Rivera A, Cedillo L, Hernández F, Romero O and Hernández MA
The aim is to present a review of the main features that point to the spiroplasmas as plant pathogens. Spiroplasmas are most often found in association with plants and insects and plants flowers, and the interactions of spiroplasma/host can be classified as commensal, pathogenic or mutualistic. Some insect-derived spiroplasmas are entomopathogens. S. melliferum and S. apis are honey bee pathogens. They cross the insect-gut barrier and reach the hemolymph, where multiply abundantly and kill the bee. Many insects spiroplasmas are not pathogenic, are often restricted to the gut and may be regarded as mutualists or incidental commensals. Among the many components important for growth of spiroplasmas, lipids are some of the most significant. Like members of the genus Mycoplasma, the spiroplasmas so far examined are incapable of the biosynthesis of cholesterol and longchain fatty acids. Spiroplasmas incorporate cholesterol and fatty acid into their membranes when these lipids are supplied in the culture medium. Because of insolubility of cholesterol in water and the toxicity of free fatty acids, the provision of cholesterol in an assimilable form and of fatty acids in nontoxic form for the growth of spiroplasmas presents a problem. Spiroplasmas are capable of chemotactic responses to certain chemical stimuli, motility and chemotaxis are clearly demonstrated by radial migration in soft agar. The existence of chemotaxis implies that spiroplasmas are able to bias random motility so as to produce net migration in a preferred direction. Recent studies have revealed that insect-microbe symbiotic systems often respond to environmental conditions like ambient temperature in an unpredictable manner, which results from complex interactions between host genotype, symbiont genotype, and environmental factors.
