Energy Requirement for Diazotrophic Growth of the Cyanobacterium Anabaena variabilis Determined from Growth Yields in the Dark

Abstract

The cyanobacterium Anabaena variabilis CCAP 1403/13a (UTEX 1444, ATCC 2941 3) was grown diazotrophically in the dark in the presence of fructose with a doubling time of 25 h at 35 "C. This was 40% of the maximum rate observed in the light. Growth rates in the dark were similar with nitrate or ammonium as nitrogen sources or under diazotrophic conditions. Darkgrown cyanobacteria reduced acetylene in the dark at 25% of the rate observed for photoautotrophic cultures in the light. Heterotrophic growth yields for dark growth with different nitrogen sources were estimated from the extent of fructose-dependent growth in batch cultures. The ratio between cell carbon and fructose carbon was 0.38 in diazotrophically grown cells, 0.38 with nitrate and 0.52 with ammonia. Thus the energy requirement for growth on molecular nitrogen is similar to the energy requirement for growth on nitrate, but greater than that for growth on ammonia. Since the diazotrophic culture always had a dissolved O2 concentration of at least 80% of air saturation, this demonstrates that there are no detectable extra energy requirements for aerobic nitrogen fixation compared to nitrate reduction, such as would result from a need for respiratory protection of nitrogenase. t Present address :

Ornithine cycle in Nostoc PCC 73102. Occurrence and localization of ornithine carbamoyl transferase, and the effects of external carbon and ornithine on nitrogenase activity and citrulline synthesis

“…Similarly in free-living Nostoc originally isolated from Cycas revoluta, fructose and sucrose stimulated both growth and nitrogenase activity in the light (Tredici et al 1988). In Anabaena variabiUs addition of external fructose stimulated nitrogenase activity (Jensen 1983), In the present study, using cells incubated in the light, additions of glucose and fructose in combination with ornithine not only stimulated growth and nitrogenase activity but also in vivo citrulline synthesis (Tab, 2), However, in darkness no stimulation of in vivo citrulline synthesis was observed. Moreover, the substantial stimulation of nitrogenase activity by additions of external glueose and fructose, both in light and darkness, was not followed by a stimulation of in vivo citrulline synthesis.…”

Physiological sources of reductant for nitrogen fixation activity in Nostoc sp. strain UCD 7801 in symbiotic association with Anthoceros punctatus

“…Such a strong enhancement of nitrogenase activity by exogenous carbohydrate in the presence of DCMU has not been observed in other cyanobacteria, whether cultured from symbiotic association (31) or as a nonsymbiont from an unknown source (20). The high concentration (100 mM) of carbohydrate we utilized is atypical; cultures are generally supplemented with 1.4, 14, or 40 mM fructose or up to 28 mM glucose (8,20,31).…”

“…Heterocysts maintain a low intracellular oxygen tension in part by the absence of a functional 02-evolving photosystem 11 (1), the presence of a respiratory 02 uptake system (8,16), and the presence of 02 diffusion barriers in their unique envelope (16). Since heterocysts possess photosystem I, the ATP required for nitrogen fixation may be provided by cyclic photophosphorylation in the light or by oxidative phosphorylation in the dark (4).…”

Engineering of crop plants to facilitate bottom-up innovation: A possible role for broad host-range nitroplasts and neoplasts

“…80 The required ATP is produced primarily by cyclic electron transport through PS I. 80,81 However, even in the dark (when PS I is of no use), some growth on N2 still takes place, 82 and nitrogenase is still active (to a significantly lesser degree), so long as O2 is present, 83 with ATP produced by oxidative phosphorylation. 84 Heterocysts protect nitrogenase from inactivation by oxygen through limited permeability to gases, 85 oxygen consumption by cytochrome oxidase, 76,86 lightdependent oxygen consumption 87 by a flavoprotein called Flv3, 88 and an uptake hydrogenase that redirects the electrons of the H2 produced by nitrogen fixation into the electron transport chain.…”