Chapter 2 Spiroplasma spp.: A Plant, Arthropod, Animal and Human Pathogen Santa Olga Cacciola, Assunta Bertaccini, SantaAntonella Olga Pane Cacciola, and Pio Assunta Maria Bertaccini, Furneri Antonella Pane and Pio Maria Furneri Additional information is available at the end of the chapter Additional information is available at the end of the chapter http://dx.doi.org/10.5772/66481 Abstract Mollicutes is a class of smallest and free-living bacteria. They have no cell wall and their plasma membrane contains cholesterol; nevertheless, cellular organization does not dif- fer from that of other prokaryotes. They are used as simple model systems for studying general biological problems, such as those concerning membrane structure and func- tions, symbiosis between arthropods and microrganisms, animal and plant pathogens. Mollicutes includes the family of Spiroplamataceae, which contains Spiroplasma genus, a group of species associated, in different manner, with arthropods (insects, mites, crusta- ceans). Spiroplasma species can be commensals or parasites and even be involved in more close symbiosis, such as synergism or mutualism. Out of 38 described Spiroplasma spe- cies, only three have been associated with plant diseases and three with arthropod dis- eases. Moreover, some species have been related to animal diseases, such as transmissible spongiform encephalopathy (TSE), and their role in human disease has been assessed. The chapter describes the taxonomic situation of the genus and reports the most impor- tant diseases due to the presence of Spiroplasma in different living organisms with special emphasis on citrus in which it causes one of the most economically damaging infectious diseases in a number of citrus growing areas worldwide. Keywords: Spiroplasma, citrus, disease, crab, transmissible spongiform encephalopathy, insect vector 1. Introduction Mollicutes is a class of microorganisms composed by the smallest and free-living bacteria, which have no cell wall. Their cellular organization does not differ from that of other prokary- otes: plasma membrane, which, however, contains cholesterol, cytoplasm, and ribosomes; © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, distribution, and reproduction in any medium, provided the original work is properly cited. and reproduction in any medium, provided the original work is properly cited. 32 Citrus Pathology their metabolic pathways are simpler than those of other eubacteria and their DNA has a low GC content. The cell biology of these organisms is interesting to many researchers who use Mollicutes as simple model systems for studying general biological problems, such as those concerning membrane structure and functions, symbiosis between arthropods and microrgan- isms, animal and plant pathogens. The genus Spiroplasma has arthropods as a peculiar host. Spiroplasma species (spiroplasmas) have developed different types of symbiosis with insects and mites, and, as recently shown, with crustaceans. Among the 38 described Spiroplasma species, only three have been associated with plant diseases. In this chapter, the relevance of the spiroplasma diseases in citrus is described together with some relevant diseases reported as associated with the presence of spiroplasma in other living organisms, such as arthropods, animals, and humans. 2. Methods Bibliographical sources have been obtained through a PubMed search, integrating the biblio- graphic citations from PMC. The used keywords to select bibliographic items were Spiroplasma, Spiroplasma pathogenesis, Spiroplasma, and human infections, Spiroplasma taxonomy. As of today, there are 709 bibliographic entries, since 1973, in PubMed and 1140 citations in PMC, since 1981. This discrepancy is due to the fact that PMC also includes sources from the con- ference proceedings, books, etc., etc. A literature search on Spiroplasma citri, Spiroplasma kun- kelii, and Spiroplasma phoeniceum was conducted on the CAB Abstract and web-based search engines, such as Google Scholar. Further references and information were obtained from experts, citations within the references, as well as from gray literature. 3. Classification and taxonomy The spiroplasmas belong to the Class of Mollicutes, Order Entomoplasmatales, Family Spiroplasmataceae, and Genus Spiroplasma [1]. Species of officially recognizedSpiroplasma are shown in Table 1. Most species have mandatory relationships with insects, with whom they develop different types of symbiosis 37,[ 38], while a number species were reported to be pathogenic for animals, arthropods, and plants and a few has been involved in human diseases. 4. Pathogenetic mechanisms and interactions with insect vectors Spiroplasma species are mainly transmitted to plants by specific insect vectors; in order to achieve the transmission, they must cross the salivary gland barrier [39]. S. citri and S. kunkelii invade the hemocoel through the gut epithelium of the insect host by a process of receptor- mediated cell endocytosis [40]. Receptors on leafhopper gut epithelial cells likely recognize specific spiroplasma membrane proteins. Several candidateS. citri attachment protein genes have been studied, including spiralin (immunodominant membrane protein) [41], P58 [42], SARP1 [43], P32 of pSci6 plasmid [44–46], and phosphoglycerate kinase (PGK) [47]. It has Spiroplasma spp.: A Plant, Arthropod, Animal and Human Pathogen 33 http://dx.doi.org/10.5772/66481 Species Host species Geographic distribution Authors Spiroplasma alleghenense Common scorpion fly (Panorpa USA (WV) [3] helena) Spiroplasma apis Honey-bee (Apis mellifera) France [4] Spiroplasma atrichopogonis Biting midge (Atrichopogon spp.) USA (MD) [5] Spiroplasma cantharicola Soldier beetle (Cantharis carulinus) USA (MD) [6] Spiroplasma chinense False bindweed (Calystegia China (Jiangsu) [7] hederacea) Spiroplasma chrysopicola Deerfly (Chrysops sp.) USA (MD) [8] Spiroplasma citri Citrus spp. USA [2] Spiroplasma clarkii Green June beetle (Cotinus nitida) USA (MD) [9] Spiroplasma corruscae Lampyrid beetle (Ellychnia USA (MD) [10] corrusca) Spiroplasma culicicola Salt marsh mosquito (Aedes Worldwide [11] sollicitans) Spiroplasma diabroticae Corn rootworm (Diabrotica USA (MD) [12] undecimpunctata) Spiroplasma diminutum Mosquito (Culex annulus) Taiwan [13] Spiroplasma eriocheiris Chinese mitten crab (Eriocheir China [14] sinesis) Spiroplasma floricola Tulip tree (Liriodendron tulipifera) USA [15] Spiroplasma gladiatoris Maryland horsefly(Tabanus USA (MD) [7] gladiator) Spiroplasma helicoids Horseflies Tabanus( USA (MD) [7] abdominalis-limbatinevris) Spiroplasma insolitum Fall flower (Bidens sp.) USA (MD) [16] Spiroplasma ixodetis Black-legged ticks (Ixodes USA (OR) [17] pacificus) Spiroplasma kunkelii Corn (Zea mays) America [18] Spiroplasma lampyridicola Firefly beetle (Photuris USA (MD) [19] pennsylvanicus) Spiroplasma leptinotarsae Colorado potato beetle USA (MD) [20] (Leptinotarsa decemlineata) Spiroplasma leucomae Satin moth larvae, (Leucoma Poland [21] salicis) Spiroplasma lineolae Striped horsefly (Tabanus lineola) USA (GE) [22] Spiroplasma litorale Horsefly (Tabanus nigrovittatus) USA (NC) [23] Spiroplasma melliferum Honey bee (Apis mellifera) worldwide [24] Spiroplasma mirum Rabbit ticks (Haemaphysalis USA (GE, MD) [25] leporispalustris) 34 Citrus Pathology Species Host species Geographic distribution Authors Spiroplasma monobiae Vespid wasp (Monobia USA (MD) [26] quadridens) Spiroplasma montanense Tabanid fly (Hybomitra opaca) USA (MN) [27] Spiroplasma penaei Pacific white shrimp (Penaeus Colombia [28] vannamei) Spiroplasma phoeniceum Periwinkle (Catharanthus roseus) Syria [29] Spiroplasma platyhelix Dragonfly (Pachydiplax USA (MD) [30] longipennis) Spiroplasma poulsonii Fruit fly (Drosophila willistonii) South America [31] Spiroplasma sabaudiense Mosquitoes (Aedes stricticus, France [32] Aedes vexans) Spiroplasma syrphidicola Syrphid fly (Eristalis Unknown [33] arbustorum) Spiroplasma tabanidicola Horsefly (Tabanus abactur) USA (OK) [7] Spiroplasma taiwanese Mosquitoes (Culex Taiwan [34] tritueniorhynchus) Spiroplasma turonicum Fly (Haematopota sp.) France [35] Spiroplasma velocicrescens Vespid wasp (Monobia USA (MD) [36] quadridens) Table 1. Spiroplasma species reported in literature after the genus description by Saglio et al. [ 2] (in bold strains recognized as pathogenic). been reported that a spiralin mutant is less effectively transmitted [41]; moreover, the spi- ralin binds to glycoproteins of its insect vector [48] and it is, therefore, a candidate molecule for insect vector specificity. It was also shown thatS. citri phosphoglycerate kinase (PGK), a glycolytic enzyme, could bind to actin of its leafhopper vector for the internalization ofS. citri into leafhopper cells [47]. In addition, the PGK protein or partial PGK peptides were shown to inhibit spiroplasma transmission by leafhoppers 49].[ A relationship between plasmids of S. citri and insect-transmissibility has been demonstrated for spiroplasmas [44–51]. The plasmid pSci6 confers insect transmissibility to a nontransmis- sible strain of S. citri [44] encoding protein P32; however, when only the p32 gene was intro- duced into the nontransmissible