KEEP YOUR FRIENDS CLOSE AND YOUR COMPETITORS CLOSER: NOVEL INTERSPECIES INTERACTION IN DESERT BIOLOGICAL SAND CRUSTS

We have identified a novel association between a green alga (Chlorella ohadii) and a filamentous cyanobacterium (Leptolyngbya ohadii) isolated from desert biological soil crusts (BSCs), one of the harshest environments on Earth. We showed that ability of C. ohadii to revive after desiccation depends on close contact with L. ohadii, an important primary producer in the BSCs.

Water storage in the cyanobacterial extracellular polysaccharides (EPS) probably provides C. ohadii cells with gradual desiccation, required to acclimate to oncoming dryness. However, axenic C. ohadii cultures are unable to resume growth even after very slow dehydration, suggesting that the protective role of EPS may extend beyond the dehydration rate. C. ohadii is also able to grow on EPS in the dark.

In spite of its enormous growth and photosynthetic capabilities, C. ohadii is present in low abundance in its natural environment and was isolated as a contamination L. ohadii culture, where confocal imaging showed a close association between the two (see image).

It is likely that association of the alga and cyanobacteria may lead to competition for resources in the BSC. Thus, it is not surprising that growth of C. ohadii is inhibited in the presence of L. ohadii in lab cultures. It seems this fascinating algal-cyanobacterial relationship is controlled by the cyanobacteria, allowing algal survival on one hand, while limiting growth on the other. We shall present our current understanding of the underlying mechanisms, including unique bacterial-originated genes in C. ohadii`s genome potentially involved.