Phosphorus Deprivation Responses and Phosphonate Utilization in a Thermophilic Synechococcus sp. from Microbial Mats

Growth response, APase activity, and absorbance spectra of OS-B′ under various P conditions. (A) Late-logarithmic-phase cells grown in +P medium were transferred growth under four different conditions: (i) +P, (ii) −P, (iii) +P medium with 0.5 mM MePhn (+P+MePhn), and (iv) −P medium with 0.5 mM MePhn (−P+MePhn). Growth of all cultures was monitored for ∼192 h. Note the log scale on the y axis for cells per ml data. (B) APase activity and growth measurements were quantified in cell cultures once every 24 h. The APase activity was measured as μg of pNPP hydrolyzed per h per 1 × 10⁶ cells. (C) Whole-cell absorption spectra of each culture between the wavelengths of 400 and 800 nm, normalized to the OD₇₅₀, at 96 h after cell transfer. Results for growth and APase activity show the means and standard deviations (error bars) from measurements taken from biological triplicates.

Quantification of relative Pho regulon transcript accumulation following P_i starvation. Specific Pho regulon transcripts, including those of the phn gene cluster, were measured over 24-h intervals under various P conditions. The top panel represents transcripts for genes encoding phosphatases, the middle panel is transcripts for genes associated with transport systems, and the bottom panel is transcripts for genes involved in Phn transport and metabolism. For each gene, relative transcript levels, presented as a ratio under −P and +P conditions, were determined at 24, 48, and 72 h following the transfer of cells to the new growth medium. In the presence of MePhn, relative transcript levels representing −P+MePhn compared to +P+MePhn are shown at 24 h, 48 h, and 72 h. The qPCR results show the means and standard deviations (error bars) for data from three technical replicates.

Quantification of Pho regulon transcript accumulation after P_i addition to P-starved cultures. Pi was added back to the growth medium after 72 h of starvation, and transcript levels were measured (as described in Fig. 3) at 96 h (i.e., 24 h after adding P_i back). Relative transcript levels are shown that compare −P to +P after P_i addition and the control, i.e., −P compared to +P prior to P_i addition but with no P_i added back. The qPCR results show the means and standard deviations (error bars) for data from three technical replicates.