Biomedical subjects

G J Herndl

Publications and source records attributed to G J Herndl.

12 recordsLinked to original sources

PubMed2002

Distribution of capsulated bacterioplankton in the North Atlantic and North Sea.

In laboratory experiments, bacterioplankton were incubated under different nutrient conditions, and the percentage of bacteria exhibiting a polysaccharidic capsule (capsulated bacteria) and that of CTC (cyanotetrazolium chloride)-positive and therefore metabolically highly active bacteria were determined. In these seawater cultures amended with nutrients more than 95% of the CTC-positive cells exhibited a capsule. During two cruises, one to the North Atlantic and one to the North Sea, we investigated the distribution of capsulated bacteria throughout the water column. Capsulated bacteria were generally more abundant in eutrophic surface waters than in deeper layers or more oligotrophic regions. In the upper 100 m of the North Atlantic, about 6-14% of the total bacterioplankton community was capsulated, while in the layers below 100 m depth, 97% of the bacteria lacked a visible capsule. The percentage of capsulated bacteria correlated with bacterial abundance and production, and chlorophyll a concentration. Also, the bioavailability of DOC (dissolved organic carbon), estimated by the ratio between bacterial production and DOC concentration, significantly correlated with the percentage of capsulated bacteria. In the North Sea, the contribution of capsulated bacteria to the total number of bacteria decreased from the surface (3 m depth) to the near-bottom (25-35 m) layers from 20% to 14% capsulated bacteria. In the nearshore area of the North Sea, about 27% of the bacteria exhibited a capsule. Overall, a pronounced decrease in the contribution of capsulated bacteria to the total bacterial abundance was detectable from the eutrophic coastal environment to the open North Atlantic. Using this epifluorescence-based technique to enumerate capsulated bacterioplankton thus allowed us to routinely assess the number of capsulated bacteria even in the oceanic water column. Based on the data obtained in this study we conclude that almost all metabolically highly active bacteria exhibit a capsule, but also some of the metabolically less active cells express a polysaccharide capsule detectable with this method.

Animals↗

PubMed2001

Terminal-restriction fragment length polymorphism (T-RFLP) screening of a marine archaeal clone library to determine the different phylotypes.

T-RFLP clone characterization (screening) was optimized for a fast and basepair-accurate characterization of clones from marine Archaea collected from the Eastern Mediterranean Sea. Because of the high sensitivity of T-RFLP fingerprinting, a protocol was developed where 10 initial PCR cycles gave detectable terminal fragments from clones. Additionally, forward and reverse primers for PCR were individually labeled and detected simultaneously to assess the suitability of the forward and reverse fragments for T-RFLP screening. Based on independent restriction digests with the tetrameric restriction enzymes HhaI, RsaI and HaeIII to characterize the 49 archaeal clones in our library, the clones were grouped into 13 T-RFLP operational taxonomic units (OTUs). Reverse fragments generally gave less heterogeneous fragments in size. The accuracy of T-RFLP screening was evaluated by sequencing representative clones. Closely related clones ( approximately 97% similarity) could only be resolved with multiple restriction digests where forward and reverse fragments were included in the analysis. All fragments from the clone library were detected in the T-RFLP fingerprint from the complex archaeal community. We found representatives of marine group I, II and III Archaea. Thus, the recently discovered low abundant marine group III Archaea could be clearly differentiated from the other clones in our library and comprised a considerable fraction of the clone library ( approximately 12%). Therefore, our T-RFLP screening approach proved successful in characterizing novel archaeal sequences from the marine environment.

Archaea↗

PubMed2001

Assessing the diversity of marine bacterial beta-glucosidases by capillary electrophoresis zymography.

We propose a new method for the fast separation and detection of beta-glucosidases in environmental samples. With this approach, beta-glucosidases extracted from bacteria are evidenced by substrate-incorporated capillary electrophoresis (CE zymography) and their kinetic parameters can be determined by repeated injections using different substrate concentrations. Preliminary results obtained with natural bacterial communities from the coastal North Sea suggest that the diversity of beta-glucosidases in the marine environment might be much higher than previously observed.

Electrophoresis, Capillary↗

PubMed2001

Impact of UV radiation on bacterioplankton community composition.

The potential effect of UV radiation on the composition of coastal marine bacterioplankton communities was investigated. Dilution cultures with seawater collected from the surface mixed layer of the coastal North Sea were exposed to different ranges of natural or artificial solar radiation for up to two diurnal cycles. The composition of the bacterioplankton community prior to exposure was compared to that after exposure to the different radiation regimes using denaturing gradient gel electrophoresis (DGGE) of 16S rRNA and 16S ribosomal DNA. Only minor changes in the composition of the bacterial community in the different radiation regimes were detectable. Sequencing of selected bands obtained by DGGE revealed that some species of the Flexibacter-Cytophaga-Bacteroides (FCB) group were sensitive to UV radiation while other species of the FCB group were resistant. Overall, only up to approximately 10% of the operational taxonomic units present in the dilution cultures appeared to be affected by UV radiation. Thus, we conclude that UV radiation has little effect on the composition of coastal marine bacterioplankton communities in the North Sea.

Animals↗

PubMed2000

Interspecific variability in sensitivity to UV radiation and subsequent recovery in selected isolates of marine bacteria.

The interspecific variability in the sensitivity of marine bacterial isolates to UV-B (295- to 320-nm) radiation and their ability to recover from previous UV-B stress were examined. Isolates originating from different microenvironments of the northern Adriatic Sea were transferred to aged seawater and exposed to artificial UV-B radiation for 4 h and subsequently to different radiation regimens excluding UV-B to determine the recovery from UV-B stress. Bacterial activity was assessed by thymidine and leucine incorporation measurements prior to and immediately after the exposure to UV-B and after the subsequent exposure to the different radiation regimens. Large interspecific differences among the 11 bacterial isolates were found in the sensitivity to UV-B, ranging from 21 to 92% inhibition of leucine incorporation compared to the bacterial activity measured in dark controls and from 14 to 84% for thymidine incorporation. Interspecific differences in the recovery from the UV stress were also large. An inverse relation was detectable between the ability to recover under dark conditions and the recovery under photosynthetic active radiation (400 to 700 nm). The observed large interspecific differences in the sensitivity to UV-B radiation and even more so in the subsequent recovery from UV-B stress are not related to the prevailing radiation conditions of the microhabitats from which the bacterial isolates originate. Based on our investigations on the 11 marine isolates, we conclude that there are large interspecific differences in the sensitivity to UV-B radiation and even larger differences in the mechanisms of recovery from previous UV stress. This might lead to UV-mediated shifts in the bacterioplankton community composition in marine surface waters.

Bacteria↗

PubMed1999

Optimization of terminal-restriction fragment length polymorphism analysis for complex marine bacterioplankton communities and comparison with denaturing gradient gel electrophoresis.

The potential of terminal-restriction fragment length polymorphism (T-RFLP) and the detection of operational taxonomic units (OTUs) by capillary electrophoresis (CE) to characterize marine bacterioplankton communities was compared with that of denaturing gradient gel electrophoresis (DGGE). A protocol has been developed to optimize the separation and detection of OTUs between 20 and 1, 632 bp by using CE and laser-induced fluorescence detection. Additionally, we compared T-RFLP fingerprinting to DGGE optimized for detection of less abundant OTUs. Similar results were obtained with both fingerprinting techniques, although the T-RFLP approach and CE detection of OTUs was more sensitive, as indicated by the higher number of OTUs detected. We tested the T-RFLP fingerprinting technique on complex marine bacterial communities by using the 16S rRNA gene and 16S rRNA as templates for PCR. Samples from the Northern and Middle Adriatic Sea and from the South and North Aegean Sea were compared. Distinct clusters were identifiable for different sampling sites. Thus, this technique is useful for rapid evaluation of the biogeographical distribution and relationships of bacterioplankton communities.

Animals↗

PubMed1999

Interaction between specific hydrological and microbial activity leading to extensive mucilage formation in the northern Adriatic Sea.

The massive formation of marine snow and the senescent stage of it, the mucilage, is a phenomenon largely restricted to the Adriatic Sea. In this contribution the major environmental factors potentially leading to the formation of this mucilage are discussed. It is proposed that the specific hydrological conditions in combination with severe phosphorus depletion lead to excessive formation of colloidal organic matter by phytoplankton. This colloidal organic matter coagulates to marine snow due to the low-turbulence regimes prevailing in the water column. Subsequently, this marine snow is colonized by bacteria which, in turn, produce and release copious amounts of capsular polymers into the matrix of marine snow. It is speculated that a significant fraction of the later stages of marine snow (mucilage) consists of bacterial-derived organic matter which has been shown to be semi-labile to refractory for further bacterial utilization. The marine snow matrix acts as efficient adsorption site and allows the bacteria to utilize scavenged molecules from the ambient water. Thus it is proposed that the matrix ages without significant biotic degradation.

Colloids↗

PubMed1997

Rapid Recovery of Marine Bacterioplankton Activity after Inhibition by UV Radiation in Coastal Waters.

Laboratory and in situ experiments were performed in order to evaluate the role of UV radiation on bacterial activity. Particular attention was given to the determination of the role of UV-A and photosynthetic active radiation (PAR) and different nutrient conditions on the recovery of bacterial activity. Laboratory experiments with nearly natural radiation intensities indicated a 20 to 40% reduction from the initial level of bacterial activity after UV-B exposure for 2 to 4 h. Bacterial activity in freshly collected seawater showed a more pronounced inhibition and faster recovery than bacterial activity in aged, nutrient-depleted seawater. The results of in situ experiments with filtered water (0.8-(mu)m-pore-size filter) and natural surface solar radiation levels agreed with those of the laboratory experiments and revealed that UV-A and PAR are important for the recovery of bacterial activity and result in levels of bacterial activity that are higher than those prior to exposure to full solar radiation. Bacterioplankton exposed to full solar radiation for 3 h and subsequently incubated at different depths within the upper mixed water column showed an increase in bacterial activity with increased depth; the highest bacterial activity was detected at depths of 5.5 to 10.5 m, where the short-wavelength UV-B was already largely attenuated, but enough long wavelength UV-A and short PAR were available to allow recovery. This elevated bacterial activity following exposure to UV-B was attributed to the photolysis of dissolved organic matter (DOM) exposed to near-surface radiation and to the rapid recovery of bacteria from UV stress once they were mixed into deeper layers of the upper mixed water column, where they efficiently utilize the photolytically cleaved DOM. It is concluded that studies on the role of UV on the carbon and energy flux through the upper layer of the ocean should take into account the highly dynamic radiation conditions.

Journal Article↗

PubMed1997

Inhibitory effect of solar radiation on thymidine and leucine incorporation by freshwater and marine bacterioplankton.

We studied the effect of solar radiation on the incorporation of [(sup3)H]thymidine ([(sup3)H]TdR) and [(sup14)C]leucine ([(sup14)C]Leu) by bacterioplankton in a high mountain lake and the northern Adriatic Sea. After short-term exposure (3 to 4 h) of natural bacterial assemblages to sunlight just beneath the surface, the rates of incorporation of [(sup3)H]TdR and [(sup14)C]Leu were reduced at both sites by up to (symbl)70% compared to those for the dark control. Within the solar UV radiation (290 to 400 nm), the inhibition was caused exclusively by UV-A radiation (320 to 400 nm). However, photosynthetically active radiation (PAR) (400 to 700 nm) contributed almost equally to this effect. Experiments with samples from the high mountain lake showed that at a depth of 2.5 m, the inhibition was caused almost exclusively by UV-A radiation. At a depth of 8.5 m, where chlorophyll a concentrations were higher than those in the upper water column, the rates of incorporation of [(sup3)H]TdR were higher in those samples exposed to full sunlight or to UV-A plus PAR than in the dark control. In laboratory experiments with artificial UV light, the incorporation of [(sup3)H]TdR and [(sup14)C]Leu by mixed bacterial lake cultures was also inhibited mainly by UV-A. In contrast, in the presence of the green alga Chlamydomonas geitleri at a chlorophyll a concentration of 2.5 (mu)g liter(sup-1), inhibition by UV radiation was significantly reduced. These results suggest that there may be complex interactions among UV radiation, heterotrophic bacteria, and phytoplankton and their release of extracellular organic carbon. Our findings indicate that the wavelengths which caused the strongest inhibition of TdR and Leu incorporation by bacterioplankton in the water column were in the UV-A range. However, it may be premature to extrapolate this effect to estimates of bacterial production before more precise information on how solar radiation affects the transport of TdR and Leu into the cell is obtained.

Journal Article↗

PubMed1996

Relationship between the Intracellular Integrity and the Morphology of the Capsular Envelope in Attached and Free-Living Marine Bacteria.

The integrity of the intracellular structures and the presence and dimension of the capsular envelope were investigated in marine snow-associated and marine free-living bacteria by transmission electron microscopy and special fixation techniques. Three categories depending on the presence of internal structures were differentiated. In marine snow, 51% of the marine snow-associated bacterial community was considered intact, 26% had a partly degraded internal structure, and 23% were empty with only the cell wall remaining. For the free-living bacterial community, 34% were intact cells, 42% exhibited damage, and 24% of the cells were lacking any internal structure. We also investigated the morphology and the extent of the bacterial capsular envelope. More than 95% of all intact marine snow-associated bacteria were surrounded by a capsule while (apprx=)55% of empty marine snow-associated bacteria had no capsule. For free-living bacteria, (apprx=)65% of the intact cells had a capsule while (apprx=)80% of the empty free-living bacteria lacked a capsule. Thus there is a clear trend from intact cells which are commonly surrounded by a capsular envelope to empty bacteria for which only the cell wall is remaining. Since bacterioplankton represent the largest living surface in the ocean, it is concluded that the release of intracellular material from bacteria into the environment as well as the release of extracellular capsular material might fuel the dissolved organic matter pool of the ocean.

Journal Article↗

PubMed1995

Formation and microbial utilization of amorphous aggregates in the sea: ecological significance.

Amorphous organic particles, ("marine snow"), are thought to play a vital role in the transfer of carbon and energy from the euphotic layers of the ocean to the deep sea bed. These particles are mainly derived from phytoplankton extracellular release. As 10 to 40% of the dissolved organic carbon consists of colloidal material, colloids may represent a prominent role in these transfer processes. These colloids adsorb charged molecules efficiently and can coagulate further to form the recently described transparent exopolymer particles and eventually the ubiquitous macroscopic marine snow. The other mechanism proposed leading ultimately to marine snow formation is inefficient top-down control of phytoplankton growth by zooplankton. In the senesce of the phytoplankton bloom the cell surface becomes sticky due to the release of polysaccharides, and single phytoplankton cells then aggregate. Subsequently these aggregates become densely colonized by auto- and heterotrophic microbes, but while the abundance of these microorganisms is from 2 to 4 orders of magnitude higher than in the ambient water, their growth rates are usually not significantly increased in the aggregates. In this review, the reasons for this conspicuous pattern are discussed and recently investigated novel types of particles and their significance in the light of oceanic carbon transfer are presented.

Colloids↗

PubMed1994

Characteristics and Diversity of beta-d-Glucosidase (EC 3.2.1.21) Activity in Marine Snow.

Large amorphous aggregates commonly described as marine snow were sampled in the water column of the northern Adriatic Sea in August 1991. beta-d-Glucosidase activity associated with these aggregates was characterized. Enzymatic activity was measured with the fluorogenic substrate analog 4-methylumbelliferyl-beta-d-glucoside and found to be mainly associated with particles; on average, only 24% of the whole beta-d-glucosidase activity remained in the supernatant after centrifugation. Although the temperature optimum for beta-d-glucosidase activity was approximately 40 degrees C, incubation of the previously liberated particle-attached enzyme at 50 degrees C for 20 min caused a >90% reduction of enzymatic activity relative to the activity at 40 degrees C. The level of inactivation of beta-d-glucosidase was much lower, however, when whole marine snow was incubated, indicating qualitative modifications of beta-d-glucosidase in marine snow. Separation of beta-d-glucosidase by different approaches indicated that the diversity of isoenzymes is restricted. In samples taken from the pycnocline, only one major isoenzyme was present in noticeable amounts. This isoenzyme contributed up to 70% of the whole beta-d-glucosidase activity detectable by two different chromatographic separations (anion-exchange chromatography and size exclusion chromatography). Although the same isoenzyme was dominant in marine snow taken from surface waters (0.5-m depth), we found a second peak of activity which eluted at lower NaCl concentrations from the anion-exchange column. Generally, the diversity of isoenzymes exhibiting beta-d-glucosidase activity seems to be surprisingly small in amorphous pelagic aggregates.

Journal Article↗