most likely biological sources. Herr et al. (1981) and Scranton et al (1982) suggest that
nitrogen-fixing microorganisms are the dominant hydrogen producers in the ocean.
While these microorganisms undoubtedly are capable of evolving hydrogen, there is little
direct evidence to suggest that they are the main source of the dissolved hydrogen in the
water column.
On the other hand, there is evidence that fermentative bacteria are active in marine
hydrogen production. In the Gulf of Cadiz, Seiler and Schmidt (1974) noted a large
hydrogen maximum at the interface between Mediterranean and North Atlantic water
masses. From the same area, Junge et al. (1972) isolated several species of heterotrophic
hydrogen-producing bacteria from near the interface, at depths of 700 and 900 meters. At
several stations in the north Atlantic, Herr and Barger (1978) observed hydrogen maxima
associated with the pycnocline. Suspended particulate maxima sometimes occur at sharp
gradients in water densities (Pak et al., 1980) and Bishop (1977) found that bacteria
compose from 20 - 45 % of the organic carbon in a <53 µm particulate fraction from the
equatorial Atlantic. These facts suggest that bacteria associated with particulate maxima
could be responsible for the observed hydrogen maxima. Particles could serve as anaerobic microenvironments (Knowles, 1978) where hydrogen production could take place.
To test the hypothesis that hydrogen-producing bacteria are associated with oceanic
particulates, we have collected samples from particulate maxima, tested them for hydrogen production, and isolated hydrogen-producing bacteria from them. On previous
cruises to the Mediterranean Sea and Caribbean Sea, we have detected hydrogen production in samples of concentrated particulates from surface waters but cultures from the
samples lost viability within a few weeks (Schropp and Schwarz, unpublished data). On a
recent cruise to the subtropical Atlantic, we extended our observations of the potential for
hydrogen production and were able to successfully isolate pure cultures of hydrogenproducing bacteria from oceanic water against which antisera were produced. These
antibodies were then utilized in an indirect fluorescent antibody assay procedure to
enumerate the number of hydrogen producing bacteria present in nepheloid layer water
samples.
MATERIALS AND METHODS
Station locations.
Samples for these experiments were collected on cruise 710-82 of the U.S.N.S. Lynch, 4
-25 June, 1982 and cruise 84-G-5 of the R/V Gyre, 1-13 May, 1984. Microbiological
sampling was done at five stations in the subtropical Atlantic, located within or near the
Sargasso Sea (Fig. 1).
Sample collection.
Water samples were taken with 30-1 Niskin bottles mounted on a rosette sampler
(General Oceanics). The rosette was positioned in the particle maxima by means of
real-time light scattering data from a rosette-mounted nephelometer or transmissometer.
The samples from the U.S.N.S. Lynch cruise were concentrated using reverse-flow filter
units, usually containing a 3-µm pore diameter membrane filter (Schropp and Schwarz
1983). The filter units were constructed of clear plexiglass and had a volume of 2.21 in
both the upper and lower chambers. Before each use the filter units, Niskin bottles, and
connecting tubing were washed with ethanol. A very gentle concentration of suspended
matter was achieved at a flow rate of ca. 11 min -1 . At each station, 58 l of water were
concentrated by a factor of 26.5:1. At station 11, effluent from the reverse flow units
2UU
nitrogen-fixing microorganisms are the dominant hydrogen producers in the ocean.
While these microorganisms undoubtedly are capable of evolving hydrogen, there is little
direct evidence to suggest that they are the main source of the dissolved hydrogen in the
water column.
On the other hand, there is evidence that fermentative bacteria are active in marine
hydrogen production. In the Gulf of Cadiz, Seiler and Schmidt (1974) noted a large
hydrogen maximum at the interface between Mediterranean and North Atlantic water
masses. From the same area, Junge et al. (1972) isolated several species of heterotrophic
hydrogen-producing bacteria from near the interface, at depths of 700 and 900 meters. At
several stations in the north Atlantic, Herr and Barger (1978) observed hydrogen maxima
associated with the pycnocline. Suspended particulate maxima sometimes occur at sharp
gradients in water densities (Pak et al., 1980) and Bishop (1977) found that bacteria
compose from 20 - 45 % of the organic carbon in a <53 µm particulate fraction from the
equatorial Atlantic. These facts suggest that bacteria associated with particulate maxima
could be responsible for the observed hydrogen maxima. Particles could serve as anaerobic microenvironments (Knowles, 1978) where hydrogen production could take place.
To test the hypothesis that hydrogen-producing bacteria are associated with oceanic
particulates, we have collected samples from particulate maxima, tested them for hydrogen production, and isolated hydrogen-producing bacteria from them. On previous
cruises to the Mediterranean Sea and Caribbean Sea, we have detected hydrogen production in samples of concentrated particulates from surface waters but cultures from the
samples lost viability within a few weeks (Schropp and Schwarz, unpublished data). On a
recent cruise to the subtropical Atlantic, we extended our observations of the potential for
hydrogen production and were able to successfully isolate pure cultures of hydrogenproducing bacteria from oceanic water against which antisera were produced. These
antibodies were then utilized in an indirect fluorescent antibody assay procedure to
enumerate the number of hydrogen producing bacteria present in nepheloid layer water
samples.
MATERIALS AND METHODS
Station locations.
Samples for these experiments were collected on cruise 710-82 of the U.S.N.S. Lynch, 4
-25 June, 1982 and cruise 84-G-5 of the R/V Gyre, 1-13 May, 1984. Microbiological
sampling was done at five stations in the subtropical Atlantic, located within or near the
Sargasso Sea (Fig. 1).
Sample collection.
Water samples were taken with 30-1 Niskin bottles mounted on a rosette sampler
(General Oceanics). The rosette was positioned in the particle maxima by means of
real-time light scattering data from a rosette-mounted nephelometer or transmissometer.
The samples from the U.S.N.S. Lynch cruise were concentrated using reverse-flow filter
units, usually containing a 3-µm pore diameter membrane filter (Schropp and Schwarz
1983). The filter units were constructed of clear plexiglass and had a volume of 2.21 in
both the upper and lower chambers. Before each use the filter units, Niskin bottles, and
connecting tubing were washed with ethanol. A very gentle concentration of suspended
matter was achieved at a flow rate of ca. 11 min -1 . At each station, 58 l of water were
concentrated by a factor of 26.5:1. At station 11, effluent from the reverse flow units
2UU