Distribution of chloropigments in suspended particulate matter and benthic microbial mat of a meromictic lake, Lake Kaiike, Japan |
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Authors: | Nakajima Yoji Okada Hisatake Oguri Kazumasa Suga Hisami Kitazato Hiroshi Koizumi Yoshikazu Fukui Manabu Ohkouchi Naohiko |
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Institution: | Graduate School of Science, Hokkaido University, Sapporo, 060–0810, Japan.; Institute for Frontier Research on Earth Evolution, Yokosuka, 237–0061, Japan.; Department of Biology, Tokyo Metropolitan University, Tokyo, 192–0397, Japan. |
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Abstract: | We investigated the distribution of chloropigments in a small meromictic lake, Lake Kaiike, south-west Japan. In the water-column, concentrations of Chl a related to cyanobacteria, BChl a related to purple sulphur bacteria, and three types of BChl e homologues (BChls e1, e2 and e3) related to brown-coloured green sulphur bacteria, were maximal at the redox boundary. Below the redox boundary, absolute concentrations of Chl a and BChl a gradually decreased with depth, whereas BChls e remained rather constant. Suspended particulate matter (SPM) at the deeper region of the anoxic water-column was enriched in highly alkylated BChl e homologues compared with SPM at the redox boundary. The shift in the relative content of highly alkylated BChl e homologues beneath the boundary was associated with community related adaptation of brown-coloured green sulphur bacteria to changes in light quality/quantity, resulting from the optical absorption and reflectance of SPMs in the overlying water-column. Benthic microbial mats were characterized by high abundances of BChls e, in which highly alkylated homologues were substantially abundant. This suggests that the BChls e in the microbial mat may be derived from the low-light adapted brown-coloured green sulphur bacteria forming the bacterial mat. |
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