Bacterial Activity In Sediments Research Articles

Siderophore production by bacteria isolated from mangrove sediments: A microcosm study

Mangroves are one of the most productive ecosystems worldwide covering up to 75% of the coastline in the tropics and subtropics. They support a highly diverse community (marine and terrestrial) and serves as reservoirs of nutrients for coastal and shelf waters. Bacterial diversity in mangroves includes heterotrophs, autotrophs (nitrogen fixation) and pathogens (phytopathogens, marine, and human). All these bacterial groups require sequestration of bioavailable iron, which is largely done by the production of siderophores. In this study, microcosm experiments were conducted to test the effect of incubation conditions (temperature, iron concentration, pH, and carbon source) on growth and siderophore production in four mangrove sediment bacterial isolates- Escherichia vulneris, Enterobacter cancerogenus, Pantoea agglomerans, and Enterobacter bugandensis. Our study showed that all isolates produce more siderophores (30 to 60%) at low iron concentrations (10 nM to 1 μM) during lag-phase and early log-phase of growth. Low temperature suppressed bacterial growth without significantly altering the siderophore production, whereas low pH suppressed both growth and siderophore production in these isolates. Although all isolates could produce siderophores when using different carbon sources, glucose served as an ideal carbon source. The observed changes in growth and siderophore production may be attributed to species-specific physiological traits, changes in bioavailability of iron and/or combination of both. Our results suggest that in a changing global environment, warming of the surrounding waters may not reduce the siderophore production and hence, they will be essential in sustaining bacterial activity in sediments.

Persistent Hg contamination and occurrence of Hg-methylating transcript (hgcA) downstream of a chlor-alkali plant in the Olt River (Romania).

Chlor-alkali plants using mercury(Hg) cell technology are acute point sources of Hg pollution in the aquatic environment. While there have been recent efforts to reduce the use of Hg cells, some of the emitted Hg can be transformed to neurotoxic methylmercury (MeHg). Here, we aimed (i) to study the dispersion of Hg in four reservoirs located downstream of a chlor-alkali plant along the Olt River (Romania) and (ii) to track the activity of bacterial functional genes involved in Hg methylation. Total Hg (THg) concentrations in water and sediments decreased successively from the initial reservoir to downstream reservoirs. Suspended fine size particles and seston appeared to be responsible for the transport of THg into downstream reservoirs, while macrophytes reflected the local bioavailability of Hg. The concentration and proportion of MeHg were correlated with THg, but were not correlated with bacterial activity in sediments, while the abundance of hgcA transcript correlated with organic matter and Cl(-) concentration, indicating the importance of Hg bioavailability in sediments for Hg methylation. Our data clearly highlights the importance of considering Hg contamination as a legacy pollutant since there is a high risk of continued Hg accumulation in food webs long after Hg-cell phase out.

Can mercury in fish be reduced by water level management? Evaluating the effects of water level fluctuation on mercury accumulation in yellow perch (Perca flavescens).

Mercury (Hg) contamination of fisheries is a major concern for resource managers of many temperate lakes. Anthropogenic Hg contamination is largely derived from atmospheric deposition within a lake's watershed, but its incorporation into the food web is facilitated by bacterial activity in sediments. Temporal variation in Hg content of fish (young-of-year yellow perch) in the regulated lakes of the Rainy-Namakan complex (on the border of the United States and Canada) has been linked to water level (WL) fluctuations, presumably through variation in sediment inundation. As a result, Hg contamination of fish has been linked to international regulations of WL fluctuation. Here we assess the relationship between WL fluctuations and fish Hg content using a 10-year dataset covering six lakes. Within-year WL rise did not appear in strongly supported models of fish Hg, but year-to-year variation in maximum water levels (∆maxWL) was positively associated with fish Hg content. This WL effect varied in magnitude among lakes: In Crane Lake, a 1 m increase in ∆maxWL from the previous year was associated with a 108 ng increase in fish Hg content (per gram wet weight), while the same WL change in Kabetogama was associated with only a 5 ng increase in fish Hg content. In half the lakes sampled here, effect sizes could not be distinguished from zero. Given the persistent and wide-ranging extent of Hg contamination and the large number of regulated waterways, future research is needed to identify the conditions in which WL fluctuations influence fish Hg content.

Depth distribution of active bacteria and bacterial activity in lake sediment

The bacterial activity in sediments is often low considering the generally high bacterial abundance. Still, a large fraction of bacteria have been found active even in deep sediments. These findings suggest that sediment bacteria have comparatively low cell-specific production. We studied bacterial activity and the active fraction of bacteria in a lake sediment profile. Bacterial production and metabolism were measured by thymidine and leucine incorporation and by microcalorimetry. In addition to counts of total bacteria, we estimated the nucleoid-containing fraction of the bacteria by adding a destaining step to the DAPI staining method, and the live fraction using the Live/Dead Baclight bacterial viability kit. The bacterial activity and abundance decreased with sediment depth, while the proportion of active bacteria remained similar at all depths. Between 57 and 63% of the bacteria were scored viable, and 13–52% were scored as nucleoid-containing cells. Consequently, there was no accumulation of dead bacterial cells in deeper sediments. Cell-specific production of sediment bacteria may be severely underestimated if the active fraction of the sediment bacterial community is not considered during enumeration.

Bacterial activity in sediments of the deep Arabian Sea in relation to vertical flux

In the Arabian Sea, productivity in the surface waters and particle flux to the deep sea are controlled by monsoonal winds. The flux maxima during the South-West (June–September) and the North-East Monsoon (December–March) are some of the highest particle fluxes recorded with deep-sea sediment traps in the open ocean. Benthic microbial biomass and activities in surface sediments were measured for the first time in March 1995 subsequent to the NE-monsoon and in October 1995 subsequent to the SW-monsoon. These measurements were repeated in April/May 1997 and February/March 1998, at a total of six stations from 1920 to 4420 m water depth. This paper presents a summary on the regional and temporal variability of microbial biomass, production, enzyme activity, degradation of 14 C -labeled Synechococcus material as well as sulfate reduction in the northern, western, eastern, central and southern Arabian deep sea. We found a substantial regional variation in microbial biomass and activity, with highest values in the western Arabian Sea (station WAST), decreasing approximately threefold to the south (station SAST). Benthic microbial biomass and activity during the NE-monsoon was as high or higher than subsequent to the SW-monsoon, indicating a very rapid turnover of POC in the surface sediments. This variation in the biomass and activity of the microbial assemblages in the Arabian deep sea can largely be explained by the regional and temporal variation in POC flux. Compared to other abyssal regions, the substantially higher benthic microbial biomasses and activities in the Arabian Sea reflect the extremely high productivity of this tropical basin.

Pelagic‐benthic coupling: Profundal benthic community response to spring diatom deposition in mesotrophic Lake Erken

Phytodetrital sedimentation, bacterial activity in sediments, and benthic macro‐ and meiofauna abundance were measured to calculate a carbon budget for pelagic‐benthic coupling in Lake Erken. Bacterial activity in surficial sediment was limited by temperature in spring, although a significant correlation with the input of spring‐bloom phytodetritus was noted. Population dynamics of benthic meiofauna during a period of increased food availability in spring were highly taxon‐specific and closely correlated to feeding behavior. Abundances of ostracods and nematodes rapidly increased when phytodetritus became available in hypolimnetic water and surficial sediment, respectively. Considerable time lags (months) were found between phytodetritus deposition and population development of harpacticoid copepods and chydorids.Carbon budget calculations based on sedimentation data (traps) and surficial sediment C content showed that during spring between 1.1 and 7.2% of deposited phytodetritus is assimilated by benthic meiofauna, whereas the dominant macroinvertebrates, sedentary chironomids, assimilated between 2.4 and 6.0%. On average, between 1.9 and 12.4% of the deposited phytodetritus was mineralized by sediment bacteria. A significant negative correlation was found between abundances of benthic meiofauna and bacteria in the sediment. Chlorophyll a analysis of surficial sediment was a necessary, complementary tool to detect sedimentation that was not detected by the traditional, cylindric sediment traps.

Comparison of leucine uptake methods and a thymidine incorporation method for measuring bacterial activity in sediment

Three [ 14C]leucine uptake methods and a [ 3H]thymidine method for measuring bacterial activity in sediment were compared. For leucine uptake, a combustion method, in which prior to combustion sediment was washed with ethanol, yielded the most consistent results. The TCA extraction methods with a filtration step yielded very variable and much lower results than the combustion method. A high concentration of leucine was needed to reach the saturation level (13.7 μM), but that was not found to enhance bacterial activity. No clear saturation level for thymidine incorporation was achieved for two of the four lake sediments tested. Therefore, and because of other weaknesses of the method, the thymidine incorporation underestimated the bacterial carbon production in sediment.

Comparison of Methods for Inhibiting Bacterial Activity in Sediment

Dilute formaldehyde was the most suitable treatment to inhibit sediment bacteria, since bacterial activity remained low during long-term incubations and the chemical changes in the sediment were minimal. The inhibiting effects of HgCl(2), autoclaving, and gamma radiation were diminished during longer incubations; these treatments also caused increases in dissolved nutrients.

Organic geochemistry of sediments from chemosynthetic communities, Gulf of Mexico slope

We used a research submersible to obtain 33 sediment samples from chemosynthetic communities at 541–650 m water depths in the Green Canyon (GC) area of the Gulf of Mexico slope. Sediment samples from beneath an isolated mat of H2S-oxidizing bacteria at GC 234 contain oil (mean = 5650 ppm) and C1–C5 hydrocarbons (mean = 12,979 ppm) that are altered by bacterial oxidation. Control cores away from the mat contain lower concentrations of oil (mean = 2966 ppm) and C1–C5 hydrocarbons (mean = 83.6 ppm). Bacterial oxidation of hydrocarbons depletes O2 in sediments and triggers bacterial sulfate reduction to produce the H2S required by the mats. Sediment samples from GC 185 (Bush Hill) contain high concentrations of oil (mean = 24,775 ppm) and C1–C5 hydrocarbons (mean = 11,037 ppm) that are altered by bacterial oxidation. Tube worm communities requiring H2S occur at GC 185 where the sea floor has been greatly modified since the Pleistocene by accumulation of oil, thermogenic gas hydrates, and authigenic carbonate rock. Venting to the water column is suppressed by this sea-floor modification, enhancing bacterial activity in sediments. Sediments from an area with vesicomyid clams (GC 272) contain lower concentrations of oil altered by bacterial oxidation (mean = 1716 ppm) but C1–C5 concentrations are high (mean = 28,766 ppm). In contrast to other sampling areas, a sediment associated with the methanotrophic Seep Mytilid I (GC 233) is characterized by low concentration of oil (82 ppm) but biogenic methane (C1) is present (8829 ppm).

The isotopic composition of strontium and sulfur in seawater of Late Permian (Zechstein) age

The Paleozoic minima of 87 Sr 86 Sr ratios and δ 34S values in seawater are observed in anhydrite layers of the Stassfurt (A-2) and Aller (A-4) cycles of evaporation of Late Permian age in Germany. These minima were probably caused by extremely low rates of continental runoff and bacterial sulfate reduction. Thereafter conditions changed suddenly, with a steeply increasing supply of radiogenic Sr and of nutrients into seawater. The latter induced a large growth in the production of organic material, in bacterial activity in sediments, and in the flow of isotopically heavy sulfur back into the oceans. This large change in the cycles of S and Sr (as well as of C and O) within the relatively short Zechstein period (2–5 Ma) reflects a considerable modification of the plate tectonic and environmental conditions shortly before the beginning of the Mesozoic era. The Ochoan deposition in the USA is probably of the same age as the Stassfurt-Leine evaporation in W Europe.

Bacterial activity in sediments of lakes receiving acid precipitation

Bacteriological data for water and sediment cores from some of the lakes receiving acid precipitation near Sudbury, Ontario, show a strong relationship between lake acidification and bacteria. pH values below about 5·5 appear to be critical for respiring and aerobic heterotrophic bacteria. Total bacteria in the waters of these lakes existed in the 10 6 ml −1 range while the viable or active populations were approximately two orders of magnitude lower. In the sediments, a relationship was demonstrated between pH, bacterial populations, sediment microbial activity, and total organic matter. In the acid-stressed Silver Lake (pH 3·8) the sediment respiration was 10–20% of that in the non-acid-stressed McFarlane Lake (pH 7·2). Associated with this, a strong correlation was demonstrated between pH and total organic matter in surficial sediments.

Bacterial activity in sediments of shallow marine bays

Complete mineralization of organic matter results from a multitude of complex bacterial activities which must involve more than one species of bacteria. The diverse bacterial activities influence the pH, redox potential, production of gases and their resulting disfiguration of the sediment, concentration of certain elements, precipitation and solution of carbonates, diagenesis of silicates, the production of complex organic compounds such as surface-active agents and many other properties of sediments. The bacterial activities are not constant but proportional to the amount of organic matter, pH, sediment particle size, temperature, sequence of physical changes caused by the bacteria in the sediment and the sequence of the production of organic by-products during decomposition.