Light-harvesting chlorophyll c-like pigment in Prochloron.

Abstract

A chlorophyll c-like pigment, similar to magnesium-3,8-divinyl pheoporphyrin as monomethyl ester, has been isolated from Prochloron sp. obtained from five species of didemnid ascidians from the Great Barrier Reef, Australia, and from Palau, Micronesia. The pigment represents 4-15% of the total chlorophyll content and is shown to function in a light-harvesting pigment protein complex of Prochloron. The observation that all ofthe major chlorophylls (a+b+c) function in a light-harvesting role in Prochloron and possibly in other prochlorophytes is discussed in terms of the phylogeny of the prochlorophytes.The discovery of Prochloron sp., a symbiotic prokaryotic alga with chlorophyll (Chl) b and Chl a (1, 2), stimulated debate as to the origin of chloroplasts. Discussion has continued to the present time, fueled by the recent discoveries of two other prochlorophytes-the filamentous freshwater alga Prochlorothrix hollandica (3) and the small, unicellular, free-living planktonic alga Prochlorococcus marinus (4). Some view the prochlorophytes as allied to the ancestors of green chloroplasts (4,5), while others consider them as members of the cyanobacteria, which have lost phycobiliproteins and gained Chl b, probably independently, in each group (6-10). The presence of a Chl c-like pigment, tentatively identified as magnesium 3,8-divinylphaeoporphyrin a5 monomethyl ester (MgDVP), has been claimed for Prochlorococcus (4,11), although only the peak wavelengths of the natural and demetallated pigment were provided (11). It also has been claimed that MgDVP occurs in Prochlorothrix hollandica (11) in low concentrations. Here we present evidence, based on the spectra of pigments resolved by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC), that a Chl c-like pigment tentatively identified as MgDVP occurs in Prochloron in concentrations that are 4-15% of the total Chl. Moreover, the pigment is shown to be located in a light-harvesting Chl pigment-protein complex (LHC) and to act as a lightharvesting pigment. MATERIALS AND METHODSProchloron spp. were isolated from five didemnid ascidians (Table 1) at One Tree Reef, Capricorn Section, Great Barrier Reef, as described (15).Analysis ofthe pigments ofProchloron was done on site by reverse-phase HPLC using a Waters 600E quaternary pump system with a Waters 990 photodiode array detector and a Shimadzu RF-551 spectrofluorimeter. The reverse-phase system was used with a C18 column (3.9 x 150 mm Waters Novapak 36975; 4-,um particle size, spherical end-capped material with a low carbon load), and gradient elution with acetonitrile/methanol/water (method 1) was applied as folThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.lows: initial conditions, 95% solvent A/5% solvent B; linear gradient to 1% A/99% B in 15 min; and then held at 1%A/99%o B for 15 min [solvent A = 50% water/25% acetonitrile...

Another View on the Role of Photosynthetic Pigments in Taxonomy of Oxygenic-Phototrophic Bacteria: Proposed Rejection of the Order Prochlorales Florenzano, Balloni, and Materassi 1986 (Emend. Burger-Wiersma, Stal, and Mur 1989), the Family Prochloraceae Florenzano, Balloni, and Materassi 1986, and the Family Prochlorotrichaceae Burger-Wiersma, Stal, and Mur 1989

“…The alignment of amino acid sequences reveals a phylogenetic relationship of this apoprotein to Chl ah-binding polypeptides (29). One has to remember that in accordance with recent evidence, P. marinus and P. didemni contain a Chl c-like pigment together with (divinyl) Chls a and b (7,15). Research with the respective apoprotein(s), especially sequence alignment to the Chl alblc-protein of M. squamata, would explain the molecular evolution of this LHC.…”

“…marinus and P. didemni have both (divinyl) Chl b and a Chl c-like pigment (7,15). In the anonymous marine oxygenicphototrophic bacterium, Chl b coexists with phycoerythrin (13), whereas a small amount of a Chl b-like pigment is present in the phycoerythrin-rich freshwater cyanobacterium Synechococcus sp.…”

“…Thus, divinyl-Chls a and b were discovered in Prochlorococcus marinus (7), whereas a Chl c -like pigment was reported in Prochloron didemni (15) and Prochlorococcus marinus (7). A phycobilisome-less symbiont of colonial ascidians, provisionally named Acaryochloris marina, has been recently shown to contain Chl d as a major pigment (20).…”

Hyperspectral imaging of oil producing microalgae under thermal and nutritional stress.

“…It is more likely that this component is chlorophyll c (chl c). 43,45 However, the spatial distributions of these components are not highly colocalized with the chl a components, so it is unlikely they are involved in the light harvesting complex. Finally, again we see the weak, broad, long wavelength emission as Component 7 suspected to be fucoxanthin.…”

The Microenvironment and Photosynthetic Performance of Prochloron SP. in Symbiosis with Didemnid Ascidians

“…In Prochlorothrix hollandica three Pcb's (A, B & C) have been found; however in Prochloron only one Pcb gene has been found (allied to PcbA/B), along with an isiA protein (La Roche et al 1996). In Prochloron the Pcb protein binds [3,8-divinyl]-protochlorophyllide (Mg-2, 4-divinyl phaeoporphyrin A 5 monomethyl ester), as well as chl's a and b, in a light-harvesting capacity (Larkum et al 1994;Helfrich et al 1999).…”