Prochlorococcus , a Marine Photosynthetic Prokaryote of Global Significance

Abstract

SUMMARY The minute photosynthetic prokaryote Prochlorococcus, which was discovered about 10 years ago, has proven exceptional from several standpoints. Its tiny size (0.5 to 0.7 μm in diameter) makes it the smallest known photosynthetic organism. Its ubiquity within the 40°S to 40°N latitudinal band of oceans and its occurrence at high density from the surface down to depths of 200 m make it presumably the most abundant photosynthetic organism on Earth. Prochlorococcus typically divides once a day in the subsurface layer of oligotrophic areas, where it dominates the photosynthetic biomass. It also possesses a remarkable pigment complement which includes divinyl derivatives of chlorophyll a (Chl a) and Chl b, the so-called Chl a2 and Chl b2, and, in some strains, small amounts of a new type of phycoerythrin. Phylogenetically, Prochlorococcus has also proven fascinating. Recent studies suggest that it evolved from an ancestral cyanobacterium by reducing its cell and genome sizes and by recruiting a protein originally synthesized under conditions of iron depletion to build a reduced antenna system as a replacement for large phycobilisomes. Environmental constraints clearly played a predominant role in Prochlorococcus evolution. Its tiny size is an advantage for its adaptation to nutrient-deprived environments. Furthermore, genetically distinct ecotypes, with different antenna systems and ecophysiological characteristics, are present at depth and in surface waters. This vertical species variation has allowed Prochlorococcus to adapt to the natural light gradient occurring in the upper layer of oceans. The present review critically assesses the basic knowledge acquired about Prochlorococcus both in the ocean and in the laboratory.

Changes in water color shift competition between phytoplankton species with contrasting light‐harvesting strategies

“…As predicted, these two genera coexist in many regions across the global ocean but their distributions do not completely overlap (Ting et al 2002, Flombaum et al 2013. In agreement with the model predictions, Prochlorococcus uses chlorophyllbased light-harvesting antennae and is particularly abundant in blue waters of the oligotrophic subtropical gyres (Partensky et al 1999, Biller et al 2015, whereas the PBS-containing Synechococcus prevails in slightly more turbid oceanic and coastal waters dominated by greenish blue and green light (Scanlan and West 2002, Ting et al 2002, Gr ebert et al 2018. Moreover, the highly diverse Synechococcus genus comprises several pigment types, that have branched out over a wide range of aquatic ecosystems in accordance with the underwater light colors that can be captured by their phycobili-pigments (Stomp et al 2007, Gr ebert et al 2018).…”

Wide genetic diversity of picoplanktonic green algae (Chloroplastida) in the Mediterranean Sea uncovered by a phylum‐biased PCR approach

“…The importance of Chloroplastida in marine environments was first established by the pioneering work of Johnson and Sieburth (1982) using electron microscopy on natural samples. Later, the detection of chlorophyll b, a characteristic pigment of green algae, in different oceanic and coastal environments (Rodríguez et al, 2002) confirmed the ubiquity of Chloroplastida in marine waters, although in very oligotrophic regions part of this chlorophyll b can in fact be divinyl chlorophyll b originating from the cyanobacterium Prochlorococcus (Partensky et al, 1999). More recently, quantitative analyses using specific molecular probes detected by fluorescent in situ hybridization (FISH) have demonstrated that green algae, and particularly prasinophytes, can be one of the principal components of picoeukaryotic communities .…”

Bacterial community structure of a lab‐scale anammox membrane bioreactor

“…Prochlorococcus species are photosynthetic cyanobacteria that have been aimed at important microorganisms in primary production at global scale. 40 Low-light radiation adapted Prochlorococcus species have been identified at sea ecosystems. 41 Also, syntrophy between anammox bacteria and picocyanobacteria in the cycle of nitrite, nitrate, and nitrous oxide at oxygen minimum zones of northern Chile sea has been proposed.…”