Ecological physiology of the black band disease cyanobacterium Phormidium corallyticum

Abstract

Laboratory studies were carried out to assess the photosynthetic and nitrogen-fixing capabilities of the gliding, filamentous cyanobacterium Phormidium corallyticum. This species is found on coral reefs, and is one of the members of a pathogenic microbial consortium called black band disease of corals, a unique horizontally migrating microbial mat with an active sulfuretum. It was determined that P. corallyticum can perform oxygenic photosynthesis in the presence or absence of sulfide, but cannot conduct (DCMU-forced) anoxygenic photosynthesis with sulfide as electron donor. Photosynthesis vs. irradiance curves revealed a very low threshold for Pmax of <30 μE m −2 s −1. Temperature optima for photosynthetic activity were at and above 30°C. Neither a laboratory culture of P. corallyticum nor freshly collected samples of the black band microbial consortium were capable of fixing N 2. Results are discussed in terms of the ecology of this coral disease.