fibrils arising from posterior kinetosomes of a particular meridional array. Sections at the level of the ciliary kinetosomes reveal an additional fiber system, the infraciliary lattice system, which is separate and distinct from the kinetodesmal system. This system consists of a fibrous network of irregular polygons and runs roughly parallel to the surface of the animal. Mitochondria have a fine structure similar in general features to that described for a number of mammalian cell types, but different in certain details. The structures corresponding to cristae mitochondriales appear as finger-like projections or microvilli extending into the matrix of the organelle from the inner membrane of the paired mitochondrial membrane. The cortical cytoplasm contains also a particulate component and a system of vesicles respectively comparable to the nucleoprotein particles and to the endoplasmic reticulum described in various metazoan cell types. An accessory kinetosome has been observed in oblique sections of a number of non-dividing specimens slightly removed from the ciliary kinetosome and on the same meridional line as the cilia and trichocysts. Its position corresponds to the location of the kinetosome of the newly formed cilium in animals selected as being in the approaching fission stage of the life cycle.

Telomerase recruitment by the telomere end binding protein-beta facilitates G-quadruplex DNA unfolding in ciliates

The telomeric G-overhangs of the ciliate Stylonychia lemnae fold into a G-quadruplex DNA structure in vivo. Telomeric G-quadruplex formation requires the presence of two telomere end binding proteins, TEBPalpha and TEBPbeta, and is regulated in a cell-cycle dependent manner. Unfolding of this structure in S phase is dependent on the phosphorylation of TEBPbeta. Here we show that TEBPbeta phosphorylation is necessary but not sufficient for a G-quadruplex unfolding rate compatible with telomere synthesis. The telomerase seems to be actively involved in telomeric G-quadruplex DNA structure unfolding in vivo. Significantly, the telomerase is recruited to telomeres by phosphorylated TEBPbeta, and hence telomerase recruitment is cell-cycle regulated through phosphorylation. These observations allow us to propose a model for the regulation of G-quadruplex unfolding and telomere synthesis during the cell cycle.

Microplastic and soil protists: A call for research

Microplastic is an emerging contaminant of concern in soils globally, probably gradually increasing in soil due to slow degradation. Few studies on microplastic effects on soil biota are available, and no study in a microplastic contamination context has specifically addressed soil protists. Soil protists, a phylogenetically and functionally diverse group of eukaryotic, unicellular soil organisms, are major consumers of bacteria in soils and are potentially important vehicles for the delivery of microplastics into the soil food chain. Here we build a case for focusing research on soil protists by drawing on data from previous, older studies of phagocytosis in protist taxa, which have long made use of polystyrene latex beads (microspheres). Various soil-borne taxa, including ciliates, flagellates and amoebae take up microplastic beads in the size range of a few micrometers. This included filter feeders as well as amoebae which engulf their prey. Discrimination in microplastic particle uptake depended on species, physiological state as well as particle size. Based on the results of the studies we review here, there is now a need to study microplastic effects in a pollution ecology context: this means considering a broad range of particle types under realistic conditions in the soil, and exploring longer-term effects on soil protist communities and functions.

THE STRUCTURE AND FORMATION OF CILIA AND FILAMENTS IN RUMEN PROTOZOA

The large oligotrich rumen protozoa Diplodinium ecaudatum and Ophryoscolex caudatus have been studied by electron microscopy during interphase and division. The structure of mature cilia is contrasted with that seen during their formation particularly in a tuft where development lags and is arrested. Here the shaft is only a few micra long and is composed of filaments that have circular cross-sections not in the typical circular arrangement. In their diameter and appearance the filaments are similar to filaments associated with the nuclei during division. The macronucleus has within it randomly directed filaments, while the micronucleus contains well aligned filaments and other arrangements typical of an intranuclear mitotic process. An extranuclear filament system is also present and is elaborated during division. The infraciliary filament system is particularly elaborate in these organisms. Filaments ranging from 14 to 22 mµ have been observed with some tendency for a bimodal distribution in diameters of 15 and 21 mµ. Formation of such filaments has been observed and consists of an initial orientation of very fine elements followed by filament formation. The observations are discussed in relation to filament involvements in cell movements. The concepts are discussed that filaments are metastable structures and that the transitions from one state to another are functionally significant.

Some factors influencing the chemical composition of mixed rumen bacteria

1. Sheep, cows and calves fitted with rumen cannulas were given diets mostly containing 10–16 g nitrogen/kg dry matter and consisting of roughage and cereals. Mixed bacteria were separated from samples of their rumen contents.

2. Bacteria taken 4–6 h after a feed from calves which were kept in an experimental calf-house with no contact with adult animals (environment A) contained more α-dextran, less total N and higher nucleic acid:total N ratios than similar bacteria from calves reared in contact with adult sheep (environment C) but otherwise treated in an identical way.

3. Mixed bacteria taken 4–6 h after a feed from sheep and cows were similar in composition, with respect to nitrogenous components, to those from the ‘environment C’ calves. This composition did not vary significantly when diets containing differing proportions of roughage were given.

4. The ‘environment A’ calves were free of ciliate protozoa. When they were placed in contact with, and were inoculated with rumen contents from, adult cattle (environment B), they rapidly developed a normal protozoal population and the chemical composition of their rumen bacteria became like that of the bacteria from the ‘environment C’ calves.

5. Mixed bacteria taken just before a feed, from either cows or ‘environment A’ calves, showed significantly lower RNA-N:total N ratios and slightly (but not usually significantly) higher DNA-N:total N ratios than bacteria taken 4–6 h after feeding. Total N contents of the bacteria did not change consistently with time after feeding.

6. The possible significance of these differences in relation to the nutrition of the host animal is discussed.

The role of ciliate protozoa in nutrition of the ruminant

The effects of ciliate protozoa on the ruminal ecosystem, digestion in different parts of the gut, the nature of nutrients available for absorption and their effects upon the nutrition and productivity of their host are reviewed. Compared with fauna-free ruminants, the presence of ciliate protozoa results in a more stable ruminal fermentation, higher levels of ammonia, reduced numbers of bacteria, as well as changes in dry matter (%), liquid volume and turnover rate of ruminal contents. Associated with these differences in the rumen are higher ruminal and total tract digestion of organic matter and fiber in faunated animals. A reduction in net microbial synthesis and an increase in dietary protein degradation in the rumen results in the flow of protein to the small intestine being lower in faunated ruminants. The major nutritional effect of the ciliate protozoa is to change the ratio of protein to energy in the nutrients absorbed, with faunated animals having lower protein and higher energy availabilities compared with ciliate-free ruminants. Of the nutrients available for absorption, the ciliates have no consistent effect on the proportions of volatile fatty acids or amino acids. However, there is evidence that hydrogenation of lipids is increased, as is the supply of choline, and that the bioavailability of copper is reduced by the presence of ciliates. Defaunation of young growing ruminants that are fed high energy diets, containing low levels of ruminal nondegradable protein, results in increased growth rate and feed efficiency. It is unlikely, with the possible exception of wool growth, that there are other situations in which defaunation will be beneficial; and it is more likely to be detrimental to animal productivity. It remains to be determined whether manipulation of the types of ciliate protozoa in the rumen could improve animal performance. Information for this review was largely derived from comparisons of faunated and fauna-free animals. However, it is indicated that there are large differences in protozoa numbers and types between naturally faunated individuals in the same flock or herd, and that the effects of such variations on their host's nutrition are unknown.

An electron microscope study of the cytology of the protozoan Euplotes patella

1. Structurally the "sensory bristles" in Euplotes patella are typical cilia, but no ciliary rootlets connect their bases. 2. The "neuromotor fibrils" are composed of filaments 21 mmicro in diameter. At the point of junction of the filaments with the peripheral ciliary fibrils a granular structure 65 to 90 mmicro in diameter is seen which has dense central and peripheral zones separated by a less dense layer. Information on the interconnection of organelles is expanded. 3. A system of subpellicular fibrils is described. The external fibrillar system described by others could not be found. 4. The motorium is shown to be a mass of intertwining rootlet filaments. 5. The micronucleus is shown to have a spongy, dense material in a less dense material, all of which is surrounded by a double-layered membrane. 6. The double-layered macronuclear membrane contains annuli whose outside diameter is 70 mmicro; the macronuclear bodies are sometimes closely applied to the membrane. In the macronuclear reorganization bands, the solution plane is a fine network, while the reconstruction plane is devoid of structure at the level of resolution observed. 7. The mitochondria are composed of tubules, only occasionally oriented, usually embedded in a surrounding material of lower density. 8. Microbodies whose diameters are 250 to 350 mmicro are frequently observed in close association with mitochondrial surfaces. 9. The food vacuoles, contractile vacuoles, and ciliary vacuoles are bounded by single-layered membranes. In the food vacuoles, the bacteria are surrounded by membranes individually or in small groups. 10. Cytoplasmic rods localized in the oral region, and cytoplasmic granules dispersed at random, are described. No typical ergastoplasm, endoplasmic reticulum, or Golgi material was observed.

The effect of the absence of rumen ciliate protozoa on growing lambs fed on a roughage-concentrate diet

1. Lambs were removed form their dams at 2 d of age, and at 5 weeks of age eitht of one group were incoulated with a mixed rumen ciliate and seven in a second group were maintained ciliate-free throughout the 61 weeks of the experiment. Performance of the groups was compared when given a 2:1 roughage:concentrate diet as a set ration and withad lib.roughage.

2. Mixed ciliate populations developed in all faunated lambs and average-sized populations were maintained. Large numbers of flagellate protozoa developed in the ciliate-free animals after flagellates had been introduced into the building with the ciliate-free animals after flagellates had been introduced into the building with the ciliate inoculum.

3. Higher numbers of rumen bacteria were found in the ciliate-free group.

4. Only between the 14th and 21st weeks was there a significant different between groups in weight gain and this was infavour of the faunated group. The only significant different in body measurements was greater girth in the ciliate-free lambs.

5. Only minor differences were found between the groups in calorimetric trials, digestibility and nitrogen balanes. There were no differences between groups in concentration of total protein N and soluble sugar in the rumen. The ammonis concentration was significantly higher in the faunated group.

6. The concentrations of total rumen volatile fatty acids (VFA) were higher in the faunated group. Differences, between groups, in proportions of VFA were attributed to the activity of the rumen bacteria rather than the ciliatesper se.

7. No differences between groups were found in the concentrations of blood sugar and haemoglobin.

8. It was concluded that the changes due to the presence of rumen ciliates were not great enough to be reflected in animal performance under the conditions of this experiment.