ROLE OF DTDP-L-RHAMNOSE-DEFICIENT LIPOPOLYSACCHARIDE IN SYMBIOSIS BETWEEN CYANOBACTERIA AND SPONGE

Sponges are filter feeders that take up microorganisms from seawater and digest them by phagocytosis. At the same time, many sponges are known as hosts to a wide diversity of bacteria. The coexistence of food bacteria and symbiotic bacteria inside the sponge raises the question about mechanisms of differentiation between them. A previous study compared symbiont genomes to those of free-living cyanobacteria, and potential adaptation mechanisms to life inside the sponge were revealed. One of these mechanisms was the common loss of genes involved in the production of dTDP-L-rhamnose (which is a residue of the O-antigen of lipopolysaccharide) in symbiotic cyanobacteria.

The purpose of this project is to perform knockout to the gene dTDP-4-dehydrorhamnose reductase (rfbD, EC 1.1.1.133) in the free-living cyanobacterium Synechococcus sp. WH8102, and so to disrupt the formation of normal dTDP-L-rhamnose in this bacterium. To obtain a knockout mutant we have constructed a donor bacterium, which contains a mobilizable suicide plasmid with an interrupted version of the gene that will be transferred to Synechococcus sp. WH8102 by conjugation, thus replacing the wild type gene. The knockout cyanobacterium will then be fed to sponges and its retention and phagocytosis will be compared to that of the wild type cyanobacterium.

Our hypothesis is that the mutated free-living cyanobacterium will not be recognized as food, due to lack of the typical O-antigen, and thus will not be digested by the sponge cells, and rather be stored inside the sponge.