Mesosomes and vesicles inRhodopseudomonas acidophila

Abstract

Mesosomes are membranous organelles found in Gram-positive bacteria and only occasionally in Gramnegative bacteria [ 11. Rhodopseudomonas acidophila (Rps. acidophila), like all other photosynthetic bacteria is Gram-negative. Mesosomes have been reported to appear among green photosynthetic bacteria (Chlorobiaceae) [2,3] and “grosse mesosomenahnliche Membrankomplexe” have been reported for Rhodospirillum rubrum (R. rubrum) [4] under N-limited growth conditions. Similar structures have also been observed in R. rubrum when grown in the presence of an inhibitor of carotenoid synthesis [S]. Rhodospirrillum, Rhodopseudomonas and Rhodomicrobium form the family Rhodospirilkeae (“non-sulfur purple bacteria”), which together with the Chromatiaceae (“sulfur purple bacteria”) and the green bacteria form the photosynthetic bacteria. Mesosomes have not been reported for the purple bacteria under normal growth conditions. The photosynthetic apparatus is located mainly in intracytoplasmic membranes (ICM). These membranes have different arrangements in different species. Thus, R. rubrum, Rps. sphaeroides and Rps. capsulata have vesicles and Rps. palustris, Rps. viridis, Rps. acidophila and Rhodomicrobium vannielli have lamellae that are parallel to the cytoplasmic membrane [6,7] When Rps. acidophila was characterized taxonomitally [8] it was reported that all the isolated strains have an arrangement of ICM similar to that of Rps. palustris, but no pictures were published. The ultrastructure of Rps. acidophila was later studied with emphasis on differences as compared with Rps. palustris [9]. In this report the presence of membranous vesicles, in addition to the expected lamellae, is shown. They are discussed in relation to the prevailing theories on ICM-formation in photosynthetic bacteria.