High vertical and low horizontal diversity of Prochlorococcus ecotypes in the Mediterranean Sea in summer.
Natural populations of the marine cyanobacterium Prochlorococcus exist as two main ecotypes, inhabiting different layers of the ocean's photic zone. These so-called high light- (HL-) and low light (LL-) adapted ecotypes are both physiologically and genetically distinct. HL strains can be separated into two major clades (HLI and HLII), whereas LL strains are more diverse. Here, we used several molecular techniques to study the genetic diversity of natural Prochlorococcus populations during the Prosope cruise in the Mediterranean Sea in the summer of 1999. Using a dot blot hybridization technique, we found that HLI was the dominant HL group and was confined to the upper mixed layer. In contrast, LL ecotypes were only found below the thermocline. Secondly, a restriction fragment length polymorphism analysis of PCR-amplified pcb genes (encoding the major light-harvesting proteins of Prochlorococcus) suggested that there were at least four genetically different ecotypes, occupying distinct but overlapping light niches in the photic zone. At comparable depths, similar banding patterns were observed throughout the sampled area, suggesting a horizontal homogenization of ecotypes. Nevertheless, environmental pcb gene sequences retrieved from different depths at two stations proved all different at the nucleotide level, suggesting a large genetic microdiversity within those ecotypes.
Garczarek
Laurence
L
Station Biologique, UMR 7144 CNRS & Université Pierre et Marie Curie, Roscoff, France. garczare@sb-roscoff.fr
Dufresne
Alexis
A
Rousvoal
Sylvie
S
West
Nyree J
NJ
Mazard
Sophie
S
Marie
Dominique
D
Claustre
Hervé
H
Raimbault
Patrick
P
Post
Anton F
AF
Scanlan
David J
DJ
Partensky
Frédéric
F
D001426:Bacterial Proteins / Q000235:genetics*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D017753:Ecosystem; D014644:Genetic Variation; D005843:Geography; D045342:Light-Harvesting Protein Complexes / Q000235:genetics*; D008522:Mediterranean Sea; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D048929:Prochlorococcus / Q000145:classification / Q000235:genetics*; D017422:Sequence Analysis, DNA
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D045342:Light-Harvesting Protein Complexes