Production and consumption of carbon monoxide in a eutrophic lake1

Abstract

CO concentrationswere measured in the water of a eutrophic lake by a technique which allowed the detection of 30.5 nl CO* liter-l of water. In spring, when the lake was aerobic to the bottom, CO distribution was relatively homogeneous with concentrations of 40-130 nlaliter-l.In summer, CO concentrations ranged between 20 and 615 nleliter-' in the aerobic epilimnion and metalimnion, but reached values of >8,000 nl* liter-' in the anaerobic hypolimnion. CO increased during the morning and decreased during the afternoon in the upper water layers as well as in the dark hypolimnion.Incubation of lake water samples from different depths under daylight conditions resulted in a strong CO production. The lightdependent CO production was stimulated by the high numbers of Oscillatoria rubescens in the metalimnion, but also by material from the lake sediment. Incubation of lake water samples in darkness resulted in CO consumption under both aerobic and anaerobic conditions.

hypD as a Marker for [NiFe]-Hydrogenases in Microbial Communities of Surface Waters

“…This is also in line with the presence of group 3d hydrogenases in coastal (nutrient-rich environments) and their absence in nutrient-poor open ocean regions (9). Previous studies on hydrogen concentrations in freshwater lakes found the highest concentrations near the surface that coincided with the maximum of primary production and that of the chlorophyll maximum (18,19). Daily maxima were found especially at dawn (18).…”

“…Both could enable the respective bacteria to participate in hydrogen oxidation and could open access to an additional energy source. Therefore, hydrogen consumption in surface waters as measured in a number of studies of freshwater lakes (18,19) probably originates from these two groups of [NiFe]-hydrogenases expressed in Burkholderiales, acidobacteria, and actinobacteria.…”

“…Since hydrogen leakage from anaerobic habitats is negligible and does not contribute to a significant extent to H 2 levels in the atmosphere (18)(19)(20), microbial influence on its atmospheric concentration apart from nitrogen fixation mainly relies on [NiFe]-hydrogenases. A few studies already attempted to analyze the occurrence of these hydrogenases in the environment by using primers specific for one group of the nine different known groups and subgroups of [NiFe]-hydrogenases (9,21,22) or by using a microarray with a specific set of genes (23), but there is no study that tried to unravel the whole set present.…”

“…The most promising candidate of all maturation genes is the highly conserved hypD, encoding a protein with a ferredoxin:thioredoxin reductase-like [4Fe-4S] cluster and additional cysteine residues that probably work as a redox cascade. In concert with HypC, it works as a scaffold protein that allows the insertion of the Fe(CN) 2 (CO) in the correct oxidation state into the active site of the [NiFe]-hydrogenases (11-17).Since hydrogen leakage from anaerobic habitats is negligible and does not contribute to a significant extent to H 2 levels in the atmosphere (18)(19)(20), microbial influence on its atmospheric concentration apart from nitrogen fixation mainly relies on [NiFe]-hydrogenases. A few studies already attempted to analyze the occurrence of these hydrogenases in the environment by using primers specific for one group of the nine different known groups and subgroups of 21,22) or by using a microarray with a specific set of genes (23), but there is no study that tried to unravel the whole set present.…”

A soil actinobacterium scavenges atmospheric H 2 using two membrane-associated, oxygen-dependent [NiFe] hydrogenases

“…Because of intra-and interspecies hydrogen cycling, most microbial H 2 -oxidizing and H 2 -producing processes are balanced and hence make minor or null net contributions to the global hydrogen budget (5). It has nevertheless been known for several decades that soil ecosystems can oxidize tropospheric H 2 in an apparent enzymatic process (6)(7)(8). This ecologically essential process is estimated to be accountable for 80% of the net loss of tropospheric H 2 (3).…”