Christopher P. Dionigi

Evaluation of geosmin and 2-methylisoborneol on the histidine dependence of TA98 and TA100 Salmonella typhimurium tester strains☆

Low (ca 0.01 ppb) concentrations of the naturally occurring terpene derivatives geosmin (1α, 10β-dimethyl-9α-decalol) and 2-methylisoborneol [(1-R-exo)-1,2,7,7-tetramethyl-bicyclo-(2,2,1)-heptan-2-ol] (MIB), impart earthy/muddy “off-flavors” to many water and food resources. The presence of these “off-flavors” often elicits public concern over the safety of the affected resources. The “Ames test”, assesses the induction of reverse mutation at the histidine locus in specially constructed Salmonella typhimurium tester strains, and is a widely used index of mutagenicity. This investigation indicated that neither MIB nor geosmin, when tested up to cytotoxic levels in both the presence and absence of exogenous metabolic activation, induced a mutagenic response in either strain TA98 or TA 100 compared to controls. Doses of MIB and geosmin above 45.2 and 18.1 ppm, respectively, inhibited tester strain growth, indicating that high concentrations of these metabolites may exhibit an antimicrobial activity, possibly by a mechanism similar to that reported for certain other terpene derived alcohols. Food or water resources containing similar concentrations of geosmin or MIB would be extremely unpalatable and would probably not be consumed.

EVALUATING THE RELATIONSHIP BETWEEN PHOTOPIGMENT SYNTHESIS AND 2-METHYLISOBORNEOL ACCUMULATION IN CYANOBACTERIA

 The relationship between photopigments and the terpene‐derived secondary metabolite, 2‐methylisoborneol (MIB), was analyzed in photoacclimated cultures of Pseudanabaena articulata Skuja throughout growth, during the diel cycle, and following chemical‐induced inhibition of the isoprenoid pathway. Accumulation of MIB coincided with the accumulation of lipophilic and phycobilin pigments during the early to mid‐exponential portion of the growth cycle with the greatest accumulation of MIB during the late‐exponential phase. Cellular release of MIB occurred as culture populations entered mid‐ to late‐logarithmic phase of growth and was greatest in irradiance‐stressed cultures. The greater correspondence of MIB accumulation with photopigments was seen in cultures transferred from a 12:12 h LD photoperiod alone and the consistent relationship between MIB and photopigment accumulation under varying irradiance suggested a photopigment‐dependent regulation for MIB synthesis. However, the consistent allocation of carbon into MIB during instances of phytofluene and tetrapyrrole biosynthetic inhibition within P. articulata and Oscillatoria perornata Skuja indicated that MIB accumulation is not limited by isopreniod‐carbon availability and does not appear to serve as an “overflow” product. Rather, MIB accumulation simply appears to reflect overall carbon accumulation resulting from increased cell metabolism.

PIGMENT AND PHOTOSYNTHETIC RESPONSES OF OSCILLATORIA AGARDHII (CYANOPHYTA) TO PHOTON FLUX DENSITY AND SPECTRAL QUALITY1

The effects of photon flux density (PFD) and spectral quality on biomass, pigment content and composition, and the photosynthetic activity of Oscillatoria agardhii Gomont were investigated in steady‐state populations. For alterations of PFD, chemostat populations were exposed to 50, 130 and 230 μmol photons·m−2·s−1 of photosynthetic active radiation (PAR). Decreases in biomass, chlorophyll a (Chl a) and c‐phycocyanin (CPC) contents, and CPC: Chl a and CPC: carotenoid content was not altered. Increases in the relative abundances of myxoxanthophyll and zeaxanthin and deceases in the relative abundances of echinenone and β‐carotene within the carotenoid pigments coincided with increasing PFD. Increases in Chl a‐specific photosynthetic rates and maxima and decreases in biomass‐specific photosynthetic rates and maxima with increasing PFD were attributed to increased light harvesting by carotenoids per unit Chl a and reduction in total pigment content, respectively.

HIGH-RESOLUTION AIRBORNE REMOTE SENSING OF BLOOM-FORMING PHYTOPLANKTON1

Remote sensing of highly turbid finfish aquaculture impoundments using the Calibrated Airborne Multispectral Scanner (CAMS) mounted on a Lear jet flown at 900 m was conducted in central Mississippi on 16 May 1990. Concurrent in situ data consisted of phytoplankton pigment concentrations and standing crop, water color, turbidity, and surface‐water temperature. Surface and near‐surface assemblages of cyanophytes and chlorophytes varied dramatically among impoundments; total chlorophyll concentrations and standing crop values ranged from 8 to 483 mg·m−3 and 8.0 × 102 to 2.2 × 106 cells‐mL−1, respectively. Regression models fit to CAMS data provided reliable estimates for and produced accurate digital cartographs of total chlorophyll and carotenoid concentrations, phytoplankton standing crop, and turbidity. Although a model to effectively estimate in situ c‐phycocyanin concentrations was not identified, the lack of a suitable model may have resulted from variability of pigment extraction during quantification rather than failure of remotely sensed imagery to detect c‐phycocyanin. Models derived from imagery of impoundments directly beneath the aircraft sufficiently described in situ parameters in imagery of adjacent series of impoundments not directly below the aircraft. High‐resolution airborne remote sensing provides a means for monitoring local phytoplankton dynamics in temporal and spatial scales analogous to biotic and abiotic processes affecting such dynamics and necessary for applications to ecological research and fisheries or aquacultural management.

Biofuel vs Bioinvasion: Seeding Policy Priorities

Desirable biofuel crops may amount to mass cultivation of potentially invasive species—How should policy keep these agroecosystems in check?

SIMAZINE-INDUCED INHIBITION IN PHOTOACCLIMATED POPULATIONS OF ANABAENA CIRCINALIS (CYANOPHYTA)1

The effects of the triazine herbicide, simazine, on photosynthetic oxygen evolution and growth rate in photoacclimated populations of Anabaena circinalis Rabenhorst were investigated. Chemostat populations were acclimated to photon flux densities (PFDs) of 50, 130, and 230 μmol·m−2·s−1 of photosynthetic active radiation (PAR), Decreases in chlorophyll a (Chl a). c‐phycocyanin (CPC), and total carotenoid (TCar) contents and CPC: Chl a and CPC: TCar ratios of populations coincided with increasing PFD, Polynomial regression models that characterize inhibition of photosynthesis for populations acclimated to 50 and 130 μmol photons·m−2·s−1 PAR were distinct from the model for populations acclimated to 230 μmol photons·m−2·s−1 PAR. Simazine concentrations that, depressed oxygen evolution 50% compared to controls decreased with increasing PFD. Increases and decreases in both biomass and growth rate coincided with increasing PFD and simazine concentration, respectively. Simazine concentrations that depressed growth rate 50% compared to controls increased with decreasing PFD. The differences in photosynthetic and growth inhibition among photoacclimated populations indicate that sensitivity to photosystem II inhibitors is affected by alterations in pigment contents.

Evaluation of Ferulic Acid for Controlling the Musty-Odor Cyanobacterium, Oscillatoria perornata, in Aquaculture Ponds

Abstract The cyanobacterium Oscillatoria perornata f. attenuata, a common inhabitant of channel catfish, Ictalurus punctatus, aquaculture ponds, produces the musty compound 2-methylisoborneol that causes fish to become off-flavor and unmarketable. Previous laboratory studies suggest that the natural compound trans-ferulic acid (4-hy-droxy-3-methoxycinnamic acid) is selectively toxic against O. perorna-ta. The present study was conducted to determine the effectiveness of the compound for controlling the growth of O. perornata under field conditions. The study was conducted in 12 0.1-ha earthern ponds in northwest Mississippi. Ponds contained 20,000 catfish/ha and were managed according to commercial culture practices. Half of the ponds were treated six times over a 2-month period with 5μM (0.97 mg/L) trans-ferulic acid, and the other half were untreated controls. Water samples obtained from all ponds preceding and following treatment were analyzed for phytoplankton community structure and concentrations of chlorophyll a, ferulate, and 2-methylisoborneol. Abundance of cyanobacteria, including O. perornata was not consistently affected by applications of ferulic acid. Only one of the six ferulic acid applications resulted in a decrease in abundance of O. perornata in treated ponds relative to untreated ponds (P <0.1). The ineffectiveness of trans-ferulic acid as a cyanobacterial algicide in catfish ponds appears to be caused by rapid dissipation of ferulic acid from pond waters. Use of trans-ferulic acid was neither an effective nor an economical approach to preventing musty off-flavor in pond-cultured channel catfish.

PREFACE THE IMPORTANCE OF UNDERSTANDING THE MOLECULAR, CELLULAR, AND ECOPHYSIOLOGICAL BASES OF HARMFUL ALGAL BLOOMS

In clear recognition of their concern for environmental quality and human health, the Phycological Society of America and the U.S. Department of Agriculture funded the symposium, ‘‘Molecular, Cellular, and Ecophysiological Bases of Noxious and Harmful Algal Blooms,’’ held on 5 August 1998 during the 52nd Annual Meeting of the Phycological Society of America in Flagstaff, Arizona. Sixteen scientists from disciplines ranging from methodological development to the study of algal molecular, cellular, and system-level ecological processes accepted invitations to present oral and/or poster papers. The symposium provided a unique forum for a diverse group of researchers to: (1) be advised of the current level of understanding of molecular, cellular, and ecophysiological processes that regulate harmful algal growth and proliferation; (2) delineate how toxins and taste/odor metabolite syntheses reflect molecular-, cellular-, and population-level responses to key environmental parameters; (3) assess current and future instrumentaland molecular-based identification and quantification technologies; and (4) coordinate an enhanced research response to harmful algal blooms. By bringing together researchers from divergent subject disciplines that would not typically meet, the symposium provided a forum for increasing communication among key laboratories and denoted clear avenues for expanded collaborative research.

Production of the taste/odor-causing compound, trans-2, cis-6 nonadienal, within the Synurophyceae

Although several species of the Synurophyceae have been associated with taste and odor problems in potable water supplies, electron microscopic-based field studies linked problematic blooms only toSynura petersenii Korshikov. Eventually, the organic compoundtrans-2,cis-6-nonadienal was implicated to cause the associated ‘cucumberlike’ odors. The objective of this study was to survey unialgal cultures of various Synurophycean species for the occurrence oftrans-2,cis-6-nonadienal. The compound was detected throughout a 24-day growth assay with aS. petersenii isolate, but was not detected in an identical assay withSynura sphagnicola (Korshikov) Korshikov. In separate 24-day cultures,trans-2,cis-6-nonadienal was detected in two isolates from theS. petersenii species complex, but was not detected in isolates of twoMallomonas or fourSynura taxa not from theS. petersenii complex. These results support the hypothesis that production oftrans-2,cis-6-nonadienal is unique to taxa within theS. petersenii complex. When contrast-enhancing optics and specific specimen preparation techniques are employed, light microscopy can be used to distinguish taxa in theS. petersenii complex from all other Synurophycean taxa. These methods are suggested as an efficient way to monitortrans-2,cis-6-nonadienal-producing taxa in potable water supplies.

The Recovery of Flavor Quality by Channel Catfish

Abstract Intensive production of channel catfish Ictalurus punctatus requires copious feeding. Nutrients from uneaten feeds and fish excreta contribute to the growth of microorganisms. Certain microbes that occur frequently in aquaculture systems produce the “muddy and earthy” off-flavor metabolites 2-methylisoborneol (MIB) and geosmin. Fish containing MIB or geosmin can exhibit an off-flavor that makes them unacceptable for harvest as food fish. Following the cessation of exposure to MIB or geosmin, fish depurate off-flavors. The minimum period required for fish to regain flavor quality is a critical concern for aquaculturists; scant information concerning this period prompted our investigation. Channel catfish were harvested from three commercial ponds, and fish from each pond were sorted into four size-classes (0.4–0.8 kg, 0.8–1.3 kg, 1.3–1.6 kg, and 1.6–2.3 kg) on 30 August (summer) and on 18 October (autumn) 1993. Each group of fish was transferred into individual 2,000-L fiberglass tanks, and each t...