A comparative study of digestion in a raptorial ciliate and in the facultative carnivorous form of a filter feeding ciliate

Digestion in the carnivorous form (giant) of the filter feeding ciliateOxytricha bifaria and in the obligatory carnivorous, raptorial feeding ciliateLitonotus lamella were studied and compared at the ultrastructural level. It was found that whenO. bifaria, shifts from the normal, bacterivorous to the gigantic carnivorous form, it modifies its morphology, acquiring new and more effective feeding devices but maintaining unaltered the digestion pattern and mode of food absorption. This takes place through pinocytotic activity at the food vacuolar membrane. The digestive process inLitonotus is far more rapid: within 10 min the vacuolar membrane disappears; in this way the cytoplasm of the prey, not yet completely digested, is mixed with that of the predator and a pinocytotic mechanism does not seem to he necessary for nutrient assimilation. In general, results demonstrate that filter feeders and raptorial ciliates differ not only in their food intake mechanism, but also in the pattern and the timing of their digestive process, even when they ingest similar kinds of food.     

Mitosis-like macronuclear division in a ciliate

The macronucleus of a small marine ciliate of the genus Protocrucia consists of a cluster of ten vesicles which give rise to 20 distinct chromosomal elements in the course of prophase-like condensation stages. Size differences of vesicles and chromosomes are cytological indications of their genetic individuality. In an anaphase-like stage, the chromosomal elements are separated in two daughter groups which re-form 10 vesicles each. The micronucleus divides simultaneously. The existence of a precisely functioning mode of chromosome distribution is also indicated by DNA measurements. Since the macronucleus contains much more DNA than the micronucleus, the macronuclear chromosomes are thought to be oligotenic. This hypothesis is supported by the much larger size of the macronuclear chromosomes. In contrast to other modes of macronuclear division known so far, this ciliate has retained some essential features of mitosis.     

The feeding apparatus of a chitinivorous ciliate

The chitinivorous ciliate Ascophrys, an ectosymbiont of the shrimp Palaemon serratus, is enclosed by a thick cyst wall except for a ventral hiatus exposing a circular area of exoskeleton to the interior of the cyst. The exoskeleton underlying the cyst wall remains intact, but the circular area of exoskeleton is dissolved enzymatically and ingested. The feeding ciliate forms a cavity in the exoskeleton into which it sinks. Its complex oral apparatus resembles a pump encircled by cytoplasm containing Golgi and high concentrations of coated vesicles that join pellicular pores between cilia. The ingestive apparatus is formed of microtubular lamellae that originate in the midplane of the body, descend toward a coated membrane on the surface, and ascend again as a lamellar lining to a complex food tube that ends in the middle of the body surrounded by food vacuoles. The cytoplasm enclosed between the descending lamellae and the food tube is crowded with membrane organelles that recycle as food vacuole membranes at the coated membrane. We hypothesize that vacuoles containing dissolved exoskeleton are drawn up into the oral tube and are released into the cytoplasm at the terminus of the tube, where their contents are concentrated and excess vacuolar membrane collapsed into membrane organelles.     

Competition-colonization trade-offs in a ciliate model community

There is considerable theoretical evidence that a trade-off between competitive and colonization ability enables species coexistence. However, empirical studies testing for the presence of a competition–colonization (CC) trade-off and its importance for species coexistence have found mixed results. In a microcosm experiment, we looked for a CC trade-off in a community of six benthic ciliate species. For each species, we measured the time needed to actively disperse to and colonize an empty microcosm. By measuring dispersal rates and growth rates of the species, we were able to differentiate between these two important components of colonization ability. Competitive ability was investigated by comparing species’ growth with or without a competitor in all pairwise species combinations. Species significantly differed in their colonization abilities, with good colonizers having either high growth rates or high dispersal rates or both. Although species showed a clear competitive hierarchy, competitive and colonization ability were uncorrelated. The weakest competitors were also the weakest colonizers, and the strongest competitor was an intermediate colonizer. However, some of the inferior competitors had higher colonization abilities than the strongest competitor, indicating that a CC trade-off may enable coexistence for a subset of the species. Absence of a community-wide CC trade-off may be based on the lack of strong relationships between the traits underlying competitive and colonization ability. We show that temporal effects and differential resource use are alternative mechanisms of coexistence for the species that were both slow colonizers and poor competitors.     

Genetic diversity in populations of a freshwater ciliate

RAPD fingerprinting with nine different primers revealed that all of 18 E. aediculatus isolates from nine ponds and streams in western Germany, France and the U.S.A. were genetically different. The extent of genetic similarity between genotypes from different waters did not show a significant relationship with the geographical distance among habitats, although genotypes isolated from the same habitat showed a higher genetic similarity than genotypes isolated from different habitats. Phylogenetic analyses of RAPD patterns indicate a separation of E. aediculatus strains into subgroups within one species, but all strains were genetically more similar to one another than to strains from two other Euplotes species. Crossings of the different E. aediculatus strains revealed they belonged to seven mating types of one gene pool. The high genetic diversity observed is explained by a frequent occurrence of conjugation in the studied populations.     

Cytomembrane differentiation in a ciliate,Tetrahymena pyriformis

Summary Two special kinds of smooth surfaced differentiations of the endoplasmic reticulum (ER) of the ciliate Tetrahymena pyriformis are described. (A) A novel type of cytomembrane structure is represented by localized bifacial regions in which one side of the cisterna is studded with ribosomes, flexible in outline and of a cytomembraneous ultrastructure and the other side has a smooth, straight profile and a plasma membrane-like triple-layered appearance. Such smooth patches of predominantly rough ER-cisternae have a tendency to pair with a separation of ca. 250 Å. The micrographs suggest a participation of such patches in the formation of vesicles and/or dictyosomes. (B) Tubular structures, including those with microtubular as well as with macrotubular (300–650 Å) diameters, can be in continuity with ER profiles. Possible origins and functions of these tubular forms are discussed.The work was supported in part by the Deutsche Forschungsgemeinschaft.The authors are indebted to Miss Sigrid Krien for skilful technical assistance as well as to Drs. Ch. Bracker, D. J. Morré (both Purdue University, Lafayette, U.S.A), and H. Falk (this institute) for helpful discussions.     

Estimation of the size of freshwater ciliate populations by a sub-sampling technique

A technique is described for the estimation of the size of ciliate populations based on replicated counts. Sample drops were taken by automatic pipettes of different volume from activated sludge and from a small oligotrophic stream. Specific aims were: 1) the estimation of the number of species; 2) the estimation of the number of individual in each species; 3) the selection of a suitable sub-sample size and number of replicates. For each volume the cumulative increase in species taken in successive sub-samples was determined. For each species the minimum permissible sub-sample volume and the number of replicates required for an allowable error of 10% and 25% were determined. Lastly, the relationship between the mean number of individuals counted for each species and the relative coefficient of variation was visualized.     

Chemoattraction of a bactivorous ciliate to bacteria surface compounds

The locomotory response to cell surface compounds extracted from two prey species,Vibrio natriegens andVibrio neries, was tested for a bacterivorous ciliate,Pseudochnilembus marinus Thompson 1966. Chemoattraction of the ciliate to the surface compounds stabilized in agarose baits was not equal for the two prey species. Fractionation of the extracts suggested the attractive substance was a high molecular weight compound. The expression of the differential response was dependant on the physiological condition and prior prey species exposure of the ciliate test population. The recognition and response to material normally found on the surface of prey cells supports evidence for the involvement of chemical sensing of gradients of prey particles and dissolved compounds of prey origin in the natural swimming behavior of bacterivorous ciliates. The prey species-specific reactions and influence of ciliate physiological state on chemosensory response suggest ciliate-bacteria interactions may be more complex than preciously assumed.     

On the evolution of the karyorelict ciliate life cycle: heterophasic ciliates and the origin of ciliate binary fission

Karyorelict ciliates have near diploid somatic nuclei (macronuclei) incapable of division. If selective pressure favors nuclear division, how could such macronuclei have evolved? I propose that they initially evolved in the context of a diplophase stage that consisted entirely of a non-dividing trophont that was terminated by the induction of meiosis. The diploid macronucleus then differentiated, functioned and was destroyed in the absence of cell division. Such a life cycle would necessarily be heterophasic, i.e. with alternating haploid and diploid generations. I call these ancestors heterophasic ciliates. I further propose that the ability of this diploid trophont to undergo binary fission arose de novo. Ciliate binary fission would then be a derived characteristic, which possibly evolved indepedently in more than one heterophasic ciliate lineage. A progression of steps, leading to the reduction of the haplophase and the generation of the karyorelict life cycle, is proposed. The shared possession of nuclear dimorphism with non-dividing macronuclei, conjugation, and a putative heterophasic ancestry invites further investigation of the phylogenetic relationship between heterokaryotic foraminifera and karyorelict ciliates.     

Serotypes of the lower ciliate Dileptus anser

The author's data on the serotype composition in various clones of Dileptus anser are reviewed. This species is a novel subject of choice for studying the serotype problem in ciliates. The results obtained for serotypes of D. anser demonstrated several features shared also by some higher ciliates of the genera Paramecium and Tetrahymena, i.e. the well known classical models for serotype research. At the same time, some particular data obtained for D. anser do not fit in with the generally accepted picture of relevant events. Special attention is paid to a poor knowledge of the sexual process in this ciliate, which obviously hampers the true understanding of many events. Nevertheless, D. anser may be regarded as a suitable model for studying such important problems of general biology as epigenetic variability or inheritance.     

Sequence-specific fragmentation of macronuclear DNA in a holotrichous ciliate

Macronuclear DNA from the protozoan G. chattoni, a holotrichous ciliate, was analyzed. Most, if not all, of the macronuclear DNA is subchromosomal, ranging in size from above 100 kb down to 2.1 kb, with molecules in the lower molecular weight range being resolvable by gel electrophoresis into reproducible, specific, discrete size classes. A prominent class of linear 9.3 kb molecules consists of single free rRNA genes. Upon denaturation and partial renaturation, a high percentage of total macronuclear DNA was found as single-stranded circles. Sequence analysis showed that a minimum of 38 tandem repeats of the sequence CCCCAA is present in inverted orientation at each end of most or all Glaucoma macronuclear DNA molecules, including the rDNA. This sequence must therefore be recognized during site-specific fragmentation of chromosomes in macronuclear development.     

The copepod Centropages abdominalis as a carrier of the stalked ciliate Zoothamnium

Adult specimens of the calanoid copepod Centropages abdominalis collected from February through April 1986 in Shinhamako, a saline lake connected to Tokyo Bay, were heavily infested with the stalked ciliate Zoothamnium. The number of copepods and those infested varied during the infestation period; in February when the copepod population was large, the incidence of infestation was low, whereas in March when the copepod population was small, copepods infested with Zoothamnium were proportionally more abundant. Numerical variations of infested copepods may correspond to changes in the Zoothamnium population. No specimens of Acartia omorii, which coexists with C. abdominalis, were infested in 1986, although a small number of A. omorii were infested with peritrich ciliates in 1985. Some shrimp larvae were also covered with the same peritrichs as copepods. Nevertheless, as a whole, the relationship between the phoront and its carrier seems to be specific. The highest incidence of infested copepods was approximately 30% similar to that in 1985. The sex ratio of C. abdominalis changed on each sampling date but in general females were more numerous than males. The percentage of infested males was higher than that of infested females, suggesting that the former can be attached to more easily than the latter.