Studies on culture age versus exometabolite production in batch cultures of the cyanobacterium Nostoc insulare

Changes in the content of exometabolites excreted by the cyanobacterium Nostoc insulare during batch cultivation were determined. During linear growth, only the non-toxic compound N,N'-(4,5-dimethyl-1,2-phenylene)-bis-acetamide was detectable in appreciable quantities in the medium, whereas during stationary growth the antimicrobial and cytotoxic exometabolites 4,4'-dihydroxybiphenyl and 9H-pyrido(3,4-b)indole (norharmane) were also present to an increasing degree. Hence it is proposed that biosynthesis of N,N'-(4,5-dimethyl-1,2-phenylene)bis-acetamide in N. insulare is associated with cell proliferation and primary metabolism of this organism. 4,4'-Dihydroxybiphenyl and norharmane, however, are proposed to be products of secondary metabolism that are excreted by N. insulare primarily under nutrient-restricted conditions and under increased pressure of competition with other organisms.