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Brief History of S. elongatus sp. PCC 7942

Synechococcus elongatus sp. PCC 7942 is the official name of a cyanobacterium that was isolated prior to 1973 from a local freshwater source by students taught by K.W. Floyd at California State University, San Francisco.

Several samples were transferred to S.V. Shestakov of Moscow State University, whose laboratory demonstrated that one of the isolates, termed R-2, was transformable by chromosomal DNA from an antibiotic-resistant strain in their collection called Anacystis nidulans 602. The California isolate became known for many years as A. nidulans R2.

In 1978 C.A.M.J.J. van den Hondel brought the strain from Moscow to the laboratory of G. van Arkel (University of Utrecht), where he was able to isolate mutants that carried the selectable transposon Tn901 in the small endogenous plasmid of A. nidulans R2. This work began the era of recombinant DNA-based molecular genetics research in cyanobacteria.

Drs van den Hondel and van Arkel deposited the strain in the Pasteur Culture Collection, where it was given the accession number PCC 7942. A re-evaluation of the taxonomic structure of the cyanobacteria in the mid-1980s resulted in a renaming of previous Anacystis strains to the genus Synechococcus. For a period of several years, publications regarding this organism referred to it as Synechococcus sp. strain PCC 7942 without a species designation. A second edition of Bergey’s Manual of Systematic Bacteriology was published in 2001 which included a section on the classification of cyanobacteria. A chapter by M. Herdman, R. Castenholz, J. Waterbury, and R. Rippka described the Synechococcus clade Cluster 1.1, typified by PCC 6301, which is so closely related to PCC 7942 as to be members of the same species. These authors proposed the binomial Synechococcus elongatus, which is a name in keeping with the Botanical Code of Nomenclature.

Most papers published since that date refer to the former A. nidulans R2 as S. elongatus PCC 7942. Note that the name Synechococcus elongatus had been used previously with reference to thermophilic cyanobacteria that are phylogenetically distant from PCC 6301 and 7942. The name Thermosynechococcus elongatus is now used for those thermophilic strains, but care is advisable in reading the literature to distinguish the S. elongatus that refers to PCC 7942 and PCC 6301, typically grown at 30°C, from the relatives of T. elongatus, typically grown at 45–50°C.

Know your bacteria! 😎 (Box 2 from article)

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