Environmental Engineering Reference
In-Depth Information
nitrate that usually disappears above the sulfide onset suggests that nitrate is of
minor importance in oxidizing sulfide. A high density of nitrifying bacteria of
up to 10
4
cells ml
−
1
was observed in the oxycline and nitrifiers were suggested
to account for over 50% of the Black Sea chemosynthesis [33]. Sorokin [52]
however argued that the CO
2
-fixation rate by nitrifiers may contribute to not
more than 1% of the chemosynthesis by thiobacilli at the oxic/anoxic interface.
Recently Kuypers et al. [21] reported the occurrence of 'anammox' bacteria in
the Black Sea chemocline capable of oxidizing ammonium with nitrite/nitrate
under anaerobic conditions. Using fluorescence in situ hybridization (FISH)
analyses the authors estimated the highest density of these bacteria at the nitrite
peak of 1.9 (
10
3
cells ml
−
1
or about 0.75% of the total number of bacte-
ria detectable with DAPI [21, Kuypers et al., this volume]. Calculations showed
that microorganisms oxidizing ammonium together with denitrifiers may play
an important role in the loss of fixed inorganic nitrogen; however given their
low cell numbers and biomass, they are unlikely to have any notable effect on
the carbon cycle of the Black Sea.
±
0.8)
×
Mn(II)-Oxidizing and Mn(IV)-Reducing Bacteria.
Mn(II) oxidation is
microbiologically mediated process and its maximum rates between 1 and 68
nM Mn(II) oxidized per hour have been measured in the Black Sea suboxic zone
[46, 55]. These studies unambiguously showed that anaerobic Mn(II) oxidation
with nitrate, nitrite, or iodate in the Black Sea water column hypothesized in
earlier geochemical studies is absent and dissolved oxygen is the only possi-
ble electron acceptor for Mn(II) oxidation. Furthermore Schippers et al. [46]
argued that lateral intrusions of oxygen in the western Black Sea were respon-
sible for ventilation of the suboxic zone and could explain the observed Mn(II)
oxidation rates in the chemocline. Morphologies of Mn(IV) aggregates found
in lakes and usually associated with several Mn(II)-oxidizing genera such as
Metallogenium, Siderococcus, and Siderocapsa
were found in the Black Sea
water column, but pure cultures of these bacteria were not isolated. Mn(II)-
oxidizing and Mn(IV)-reducing bacteria are mostly probably associated with
those Mn(III,IV)-rich aggregates. Nealson et al. [30] isolated several groups of
Mn(IV)-reducing microorganisms related to
Shewanella, Pseudomonas, Bacil-
lus,
and some unidentified Gram-negative rods and coccobacilli. These strains
were capable to reduce Fe(III) in addition to Mn(IV).
Bacteria and Archaea Involved in Methane Cycling.
The presence of
ether-linked isoprenoids suggested that Archaea are widely distributed through-
out the Black Sea water column. The analyses suggested that a number of
psychrophilic Archaea, representing both, methanogens and thermophilic-type
Archaea are common groups [13, 17].
13
C depleted archaeal biphytanes (up to
-58‰) occurring in the anoxic Black Sea suggested the presence of a methane
oxidizing archaeal community [47, 60].
