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The filamentous fungus Ashbya gossypii is used for riboflavin biosynthesis on an industrial scale, but even the wild type displays overproduction. Because riboflavin overproduction was known to start at the transition between growth and stationary phase, it was suspected that overproduction was induced at low growth rates. However, chemostatic cultivations performed at different growth rates did not result in any detectable riboflavin formation. In this study, we report that it was not the final growth rate that triggered riboflavin overproduction but a decline in growth rate. Therefore, continuous fermenter cultivations with dilution rate shifts were performed. Peaks of riboflavin overproduction were observed in the wild type and in a RIB3placZ reporter strain after downshifts in dilution rate. Accumulation of riboflavin correlated with an increased expression of lacZ reporter activity. The step size of the downshifts corresponded to the peak size of riboflavin formation and reporter activity. Expression of further RIB genes encoding riboflavin biosynthetic enzymes was analyzed by RT-PCR. RIB mRNA levels of the ribulose-5-phosphate branch of the divided riboflavin biosynthesis pathway (RIB3, RIB4, and RIB5) were found to increase in the riboflavin production phase, whereas the RIB2 and RIB7 mRNA levels belonging to the GTP branch remained constant. We propose that a decline in growth rate triggers the increased expression of RIB3, RIB4, and RIB5 resulting in riboflavin overproduction. Because although a reduction in oxygen supply, temperature increase or decrease, or salt stress did affect growth, but neither did lead to riboflavin overproduction nor did induce RIB3 reporter expression, we conclude that declining nutrition must be the stress stimulus. Because about half of the cells in the hyphae of Ashbya gossypii did not accumulate riboflavin, the regulatory response on the cellular level can be estimated to be at least twice as great in comparison to what we detected as overall signals.

Seafloor oil seepage on the continental slope of the Gulf of Mexico drives a number of distinct biological, chemical and geological processes. Macroseepage of oil and gas controls the extent and distribution of chemosynthetic “oil seep” communities, the seafloor configuration, sediment character and sediment geochemistry [Kennicutt et al., 1985; Brooks et al., 1986, 1987; MacDonald et al., 1989, 1990; Roberts et al., 1987]. Besides providing substrates for chemosynthetic communities, these macroseeps charge the sediments with gas and oil resulting in acoustic wipe-out zones [MacDonald et al., 1989], the formation of gas hydrates [Brooks et al., 1986]. massive carbonate formation [Roberts et al., 1987] and in extreme cases, create mud volcanos with blow-out craters [Prior et al., 1989]. Besides gas and oil, brine is also seeping upward into and out of Gulf of Mexico continental slope sediments. In many areas the gas and salt migrate together, forming seabottom salt pools charged with methane and hydrogen sulfide, which support chemosynthetic organisms [MacDonald et al., 1990].

Low molecular weight hydrocarbons (LMWHs, C/sub 1/-C/sub 4/) were measured from the water column and sediments around an oil and gas field. No significant differences in mean methane levels were observed between platforms that were and were not discharging brine. However, in the 20-station grid, the relative standard deviations were greater and the highest individual methane and ethane concentrations were found in surface waters near the platform discharging brine. Higher methane values at all depths observed during summer coinciding with decreased ethane/ethene ratios in a near-bottom nepheloid layer provided direct evidence of in situ biological production associated with increases in zooplankton and bacterial biomass in the water column. The sediment LMWHs are predominantly of thermogenic origin probably due to seepage from the subsurface, as evidenced by high levels of methane and elevated ethane/ethene ratios. The LMWH input from brine discharge in the field is estimated at 283 g/day.

In May 1986, we investigated processes contributing to the unique characteristics of oceanic fronts in the western Mediterranean Sea. Simulated in situ measurements of 14C-based primary production were made in conjunction with precise chemical, physical and optical analyses coordinated with remote sensing. Eight transects consisting of 4–7 vertical stations were made across density fronts associated with the Almeria Gyre and the Algerian Current. A model was developed to describe the relationship between chlorophyll-specific primary production (mg C mg Chl−1h−1) and depth in the water column. Model regressions for Modified Atlantic Water (MAW, salinity = 36.5–36.8), Mediterranean water (37.6–38.0), and intermediate frontal water were not significantly different, and a single equation based on the pooled data was used to estimate regional production. East of 0° longitude, primary production integrated over the upper 100 m (ΣP) in Mediterranean water was 0.47 g C m−2 d−1 (range0.33–0.60) and 0.88 g C m−2 d−1 (range 0.50–1.30) in MAW and frontal regions. higher ΣP in MAW and frontal regions could be attributed partially to higher integrated chlorophyll, although locationof the chlorophyll maximum higher in the water column was also an important contributing factor. The chlorophyll maximum was shallower in MAW than in Mediterranean-type water. The depth of chlorophyll maxima generally coincided with the nitracline rahter than isopycnal surfaces, supporting the view that chlorophyll distributions and primary production were primarily influenced by nutrient supply.

Analysis of sulfur and oxygen isotopic compositions of dissolved sulfate from a vertical water profile in the anoxic, hypersaline Orca Basin provides important constraints upon the provenance of the sulfate. Results support a dissolution origin of the brine from a Jurassic evaporitic salt. However, mass balance considerations and the observed minima in the vertical δ18O-sulfate profile at the brine-seawater interface are not reconcilable with only a simple two box brine-seawater mixing model. Instead, the data imply contributions from the oxidation of sulfides.

Hydrogen peroxide, micronutrients, chlorophyll, primary production and light were measured at a series of stations in the western Mediterranean Sea. Hydrogen peroxide concentrations greater than 100 nmol 1−1 were found in this region. There was a significant relationship between hydrogen peroxide and primary production rates near the surface where the light intensity was high. This link between hydrogen peroxide and biological activity may have resulted from photochemically reactive organic compounds that were excreted during photosynthesis or from the direct biological production of hydrogen peroxide. Elevated concentrations were not found in the deep chlorophyll maximum however, which indicates that high light intensities are necessary for biogenic hydrogen peroxide production in this area. Hydrogen peroxide concentrations decreased much more slowly with depth than did light. The decoupling of light and hydrogen peroxide must have been due to a combination of a slow decay rate and rapid vertical transport. However, simple calculations indicate that eddy diffusion alone could not have transported enough hydrogen peroxide to produce the effects that were seen. Large anomalies in the concentration profiles that were detected in frontal regions indicate that hydrogen peroxide can be a useful tracer of vertical transport in the upper ocean. The size of the anomalies appears to be coupled to the salinity gradient across the front, which drives the frontal circulation.

The composition of light hydrocarbon gases in the Orca Basin, an anoxic, hypersaline intraslope depression on the continental slope of the northern Gulf of Mexico, indicates that both methane and ethane are biogenic in nature with a C1(C2 + C3) ratio of 730 and a δ13C of methane of −73%. relative to the PDB standard. The concentrations of methane (750 mM) and ethane (1300 mM) in the Orca Basin brine are higher than any other marine anoxic basin. These high levels result not from high rates of productivity, but from the long residence time of the brine in the basin, due to its high stability toward mixing with overlying seawater (Δσ1ΔZ = 3.2m). Both methane and ethane show well mixed distributions in the brine. These distributions probably result from convective mixing of the isohaline brine pool due to normal heat flow from the basin sediments. Methane and ethane maxima above the pycnocline at the brine/seawater interface reflect in situ production and/or consumption in the aerobic water column. Concurrent maxima in suspended particulate material distributions in this region suggest methane may be produced there in anaerobic microenvironments associated with the suspended matter. Reduced rates of anaerobic decomposition (including sulfate reduction) in the brine sediments are inferred from preserved Sargassum fronds in the sediments, vertical sulfate profiles in most cores, and the sediment organic carbon content which is two to three times higher in sediments below the high salinity brine than in the normal Gulf sediments nearby.

We have characterized the volatile liquid hydrocarbons in the oil, discharge brine and surface receiving waters from an oil and gas production platform discharging brine into the Gulf of Mexico. The mean VLH concentrations were 450,000 μg/g (oil), 21,600 μg/L (brine) and 1900 ng/L (surface waters). Light aromatic compounds comprised over 80% of VLH in the brine and surface waters, with benzene, toluene, ethylbenzene, m-, p-, and o-xylene being the predominant compounds. VLH concentrations around a control platform 3 km distant were four times lower, indicating rapid dilution. The 2 μg/L concentration of VLH around platform 296-B is twice the concentration that SAUER (1980) suggested could be detrimental to the life processes of many marine organisms. If this value is representative of the complete water column and considering the fact that the Buccaneer field has been discharging brine at this location for over twenty years, with no obvious harm to the biota, the lower limit for VLH to cause detrimental long term effects on marine organisms may have to be reevaluated.

In an investigation of gas hydrates in deep ocean sediments, gas samples from Deep Sea Drilling Project Site 533 on the Blake Outer Ridge in the northwest Atlantic were obtained for molecular and isotopic analyses. Gas samples were collected from the first successful deployment of a pressure core barrel (PCB) in a hydrate region. The pressure decline curves from two of the four PCB retrievals at in situ pressures suggested the presence of small amounts of gas hydrates. Compositional and isotopic measurements of gases from several points along the pressure decline curve indicated that (1) biogenic methane (δC = -68‰; CJ/CJ = 5000) was the dominant gas (>90%); (2) little fractionation in the C,/ C2 ratio or the C carbon isotopic composition occurred as gas hydrates decomposed during pressure decline experiments; (3) the percent of C3, i-C4, and CO2 degassed increased as the pressure declined, indicating that these molecules may help stabilize the hydrate structure; (4) excess nitrogen was present during initial degassing; and (5) Cj/Q ratios and isotopic ratios of C gases were similar to those obtained from conventional core sampling. The PCB gas also contained trace amounts of saturated, acyclic, cyclic, and aromatic C5-C14 hydrocarbons, as well as alkenes and tetrahydrothiophenes. Gas from a decomposed specimen of gas hydrate had similar molecular and isotopic ratios to the PCB gas (δC of -68% for methane and a q / Q ratio of -6000). Regular trends in the δC of methane ( 95 60%) and C{/C2 ratios (-25000 — 2000) were observed with depth. Capillary gas chromatography (GC) and total scanning fluorescence measurements of extracted organic material were characteristic of hydrocarbons dominated by a marine source, though significant amounts of perylene were also present.

Although extensive offshore oil and gas development has occurred in the outer continental shelf (OCS) areas of Texas and Louisiana, few multidisciplinary programs have been undertaken to study the environmental consequences of such development. One of the few programs to study the effects of Gulf of Mexico petroleum development is the “Environmental Assessment of the Buccaneer Gas and Oil Field in the Northwestern Gulf of Mexico”. This program, initiated in 1975, was funded by the Environmental Protection Agency through interagency agreement with the National Oceanic and Atmospheric Administration and managed by the National Marine Fisheries Service, Southeast Fisheries Center, Galveston Laboratory in Galveston, Texas. Objectives of the project were (1) to identify and document the types and extent of biological, chemical and physical alterations of the marine ecosystem associated with Buccaneer Field, (2) to determine specific pollutants, their quantity and effects, and (3) to develop the capability to describe and predict fate and effects of Buccaneer Field contaminants. After a survey study initiated in 1975, four successive one-year programs were undertaken to study various aspects of biology, chemistry, physics, and geology at the Buccaneer Field. This paper reports surficial sediment and suspended particulate studies undertaken in 1978–1979 (third year) and 1979–1980 (fourth year).