Photosynthesis of an endolithic <i>Chlorococcum</i> alga (Chlorophyta, Chlorococcaceae) from travertine calcium carbonate rocks of a tropical limestone Spring
Creators: name: Ritchie, Raymond J.
name: Sma-Air, Suhailar
Publisher: name: Taylor & Francis
Year: 2022
Subjects: subject: Space Science
subject: Medicine
subject: Microbiology
subject: FOS: Biological sciences
subject: Cell Biology
subject: 59999 Environmental Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: Ecology
subject: 69999 Biological Sciences not elsewhere classified
subject: Inorganic Chemistry
subject: Plant Biology

description: A green alga, <i>Chlorococcum</i> sp. (Chlorococcales, Chlorophyceae), was grown from scrapings of the travertine rocks from the outlet stream of the Emerald Pool, Khlong Thom Nuea, Khlong Thom District Krabi province in Southern Thailand – a classic karstic stream habitat. It was a recalcitrant alga: organic solvents did not extract chlorophyll (Chl) from the algae very well but heated Dimethylsulphoxide (DMSO) was effective. Rapid light curve PAM experiments were used to quantify photosynthetic parameters: E<sub>opt</sub> = 275 ± 9.7 µmol photons m<sup>–2</sup> s<sup>–1</sup>, ETR<sub>max</sub> = 277 ± 5.99 µmol e<sup>–</sup> g<sup>–1</sup> Chl <i>a</i> s<sup>–1</sup>, photosynthetic efficiency (Alpha, α<sub>0</sub>) = 2.248 ± 0.112 e<sup>–</sup> g<sup>–1</sup> Chl <i>a</i>. For <i>Chlorococcum</i> sp. deliberately grown in very low light, E<sub>opt</sub> = 290 ± 4.89 µmol photons m<sup>–2</sup> s<sup>–1</sup> but ETR<sub>max</sub> = 109 ± 0.97 µmol e<sup>–</sup> g<sup>–1</sup> Chl <i>a</i> s<sup>–1</sup>, Alpha (α<sub>0</sub>) = 1.010 ± 0.192 e<sup>–</sup> g<sup>–1</sup> Chl <i>a</i>. Overall, the amount of Chl <i>b</i> compared with Chl <i>a</i> was relatively low for most Chl <i>a + b</i> organisms (Chl <i>b/a</i> ≈ 0.21) but the ratio was not strongly affected by irradiance. The changes in ETR<sub>max</sub> and α<sub>0</sub> indicate that the <i>Chlorococcum</i> sp, responded to very low irradiance by increasing total Chl as Chl <i>a</i>, a marginal decrease in Chl <i>b/a</i> ratio but no substantial change in far-red absorption. The spectrum stripping technique confirmed <i>Chlorococcum</i> sp, is a Chl <i>a + b</i> organism albeit with a low Chl <i>b</i> content. Photosynthesis in this species was not very sensitive to pH in the range pH 5–9 but was inhibited at pH 10, indicating that it was very capable of using HCO<sub>3</sub><sup>–</sup> as an inorganic carbon source. <i>Chlorococcum</i> has a carbon concentrating mechanism (CCM), however based on its insensitivity to the depolarizing effects of high [K<sup>+</sup>], it is unlikely to be dependent on the membrane potential across the cell membrane. The alga is homiochlorophyllous and recovers rapidly from dessication without synthesis of new chlorophyll. The green unicellular alga <i>Chlorococcum</i> was found growing in travertine rock,Has Chl <i>b/a</i> ratio typical of green algae, contrasting with <i>Ostreobium</i>,Rapid light curves show optimum irradiance at about 300 µmol photons m<sup>–2</sup> s<sup>–1</sup>,<i>Chlorococcum</i> has a carbon concentrating mechanism (CCM),Homiochlorophyllous alga quickly recovering from desiccation without synthesizing new chlorophyll. The green unicellular alga <i>Chlorococcum</i> was found growing in travertine rock, Has Chl <i>b/a</i> ratio typical of green algae, contrasting with <i>Ostreobium</i>, Rapid light curves show optimum irradiance at about 300 µmol photons m<sup>–2</sup> s<sup>–1</sup>, <i>Chlorococcum</i> has a carbon concentrating mechanism (CCM), Homiochlorophyllous alga quickly recovering from desiccation without synthesizing new chlorophyll.