Most nitrogen and phosphorus transported by world rivers to the oceans is associated with dissolved organic matter. However, organic matter as a potential source of N and P has hitherto been largely neglected in studies of coastal microbial food webs. We examined 50 rivers, draining a major part of the Baltic Sea watershed, with respect to summer concentrations, chemical composition, and biological availability of N and P. The broad spectrum of rivers studied enabled us to assess whether the input of terrigenous organic matter can be an important nutrient source, at various levels of anthropogenic loading of inorganic N and P.Concentrations of total N and P ranged from 9 to 220 mol/L and from 0.14 to 5.56 mol/L, respectively, with the highest concentrations in the southern part of the Baltic Sea drainage area and in several rivers on the Finnish western coast. Urea and dissolved combined amino acids (DCAA) each constituted 4-20% of dissolved organic nitrogen (DON), while dissolved free amino acids (DFAA) made up Ͻ3% of DON. The contribution of urea and amino acids to the DON pool was inversely correlated with DON concentration. Bacterial regrowth bioassays in selected rivers demonstrated that ϳ30% of DON and ϳ75% of dissolved organic phosphorus (DOP) was potentially available to the indigenous bacterial assemblage of the Baltic Sea, and hence susceptible to mineralization within the pelagic food web. Our study is among the first to demonstrate that bacterioplankton are able to utilize a major part of DON and DOP from a broad spectrum of natural waters.The C:N ratio, absorbance spectra, and fluorescence properties of the organic matter suggest that the observed high bioavailability of DON and DOP was due to a large contribution of organic matter from riverine primary production compared to the humic matter derived from terrestrial vascular plants. In addition, algal and bacterial cells dominated the transport of particulate organic material, further enhancing productivity of coastal waters. No correlations were found between DON bioavailability and the fraction of DON bound in urea and amino acids, indicating a utilization of other N compounds (e.g., amides) by the bacteria.We estimate that the input of summer riverine N to the Baltic Sea consists of 48% dissolved inorganic N, 41% DON, and 11% particulate N. Corresponding values for phosphorus are 46%, 18%, and 36% of dissolved inorganic P, DOP, and particulate P, respectively. During the thermal summer stratification, when freshwater inputs are trapped in the surface layer, rivers contribute ϳ30% of N and ϳ5% of P needed to support the export production (plankton sedimenting out of the photic layer) in the Baltic Sea. The high availability to bacteria suggests that DOP is a major stimulator of pelagic productivity in the P-limited northern part of the Baltic Sea. Based on reported concentrations in other areas, we suggest that the global contribution of riverine organic N and P to the primary production of coastal waters is comparable to the contribution of inorg...
The effects of virus infection and lysis of a marine Vibrio sp. on C, N, and P turnover and the growth efficiency of noninfected bacterioplankton were studied in a series of dilution cultures. The cultures were enriched with various sources of organic matter and N and P. The growth of the Vibrio host and the growth of the natural bacterioplankton were measured by immunofluorescence and 4,6-diamidino-2-phenylindole staining methods, respectively. Lysis products resulting from infection of the Vibrio sp. caused an increase in metabolic activity and cell production by the noninfected bacterioplankton. In P-limited cultures, the addition of viruses increased the uptake of dissolved organic carbon by 72% and the potential alkaline phosphatase activity by 89% compared with control cultures without viruses. Our data suggest that input of available phosphorus through virus-induced Vibrio lysates occurred, which caused an increase in the bacterial nutrient uptake. The growth efficiency of noninfected bacteria was reduced in the presence of viruses compared with the control without viruses (growth efficiencies, 0.08 ؎ 0.03 and 0.24 ؎ 0.02, respectively). We suggest that the decrease in growth efficiency may be explained by an increase in bacterial energy demand associated with extracellular degradation of polymeric organic nitrogen and phosphorus in cell lysates.
Species classified within the genus Kitasatosporia share many of the phenotypic characteristics typical of streptomycetes. By using a probabilistic identification scheme, they were identified with Streptomyces exfoliatus cluster 5, a species group within Streptomyces. The four species studied hybridized with a 16S rRNA genus probe for Streptomyces spp., indicating a close relationship between the two genera. The kitasatosporias were resistant to selected polyvalent streptomycete phages tested. Quantitative analysis showed that meso-diaminopimelic acid varied from 49 to 89% in Kitasatosporia species and from 1 to 16% in Streptomyces species depending on growth conditions. On the basis of 16S rRNA analysis, it is proposed to reduce Kitasatosporia to synonymy with Streptomyces. As a result, the new names proposed are Streptomyces mediocidicus comb. nov., Streptomyces phosalacineus comb. nov., Streptomyces setae comb. nov., and Streptomyces griseolosporeus comb. nov., nom. nov.
The effects of solar radiation on concentrations and microbial utilization of various carbon and nitrogen compounds were studied in July in a thermally stratified lake in southern Sweden. Exposure of bacteria‐free water to natural sunlight in the surface of the lake for 7 h around noon led to higher concentrations of inorganic carbon (39–80%), amino acids (0–23%) and carbohydrates (0–15%), while lower concentrations of monosaccharides (0–38%), nitrate (0–23%) and urea (0–27%) were measured. Ammonium was unchanged. Lake bacteria were inoculated into the irradiated water and into water that had not been exposed to solar radiation (dark controls). The bacterial production was 35 to 80% higher during exponential growth (20 h after inoculation) in the irradiated samples than in the controls. The bacterial utilization of specific carbon and nitrogen compounds in the irradiated samples differed from that in the controls, but the changes in the epilimnion and the hypolimnion varied. Dominant nutrients to the bacteria were carbohydrates, amino acids, glucose and ammonium. In the controls a release of combined amino acids (epilimnion) or carbohydrates (hypolimnion) occurred. An apparent non‐biological removal of urea in the irradiated hypolimnion samples was found, since the microbial urea degradation was only 1% of the reduction in concentration. Our results suggest that biogeochemical cycling in natural waters is influenced by sunlight, due to changes of microbially available components that were not reported previously, including amino acids, carbohydrates, nitrate and urea.
The contributions of different organic and inorganic nitrogen and organic carbon sources to heterotrophic bacterioplankton in batch cultures of oceanic, estuarine, and eutrophic riverine environments were compared. The importance of the studied compounds was surprisingly similar among the three ecosystems. Dissolved combined amino acids (DCAA) were most significant, sustaining from 10 to 45% of the bacterial carbon demands and from 42 to 112% of the bacterial nitrogen demands. Dissolved free amino acids (DFAA) supplied 2 to 7% of the carbon and 6 to 24% of the nitrogen incorporated into the bacterial biomass, while dissolved DNA (D-DNA) sustained less than 5 and 12% of the carbon and nitrogen requirements, respectively. Ammonium was the second most important source of nitrogen, meeting from 13 to 45% of the bacterial demand in the oceanic and estuarine cultures and up to 270% of the demand in riverine cultures. Nitrate was taken up in the oceanic cultures (uptake equaled up to 46% of the nitrogen demand) but was released in the two others. Assimilation of DCAA, DFAA, and D-DNA combined supplied 43% of the carbon demand of the bacteria in the oceanic cultures, while approximately 25% of the carbon requirements were met by the three substrates at the two other sites. Assimilation of nitrogen from DCAA, DFAA, D-DNA, NH4", and N03-, on the other hand, exceeded production of particulate organic nitrogen in one culture at 27 h and in all cultures over the entire incubation period (50 h). These results suggest that the studied nutrient sources may fully support the nitrogen needs but only partially support the carbon needs of microbial communities of geographically different ecosystems. Furthermore, a comparison of the initial concentrations of the different substrates indicated that relative pool sizes of the substrates seemed to influence which substrates were primarily being utilized by the bacteria.
Arctic soils are known to be important methane (CH 4) consumers and sources. This study integrates in situ fluxes of CH 4 between upland and wetland soils with potential rates of CH 4 oxidation and production as well as abundance and diversity of the methanotrophs and methanogens measured with pyrosequencing of 16S DNA and rRNA fragments in soil and permafrost layers. Here, the spatial patterns of in situ CH 4 fluxes for a 2,000 years old Arctic landscape in West Greenland reveal similar CH 4 uptake rates (-4 ± 0.3 lmol m-2 h-1) as in other Arctic sites, but lower CH 4 emissions (14 ± 1.5 lmol m-2 h-1) at wetland sites compared to other Arctic wetlands. Potential CH 4 oxidation was similar for upland and wetland soils, but the wetter soils produced more CH 4 in active and permafrost layers. Accordingly, the abundance of methanogenic archaea was highest in wetland soils. The methanotrophic community also differed between upland and wetland soils, with predominant activity of Type II methanotrophs in the active layer for upland soils, but only Type I methanotrophs for the wetland. In the permafrost of upland and wetland soils, activity of the methanotrophs belonging to Type I and Type II as well as methanogens were detected. This study indicates that the magnitude of CH 4 oxidation and the direction of the flux, i.e. uptake or emission, are linked to different methanotrophic communities in upland and wetland soils. Also, the observed link between production/consumption rates and the microbial abundance and activity indicates that the age of an Arctic landscape is not important for the CH 4 consumption but can be very important for CH 4 production. Considering the prevalence of dry landscapes and contrasting ages of high Arctic soils, our results highlight that well-drained soils should not be overlooked as an important component of Arctic net CH 4 budget.
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