Localized Tetrazolium Reduction in Relation to N ₂ Fixation, CO ₂ Fixation, and H ₂ Uptake in Aquatic Filamentous Cyanobacteria

Abstract

The aquatic filamentous cyanobacteria Anabaena oscillarioides and Trichodesmium sp. reveal specific cellular regions of tetrazolium salt reduction. The effects of localized reduction of five tetrazolium salts on N2 fixation (acetylene reduction), 14CO2 fixation, and 3H2 utilization were examined. During short-term (within 30 min) exposures in A. oscillarioides, salt reduction in heterocysts occurred simultaneously with inhibition of acetylene reduction. Conversely, when salts failed to either penetrate or be reduced in heterocysts, no inhibition of acetylene reduction occurred. When salts were rapidly reduced in vegetative cells, 14CO2 fixation and 3H2 utilization rates decreased, whereas salts exclusively reduced in heterocysts were not linked to blockage of these processes. In the nonheterocystous genus Trichodesmium, the deposition of reduced 2,3,5-triphenyl-2-tetrazolium chloride (TTC) in the internal cores of trichomes occurs simultaneously with a lowering of acetylene reduction rates. Since TTC deposition in heterocysts of A. oscillarioides occurs contemporaneously with inhibition of acetylene reduction, we conclude that the cellular reduction of this salt is of use in locating potential N2-fixing sites in cyanobacteria. The possible applications and problems associated with interpreting localized reduction of tetrazolium salts in cyanobacteria are presented.

Limitation of N2 fixation in coastal marine waters: Relative importance of molybdenum, iron, phosphorus, and organic matter availability1

“…Research sites and materials studied-Atlantic coastal waters and estuaries bordering North Carolina host numerous potential NZfixing microbial habitats, or microzones, available for experimental use (Paerl 1984(Paerl , 1985. Among these are intertidal benthic microbial mats, suspended and settled detritus comprised in part of decaying Spartina (marsh grass) and Zostera (eel grass), periodic blooms of colonial cyanobacteria, including marine Trichodesmium and brackish-freshwater Anabaena, Oscillatoria, and Aphanizomenon.…”

“…Both Spartina alterniflora and Zostera marina are representative of coastal regions of North Carolina (Beal 1977). The contributions of these plants to suspended and settled detritus are obvious upon microscopic examinations of nearshore seston and epibenthic detritus (Paerl 1984). Accord-ingly, we examined potential impacts of these detrital sources on N2 fixation potential.…”

“…This was accomplished by transferring 20-ml subsamples into 30-ml serum-stoppered Erlenmeyer flasks, followed by substitution of the headspace gas with either oxygen-depleted or -enriched air. A vacuum manifold, equipped with syringe ports and a three-way vacuum/gas supply valve was used to substitute gas phases in the headspace (Paerl 1978). Resulting changes in dissolved oxygen levels among a variety of treatments were measured with a Clark-type electrode (YSI-5739).…”

“…A direct approach for testing potential limiting factors is the execution of specific nutrient enrichment experiments on natural microbial communities (see Dugdale 1967;Falkowski 1980;Paerl 1982) wherein adding a limiting nutrient elicits or enhances N2 fixation. We report on such studies conducted on North Carolina coastal waters, which typify N-depleted, full-salinity marine habitats (Thayer 1974).…”

Consortial N2 fixation: a strategy for meeting nitrogen requirements of marine and terrestrial cyanobacterial mats

“…Localized reduction of the tetrazolium salt 2,4,5triphenyltetrazolium chloride (TTC) has demonstrated the presence of anaerobic microzones around the Microcoleus spp. growing in the RCNERR mat [33,34] (Fig. 4B) and the Utah soil crust (not shown).…”