Cyanobacterial blue color formation during lysis under natural conditions

Abstract

Cyanobacteria produce numerous volatile organic compounds (VOCs), such as β-cyclocitral, geosmin, and 2-methylisoborneol, which show lytic activity against cyanobacteria. Among these compounds, only β-cyclocitral causes a characteristic color change from green to blue (blue color formation) in the culture broth during the lysis process. In August 2008 and September 2010, the lysis of cyanobacteria involving blue color formation was observed at Lake Tsukui in northern Kanagawa Prefecture, Japan. We collected lake water containing the cyanobacteria and investigated the VOCs, such as β-cyclocitral, β-ionone, 1-propanol, 3-methyl-1-butanol, and 2-phenylethanol, as well as the number of cyanobacterial cells and their damage and pH changes. As a result, the following results were confirmed: the detection of several VOCs, including β-cyclocitral and its oxidation product, 2,2,6-trimethylcyclohexene-1-carboxylic acid; the identification of phycocyanin based on its visible spectrum; the lower pH (6.7 and 5.4) of the lysed samples; and characteristic morphological change in the damaged cyanobacterial cells. We also encountered the same phenomenon on 6 September 2013 in Lake Sagami in northern Kanagawa Prefecture and obtained almost the same results, such as blue color formation, decreasing pH, damaged cells, and detection of VOCs, including the oxidation products of β-cyclocitral. β-Cyclocitral derived from Microcystis has lytic activity against Microcystis itself but has stronger inhibitory activity against other cyanobacteria and algae, suggesting that the VOCs play an important role in the ecology of aquatic environments.

FIG 1

Cyanobacterial blue color formation during the lysis process on 3 August 2001 (A), 5 August 2008 (B), 14 September 2010 (C), and 6 September 2013 (D).

FIG 2

Map of the sampling sites and the places where formation of blue color occurred near the dam at Lake Sagami (A) and Lake Tsukui (B). The gray shading indicates dense cyanobacterial blooms.

FIG 3

The collected sample (right) and the filtrate (left) from Lake Tsukui on 5 August 2008.

FIG 4

Light micrographs of scum samples collected from Lakes Tsukui and Sagami. (A) Living cells of cyanobacteria collected at Lake Tsukui on 5 August 2008. (B) Dead cells of cyanobacteria collected on 12 August 2008. (C) Most of the vegetative cells of Microcystis and Anabaena were lysed in the sample from 6 September 2013 from Lake Sagami. (D and E) Heterocysts of Anabaena (D) and P. mucicola (E) remained in a sample from 6 September 2013 from Lake Sagami. M. a, M. aeruginosa; A. a, A. affinis; A. f, A. flos-aquae; A. c, A. crasssa. Panels A to D are phase-contrast micrographs, and panel E is an epifluorescence microscopy image (excitation wavelength, 530 to 550 nm).

FIG 5

Species composition of cyanobacteria collected on 5 and 12 August 2008, 14 September 2010, and 6 September 2013. The asterisks indicate the occurrence of blue color formation.

FIG 6

Structures of β-cyclocitral and its oxidation products, together with β-ionone, detected in samples collected from Lake Sagami on 6 September 2013.