Deciphering the relationship among phosphate dynamics, electron-dense body and lipid accumulation in the green alga Parachlorella kessleri.

Shuhei Ota,Tsuyoshi Takeshita,Kenshiro Oshima,Shigeyuki Kawano,Aiko Hirata,Vilém Zachleder,Mami Konomi,Kateřina Bišová,Mai Yoshihara,Tomokazu Yamazaki,Masahira Hattori

doi:10.1038/srep25731

Abstract

Phosphorus is an essential element for life on earth and is also important for modern agriculture, which is dependent on inorganic fertilizers from phosphate rock. Polyphosphate is a biological polymer of phosphate residues, which is accumulated in organisms during the biological wastewater treatment process to enhance biological phosphorus removal. Here, we investigated the relationship between polyphosphate accumulation and electron-dense bodies in the green alga Parachlorella kessleri. Under sulfur-depleted conditions, in which some symporter genes were upregulated, while others were downregulated, total phosphate accumulation increased in the early stage of culture compared to that under sulfur-replete conditions. The P signal was detected only in dense bodies by energy dispersive X-ray analysis. Transmission electron microscopy revealed marked ultrastructural variations in dense bodies with and without polyphosphate. Our findings suggest that the dense body is a site of polyphosphate accumulation, and P. kessleri has potential as a phosphate-accumulating organism.

Highlights

An emission wavelength of 475–525 nm[24], which produces a yellowish color
DAPI staining of poly-P in S-depleted P. kessleri cells
DIC and fluorescent microscopy revealed that DAPI-stained poly-P granules were evident in P. kessleri cells cultured under S-depleted conditions or in S-deficient medium (Fig. 1a,b, Fig. S1)

Summary

Introduction

An emission wavelength of 475–525 nm[24], which produces a yellowish color. This DAPI-staining method is commonly used to detect poly-P-rich organelles in vivo and in vitro[16,25,26]. Macronutrient (nitrogen, phosphate, and sulfur) limitation is a trigger for enhancing lipid accumulation in microalgae[27]. We revealed the relationship between DBs and poly-P dynamics under sulfur-deficient conditions in Parachlorella kessleri. The association between lipid accumulation and S-deficiency has been reported[32,33], the relationship between Pi dynamics and nutrient limitation remains unknown, and the site of poly-P accumulation in S-depleted Chlorella cells is unclear. To address this question, we examined the time course of total phosphate (total-P) and poly-P accumulation under S- and P-depleted conditions. To examine the transcriptomic responses of genes related to S metabolism, such as phosphate transporters and copper transporters/chaperones, we re-analyzed RNA-Seq data[35] of 2-day-old cells cultured under S-depleted and -replete conditions

Methods

Results

Conclusion