Abstract
Protists appeared relatively early in evolution, about 1.8 billion years ago, soon after the first prokaryotic organisms. During this time period, most species developed a variety of behavioral, morphological, and physiological strategies intended to improve the ability to capture prey or to avoid predation. In this scenario, a key role was played by specialized ejectable membrane-bound organelles called extrusomes, which are capable of discharging their content to the outside of the cell in response to various stimuli. The aim of this chapter is to describe the two main strategies adopted in ciliate predator-prey interactions: (a) the first is mediated by mechanical mechanisms and involves, for example, extrusomes called trichocysts and (b) the second is mediated by toxic secondary metabolites and involves different kinds of chemical extrusomes.
Keywords
- protists
- ciliates
- extrusomes
- secondary metabolites
- chemical offense
1. Introduction
A common definition for predatory behavior describes it as the process through which one animal, the predator, captures and kills another animal, the prey, before eating it in part or entirely [1]; however, according to the opinion of a number of microbiologists and protistologists, this definition should be also extended to different organisms included in other life Kingdoms, with particular regard to microorganisms. Indeed, especially in the last 30 years, a lot of studies have been devoted to describing the predator-prey interactions among unicellular eukaryotic organisms like protists. Whittaker [2] originally defined protists as those “organisms which are unicellular or unicellular-colonial and which form no tissues,” and for this reason they must carry out at the cellular level all the basic functions which can be observed in multicellular eukaryotes. Among these functions, self-nonself recognition mechanisms are represented by a large repertoire in protists and can trigger either autocrine or paracrine processes in some ciliates (see [3] for a review), together with the capability to detect prey (food) or predators in others. In this regard, it is known that protists have developed a variety of strategies of feeding behaviors especially in response to different environmental factors, together with a diverse kind of food available in micro-habitats. Figure 1 shows a general scheme of predator-prey interactions, where the predator recognizes the presence of the prey (step 1) and can attack it (step 2). On the other hand the prey recognizes the presence of the predator (step 1′) and it can organize its defense mechanisms (step 2′) [4]. This scheme should be considered functional for both animals and protists, and indeed several studies have shown that the food recognition and the offense-defense mechanisms adopted by some groups of protists can be compared, in terms of complexity and variability, with those observed in animals.
In this context, a common feeding mechanism found in heterotrophic protists is phagocytosis, a process which requires specific organelles for food assimilation and which occurs in three steps: food capture, phagosome formation, and food digestion [5]. Different techniques of phagocytosis have been described in various protists, where they have especially been investigated in ciliates [5, 6, 7]. Verni and Gualtieri [5] describe three main phagocytotic processes in ciliates: filter feeding, suctorial feeding, and raptorial feeding. The authors compare them to the strategies used in fishing, like netting, trapping, and harpooning. In filter-feeding ciliates, the food, represented by small organisms or edible debris of various types, was pushed into the ciliate buccal cavity by the rhythmical beats of the cilia located in its adoral apparatus. Suctorial-feeding ciliates are represented by sessile or sedentary species that for most of their lives remain attached to other organisms or various substrates, intercepting the food particles with their specialized tentacles. Finally, raptorial ciliates are able to directly catch other organisms using peculiar organelles to paralyze and/or kill their prey, generally called extrusomes.
2. Extrusomes, the specialized organelles for predator-prey interaction
The term “extrusome” was proposed, for the first time, by Grell in 1973 for extrusive (ejectable) bodies, which occur widely in protists [8]. They are membrane-bound organelles usually located in the cell cortex, attached to the cell membrane. They can display differences in structure and morphology, but they share the common characteristic of discharging their contents to the outside of the cell in response to mechanical or chemical stimuli. Remarkably, when the extrusomes are discharged, the cell remains intact and functional. Studies on extrusomes and related organelles have been reviewed by Hausmann [9], Dragesco [10], Kugrens et al. [11], Hausmann and Hülsmann [12], and Rosati and Modeo [13]. Typical examples of these organelles include toxicysts, trichocysts, mucocysts, cortical, or pigment granules in ciliates and flagellates, haptocysts in suctorians, and kinetocysts in heliozoan actinopods. Some extrusomes are known to be related in predator-prey interactions, for example, to catch and kill the prey (such as toxicysts, haptocysts, kinetocysts, and some cortical granules), or used as defensive organelles (such as the trichocysts and various cortical or pigment granules), but the role of other kinds of extrusomes such as the mucocysts in
3. Offensive extrusomes
Offensive extrusomes generally possessed by raptorial protists and located usually at or near the feeding apparatus are discharged after contact with a possible prey, which is immobilized, damaged, or firmly bound to the predator. Among these, organelles, certainly the most widely studied, belong to the category of toxicysts (toxic extrusomes) and they play an essential role in capturing and killing prey [7, 13]. Toxicysts are synthesized in Golgi or ER vesicles and are usually localized in the cell cortex attached to the cell membrane. Most of them are observed in species belonging to the class Litostomatea and subclass Haptoria, but they are also present in other predatory ciliates. They are usually positioned in a specific region of the cell, near the oral apparatus, and generally in the first portion which contacts the prey during the raptorial feeding [13]. Independently of the specific differences in the morphology of the cytostome, the toxicysts are always present in an appreciable number, for example, in the genera
In contrast with recent and less recent studies about the nature of the toxic secondary metabolites used by ciliates in chemical defense, no exhaustive data are yet available about the composition of the toxins stored in the toxicysts of predatory ciliates. This is essentially due to the difficulty in separating the content of extrusomes from other molecules produced by the ciliate, in order to purify them at homogeneity for subsequent chemical and structural analyses.
To date the presence of acid phosphatase has been demonstrated in the toxicysts of
3.1 The predatory behavior of Coleps hirtus
The complete analysis of the content of the toxicysts, together with observations of the predatory behavior, was also performed on another species,
Unexpectedly, the analysis of the bioactive fraction of the toxicyst discharge of
Very little is known about the role and source of phytanic acid in ciliates, this being the additional component detected in the toxicyst discharge of
It has been demonstrated that the substances discharged from the toxicysts by
Interestingly, the cells of
3.2 Didinium nasutum , a specialized hunter
Differently to
3.3 The peculiar tentacles of suctorians
In this context it is also relevant to mention the subclass Suctoria, represented by ciliates which become sessile during development and consequently lose the ciliary structure. Suctorians are able to feed on other protists and frequently on other ciliates by means of specialized tentacles. The distal ends of these tentacles are often equipped by peculiar extrusomes called haptocysts that are involved in prey capture. When a tentacle touches a possible prey, the discharge of haptocysts is able to penetrate the prey’s membrane, forming a connection between the predator and the prey and injecting the extrusome content into the latter, which also concurs to the fusion of the membranes belonging to the two organisms [13, 34]. However, the fusion of the two membranes is not always immediate, for example, in
4. Defensive extrusomes
In addition to predatory behavior, ciliated protists have also evolved different defense strategies, many based on the discharge of extrusomes. Two different mechanisms involved in their defense behavior are essentially observed: the first is mediated by the mechanical actions of trichocysts as in
4.1 The mechanical defense
Spindle trichocysts (or simply, trichocysts) are spindle-shaped organelles which discharge their content in the form of a thread. They are found in some ciliates and flagellates and are sometimes furnished with a specially constructed tip [9]. The best known and studied trichocysts are those in the genus
Maupas, one of the pioneers of protozoology, first proposed the defensive function of trichocysts in
To summarize, the mechanical defense by trichocysts and related extrusomes appear to be multiple, including quick physical displacement, the thrust into a predator, and protection against the predator’s toxins, increasing the chance for the prey to survive and escape. However, especially in ciliates and flagellates, other kinds of extrusomes used for defense were found, ones that, unlike trichocysts, are capable of discharging toxic materials in response to predatory behavior.
4.2 The chemical defense
Karyorelictean ciliates also possess pigment granules which are similar in size, structure, and distribution to those in the heterotrichs, but principally due to the difficulties to the growing species of karyorelictid in the laboratory, the chemical nature of their pigments is still unknown. The most studied species is freshwater
Pigmented granules are found also in other groups of ciliates as the Spirotrichea, and mainly in the genus
Other organelles strictly related to pigment granules are the colorless
This toxin may be chemically classified within a large group of natural compounds known as resorcinolic lipids (also called alkylresorcinols or 5-alkylresorcinols), widely detected in prokaryotes and eukaryotes [73] and with reported antimicrobial, antiparasitic, antitumoral, and genotoxic activities (see [74] for a review).
A typical defensive behavior of
If the defensive function of cortical granules in
Besides the natural role of climacostol and thanks to the availability of a straightforward method for its chemical synthesis [78], other bioactivities of the toxin and its potential application to human health are, to date, investigated in various biological systems. The toxicity of climacostol proves very effective against pathogenic Gram-positive bacteria such as
Returning to the topic of this chapter, different secondary metabolites have been also isolated and characterized from other heterotrics, such as
4.3 The inducible defense
Another peculiar defensive mechanism, reported as inducible defense, has been described for some
It could be interesting to study the efficiency of the inducible defenses, if compared to mechanical and chemical defense by means of extrusomes. In this regard, a first study was performed to compare the efficiency of the defense mediated by trichocysts in
5. Conclusions
In a general perspective, it is clear that the researches on predatory behavior and on the related defensive mechanisms in protists not only represent progress in knowledge about the ecological role played in nature by predator-prey interactions in aquatic microhabitats but will also provide new research opportunities for evolutionary biology and may also represent a relevant source of new natural products.
Acknowledgments
We are grateful to Dr. Gill Philip (University of Macerata) for the linguistic revision of the chapter. Financial support was provided by University of Macerata, Italy.
References
- 1.
Minelli A. Predation. In: Jørgensen SE, editor. Encyclopedia of Ecology. 1st ed. Amsterdam: Elsevier B.V.; 2008. pp. 2923-2929 - 2.
Whittaker RH. New concepts of kingdoms of organisms. Science. 1969; 163 (3863):150-160. DOI: 10.1126/science.163.3863.150 - 3.
Luporini P, Alimenti C, Vallesi A. Ciliate pheromone structures and activity: A review. The Italian Journal of Zoology. 2015; 82 (1):3-14. DOI: 10.1080/11250003.2014.976282 - 4.
Harumoto T. Interazione cellulare interspecifica tra predatore e preda nei ciliati: Organelli e molecole che partecipano all'interazione [PhD thesis]. Italy: University of Camerino; 1993 - 5.
Verni F, Gualtieri P. Feeding behaviour in ciliated protists. Micron. 1997; 28 (6):487-504. DOI: 10.1016/S0968-4328(97)00028-0 - 6.
Radek R, Hausmann K. Phagotrophy of ciliates. In: Hausmann K, Bradbury PC, editors. Ciliates: Cells as Organisms. Stuttgart: Gustav Fischer Verlag; 1996. pp. 197-219 - 7.
Hausmann K. Food acquisition, food ingestion and food digestion by protists. Japanese Journal of Protozoology. 2002; 35 (2):85-95 - 8.
Grell KG. Protozoology. Berlin and New York: Springer-Verlag; 1973 - 9.
Hausmann K. Extrusive organelles in protists. International Review of Cytology. 1978; 52 :197-276. DOI: 10.1016/S0074-7696(08)60757-3 - 10.
Dragesco J. Capture et ingestion des proies chez les Infusories Ciliés. Bulletin Biologique de la France et de la Belgique. 1962; 96 :123-167 - 11.
Krugens P, Lee RE, Corliss JO. Ultrastructure, biogenesis and functions of extrusive organelles in selected non-ciliate protists. Protoplasma. 1994; 181 :164-190. DOI: 10.1007/BF01666394 - 12.
Hausmann K, Hülsmann N, editors. Protozoology. 2nd ed. New York: Thieme; 1996 - 13.
Rosati G, Modeo L. Extrusomes in ciliates: Diversification, distribution, and phylogenetic implications. Journal of Eukaryotic Microbiology. 2003; 50 :383-402. DOI: 10.1111/j.1550-7408.2003.tb00260.x - 14.
Wessenberg H, Antipa G. Capture and ingestion of Paramecium byDidinium nasutum . Journal of Protozoology. 1970;17 :240-270. DOI: 10.1111/j.1550-7408.1970.tb02366.x - 15.
Fauré-Fremiet E. Pouvoir lytique et phosphatase acid chez le Ciliés. Comptes Rendus de l'Académie des Sciences. 1962; 254 :2691-2693 - 16.
Foissner W, Berger H, Scaumburg J, editors. Identification and Ecology of Limnetic Plankton Ciliates. München: Bayerisches Landesamt für WasserWirtschaft; 1999. pp. 272-287 - 17.
Mazanec A, Trevarrow B. Coleps , scourge of the baby Zebrafish. Zebrafish Science Monitor. 1998;5 :1 - 18.
Auer B, Czioska E, Hartmut A. The pelagic community of a gravel pit lake: Significance of Coleps hirtus viridis (Prostomatida) and its role as a scavenger. Limnologica. 2004;34 :187-198. DOI: 10.1016/S0075-9511(04)80044-6 - 19.
Buonanno F, Anesi A, Guella G, Kumar S, Bharti D, La Terza A, Quassinti L, Bramucci M, Ortenzi C. Chemical offense by means of toxicysts in the freshwater ciliate, Coleps hirtus . Journal of Eukaryotic Microbiology. 2014;61 (3):293-304. DOI: 10.1111/jeu.12106 - 20.
Buonanno F, Ortenzi C. Cold-shock based method to induce the discharge of extrusomes in ciliated protists and its efficiency. Journal of Basic Microbiology. 2016; 56 (5):586-590. DOI: 10.1002/jobm.201500438 - 21.
Fu M, Koulman A, van Rijssel M, Lützen A, De Boer MK, Tyl MR, Liebezeit G. Chemical characterisation of three haemolytic compounds from the microalgal species Fibrocapsa japonica (Raphidophyceae). Toxicon. 2004;43 :355-363. DOI: 10.1016/j.toxicon.2003.09.012 - 22.
Pezzolesi L, Cucchiari E, Guerrini F, Pasteris A, Galletti P, Tagliavini E, Totti C, Pistocchi R. Toxicity evaluation of Fibrocapsa japonica from the Northern Adriatic Sea through a chemical and toxicological approach. Harmful Algae. 2010;9 :504-514. DOI: 1016/j.hal.2010.03.006 - 23.
De Boer MK, Boerée C, Sjollema SB, de Vries T, Rijnsdorp AD, Buma AGJ. The toxic effect of the marine raphidophyte Fibrocapsa japonica on larvae of the common flatfish sole (Solea solea ). Harmful Algae. 2012;17 :92-101. DOI: 10.1016/j.hal.2012.03.005 - 24.
Mancini I, Defant A, Mesaric T, Potocnik F, Batista U, Guella G, Turk T, Sepcic K. Fatty acid composition of common barbel ( Barbus barbus ) roe and evalutaion of its haemolytic and cytotoxic activities. Toxicon. 2011;57 :1017-1022. DOI: 10.1016/j.toxicon.2011.04.004 - 25.
Rontani J-F, Volkman JK. Lipid characterization of coastal hypersaline cyanobacterial mats from the Camargue (France). Organic Geochemistry. 2005; 36 (2):251-272. DOI: 10.1016/j.orggeochem.2004.07.017 - 26.
Vencl FV, Morton TC. The shield defense of the sumac flea beetle, Blepharida rhois (Chrysomelidae: Alticinae). Chemoecology. 1998;8 :25-32. DOI: 10.1007/PL00001800 - 27.
Komen JC, Distelmaier F, Koopman WJH, Wanders RJA, Smeitink J, Willems PHMG. Phytanic acid impairs mitochondrial respiration through protonophoric action. Cellular and Molecular Life Sciences. 2007; 64 :3271-3281. DOI: 10.1007/s00018-007-7357-7 - 28.
Guella G, Skropeta D, Di Giuseppe G, Dini F. Structures, biological activities and phylogenetic relationships of terpenoids from marine ciliates of the genus Euplotes . Marine Drugs. 2010;8 :2080-2116. DOI: 10.3390/md8072080 - 29.
Savoia D, Avanzini C, Allice T, Callone E, Guella G, Dini F. Antimicrobial activity of Euplotin c, the sesquiterpene taxonomic marker from the marine ciliate Euplotes crassus . Antimicrobial Agents and Chemotherapy. 2004;48 (10):3828-3833. DOI: 10.1128/AAC.48.10.3828-3833.2004 - 30.
Guella G, Dini F, Pietra F. Epoxyfocardin and its putative biogenetic precursor, focardin, bioactive, new-skeleton diterpenoids of the marine ciliate Euplotes focardii from Antarctica. Helvetica Chimica Acta. 1996;79 :439-448. DOI: 10.1002/hlca.19960790211 - 31.
Guella G, Callone E, Mancini I, Dini F, Di Giuseppe G. Diterpenoids from marine ciliates: Chemical polymorphism of Euplotes rariseta . European Journal of Organic Chemistry. 2012;02012 :5208-5216. DOI: 10.1002/ejoc.201200559 - 32.
Wessenberg H, Antipa G. Studies on Didinium nasutum. Structure and ultrastructure. Protistologica. 1968;4 :427447 - 33.
Miyake A, Harumoto T. Defensive function of trichocysts in Paramecium against the predatory ciliateMonodinium balbiani . European Journal of Protistology. 1996;32 :128-133. DOI: 10.1016/S0932-4739(96)80048-4 - 34.
Benwitz G. Die Entladung der Haptocysten von Ephelota gemmipara (Suctoria, Ciliata). Zeitschrift für Naturforschung. Section C. 1984;39 :812-817 - 35.
Spoon DM, Chapman GB, Cheng RS, Zane SF. Observations on the behavior and feeding mechanisms of the Suctorian Heliophrya erhardi (Rieder) Matthes preying onParamecium . Transactions of the American Microscopical Society. 1976;95 (3):443-462. DOI: 10.2307/3225137 - 36.
Adoutte A. Exocytosis: Biogenesis, transport and secretion of trichocysts. In: Gortz HD, editor. Paramecium . Berlin: Springer-Verlag; 1988. pp. 325-362 - 37.
Plattner H. Trichocysts- Paramecium 's projectile-like secretory organelles: Reappraisal of their biogenesis, composition, intracellular transport, and possible functions. Journal of Eukaryotic Microbiology. 2017;64 (1):106-133. DOI: 10.1111/jeu.12332 - 38.
Maupas E. Contribution a l'étude morphologique et anatomique des infusoires ciliés. Archives de Zoologie Expérimentale et Générale. 1883; 1 :427-664 - 39.
Pollack S. Mutations affecting the trichocysts in Paramecium aurelia : I. Morphology and description of the mutants. Journal of Protozoology. 1974;21 :352-362. DOI: 10.1111/j.1550-7408.1974.tb03669.x - 40.
Harumoto T, Miyake A. Defensive function of trichocysts in Paramecium . Journal of Experimental Zoology. 1991;260 :84-92. DOI: 10.1002/jez.1402600111 - 41.
Knoll G, Haacke-Bell B, Plattner H. Local trichocyst discharge provides an efficient escape mechanism for Paramecium cells. European Journal of Protistology. 1991;27 :381-385. DOI: 10.1016/S0932-4739(11)80256-7 - 42.
Harumoto T. The role of trichocyst discharge and backward swimming in escaping behavior of Paramecium fromDileptus margaritifer . Journal of Eukaryotic Microbiology. 1994;41 :560-564. DOI: 10.1111/j.1550-7408.1994.tb01517.x - 43.
Sugibayashi R, Harumoto T. Defensive function of trichocysts in Paramecium tetraurelia against heterotrich ciliateClimacostomum virens . European Journal of Protistology. 2000;36 :415-422. DOI: 10.1016/S0932-4739(00)80047-4 - 44.
Buonanno F, Harumoto T, Ortenzi C. The defensive function of trichocysts in Paramecium tetraurelia against metazoan predators compared with the chemical defense of two species of toxin-containing ciliates. Zoological Science. 2013;30 :255-261. DOI: 10.2108/zsj.30.255 - 45.
Miyake A. Cell-cell interaction by means of extru- somes in ciliates – Particularly on the predator–prey inteaction by extrusomal toxins. Japanese Journal of Protozoology. 2002; 35 :97-117 - 46.
Giese AC. Blepharisma . 1st ed. Stanford: Stanford University Press; 1973 - 47.
Lobban CS, Hallam SJ, Mukherjee P, Petrich JW. Photophysics and multifunctionality of hypericin-like pigments in heterotrich ciliates: A phylogenetic perspective. Photochemistry and Photobiology. 2007; 83 :1074-1094. DOI: 10.1111/j.1751-1097.2007.00191.x - 48.
Matsuoka T, Kotsuki H, Muto Y. Multi-functions of photodynamic pigments in ciliated ptotozoans. In: Méndez-Vilas A, editor. Current Research, Technology and Education Topics in Applied Microbiology and Microbial Biotechnology. Badajoz: Formatex; 2010. pp. 419-426 - 49.
Miyake A, Harumoto T, Salvi B, Rivola V. Defensive function of pigment granules in Blepharisma japonicum . European Journal of Protistology. 1990;25 :310-315. DOI: 10.1016/S0932-4739(11)80122-7 - 50.
Harumoto T, Miyake A, Ishikawa N, Sugibayashi R, Zenfuku K, Iio H. Chemical defense by means of pigmented extrusomes in the ciliate Blepharisma japonicum . European Journal of Protistology. 1998;34 :458-470. DOI: 10.1016/S0932-4739(98) 80014-X - 51.
Muto Y, Matsuoka T, Kida A, Okano Y, Kirino Y. Blepharismins, produced by the protozoan, Blepharisma japonicum , form ion-permeable channels in planar lipid bilayer membranes. FEBS Letters. 2001;508 :423-426. DOI: 10.1016/ S0014-5793(01)03110-6 - 52.
Uruma Y, Sakamoto K, Takumi K, Doe M, Usuki Y, Iio H. Assignment of 13C NMR spectrum for blepharismin C based on biosynthetic studies. Tetrahedron. 2007; 63 :5548-5553. DOI: 10.1016/j.tet.2007.04.015 - 53.
Kato Y, Matsuoka T. Photodynamic action of the pigment in ciliated protozoan Blepha-risma . Journal of Protozoology Research. 1995;5 :136-140 - 54.
Pant B, Kato Y, Kumagai T, Matsuoka T, Sugiyama M. Blepharismin produced by a protozoan Blepharisma functions as an antibiotic effective against methicillin-resistantStaphylococcus aureus . FEMS Microbiology Letters. 1997;155 :67-71. DOI: 10.1111/ j.1574-6968.1997.tb12687.x - 55.
Giese AC. A cytotoxin from Blepharisma . Biological Bullettin. 1949;97 :145-149 - 56.
Buonanno F, Anesi A, Guella G, Ortenzi C. Blepharismins used for chemical defense in two ciliate species of the genus Blepharisma ,B. stoltei andB. undulans (Ciliophora: Heterotrichida). European Zoological Journal. 2017;84 (1):402-409. DOI: 10.1080/24750263.2017.1353145 - 57.
Song P-S, Kim I-H, Rhee JS, Huh JW, Florell S, Faure B, Lee KW, Kahsai T, Tamai N, Yamazaki T, Yamazaki I. Photoreception and photomovements in Stentor coeruleus . In: Lenci E, Ghetti E, Colombetti G, Hader D-P, Song P-S, editors. Biophysics of Photoreceptors and Photornovements in Microorganisms. New York: Plenum Press; 1991. pp. 267-279 - 58.
Höfle G, Reinecke S, Laude U, Kabbe K, Dietrich S. Amethystin, the coloring principle of Stentor amethystinus . Journal of Natural Products. 2014;77 :1383-1389. DOI: 10.1021/np5001363 - 59.
Mukherjee P, Fulton DB, Halder M, Han X, Armstrong DW, Petrich JW, Lobban CS. Maristentorin, a novel pigment from the positively phototactic marine ciliate Maristentor dinoferus , is structurally related to hypericin and stentorin. Journal of Physical Chemistry. 2006;110 :6359-6364. DOI: 10.1021/jp055871f - 60.
Miyake A, Harumoto T, Iio H. Defensive function of pigment granules in Stentor coeruleus . European Journal of Protistology. 2001;37 :77-88. DOI: 10.1078/0932-4739-00809 - 61.
Finlay BJ, Fenchel T. Photosensitivity in the ciliated protozoon Loxodes : Pigment granules, absorption and action spectra, blue light perception, and ecological significance. Journal of Protozoology. 1986;33 (4):534-542. DOI: 10.1111/j.1550-7408.1986.tb05658.x - 62.
Buonanno F, Saltalamacchia P, Miyake A. Defense function of pigmentocysts in the karyorelictid ciliate Loxodes striatus . European Journal of Protistology. 2005;41 :151-158. DOI: 10.1016/j.ejop.2005.01.001 - 63.
Song W, Warren A, Roberts D, Wilbert N, Li L, Sun P, Hu X, Ma H. Comparison and redefinition of four marine coloured Pseudokeronopsis spp. (Ciliophora: Hypotrichida), with emphasis on their living morphology. Acta Protozoologica. 2006;45 :271-287 - 64.
Wirnsberger E, Hausmann K. Fine structure of Pseudokeronopsis carnea (Ciliophora, Hypotrichida). The Journal of Eukaryotic Microbiology. 1988;35 :182-189. DOI: 10.1111/j.1550-7408.1988.tb04321.x - 65.
Buonanno F, Anesi A, Di Giuseppe G, Guella G, Ortenzi C. Chemical defense by erythrolactones in the euryhaline ciliated protist, Pseudokeronopsis erythrina . Zoological Science. 2017;34 :42-51. DOI: 10.2108/zs160123 - 66.
Höfle G, Pohlan S, Uhlig G, Kabbe K, Schumacher D. Keronopsins A and B, chemical defence substances of the marine ciliate Pseudokeronopsis rubra (Protozoa): Identification by ex vivo HPLC. Angewandte Chemie International Edition. 1994;33 :1495-1497. DOI: 10.1002/anie.199414951 - 67.
Guella G, Frassanito R, Mancini I, Sandron T, Modeo L, Verni F, Dini F, Petroni G. Keronopsamides, a new class of pigments from marine ciliates. European Journal of Organic Chemistry. 2010; 3 :427-434. DOI: 10.1002/ejoc.200900905 - 68.
Anesi A, Buonanno F, Di Giuseppe G, Ortenzi C, Guella G. Metabolites from the eury-haline ciliate Pseudokeronopsis erythrina . European Journal of Organic Chemistry. 2016;7 :1330-1336. DOI: 10.1002/ejoc.201501424 - 69.
Chen X, Clamp JC, Song W. Phylogeny and systematic revision of the family Pseudokeronopsidae (Protista, Ciliophora, Hypotricha), with description of a new estuarine species of Pseudokeronopsis . Zoologica Scripta. 2011;40 :659-671. DOI: 10.1111/j.1463-6409.2011.00492.x - 70.
Strott CA. Sulfonation and molecular action. Endocrine Reviews. 2002; 5 :703-732. DOI: 10.1210/er.2001-0040 - 71.
Peck R, Pelvat B, Bolivar I, de Haller G. Light and electron microscopic observation on the heterotrich ciliate Climacostomum virens . Journal of Protozoology. 1975;22 :368-385. DOI: 10.1111/j.1550-7408.1975.tb05187.x - 72.
Larsen HF, Nilsson JR. Is Blepharisma hyalinum truly unpigmented. Journal of Protozoology. 1983;30 :90-97. DOI: 10.1111/j.1550-7408.1983.tb01039.x - 73.
Buonanno F, Quassinti L, Bramucci M, Amantini C, Lucciarini R, Santoni G, Ortenzi C. The protozoan toxin climacostol inhibits growth and induces apoptosis of human tumor cell lines. Chemico-Biological Interactions. 2008; 176 :151-164. DOI: 10.1016/j.cbi.2008.07.007 - 74.
Stasiuk M, Kozubek A. Biological activity of phenolic lipids. Cellular and Molecular Life Sciences. 2010; 67 (6):841-860. DOI: 10.1007/s00018-009-0193-1 - 75.
Miyake A, Buonanno F, Saltalamacchia P, Masaki ME, Iio H. Chemical defence by means of extrusive cortical granules in the heterotrich ciliate Climacostomum virens . European Journal of Protistology. 2003;39 :25-36. DOI: 10.1078/0932-4739-00900 - 76.
Buonanno F, Ortenzi C. The protozoan toxin climacostol and its derivatives: Cytotoxicity studies on 10 species of free-living ciliates. Biologia. 2010; 65 :675-680. DOI: 10.2478/s11756-010-0071-1 - 77.
Buonanno F, Guella G, Strim C, Ortenzi C. Chemical defence by mono-prenyl hydroquinone in a freshwater ciliate, Spirostomum ambiguum . Hydrobiologia. 2012;684 :97-107. DOI: 10.1007/s10750-011-0972-1 - 78.
Fiorini D, Giuli S, Marcantoni E, Quassinti L, Bramucci M, Amantini C, Santoni G, Buonanno F, Ortenzi C. A straightforward diastereoselective synthesis and evaluation of climacostol, a natural product with anticancer activities. Synthesis. 2010; 9 :1550-1556. DOI: 10.1055/s-0029-1218695 - 79.
Petrelli D, Buonanno F, Vitali LA, Ortenzi C. Antimicrobial activity of the protozoan toxin climacostol and its derivatives. Biologia. 2012; 67 :525-529. DOI: 10.2478/s11756-012-0030-0 - 80.
Quassinti L, Ortenzi F, Marcantoni E, Ricciutelli M, Lupidi G, Ortenzi C, Buonanno F, Bramucci M. DNA binding and oxidative DNA damage induced by climacostol-copper(II) complexes: Implications for anticancer properties. Chemico-Biological Interactions. 2013; 206 :109-116. DOI: 10.1016/j.cbi.2013.08.007 - 81.
Perrotta C, Buonanno F, Zecchini S, Giavazzi A, Proietti Serafini F, Catalani E, Guerra L, Belardinelli MC, Picchietti S, Fausto AM, Giorgi S, Marcantoni E, Clementi E, Ortenzi C, Cervia D. Climacostol reduces tumour progression in a mouse model of melanoma via the p53-dependent intrinsic apoptotic programme. Scientific Reports. 2016; 6 :27281. DOI: 10.1038/srep27281 - 82.
Catalani E, Proietti Serafini F, Zecchini S, Picchietti S, Fausto AM, Marcantoni E, Buonanno F, Ortenzi C, Perrotta C, Cervia D. Natural products from aquatic eukaryotic microorganisms for cancer therapy: Perspectives on anti-tumour proprieties of ciliate biocative molecules. Pharmacological Research. 2016; 113 :409-420. DOI: 10.1016/j.phrs.2016.09.018 - 83.
Buonanno F. The changes in the predatory behavior of the microturbellarian Stenostomum sphagnetorum on two species of toxin-secreting ciliates of the genusSpirostomum . Biologia. 2011;66 (4):648-653. DOI: 10.2478/s11756-011-0061-y - 84.
Sera Y, Masaki ME, Doe M, Buonanno F, Miyake A, Usuki Y, Iio H. Spirostomin, defense toxin of the ciliate Spirostomum teres : Isolation, structure elucidation, and synthesis. Chemistry Letters. 2015;44 :633-635. DOI: 10.1246/cl.150044 - 85.
Kuhlmann H-W, Heckmann K. Interspecific morphogens regulating prey–predator relationships in protozoa. Science. 1985; 227 :1347-1349. DOI: 10.1126/science.227.4692.1347 - 86.
Kuhlmann H-W, Heckmann K. Predation risk of typical ovoid and winged morphs of Euplotes (Protozoa, Ciliophora). Hydrobiologia. 1994;284 :219-227. DOI: 10.1007/BF00006691 - 87.
Kush J. Induction of morphological changes in ciliates. Oecologia. 1993; 94 :571-575. DOI: 10.1007/BF00566974 - 88.
Laas S, Spaak P. Chemically induced anti-predator defences in plankton: A review. Hydrobiologia. 2003; 491 (1-3):221-239. DOI: 10.1023/A:1024487804497