Supra-Optimal Temperature: An Efficient Approach for Overaccumulation of Starch in the Green Alga Parachlorella kessleri.

Vilém Zachleder,Veronika Kselíková,Milada Vítová,Tsuyoshi Takeshita,Kateřina Bišová,Shigeyuki Kawano,Ivan N Ivanov,Shuhei Ota,Vitali Bialevich

doi:10.3390/cells10071806

Abstract

Green algae are fast-growing microorganisms that are considered promising for the production of starch and neutral lipids, and the chlorococcal green alga Parachlorella kessleri is a favorable model, as it can produce both starch and neutral lipids. P. kessleri commonly divides into more than two daughter cells by a specific mechanism—multiple fission. Here, we used synchronized cultures of the alga to study the effects of supra-optimal temperature. Synchronized cultures were grown at optimal (30 °C) and supra-optimal (40 °C) temperatures and incident light intensities of 110 and 500 μmol photons m−2 s−1. The time course of cell reproduction (DNA replication, cellular division), growth (total RNA, protein, cell dry matter, cell size), and synthesis of energy reserves (net starch, neutral lipid) was studied. At 40 °C, cell reproduction was arrested, but growth and accumulation of energy reserves continued; this led to the production of giant cells enriched in protein, starch, and neutral lipids. Furthermore, we examined whether the increased temperature could alleviate the effects of deuterated water on Parachlorella kessleri growth and division; results show that supra-optimal temperature can be used in algal biotechnology for the production of protein, (deuterated) starch, and neutral lipids.

Highlights

Light and temperature are two crucial factors affecting algal growth and division, both in natural habitats and in biotechnological applications
Horizontal dashed lines indicate the number of doublings of the initial values at the beginning of the cell cycle (0 h)
We describe the effects of supra-optimal temperatures on synchronized cultures of the green alga P. kessleri

Summary

Introduction

Light and temperature are two crucial factors affecting algal growth and division, both in natural habitats and in biotechnological applications. Cell division seems to be more sensitive to temperature increases than growth does [17,18]; this has peculiar consequences; there are threshold temperatures that will only slightly or not at all affect cell growth, but will completely block cell division. The effects of such supraoptimal temperatures were described in the green algae Chlamydomonas reinhardtii [17] and Chlorella vulgaris [18]

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Conclusion