Sucrose in bloom-forming cyanobacteria: loss and gain of genes involved in its biosynthesis

M.A. KOLMAN; G.L. SALERNO

ENVIRONMENTAL MICROBIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2015

1462-2912

Bloom-forming cyanobacteria are widelydistributed in freshwater ecosystems. To cope with salinity fluctuations,cyanobacteria synthesize compatible solutes, such as sucrose, to maintain theintracellular osmotic balance. The screening of cyanobacterial genomes revealedthat homologs to sucrose-metabolism related genes only occur in fewbloom-forming strains, mostly belonging to Nostocales and Stigonematales orders.Remarkably, among Chroococcales and Oscillatoriales strains, homologs were onlyfound in M. aeruginosa PCC 7806 and Leptolyngbya boryana PCC6306, suggesting a massive loss of sucrose metabolism in bloom-forming strains ofthese orders. The complete functional characterization of sucrose genes in M.aeruginosa PCC 7806 led to the conclusion that sucrose metabolism depends on theexpression of a gene cluster that is unique amongall sucrose-containing cyanobacteria and defines a transcriptional unit. It wasalso demonstrated that the expression of the encoding genes of sucrose-relatedproteins is stimulated by salt. In view of its ancestral origin incyanobacteria, the fact that most bloom-forming strains lack sucrose metabolismindicates that the genes involved might have been lost during evolution.However, in a particular strain, like M. aeruginosa PCC 7806, sucrose-synthesisgenes were probably regained by horizontal gene transfer, which could behypothesized as a response to salinity fluctuations.