Acclimation of Trichodesmium erythraeum ISM101 to high and low irradiance analysed on the physiological, biophysical and biochemical level

Abstract

Summary• As the nonheterocystous diazotrophic cyanobacterium Trichodesmium lives both at the ocean surface and deep in the water column, it has to acclimate to vastly different irradiances. Here, we investigate its strategy of light acclimation in several ways.• In this study, we used spectrally resolved fluorescence kinetic microscopy to investigate the biophysics of photosynthesis in individual cells, analysed cell extracts for pigment and phycobiliprotein composition, measured nitrogenase activity and the abundance of key proteins, and assayed protein synthesis ⁄ degradation by radioactive labelling.• After acclimation to high light, Trichodesmium grew faster at 1000 lmol m )2 s )1 than at 100 lmol m )2 s )1 . This acclimation was associated with decreasing cell diameter, faster protein turnover, the down-regulation of light-harvesting pigments and the outer part of the phycobiliprotein antenna, the up-regulation of light-protective carotenoids, changes in the coupling of phycobilisomes to the reaction centres and in the coupling of individual phycobiliproteins to the phycobilisomes. The latter was particularly interesting, as it represents an as yet unreported light acclimation strategy.• Only in the low light-acclimated culture and only after the onset of actinic light did phycourobilin and phycoerythrin contribute to photochemical fluorescence quenching, showing that these phycobiliproteins may become quickly (in seconds) very closely coupled to photosystem II. This fast reversible coupling also became visible in the nonphotochemical changes of the fluorescence quantum yield.

Investigating the role of trichodesmium spp. in the oceanic nitrogen cycle through observations and models

“…Physiological adaptations to low irradiance have been observed in Trichodesmium in culture, including increased cell diameter for light absorption and changes in coupling of phycobilisomes with the photochemical reaction centers (Andresen et al, 2010). If, in fact, this population exhibits anomalous nitrogen fixation rates, the effect cannot be captured by this study.…”

“…On longer timescales, physiological adaptations to low irradiance have been observed in Trichodesmium in culture, including increased cell diameter for light absorption and changes in coupling of phycobilisomes with the photochemical reaction centers (Andresen et al, 2010).…”

Effects of nanomolar copper on water plants—Comparison of biochemical and biophysical mechanisms of deficiency and sublethal toxicity under environmentally relevant conditions

“…The area just before the branching (approximate size of 1.1 mm x 1.1 mm) was used for the kinetics measurement. A detailed description of the microscope and the used protocols of the Kautsky induction can be found in Küpper et al (2007a) and Andresen et al (2010). These measurements were done weekly, but values from the beginning (week 1+2), the middle (3+4), or end (5+6) of the treatment, respectively, were averaged to reduced the noise level.…”

Interactions between CCM and N2 fixation in Trichodesmium

“…In its natural habitat, Trichodesmium is subject to a highly variable light regime and so it is not surprising that Trichodesmium shows high plasticity in light acclimation (Andresen et al 2010). These acclimation mechanisms include modifications in pigment composition, enhanced protein turnover (Andresen et al 2010) and state transition, i.e., reversible uncoupling of phycobilisomes or individual pycobiliproteins from PSI and PSII (Küpper et al 2004). This high flexibility in light capture efficiency enables effective energy generation by Trichodesmium, thereby avoiding drawbacks like D1 protein degradation or superoxide production at PSII.…”