Bacteriochlorophyll and Photosynthetic Reaction Centers in Rhizobium Strain BTAi 1

Abstract

Rhizobium strain BTAi 1, which nodulates both stems and roots of Aeschynomene indica L., formed bacteriochlorophyll and photosynthetic reaction centers resembling those of purple photosynthetic bacteria when grown aerobicaHly ex planta under a light-dark cycle. Bacteriochlorophyll formation was not observed under continuous dark or light growth conditions. The amount of pigment formed was similar to that previously found in aerobic photosynthetic bacteria. Stem nodules appear to fix nitrogen photosynthetically, as illumination of A. indica stem nodules with near-infrared light resulted in an enhanced rate of acetylene reduction. Near-infrared light did not enhance acetylene reduction when either A. indica or soybean root nodules were illuminated. The BTAi 1 isolate can be differentiated from members of the family Rhodospirillaceae by several criteria.

Radiation of the Nod‐independent Aeschynomene relies on multiple allopolyploid speciation events

“…Stem nodules always develop in the vicinity of adventive root primordia (Boivin et al, 1997), but only those of the Aeschynomene and Discolobium species are considered as genuine ones owing to their connection to the stem vascular system (Loureiro et al, 1994(Loureiro et al, , 1995. Another unusual feature of these Aeschynomene species is their capacity to be nodulated by photosynthetic Bradyrhizobium strains (Evans et al, 1990;Giraud & Fleischman, 2004). The photosynthetic activity of these bradyrhizobia has been shown to facilitate ex planta survival and infectivity, and to directly supply energy to the bacterium that can be used for biological nitrogen fixation during stem nodulation (Giraud et al, 2000).…”

Flooding‐tolerant legume symbioses from the Brazilian Pantanal

“…4a-c). These 'coccoid' bacteroids are commonly observed within nodules on other aeschynomenoid species, such as peanut (Arachis hypogaea) root nodules (Sen et al, 1986), and in stem and root nodules on other Aeschynomene spp., for example A. indica ( Yatazawa et al, 1984;Vaughn & Elmore, 1985;Evans et al, 1990). As in A. indica ( Yatazawa et al, 1984;Vaughn & Elmore, 1985;Evans et al, 1990), bacteroids in A. ciliata and A. denticulata nodules contained distinctive electrontransparent vesicles and electron-dense nuclear material (Fig.…”

“…4b,c). In Aeschynomene spp., the unusual appearance of the bacteroids may be related to their ability to photosynthesize both ex planta and in planta, as many isolates from stem nodules contain bacteriochlorophyll a (Bchl a) and carotenoids (Evans et al, 1990;Hungria et al, 1992;Boivin et al, 1997;Fleischman & Kramer, 1998;Molouba et al, 1999).…”

“…Chloroplasts are considered to be a distinguishing feature of stem nodules, and it has been suggested that their close proximity to the N 2 -fixing cells may be responsible for the high nitrogenase activities reported in stemnodulated legumes (Ladha et al, 1992;Boivin et al, 1997;Fleischman & Kramer, 1998;Loureiro et al, 1998). On the other hand, chloroplasts have so far been shown to be functional only in aerial stem nodules on A. indica (Evans et al, 1990), A. scabra (Hungria et al, 1992) and S. rostrata .…”

Photosynthetic and quasi-photosynthetic bacteria

“…production of the pigment 'was repressed on richer media such as casitone-yeast extract agar' [13] Bchl content negligible in cultures grown in continuous light; Bchl production stimulated by incubation in intermittent light [14] Bchl not formed in illuminated cultures; Bchl produced in darkness and in a light/dark regimen [15] 'Pigment formation in liquid cultures of BTAi 1 was observed only with intermittent lighting; under continuous illumination or continuous darkness no pigmentation was found' [16] Cells of this aerobic 'chemoorganotrophic' species contain Bcbl; the species is said to be 'facultatively photoheterotrophic,' but it is also stated that the organism does not grow anaerobically in the light [17] a Erythrobacter sp. strain OCh 114 (ATCC 33942), also known as Roseobacter denitrificans [18], has the capacity to grow anaerobically in darkness with nitrate as the terminal electron acceptor; Bchl synthesis is severely inhibited under these growth conditions and light has no effect on the rate of anaerobic growth or denitrification [19].…”