Calcium-boron interaction in exopolysaccharide production by the cyanobacterium, Nostoc spongiaeforme

Abstract

The effect and interaction of Ca and B on exopolysaccharide (EPS) synthesis in the diazotrophically growing cyanobacterium, Nostoc spongiaeforme, was investigated. The absence of B inhibited EPS synthesis 1.56-fold (16 μg glucose equivalent/mg dry weight, 16 d) over the control cells (25 μg glucose equivalent) grown in medium containing 0.5 mM Ca and 8 μM B. When B concentration was raised to 40 μM, EPS production was stimulated 1.8-fold. Reduction of Ca concentration to one-half (0.25 mM) resulted in increased B demand (16 μM) by the cells for EPS production at par with the normal sets. However, without Ca, EPS production also increased as B increased. Addition of B to a Ca-free medium stimulated cyanobacterial diazotrophic growth as well as synthesis of Chl a and phycocyanin (0- 8 d). The data suggest B-dependent diazotrophic growth during Ca-deficiency and point to an important interactive role of Ca and B in regulation of cyanobacterial EPS synthesis.