Taxonomic characterization of the hydrogen-producing isolates showed them to consist
of only two groups of bacteria. These organisms were the ones which responded best to
the artificial conditions in the experimental system, so we cannot exclude the possibility
that other hydrogen producers such as anaerobic microaerotolerant bacteria are present
in the water but do not grow on agar plates. Nevertheless, these results suggest that if in
situ fermentative hydrogen production does occur, it will be from the activity of relatively
few species.
Other authors have suggested that nitrogen-fixing microorganisms, particularily the
cyanobacterium, Oscillatoria, are primarily responsible for dissolved hydrogen maxima
in marine waters (Herr et al., 1981; Scranton, 1983). However, Scranton et al. (1982)
found no Oscillatoria associated with dissolved hydrogen maxima in the Mediterranean
Sea. Carpenter and McCarthy (1975) concluded that Oscillatoria in the Sargasso Sea had
very slow growth rates, too slow to account for much nitrogen fixation and so, by
inference, much hydrogen production. Doremus (1982) has argued that on a large scale,
nitrogen fixation in the oceans is insignificant in the long torm because of nutrient
limitations. Thus, nitrogen-fixing cyanobacteria apparently cannot be responsible for all
of the dissolved hydrogen maxima in the oceans. Localized blooms of cyanobacters do
occur and could account for some hydrogen production. However, on a larger scale, it
appears that some other biological mechanism must contribute to dissolved hydrogen
production.
On two previous cruises we also detected fermentative hydrogen production from >35 µm
particle fractions (Schropp and Schwarz, unpublished). Junge et al. (1972) were able to
isolate hydrogen-producing bacteria from the Gulf of Cadiz, just below the depth of a
dissolved maximum. The results of all the experiments indicate that hydrogen-producing
bacteria are ubiquitous in marine waters. Under the appropriate conditions these organisms readily produce hydrogen. We believe that particulate matter can be conditioned so
that fermentative metabolism can proceed in situ. Our gas production rate and fluorescent antibody enumeration studies (Fig. 4) along with the physical data (Fig. 3) would
support this hypothesis. Particulates tend to be concentrated at a pycnocline since their
sinking rate decreases as the density of the water increases. Fermentative bacteria associated with the particles could thus contribute to the observed hydrogen maxima associated
with density gradients.
ACKNOWLEDGEMENTS
This research was supported by Contract N00014-80-C-00113 from the Oceanic Biology section of the Office of
Naval Research. We thank Drs. David Reid and James Brooks for providing the ancillary date. Dr. Paul
LaRock for providing the SEM micrographs and providing space aboard the R/V Gyre, NORDA for providing
shiptime aboard the U.S.N.S. Lynch, and Dr. Mary Scranton for her consistently dependable measurements of
water column hydrogen concentrations.
AMY P. S. and R. Y. MORITA, 1983. Starvation-survival patterns of sixteen freshly isolated open ocean bacteria.
Appl. Environ. Microbiol. 45:1109 - 1115.
BISHOP J. K. B., J. M. EDMOND, D. R. KETTEN, M. P. BACON and W. B. SILKER, 1977. The chemistry, biology,
and vertical flux of particulate matter from the upper 400 m of the equatorial Atlantic Ocean. Deep-Sea Res. 24:
511 -548.
207
of only two groups of bacteria. These organisms were the ones which responded best to
the artificial conditions in the experimental system, so we cannot exclude the possibility
that other hydrogen producers such as anaerobic microaerotolerant bacteria are present
in the water but do not grow on agar plates. Nevertheless, these results suggest that if in
situ fermentative hydrogen production does occur, it will be from the activity of relatively
few species.
Other authors have suggested that nitrogen-fixing microorganisms, particularily the
cyanobacterium, Oscillatoria, are primarily responsible for dissolved hydrogen maxima
in marine waters (Herr et al., 1981; Scranton, 1983). However, Scranton et al. (1982)
found no Oscillatoria associated with dissolved hydrogen maxima in the Mediterranean
Sea. Carpenter and McCarthy (1975) concluded that Oscillatoria in the Sargasso Sea had
very slow growth rates, too slow to account for much nitrogen fixation and so, by
inference, much hydrogen production. Doremus (1982) has argued that on a large scale,
nitrogen fixation in the oceans is insignificant in the long torm because of nutrient
limitations. Thus, nitrogen-fixing cyanobacteria apparently cannot be responsible for all
of the dissolved hydrogen maxima in the oceans. Localized blooms of cyanobacters do
occur and could account for some hydrogen production. However, on a larger scale, it
appears that some other biological mechanism must contribute to dissolved hydrogen
production.
On two previous cruises we also detected fermentative hydrogen production from >35 µm
particle fractions (Schropp and Schwarz, unpublished). Junge et al. (1972) were able to
isolate hydrogen-producing bacteria from the Gulf of Cadiz, just below the depth of a
dissolved maximum. The results of all the experiments indicate that hydrogen-producing
bacteria are ubiquitous in marine waters. Under the appropriate conditions these organisms readily produce hydrogen. We believe that particulate matter can be conditioned so
that fermentative metabolism can proceed in situ. Our gas production rate and fluorescent antibody enumeration studies (Fig. 4) along with the physical data (Fig. 3) would
support this hypothesis. Particulates tend to be concentrated at a pycnocline since their
sinking rate decreases as the density of the water increases. Fermentative bacteria associated with the particles could thus contribute to the observed hydrogen maxima associated
with density gradients.
ACKNOWLEDGEMENTS
This research was supported by Contract N00014-80-C-00113 from the Oceanic Biology section of the Office of
Naval Research. We thank Drs. David Reid and James Brooks for providing the ancillary date. Dr. Paul
LaRock for providing the SEM micrographs and providing space aboard the R/V Gyre, NORDA for providing
shiptime aboard the U.S.N.S. Lynch, and Dr. Mary Scranton for her consistently dependable measurements of
water column hydrogen concentrations.
AMY P. S. and R. Y. MORITA, 1983. Starvation-survival patterns of sixteen freshly isolated open ocean bacteria.
Appl. Environ. Microbiol. 45:1109 - 1115.
BISHOP J. K. B., J. M. EDMOND, D. R. KETTEN, M. P. BACON and W. B. SILKER, 1977. The chemistry, biology,
and vertical flux of particulate matter from the upper 400 m of the equatorial Atlantic Ocean. Deep-Sea Res. 24:
511 -548.
207