High growth rate, photosynthesis rate and increased hydrogen(ases) in manganese deprived cells of a newly isolated Nostoc-like cyanobacterium (SAG 2306)

A Nostoc-like cyanobacterium, strain SAG 2306, was isolated from a clay soil sample at Assiut region (Egypt). Morphology and analysis of 16S rDNA identified it as a member of the heterocyteous cyanobacteria (Nostocales). Unexpectedly, chlorophyll a and dry weight were higher in manganese deprived (Mn-) or in manganese double deprived (Mn--) than in replete (Mn+) cells. The latter phase of Mn-- diluted the cellular content in daughter cells to a critical minimal value of about 1.5% relative to the original 100% in Mn+. Similar to growth, Nostoc sp. exhibited a significant age-dependent biphasic impact on hydrogenases activity. Older cells of 120 h age displayed higher hydrogen evolution rates than younger ones. The results suggest inhibitory effects of the 12 μM manganese contained in BG11 medium (Mn+) not only on growth but also on hydrogen production during the first 72 h of growth.

► Hydrogen evolution and hydrogenases of Nostoc were enhanced by manganese deprivation.
► Enhanced hydrogenases may substitute inhibited MnSOD in scavenging free radicals.
► Inhibition of oxygen evolution by Mn deprivation facilitated installing anaerobiosis.
► Mn in BG11 (12 μM) medium inhibited Nostoc growth and hydrogen(ases) at early stages.
► Growth in Mn deprived medium severely decreased the calculated cellular Mn to 0.8%.