The phylogeny of Prochloron

Abstract

Prochloron, a unicellular alga that combines some features of cyanophytes with others of chlorophytes, is a phylogenetic enigma. Mounting evidence from electron microscopy, comparative biochemistry and molecular biology now suggests that prochlorophytes probably arose from blue-green algal ancestors, perhaps less than 10³ years ago.     

Antenna ring around trimeric Photosystem I in chlorophyll b containing cyanobacterium Prochlorothrix hollandica

Prochlorothrix hollandica is one of the three known species of an unusual clade of cyanobacteria (formerly called “prochlorophytes”) that contain chlorophyll a and b molecules bound to intrinsic light-harvesting antenna proteins. Here, we report the structural characterization of supramolecular complex consisting of Photosystem I (PSI) associated with the chlorophyll a/b-binding Pcb proteins. Electron microscopy and single particle image analysis of negatively stained preparations revealed that the Pcb-PSI supercomplex consists of a central trimeric PSI surrounded by a ring of 18 Pcb subunits. We conclude that the formation of the Pcb ring around trimeric PSI represents a mechanism for increasing the light-harvesting efficiency in chlorophyll b-containing cyanobacteria.     

Intracellular coagulation inhibits the extraction of proteins from Prochloron

Protein extraction from the prokaryotic alga Prochloron LP (isolated from the ascidian host Lissoclinum patella) was complicated by an irrevers     

Ultrastructural studies on the membrane systems and cell inclusions of the filamentous prochlorophyte Prochlorothrix hollandica

The outer membrane of Prochlorothrix hollandica is covered with a network of fine fibrils on its surface and separated from the cytoplasmic membrane by an electrondense peptidoglycan layer (8 to 20 nm thick). The thylakoid membranes are arranged in stacked and unstacked regions which present four characteristic fracture faces with different numbers and sizes of intramembrane particles. Cell inclusions such as polyhedral bodies (carboxysomes), ribosomes, and polyphosphate granules were found in Prochlorothrix hollandica. Another type of cell inclusions was identified by its characteristic shape (a cylindre with conical caps) and a regular striation as gas vesicles. It is concluded that the organism is in its morphological structure similar to the cyanobacteria.Abbreviations C carboxysome - CM cytoplasmic membrane - EF_s, EF_u exoplasmic fracture face of stacked and unstacked membrane area, respectively - ES exoplasmic surface - PF_s, PF_u plasmic fracture face of stacked and unstacked membrane area, respectively - PG peptidoglycan layer - TM thylakoid membrane Dedicated to Prof. Dr. D. Peters, Hamburg, on the occasion of his 75th birthday     

LIPIDS AND CHEMOTAXONOMY OF PROCHLOROTHRIX HOLLANDICA,A PLANKTONIC PROKARYOTE CONTAINING CHLOROPHYLLS a AND b1

The lipid composition of a planktonic prokaryote, Prochlorothrix hollandica Burger-Wiersma, isolated from Lake Loosdrecht (The Netherlands) has been determined. This species is only the second prokaryote that has been found to contain chlorophylls a and b. Its lipid composition is similar to that of another prochlorophyte, Prochloron didemni Lewin, as well as to some cyanobacteria and bacteria, but there are also some unique features. Major fatty acids were 14:0, 14: 1ω5, 16:0, 16: 1ω7 and two novel fatty acids 16: 1ω12 (hexadec-4-enoic acid) and a new 16:2 isomer. Double bond positions in monounsaturated fatty acids and alkenes were determined by derivatization with dimethyl disulfide followed by analysis of the products by gas chromatography-mass spectrometry. Hydrocarbons consisted mainly of the pentacyclic triterpene hop-22(29)-ene and straight-chain n-heptadecane and n-heptadec-5-ene. The presence of hopanoids, low abundance of triacylglycerols and absence of sterols clearly show that the lipid biochemistry of this organism is more closely related to that of prokaryotes than to eukaryotes even though it contains chlorophyll b which is more typical of green algae. Implications of these data to chemotaxonomic studies of this unusual group of prokaryotes are discussed.     

Prochlorophyta – a matter of class distinctions

Prochloron (a marine symbiont) and Prochlorothrix (from freshwater plankton) contain chlorophylls a and b; Prochlorococcus (common in marine picoplankton) contains divinyl-chlorophylls a and b. Like cyanophytes they are all clearly photosynthetic prokaryotes, but since they contain no blue or red bilin pigment they were assigned to a new algal sub-class, the Prochlorophyta. However, since their possible phylogenetic relationships to ancestral green-plant chloroplasts have not received support from molecular biology, it now seems expedient to consider them as aberrant cyanophytes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Lipopolysaccharide in the outer membrane of the filamentous prochlorophyte Prochlorothrix hollandica

Abstract A lipopolysaccharide (LPS) fraction was isolated from Prochlorothrix hollandica by hot phenol/water extraction. Negatively stained preparations of an aqueous LPS dispersion showed the triple-layered appearance of the LPS aggregates. Glucose (main sugar), rhamnose, fucose, galactose, mannose, xylose, and 3- O -methyl-xylose were found as the constituents of the polysaccharide moiety. Glucosamine and the 3-hydroxy fatty acids, 3-OH-16:0, 3-OH-14:0, and the rarely detected iso-3-OH-15:0, constitute the lipid A of the LPS. l -glycero- d -manno-heptose and 3-deoxy- d -manno-2-octulosonic acid (dOclA), typical components of inner core oligosaccharides from enterobacterial LPS, were lacking in the isolated LPS fraction from Prochlorothrix hollandica .