O LR (1987) 34 (I 1) E. Biological Oceanography 989

association with surficial microenvironments or microzones. Experimental results (02 profiles, and reduction of tetrazolium salt and triphenyltetrazo- lium chloride) suggest that N 2 fixation is mediated by the availability of the appropriate types of reduced microzones. Organic C enrichment appears to serve as an energy and structural source for aggregate formation. Inst. of Mar. Sci., Univ. of North Carolina, Morehead City, NC 28557, USA.

87:6485 Schropp, S.J., M.I. Scranton and J.R. Schwarz, 1987.

Dissolved hydrogen, facultatively anaerobic, hy- drogen.producing bacteria, and potential hydro- gen production rates in the western North Atlantic Ocean and Guff of Mexico. Limnol. Oceanogr., 32(2):396-402.

Dissolved hydrogen concentrations were near at- mospheric equilibrium at the surface and decreased rapidly with depth. The number of facultative hydrogen producers varied from 7 to 644 cells mL ~. At several stations, the maximum number of hydro- gen-producer cells coincided with a subsurface dissolved hydrogen maximum and particle maxi- mum. The results indicate that dissolved hydrogen concentrations are governed by a complex set of mechanisms with facultatively anaerobic, hydrogen- producing bacteria having a role in hydrogen production. Office of Coastal Mgmt., Dept. Environ. Regulations, 2600 Blair Stone Rd., Tallahassee, FL 32301-8201, USA.

87:6486 Seitzinger, S.P. and J.H. Garber, 1987. Nia'ogen

fixation and ISN 2 calibration of the acetylene reduction assay in coastal marine sediments. Mar. Ecol.-Prog. Ser., 37(1):65-73.

Simultaneous assays of di-nitrogen fixation were carried out in sediments from Narragansett Bay using the acetylene reduction technique and ~SN 2 tracer. The ratio of moles of acetylene reduced to moles of ~SN recovered in ammonium and labile organic-N pools in estuarine sediments under an- aerobic conditions ranged from approximately 10:1 to nearly 100:1, always significantly greater than the theoretical 3:1 ratio. Rates of both acetylene reduc- tion and ~SN 2 fixation increased with the addition of labile organic carbon (as sucrose) to the sediments. Ratios in the sucrose-addition sediments were lower than those found in sediments without sucrose additions, but always significantly greater than the theoretical 3:1 ratio. The use of the theoretical 3:1 ratio in assays of N 2 fixation by the acetylene reduction technique in anaerobic coastal marine sediments results in overestimates of N 2 fixation

rates. Acad. of Nat. Sci., Div. of Environ. Res., Philadelphia, PA 19103, USA.

87:6487 Sherr, B.F., E.B. Sherr and R.D. Fallon, 1987. Use of

monodispersed, fluorescently labeled bacteria to estimate in-situ protozoan bacterivory. Appl. environ. Microbiol., 53(5):958-965.

Monodispersed, fluorescently labeled bacteria (FLB) may be used to measure virtually instantaneous rates of protozoan bacterivory in natural waters. FLB can be prepared from natural bacterioplankton assem- blages or clonal isolates and stored in frozen suspension or freeze-dried without apparent loss of fluorescence intensity. They are not toxic to Pro- tozoa and can be metabolized to support bacte- rivorous protozoan growth rates equal to those on the same strain of unstained, viable bacteria. In experiments comparing uptake of FLB with uptake of fluorescent latex microspheres by protozoan assemblages in a salt marsh tidal creek, pelagic oligotrichous ciliates and phagotrophic flagellates ingested FLB with a frequency 4- to 10-fold greater than they ingested microspheres. It appears that use of latex microspheres leads to underestimation of protozoan bacterivory and that FLB technique is superior for estimating instantaneous rates of in-situ protozoan grazing. Univ. of Georgia Mar. Inst., Sapelo Island, GA 31327, USA.

87:6488 Stetter, K.O., Gerta Lauerer, Michael Thomm and

Annemarie Neuner, 1987. Isolation of extremely thermophilic sulfate reducers: evidence for a novel branch of archaebacteria. Science, 236(4803): 822-824.

A novel group of extremely thermophilic archae- bacteria isolated from marine hydrothermal systems in Italy is described, which consists of sulfate- respiring organisms that contain pure factor 420. They possess a third type of archaebacterial RNA polymerase structure previously unknown, indicat- ing an exceptional phylogenetic position. Most likely, this group represents a third major branch within the archaebacteria. The existence of sulfate reducers at extremely high temperatures could explain hydrogen sulfide formation in hot sulfate- containing environments, such as submarine hydro- thermal systems and deep oil wells. ©1987 by AAAS. Inst. fur Biochemie, Genetik und Mikrobiol., Univ. Regensburg, Universitatsstr. 3 l, D-8400 Regensburg, FRG.

87:6489 Wirsen, C.O., H.W. Jannasch, S.G. Wakeham and

E.A. Canuel, 1987. Membrane lipids of a psy-