The lowering of external pH in confined environments by thermo‐acidophilic algae (class: Cyanidiophyceae)

Abstract

The unicellular, asexual thermo-acidophilic algae of the class Cyanidiophyceae, order Cyanidiales (the 'cyanidia') include only three genera, walled Cyanidium and Galdieria, and 'naked' Cyanidioschyzon, names based on morphological and cytological characters. Most species and strains of this class live in acid hot springs or acid soils or steam vents associated with these springs at pH 0.5 to ~ 4.0 at temperatures of ~ 38-56 °C. No other phototrophs live in this combination of factors in these habitats, except for a small overlap with other acidophilic algae at the highest pH and the lowest temperature. The optimum pH for growth of the 'cyanidia' in this study was ~ 2.3. Galdieria-like walled cells of Cyanidioschyzon and naked Cyanidioschyzon cells were exposed in culture to higher pH conditions of 6.0, 5.5 and 5.0 in confined, illuminated environments (cotton plugged flasks). The subsequent acidification of the medium towards or to 2.3 occurred as growth and biomass increased. There was a direct correlation with final biomass (Chl a) and lower pH. All eight strains isolated from Yellowstone acidic conditions were able to lower the supra-optimal pH of their medium, while only two from other continents and none of the three from Japan were competent. It is probable that the ability to lower pH to an optimal level has survival value in some niches in natural habitats.

Prevalent pH Controls the Capacity of Galdieria maxima to Use Ammonia and Nitrate as a Nitrogen Source

“…In contrast, the Icelandic ACUF551 and the Turkish ACUF769, both isolated from acidic sites, showed the best growth performances at pH 6.5 and 6, respectively, during the whole experiment. As reported by Lowell and Castenholz (2013), a different ability in lowering pH was also shown by C. merolae: Eight strains isolated from Yellowstone were able to reduce the pH of the medium, while none of the three Japanese isolates was competent; the authors also highlighted variations in the final yields, ascribing them both to small differences in inoculum density and in real genetic differences among the competent strains [22]. Among our isolates, two of the Turkish strains (ACUF773, ACUF648) from non-acidic sites quickly lowered the pH to values 3.39-3.42, thus allowing a faster growth, which could be a reliable survival strategy in otherwise hostile environments.…”

“…The discovery of G. maxima strains from non-acidic thermal areas and the capacity to tolerate a wide range of initial environmental pHs are strong evidence of their potential adaptation to changing environments. As reported by Lowell and Castenholtz (2013), the ability of several Cyanidiophycean strains in lowering the pH could be an important survival strategy in confined environments, such as microbial mats, interstitial soil spaces, and endolithic niches, rendering them able to survive in non-acidic environments [22]. This could potentially serve as a connection between the thermoacidic locations as a mechanism of long-distance migration [3,20].…”

“…The acidophily was considered as one of the main factors limiting the dispersal and survival of Cyanidiophyceae; nevertheless, recent explorations in Turkey provided the ubiquity of Cyanidia in several Turkish thermal baths, mostly on neutral and sub neutral soils (pH 5.8-7), growing as thin biofilms hypolithically and endolithically [13]. The ability to lower the external pH from 6 to more acidic values was tested by Lowell and Castenholtz (2013) on several Cyanidiophiceae strains collected from Yellowstone, Japan, Philippines, and New Zealand hot springs, suggesting the importance of this process as a survival strategy in nonacidic environments during long-distance migration [3,20,22]. Growth in the sub-neutral medium was also evaluated by Henkanatte-Gedera et al (2017), both at the laboratory and field scale.…”

Prevalent pH Controls the Capacity of Galdieria Maxima to Use Ammonia and Nitrate as a Nitrogen Source

“…In contrast, the Icelandic ACUF551 and the Turkish ACUF769, both isolated from acidic sites, showed the best growth performances at pH 6.5 and 6, respectively, during the whole experiment. As reported by Lowell and Castenholz (2013) a different ability in lowering pH was also shown by C. merolae: eight strains isolated from Yellowstone were able to reduce the pH of the medium, while none of the three Japanese isolates was competent; the authors also highlighted variations in the final yields, ascribing them both to small differences in inoculum density and in real genetic differences among the competent strains [23]. Among our isolates, two of the Turkish strains (ACUF773, ACUF648) from non-acidic sites quickly lowered the pH to values 3.39-3.42, thus allowing a faster growth, which could be a reliable survival strategy in otherwise hostile environments.…”

Letter from the Editors

“…In the last paper, which is focused on the future of life on our planet, Mautner [29] regards it as a unique phenomenon and proposes exporting life into space via directed panspermia. If we actually decide to do so in the future, good candidates for such expeditions would be the red algae Cyanidiales, which are well known for dwelling in extreme environments [30].…”