Organic osmolytes in aerobic bacteria from mono lake, an alkaline, moderately hypersaline environment.

The identity and concentrations of intracellular organic solutes were determined by nuclear magnetic resonance spectroscopy for two strains of aerobic, gram-negative bacteria isolated from Mono Lake, Calif., an alkaline, moderately hypersaline lake. Ectoine (1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid) was the major endogenous solute in both organisms. Concentrations of ectoine varied with external NaCl levels in strain ML-D but not in strain ML-G, where the level was high but invariant from 1.5 to 3.0 M NaCl. Hydroxyectoine also occurred in strain ML-D, especially at elevated NaCl concentrations (2.5 and 3.0 M), but at levels lower than those of ectoine. Exogenous organic solutes that might occur in Mono Lake were examined for their effects on the de novo synthesis of ectoine. Dimethylsulfoniopropionate (DMSP) (0.1 or 1 mM) did not significantly lower ectoine levels in either isolate, and only strain ML-G showed any capacity for DMSP accumulation. With nitrogen limitation, however, DMSP (0.1 mM) substituted for ectoine in strain ML-G and became the main organic solute. Glycine betaine (GB) was more effective than DMSP in affecting ectoine levels, principally in strain ML-D. Strain ML-D accumulated GB to 50 or 67% of its organic solute pool at 2.5 M NaCl, at an external level of 0.1 or 1 mM GB, respectively. Strain ML-D also accumulated arsenobetaine. The methylated zwitterionic compounds, probably metabolic products of phytoplankton (DMSP and GB) or brine shrimps (arsenobetaine) in Mono Lake, may function as osmolytes for indigenous bacteria when present at high concentrations or under conditions of nitrogen limitation or salt stress.

The effects of therapeutic application of heat or cold followed by static stretch on hamstring muscle length.

Hamstring stretching is an important part of treatment programs aimed at decreasing the likelihood of hamstring injury. Few studies have examined the use of superficial thermal modalities in conjunction with hamstring stretching. The purpose of this study was to determine if the application of a superficial heating or cooling modality, followed by static stretch, increased the efficacy of static stretching of the hamstring muscles. This study examined 12 male and 12 female subjects, ages 18-38. All subjects received each of the following treatments: heat followed by static stretch, cold followed by static stretch, and static stretch alone. Each treatment was separated by at least 1 week. Pre- and post-treatment measurements of hamstring length were obtained using the Active-Knee-Extension (AKE) test. The data were analyzed via a 2 x 3 analysis of variance experimental design. Results indicated that there was an increase in hamstring length regardless of stretch treatment used, with F(1,23) = 35.49, p < .001. However, no significant differences were detected among stretch treatments, F < 1.0, nor among interaction effects, F < 1.0. The results of this study suggest that adequate hamstring stretching can occur without the use of a superficial thermal modality.

Demethylation of dimethylsulfoniopropionate to 3-mercaptopropionate by an aerobic marine bacterium.

A bacterium, strain BIS-6, that grew aerobically on dimethylsulfoniopropionate (DMSP) was isolated from an intertidal mud sample. Strain BIS-6 quantitatively demethylated DMSP and 3-methiolpropionate to 3-mercaptopropionate. Strain BIS-6 was a versatile methylotroph growing on the osmolytes DMSP and glycine betaine and their methylated degradation products (dimethyl glycine, sarcosine, methylamines, and dimethyl sulfide.

Aerobic and anaerobic degradation of a range of alkyl sulfides by a denitrifying marine bacterium.

A pure culture of a bacterium was obtained from a marine microbial mat by using an anoxic medium containing dimethyl sulfide (DMS) and nitrate. The isolate grew aerobically or anaerobically as a denitrifier on alkyl sulfides, including DMS, dimethyl disulfide, diethyl sulfide (DES), ethyl methyl sulfide, dipropyl sulfide, dibutyl sulfide, and dibutyl disulfide. Cells grown on an alkyl sulfide or disulfide also oxidized the corresponding thiols, namely, methanethiol, ethanethiol, propanethiol, or butanethiol. Alkyl sulfides were metabolized by induced or derepressed cells with oxygen, nitrate, or nitrite as electron acceptor. Cells grown on DMS immediately metabolized DMS, but there was a lag before DES was consumed; with DES-grown cells, DES was immediately used but DMS was used only after a lag. Chloramphenicol prevented the eventual use of DES by DMS-grown cells and DMS use by DES-grown cells, respectively, indicating separate enzymes for the metabolism of methyl and ethyl groups. Growth was rapid on formate, acetate, propionate, and butyrate but slow on methanol. The organism also grew chemolithotrophically on thiosulfate with a decrease in pH; growth required carbonate in the medium. Growth on sulfide was also carbonate dependent but slow. The isolate was identified as a Thiobacillus sp. and designated strain ASN-1. It may have utility for removing alkyl sulfides, and also nitrate, nitrite, and sulfide, from wastewaters.

A new mechanism for the aerobic catabolism of dimethyl sulfide.

Aerobic degradation of dimethyl sulfide (DMS), previously described for thiobacilli and hyphomicrobia, involves catabolism to sulfide via methanethiol (CH3SH). Methyl groups are sequentially eliminated as HCHO by incorporation of O2 catalyzed by DMS monooxygenase and methanethiol oxidase. H2O2 formed during CH3SH oxidation is destroyed by catalase. We recently isolated Thiobacillus strain ASN-1, which grows either aerobically or anaerobically with denitrification on DMS. Comparative experiments with Thiobacillus thioparus T5, which grows only aerobically on DMS, indicate a novel mechanism for aerobic DMS catabolism by Thiobacillus strain ASN-1. Evidence that both organisms initially attacked the methyl group, rather than the sulfur atom, in DMS was their conversion of ethyl methyl sulfide to ethanethiol. HCHO transiently accumulated during the aerobic use of DMS by T. thioparus but not with Thiobacillus strain ASN-1. Catalase levels in cells grown aerobically on DMS were about 100-fold lower in Thiobacillus strain ASN-1 than in T. thioparus T5, suggesting the absence of H2O2 formation during DMS catabolism. Also, aerobic growth of T. thioparus T5 on DMS was blocked by the catalase inhibitor 3-amino-1,2,4-triazole whereas that of Thiobacillus strain ASN-1 was not. Methyl butyl ether, but not CHCl3, blocked DMS catabolism by T. thioparus T5, presumably by inhibiting DMS monooxygenase and perhaps methanethiol oxidase. In contrast, DMS metabolism by Thiobacillus strain ASN-1 was unaffected by methyl butyl ether but inhibited by CHCl3. DMS catabolism by Thiobacillus strain ASN-1 probably involves methyl transfer to a cobalamin carrier and subsequent oxidation as folate-bound intermediates.

Degradation of meta-trifluoromethylbenzoate by sequential microbial and photochemical treatments.

m- and p-trifluoromethyl (TFM)-benzoates are incompletely degraded by aerobic bacteria that catabolize alkylbenzoates; biodegradation ceases after ring-fission with the accumulation of a trifluoromethyl muconate semialdehyde (2-hydroxy-6-oxo-7,7,7-trifluorohepta-2,4-dienoate, TFHOD) which is resistant to biochemical attack. A bacterium (Strain V-1), isolated from sea-water, grew aerobically on benzoate or m-toluate. Cells grown on benzoate or m-toluate oxidized both compounds at similar relative rates. Catabolism involved benzoate 1,2-dioxygenase (decarboxylating) and meta-cleavage to yield muconate semialdehydes. Cells grown on benzoate metabolized m-TFM-benzoate to TFHOD. The ring-fission products from m-toluate and TFHOD were degraded by sunlight, and equimolar fluoride was released from TFHOD. Sequential biochemical and photochemical treatment allowed the destruction of m-TFM-benzoate beyond the biochemically recalcitrant intermediate TFHOD.

Organic thiols as organolithotrophic substrates for growth of phototrophic bacteria.

Rhodopseudomonas sp. strain BB1, isolated from a coastal marine sediment, immediately metabolized mercaptomalate when grown on mercaptomalate. Sulfide was detected as an intermediate. Extracts of cells grown on mercaptomalate converted mercaptomalate or 3-mercaptopropionate to equimolar amounts of sulfide and either fumarate or acrylate, respectively. Rhodopseudomonas sp. strain BB1 gave higher growth yields on mercaptomalate than on sulfide or malate, consistent with metabolism of the carbon chain of the thiol and the liberated sulfide; i.e., the organic thiol was an organolithotrophic substrate. In contrast, Thiocapsa roseopersicina, isolated previously from a marine microbial mat, had similar growth yields on sulfide, mercaptomalate, or 3-mercaptopropionate, with fumarate or acrylate accumulation from the thiols. T. roseopersicina did not grow photoorganotrophically on fumarate or acrylate, and the thiols were only a source of sulfide for photolithoautotrophic growth.

New routes for aerobic biodegradation of dimethylsulfoniopropionate.

Dimethylsulfoniopropionate (DMSP), an osmolyte in marine plants, is biodegraded by cleavage of dimethyl sulfide (DMS) or by demethylation to 3-methiolpropionate (MMPA) and 3-mercaptopropionate (MPA). Sequential demethylation has been observed only with anoxic slurries of coastal sediments. Bacteria that grew aerobically on MMPA and DMSP were isolated from marine environments and phytoplankton cultures. Enrichments with DMSP selected for bacteria that generated DMS, whereas MMPA enrichments selected organisms that produced methanethiol (CH(3)SH) from either DMSP or MMPA. A bacterium isolated on MMPA grew on MMPA and DMSP, but rapid production of CH(3)SH from DMSP occurred only with DMSP-grown cells. Low levels of MPA accumulated during growth on MMPA, indicating demethylation as well as demethiolation of MMPA. The alternative routes for DMSP biodegradation via MMPA probably impact on net DMS fluxes to the marine atmosphere.

Coupled metabolic and photolytic pathway for degradation of pyridinedicarboxylic acids, especially dipicolinic Acid.

Three isomers of pyridinedicarboxylic acid (PDCA) (2,3-, 2,5-, and 2,6-PDCA) were partially oxidized by marine bacteria when grown aerobically on the corresponding phthalate analogs. The metabolites, unlike the parent PDCAs, absorbed light in the solar actinic range (wavelengths greater than 300 nm) and were readily degraded in sunlight. The principal product from 2,6-PDCA (dipicolinic acid) metabolism was extracted from a culture fluid, purified by column chromatography, and analyzed by UV-visible, infrared, and C nuclear magnetic resonance spectroscopy. The compound was identified as 2,3-dihydroxypicolinic acid (2,3-DHPA). 2,3-DHPA was photolyzed in aqueous solution (pH 8.0) with a half-life of 100 min. Eight photoproducts, three of which were photolabile, were detected by high-performance liquid chromatography. Ammonia was also photoproduced from 2,3-DHPA. Analysis of the photoproducts by UV-visible spectroscopy and by high-performance liquid chromatography of 2,4-dinitrophenylhydrazones indicated that the products were conjugated carbonyls and carboxylic acids. Six of the photoproducts were readily consumed by bacterial strain CC9M. In illuminated aquatic environments, coupled bio- and photodegradative mechanisms probably contribute to the degradation of PDCAs.

Sulfur-containing amino acids as precursors of thiols in anoxic coastal sediments.

Sulfur-containing amino acids were examined as precursors for thiols in anoxic coastal sediments. Substrates (10 to 100 muM) were anaerobically incubated with sediment slurries; thiols were assayed as isoindole derivatives by high-performance liquid chromatography; and microbial transformations of thiols, in contrast to their chemical binding by sediment particles, were identified by inhibition with a mixture of chloramphenicol and tetracycline. Methionine and homocysteine were transformed to methanethiol and 3-mercaptopropionate (3-MPA); methionine stimulated mainly methanethiol production, whereas homocysteine generated more 3-MPA than methanethiol. 2-Keto-4-methiolbutyrate yielded results similar to those with methionine, indicating that demethiolation yields methanethiol at the keto-acid level. Glutathione gave rise to cysteine, which was further transformed to 3-mercaptopyruvate and thence to mercaptoacetate and mercaptoethanol. Mercaptoethanol was oxidized to mercaptoacetate, which was biologically consumed. In conclusion, sulfurcontaining amino acids contribute to the range of thiols that occur in anoxic coastal sediments. New metabolic and environmental transformations were identified: the production of 3-MPA as a metabolite of methionine and the transformation of mercaptopyruvate to mercaptoethanol and mercaptoacetate.

Metabolism of pyridine compounds by phthalate-degrading bacteria.

Bacteria were isolated from marine sediments that grew aerobically on m-phthalate, p-phthalate, or dipicolinate (2,6-pyridine dicarboxylate [2,6-PDCA]). Strain OP-1, which grew on o-phthalate and was previously obtained from a marine source, was also studied. Intact cells of each organism demonstrated Na-dependent oxidation of their growth substrates. Strain PCC5M grew on dipicolinate but did not metabolize m-phthalate. The phthalate degraders, however, demonstrated Na-dependent metabolism of the appropriate PDCA analogs. 2,6-PDCA was transformed by strain CC9M when this strain was grown on m-phthalate, 2,5-PDCA was metabolized by strain PP-1 grown on p-phthalate, and 2,3-PDCA (quinolinate) was oxidized by strain OP-1 grown on o-phthalate. Spectral changes accompanying the Na-dependent transformations of the PDCA analogs suggest the formation of hydroxylated compounds. Metabolism probably occurred via phthalate hydroxylases; this is a previously unrecognized route for the environmental transformation of pyridine compounds. Hydroxylated products may feed into known pathways for the catabolism of pyridines or be photochemically degraded because of their absorbance in the solar actinic range (wavelengths > 300 nm). The results reinforce recent evidence for the broad potential of aromatic hydroxylase systems for the destruction of pollutants.

Demethylation of dimethylsulfoniopropionate and production of thiols in anoxic marine sediments.

Dimethylsulfoniopropionate (DMSP) is a natural product of algae and aquatic plants, particularly those from saline environments. We investigated whether DMSP could serve as a precursor of thiols in anoxic coastal marine sediments. The addition of 10 or 60 muM DMSP to anoxic sediment slurries caused the concentrations of 3-mercaptopropionate (3-MPA) and methanethiol (MSH) to increase. Antibiotics prevented the appearance of these thiols, indicating biological formation. Dimethyl sulfide (DMS) and acrylate also accumulated after the addition of DMSP, but these compounds were rapidly metabolized by microbes and did not reach high levels. Acrylate and DMS were probably generated by the enzymatic cleavage of DMSP. MSH arose from the microbial metabolism of DMS, since the direct addition of DMS greatly increased MSH production. Additions of 3-methiolpropionate gave rise to 3-MPA at rates similar to those with DMSP, suggesting that sequential demethylation of DMSP leads to 3-MPA formation. Only small amounts of MSH were liberated from 3-methiolpropionate, indicating that demethiolation was not a major transformation for 3-methiolpropionate. We conclude that DMSP was degraded in anoxic sediments by two different pathways. One involved the well-known enzymatic cleavage to acrylate and DMS, with DMS subsequently serving as a precursor of MSH. In the other pathway, successive demethylations of the sulfur atom proceeded via 3-methiolpropionate to 3-MPA.

A nuclear-magnetic-resonance study of the binding of novel N-hydroxybenzenesulphonamide carbonic anhydrase inhibitors to native and cadmium-111-substituted carbonic anhydrase.

Various ring- and nitrogen-substituted benzenesulphonamides have been prepared and tested as potential inhibitors of carbonic anhydrase. N-Methoxysulphonamides showed no inhibitory activity, as predicted by the classic work of Krebs on N-substituted inhibitors. By contrast, N-hydroxysulphonamides proved to be very effective inhibitors of carbonic anhydrase. Using 111Cd-NMR it has been possible to analyse the molecular interaction of 4-fluoro-N-hydroxybenzenesulphon[15N]amide, with 111Cd-substituted bovine carbonic anhydrase. A large cadmium-111:nitrogen-15 spin-coupling shows that this inhibitor is directly bound to the metal via its nitrogen rather than through an oxygen atom. The mode of this binding is similar to that for the unsubstituted sulphonamide inhibitor, 4-fluorobenzenesulphon[15N]amide. The 111Cd-chemical shift of the signal for the inhibited enzyme shows that the N-hydroxysulphonamide is bound as its anion. From the relative intensities of free and complexed enzyme signals it can be deduced that the cadmium enzyme complex with the N-hydroxysulphonamide has a longer life-time than that formed with the unsubstituted sulphonamide. By contrast, native zinc-containing bovine carbonic anhydrase shows similar I50 values with both of these sulphonamides. Attempts to monitor the binding using 15N-NMR were unsuccessful, possibly due to a very long relaxation time for the nitrogen nucleus in the N-hydroxysulphonamide when bound to the enzyme leading to loss of the 15N signal.

Bacterial Decarboxylation of o-Phthalic Acids.

The decarboxylation of phthalic acids was studied with Bacillus sp. strain FO, a marine mixed culture ON-7, and Pseudomonas testosteroni. The mixed culture ON-7, when grown anaerobically on phthalate but incubated aerobically with chloramphenicol, quantitatively converted phthalic acid to benzoic acid. Substituted phthalic acids were also decarboxylated: 4,5-dihydroxyphthalic acid to protocatechuic acid; 4-hydroxyphthalic and 4-chlorophthalic acids to 3-hydroxybenzoic and 3-chlorobenzoic acids, respectively; and 3-fluorophthalic acid to 2-and 3-fluorobenzoic acids. Bacillus sp. strain FO gave similar results except that 4,5-dihydroxyphthalic acid was not metabolized, and both 3- and 4-hydroxybenzoic acids were produced from 4-hydroxyphthalic acid. P. testosteroni decarboxylated 4-hydroxyphthalate (to 3-hydroxybenzoate) and 4,5-dihydroxyphthalate but not phthalic acid and halogenated phthalates. Thus, P. testosteroni and the mixed culture ON-7 possessed 4,5-dihydroxyphthalic acid decarboxylase, previously described in P. testosteroni, that metabolized 4,5-dihydroxyphthalic acid and specifically decarboxylated 4-hydroxyphthalic acid to 3-hydroxybenzoic acid. The mixed culture ON-7 and Bacillus sp. strain FO also possessed a novel decarboxylase that metabolized phthalic acid and halogenated phthalates, but not 4,5-dihydroxyphthalate, and randomly decarboxylated 4-hydroxyphthalic acid. The decarboxylation of phthalic acid is suggested to involve an initial reduction to 1,2-dihydrophthalic acid followed by oxidative decarboxylation to benzoic acid.

Aerobic and Anaerobic Catabolism of Vanillic Acid and Some Other Methoxy-Aromatic Compounds by Pseudomonas sp. Strain PN-1.

Vanillic acid (4-hydroxy-3-methoxybenzoic acid) supported the anaerobic (nitrate respiration) but not the aerobic growth of Pseudomonas sp. strain PN-1. Cells grown anaerobically on vanillate oxidized vanillate, p-hydroxybenzoate, and protocatechuic acid (3,4-dihydroxybenzoic acid) with O(2) or nitrate. Veratric acid (3,4-dimethoxybenzoic acid) but not isovanillic acid (3-hydroxy-4-methoxybenzoic acid) induced cells for the oxic and anoxic utilization of vanillate, and protocatechuate was detected as an intermediate of vanillate breakdown under either condition. Aerobic catabolism of protocatechuate proceeded via 4,5-meta cleavage, whereas anaerobically it was probably dehydroxylated to benzoic acid. Formaldehyde was identified as a product of aerobic demethylation, indicating a monooxygenase mechanism, but was not detected during anaerobic demethylation. The aerobic and anaerobic systems had similar but not identical substrate specificities. Both utilized m-anisic acid (3-methoxybenzoic acid) and veratrate but not o- or p-anisate and isovanillate. Syringic acid (4-hydroxy-3,5-dimethoxybenzoic acid), 3-O-methylgallic acid (3-methoxy-4,5-dihydroxybenzoic acid), and 3,5-dimethoxybenzoic acid were attacked under either condition, and formaldehyde was liberated from these substrates in the presence of O(2). The anaerobic demethylating system but not the aerobic enzyme was also active upon guaiacol (2-methoxyphenol), ferulic acid (3-[4-hydroxy-3-methoxyphenyl]-2-propenoic acid), 3,4,5-trimethoxycinnamic acid (3-[3,4,5-trimethoxyphenyl]-2-propenoic acid), and 3,4,5-trimethoxybenzoic acid. The broad specificity of the anaerobic demethylation system suggests that it probably is significant in the degradation of lignoaromatic molecules in anaerobic environments.

Ozone inhibition of tissue cholinesterase in guinea pigs.

This study sought to determine if ozone at levels known to induce bronchial hyperreactivity in guinea pigs would inhibit tissue cholinesterase activity. Male, Hartley guinea pigs were exposed to filtered air, 0.1 ppm ozone, or 0.8 ppm ozone for 1 hr. Two hours after exposure, brain, lung, and diaphragm tissue samples were frozen for assay of cholinesterase activity. Brain cholinesterase activity was only minimally inhibited in either ozone exposure group. Both levels of ozone significantly inhibited lung cholinesterase activity compared to control animals' activity: a 17% decrease in activity in the 0.1 ppm ozone group (P less than .05) and a 16% decrease in the 0.8 ppm ozone group (P less than .05). Ozone at 0.8 ppm also inhibited activity in the diaphragm by 14% (P less than .02). To determine the degree of involvement of cholinesterase inhibition in bronchial hyperreactivity, parathion pretreated animals were challenged with histamine and the pulmonary function changes monitored. Parathion-treated animals had a peak resistance increase of 330 +/- 104% (mean +/- SE), while the control vehicle animals' increase was 165 +/- 48%. The differences were not statistically significant, but show that cholinesterase inhibition may contribute to ozone-induced bronchial hyperreactivity.

Potential for biodegradation of phthalic Acid esters in marine regions.

Di-(2-ethylhexyl) phthalate was the major phthalic acid ester in the Mississippi River estuary, with mean levels of 0.1 mug/g (dry weight) in surface sediments, 1.0 mug/liter in river water, and 0.7 mug/liter in delta water. Bacteria that grew aerobically on dibutyl phthalate and o-phthalic acid were readily detected in the sediments and water. Pure cultures of bacteria were isolated on seven different phthalic acid esters from freshwater and marine sources. The marine isolates were taxonomically diverse and grew on a variety of phthalic acid esters. Dibutyl phthalate and o-phthalic acid supported growth in full-strength synthetic sea-water medium, but Na -dependent catabolism was demonstrable only for o-phthalic acid.

Degradation of phthalic acids by denitrifying, mixed cultures of bacteria.

Mixed cultures of bacteria, enriched from aquatic sediments, grew anaerobically on all three isomers of phthalic acid. Each culture grew anaerobically on only one isomer and also grew aerobically on the same isomer. Pure cultures were isolated from the phthalic acid (o-phthalic acid) and isophthalic acid (m-phthalic acid) enrichments that grew aerobically on phthalic and isophthalic acids. Cell suspension experiments indicated that protocatechuate is an intermediate of aerobic catabolism. Pure cultures which grew aerobically on terephthalic acid (p-phthalic acid) could not be isolated from the enrichments, and neither could pure cultures that grew anaerobically on any of the isomers. Cell suspension experiments suggested that separate pathways exist for the aerobic and anaerobic oxidation of phthalic acids. Each enrichment culture used only one phthalic acid isomer under anaerobic conditions, but all isomers were simultaneously adapted for the anaerobic catabolism of benzoate. Cells grown anaerobically on a phthalic acid immediately attacked the isomer under anaerobic conditions, whereas there was a lag before aerobic breakdown occurred, and, for phthalic and terephthalic acids, chloramphenicol stopped aerobic adaptation but had no effect on anaerobic catabolism. This work suggests that phthalic acids are biodegradable in anaerobic environments.

N2 fixation in the rhizosphere of Thalassia testudinum.

N2 fixation (C2H2 reduction) associated with the roots, rhizomes, and sediments (rhizosphere cores) of the seagrass Thalassia testudinum was measured at sites in South Florida (Soldier Key, Biscayne Bay) and the Bahamas (Bimini Harbor). Rates of C2H2 reduction were higher in anaerobic than in aerobic assays and were linear for several hours after an initial lag period of 1-2h. Nitrogenase activity was proportional to the weight of rhizomes plus roots but showed no correlation with the total weight of the rhizosphere cores. C2H2 reduction occurred to depths of at least 30 cm but the majority (<85%) of the activity was in the 0- to 20-cm fraction; also the ratio of activities for the 0- to 10- and 10- to 20-cm depths was about 2:1. Most investigations were carried out using anaerobic assays of the 0- to 10-cm fractions and rates calculated for the period of 3-6 h after adding C2H2. These rates were not stimulated by organic compounds (glucose, lactate, succinate) but were approximately halved by a decrease in temperature of 10 degrees C. In a seasonal study at Soldier Key the rates of N2 fixation varied about 20-fold with maximal rates in late summer and minimal rates in winter (January). On a diurnal basis, C2H2 reduction increased in the morning but was depressed in midafternoon, probably due to O2 buildup in the rhizosphere. Daily rates of N2 fixation, during the summer months of 1975-1978, varied between 5 and 24 mg N (-2)m and the estimated annual rates of N2 fixation were 10-50 kg N (-1)ha, taking into account seasonal variations and activities to a depth of 20 cm.

Assessment of microbial fouling in an ocean thermal energy conversion experiment.

A project to investigate biofouling, under conditions relevant to ocean thermal energy conversion heat exchangers, was conducted during July through September 1977 at a site about 13 km north of St. Croix (U.S. Virgin Islands). Seawater was drawn from a depth of 20 m, within the surface mixed layer, through aluminum pipes (2.6 m long, 2.5-cm internal diameter) at flow velocities of about 0.9 and 1.8 m/s. The temperature of the seawater entering the mock heat exchanger units was between 27.8 and 28.6 degrees C. After about 10 weeks of exposure to seawater, when their thermal conductivity was reported to be significantly impaired, the pipes were assayed for the accumulation of biological material on their inner surfaces. The extent of biofouling was very low and independent of flow velocity. Bacterial populations, determined from plate counts, were about 10 cells per cm. The ranges of mean areal densities for other biological components were: organic carbon, 18 to 27 mug/cm; organic nitrogen, 1.5 to 3.0 mug/cm; adenosine 5'-triphosphate, 4 to 28 ng/cm; carbohydrate (as glucose in the phenol assay), 3.8 to 7.0 mug/cm; chlorophyll a, 0.2 to 0.8 ng/cm. It was estimated from the adenosine 5'-triphosphate and nitrogen contents that the layer of live bacteria present after 10 weeks was only of the order of 1mum thick. The C/N ratio of the biological material suggested the presence of extracellular polysaccharidic material. Such compounds, because of their water-retaining capacities, could account for the related increase in thermal resistance associated with the pipes. This possibility merits further investigation, but the current results emphasize the minor degree of biofouling which is likely to be permissible in ocean thermal energy conversion heat exchangers.