Transcriptome Analysis Revealed the Advantages of Room Temperature Preservation of Concentrated Oocystis borgei Cultures for Use in Aquaculture

Abstract

Oocystis borgei, a microalgae species employed for regulating the quality of aquaculture water, demonstrates the capacity to adsorb noxious substances, curtail the growth of detrimental bacteria, and outcompete blooming cyanobacteria. It can be concentrated by natural sedimentation and stored at room temperature, making it costless and simple to transport and use. To study the mechanism of adaptation to room temperature preservation, O. borgei was concentrated (1.19 × 10⁷-1.21 × 10⁷ cell/mL) and stored for 50 days at low (5 °C, LT), normal (25 °C, NT), and high (35 °C, HT) temperatures, respectively. Polysaccharide content, lipid content, cell survival, and resuscitation were evaluated. RNA-Seq was also used to examine how concentrated O. borgei responded to temperature. During storage, there was an increase in polysaccharide content and a decrease in lipid content, with both being significantly upregulated in the LT and HT groups. Survival and cell density were highest in the NT group. The RNA-Seq analysis revealed extensive differences in transcript levels. ATP synthesis was inhibited in the LT group due to the reduced expression of PsaD, PsaE, PsaF, PsaK, and PsaL. Under HT, the formation of reactive oxygen species (ROS) was facilitated by low levels of redox-related genes (nirA) and high levels of oxidative genes (gdhA, glna, and glts). The findings suggest that storing concentrated O. borgei at room temperature is optimal for microalgae preservation, enhancing theoretical research in this field. Our study provides further theoretical and practical support for the development of O. borgei as a live ecological preparation for aquaculture microalgae ecology management.

Keywords: Oocystis borgei; RNA-Seq; photosynthesis; polysaccharides; room temperature preservation.

Figure 1

Changes in polysaccharide content (a), lipid content (b), cell density (c), specific growth rate (d), and the survival rate (e) of O. borgei. The data show that the mean value ± standard deviation (n = 3). *: intragroup significant difference between values and initial values at any time point (*: p < 0.05, **: 0.001 ≤ p < 0.01, ***: p < 0.001), and #: inter group differences, red indicates a significant difference between NT and HT, and green indicates a significant difference between LT and NT’ (#: p < 0.05, ##: 0.001 ≤ p < 0.01, and ###: p < 0.001), ns. indicates that the difference between the comparison groups was not significant.

Figure 2

PCA (a) and Venn diagram (b) of DEGs in O. borgei under different preservation temperatures. (c) Volcano plot of LT vs. NT and NT vs. HT, “LT vs. NT” is NT normalized to LT, “NT vs. HT” is HT normalized to NT. (d): RT−qPCR validation of the relative expression profiles of ten genes in O. borgei at different storage temperatures. LT: Expression in the low temperature group relative to that in the NT group. HT: expression in the high temperature group relative to that in the NT group. TAAC: ATP carrier protein, RPLI6: 60S ribosomal protein, Hsp70: heat shock protein 70, Fdhc: nitrite transporter NAR1, FAD7: chloroplast glycerolipid omega−3−fatty acid desaturase, FAD6: omega-6−fatty acid desaturase, chloroplast isoform, CBR: carotene biosynthesis−related protein, CAO: chlorophyll an oxygenase, PsAg: photosystem I reaction center subunit V, chloroplastic, and FAD12: omega−6 fatty acid desaturase, endoplasmic reticulum isozyme 2.

Figure 3

GO (a) and KEGG (b) assignment of DEGs in different temperature groups of O. borgei.

Figure 4

The pathway of polysaccharide synthesis of O. borgei.

Figure 5

Heat map of transcript levels of photosynthesis related genes.

Figure 6

O. borgei transcription model under low or high temperature storage conditions.