PI-130:

Ecological significance of chlorophyll f within a microbial mat

Chlorophyll (Chl) f is a recently discovered photosynthetic pigment, which absorbs far-red (FR) light (700-750 nm). Various species of Chl f-producing cyanobacteria have been reported and they synthesized Chl f only when grown under FR-LED as a sole light source. Therefore, we hypothesized that Chl f was distributed only in certain environments where FR light mainly existed, and it would function as antenna pigments. The lower layer of microbial mat might be one of such environments, because the photosynthetic organisms living in surface layer absorb photosynthetic active radiation (400_700 nm). In this study, we aimed to reveal the vertical distribution and functions of Chl f within a microbial mat.
A piece of about 7 mm thick microbial mat was collected at the Nakabusa hot spring in Japan. After the mat was sliced into 0.5-mm sections, the compositions of chlorophylls and microorganisms were analyzed by using HPLC and PCR-DGGE, respectively. The downward spectral irradiance at every 0.5-mm of depth in intact mat was measured by using a fiber optic spectrometer. We isolated cyanobacteria from the mat and examined their growth characteristics under FR-light.
As a result, Chl f was detected only 4.0_6.5 mm below surface in the microbial mat, where blue and red light markedly decreased and a few percent of FR light remained. PCR-DGGE analysis showed that two species of Leptolyngbya were also distributed at the same range of depth, and two species of Synechococcus were detected from all sliced sections. Among them, one species of Synechococcus and two species of Leptolyngbya were isolated. Synechococcus strain did not produce Chl f and could not grow under FR-LED. On the other hand, both of Leptolyngbya strains produced Chl f and grew under FR-LED. These results suggested that the lower layer of microbial mat was one of the niches for Chl f-producing cyanobacteria, and Chl f enabled them to coexist with other cyanobacteria in the mat.

keywords:Niche differentiation,Chlorophyll f,Cyanobacteria,Hot spring microbial mat