KEEP YOUR FRIENDS CLOSE AND YOUR COMPETITORS CLOSER: LOVE HATE RELATIONSHIP IN DESERT BIOLOGICAL SAND CRUSTS

We have identified a unique and novel mode of interspecies interaction between two desert biological soil crusts (BSCs) - inhabiting organisms, a green alga, Chlorella ohadii, and a cyanobacterium, Leptolyngbya ohadii. The latter is an important primary producer in the BSC, one of the harshest environments on Earth. Using a tailor-made chamber accurately simulating crust conditions, we show that ability of C. ohadii to revive after frequent desiccation depends on close contact with L. ohadii.

In spite of its enormous growth and photosynthetic capabilities, C. ohadii is found in low abundance in its natural environment and was originally isolated as a contamination in a decaying culture of L. ohadii; confocal imaging (FIGURE 1)showed close association between them, raising the possibility that they may compete for resources in the BSC. Indeed, laboratory experiments showed that growth of C. ohadii is severely inhibited by the presence of L. ohadii.

Water storage in the cyanobacterial extracellular polysaccharides (EPS) provides C. ohadii cells with additional time required to acclimate themselves to the forthcoming dryness. However, the fact that axenic C. ohadii cultures are unable to resume growth even after very slow dehydration, suggests that the protective role of EPS may extend beyond the dehydration rate, a possibility supported by C. ohadii ability to grow on EPS in darkness.

Apparently, this fascinating algal-cyanobacterial “arms race” is controlled by the cyanobacterium allowing the alga survival in one hand, but limiting its growth, on the other.

We shall present our current genetic-based understanding of the underlying mechanism, including unique bacterial-originated genes in C. ohadii genome.