Light–dark (12:12) cycle of carbon and nitrogen metabolism in Crocosphaera watsonii WH8501: relation to the cell cycle

Abstract

This study provides with original data sets on the physiology of the unicellular diazotrophic cyanobacterium Crocosphaera watsonii WH8501, maintained in continuous culture in conditions of obligate diazotrophy. Cultures were exposed to a 12:12 light-dark regime, representative of what they experience in nature and where growth is expected to be balanced. Nitrogen and carbon metabolism were monitored at high frequency and their dynamics was compared with the cell cycle. Results reveal a daily cycle in the physiological and biochemical parameters, tightly constrained by the timely decoupled processes of N(2) fixation and carbon acquisition. The cell division rate increased concomitantly to carbon accumulation and peaked 6 h into the light. The carbon content reached a maximum at the end of the light phase. N(2) fixation occurred mostly during the dark period and peaked between 9 and 10 h into the night, while DNA synthesis, reflected by DNA fluorescence, increased until the end of the night. Consequently, cells in G1- and S-phases present a marked decrease in their C:N ratio. Nitrogen acquisition through N(2) fixation exceeded 1.3- to 3-fold the nitrogen requirements for growth, suggesting that important amounts of nitrogen are excreted even under conditions supposed to favour balanced, carbon and nitrogen acquisitions.

Sensitivity of Trichodesmium erythraeum and Crocosphaera watsonii abundance and N<sub>2 fixation rates to varying NO<sub>3<sup>− and PO<sub>4<sup>3− concentrations in batch cultures

“…4, Table S3 in the supple ment at www.int-res.com/articles/suppl/a066 p223 _supp.pdf) (biomass C:N ratio data are not available for the 0:0.5 T. erythraeum treatment; see 'C content'). This range in biomass mol:mol C:N ratios is consistent with previously reported ranges for both Dron et al 2012). While no significant differences in C:N ratios were observed among T. erythraeum treat ments, C. watsonii cultures grown with 0.5 µM PO 4 3− (i.e.…”

“…The average C content per exponential phase Crocosphaera watsonii cell did not vary among the treatments either and ranged from 0.16 ± 0.04 to 0.23 ± 0.08 pmol C cell −1 (Fig. 3d, Table S2); these values are similar to those reported by Dron et al (2012) but are lower than those found in previous studies (Webb et al 2009), potentially due to the lower PO 4 3− concentration and/or to differences in the irradiance level used in these experiments relative to previous studies.…”

“…For the exponential phase Crocosphaera watsonii cultures, the cellular N content was similar among the treatments, ranging from 34 ± 6 to 36 ± 15 fmol N cell −1 (Fig. 3f, Table S2), and was similar to that reported by Dron et al (2012).…”

Optimizing light regimes on growth and lipid accumulation in Ankistrodesmus fusiformis H1 for biodiesel production

“…Moreover, an increased cellular neutral lipid was observed throughout the light period, but a near-liner decline during the dark period (Chauton et al, 2013). Carbon metabolism pathways (e.g., photosynthesis and carbon assimilation) appeared to be tightly regulated by photoperiod during daytime and catabolic utilization of energy reserves occurring mainly during the night (Dron et al, 2012). Therefore, it is reasonable that under the conditions of 24:0 h or 18:6 h light/dark cycles Results are expressed as the mean ± standard deviation (n = 3).…”

“…more lipids accumulated in our results. Previous report indicates that maximum photosynthetic efficiency can be achieved when the light/dark cycle approached the photosynthetic unit turnover time (Dron et al, 2012). Besides, the achievable of biodiesel form microalgae must carry out with maximum production and lowest cost.…”