TY - JOUR

T1 - Metabolic Reliance on Photosynthesis Depends on Both Irradiance and Prey Availability in the Mixotrophic Ciliate, Strombidium cf. basimorphum

AU - Hughes, Erin Ann

AU - Maselli, Maira

AU - Sørensen, Helle

AU - Hansen, Per Juel

PY - 2021

Y1 - 2021

N2 - Many species of the ciliate genus Strombidium can acquire functional chloroplasts from a wide range of algal prey and are thus classified as generalist non-constitutive mixotrophs. Little, however, is known about the influence of irradiance and prey availability on their ability to exploit the photosynthetic potential of the chloroplasts, and how this may explain their spatial and temporal distribution in nature. In this study, inorganic carbon uptake, growth, and ingestion rates were measured for S. cf. basimorphum under three different irradiances (10, 40, and 120 mmol photons m-2 s-1) when acclimated to three different prey densities (5 x 103, 1 x 104, and 4 x 104 cells mL-1), as well as when allowed to deplete the prey. After prey depletion, cultures survived without prey longest (~6 days) at the medium irradiance treatment (40 mmol photons m-2 s-1), while ciliate density, inorganic carbon uptake rates, and cellular chlacontent declined fastest at the highest irradiance treatment. This indicates that the ciliates may be unable to maintain the chloroplasts functionally without replacement at high irradiances. Ingestion rates were not shown to be significantly influenced by irradiance. The maximum gross growth efficiency (GGE) in this study (1.1) was measured in cultures exposed to the medium test irradiance and lowest prey density treatment (5 x 103 cells mL-1). The relative contribution of inorganic carbon uptake to the ciliate carbon budget was also highest in this treatment (42%). A secondary GGE peak (0.99) occurred when cultures were exposed to the highest test irradiance and the medium prey density. These and other results suggest that S. cf. basimorphum, and othergeneralist non-constitutive mixotrophs, can flexibly exploit many different environmental conditions across the globe.

AB - Many species of the ciliate genus Strombidium can acquire functional chloroplasts from a wide range of algal prey and are thus classified as generalist non-constitutive mixotrophs. Little, however, is known about the influence of irradiance and prey availability on their ability to exploit the photosynthetic potential of the chloroplasts, and how this may explain their spatial and temporal distribution in nature. In this study, inorganic carbon uptake, growth, and ingestion rates were measured for S. cf. basimorphum under three different irradiances (10, 40, and 120 mmol photons m-2 s-1) when acclimated to three different prey densities (5 x 103, 1 x 104, and 4 x 104 cells mL-1), as well as when allowed to deplete the prey. After prey depletion, cultures survived without prey longest (~6 days) at the medium irradiance treatment (40 mmol photons m-2 s-1), while ciliate density, inorganic carbon uptake rates, and cellular chlacontent declined fastest at the highest irradiance treatment. This indicates that the ciliates may be unable to maintain the chloroplasts functionally without replacement at high irradiances. Ingestion rates were not shown to be significantly influenced by irradiance. The maximum gross growth efficiency (GGE) in this study (1.1) was measured in cultures exposed to the medium test irradiance and lowest prey density treatment (5 x 103 cells mL-1). The relative contribution of inorganic carbon uptake to the ciliate carbon budget was also highest in this treatment (42%). A secondary GGE peak (0.99) occurred when cultures were exposed to the highest test irradiance and the medium prey density. These and other results suggest that S. cf. basimorphum, and othergeneralist non-constitutive mixotrophs, can flexibly exploit many different environmental conditions across the globe.

U2 - 10.3389/fmicb.2021.642600

DO - 10.3389/fmicb.2021.642600

M3 - Journal article

C2 - 34220736

VL - 12

JO - Frontiers in Microbiology

JF - Frontiers in Microbiology

SN - 1664-302X

M1 - 642600

ER -