Attached and Free-Floating Bacteria in a Diverse Selection of Water Bodies

Identification of bacterial contaminants from calcium carbonate filler production lines and an evaluation of biocide based decontamination procedures

The aim of this study was to analyze the bacterial community in the production line of a calcium carbonate filler production company and to investigate possible causes for bacterial presence. Throughout 2012, 24 carbonate slurry and six groundwater samples were analyzed. Pseudomonas and Microbacterium were the most frequent contaminants in the slurry, whereas Pseudomonas and Brevundimonas dominated the groundwater samples. Of the 43 different bacterial strains isolated, only five were found both in the slurry and the groundwater, indicating that the latter was not a major source of contamination. The efficacy of 54 commercial biocidal formulations was tested against an artificial bacterial consortium composed of selected slurry isolates. A formulation containing 7.5-15% (v v^-1) bronopol and 1.0-2.5% (v v^-1) [chloroisothiazolinone (CIT) + methylisothiazolinone (MIT)] exhibited the highest efficacy. Of the possible causes for bacterial presence, sporogenesis and biocide adsorption to carbonate particles were found to be less probable compared to bacterial adsorption to particles, and the acquisition of resistance to biocides.

Prevalence of antibiotic resistance genes in bacterial communities associated with Cladophora glomerata mats along the nearshore of Lake Ontario

The alga Cladophora glomerata can erupt in nuisance blooms throughout the lower Great Lakes. Since bacterial abundance increases with the emergence and decay of Cladophora, we investigated the prevalence of antibiotic resistance (ABR) in Cladophora-associated bacterial communities up-gradient and down-gradient from a large sewage treatment plant (STP) on Lake Ontario. Although STPs are well-known sources of ABR, we also expected detectable ABR from up-gradient wetland communities, since they receive surface run-off from urban and agricultural sources. Statistically significant differences in aquatic bacterial abundance and ABR were found between down-gradient beach samples and up-gradient coastal wetland samples (ANOVA, Holm-Sidak test, p < 0.05). Decaying and free-floating Cladophora sampled near the STP had the highest bacterial densities overall, including on ampicillin- and vancomycin-treated plates. However, quantitative polymerase chain reaction analysis of the ABR genes ampC, tetA, tetB, and vanA from environmental communities showed a different pattern. Some of the highest ABR gene levels occurred at the 2 coastal wetland sites (vanA). Overall, bacterial ABR profiles from environmental samples were distinguishable between living and decaying Cladophora, inferring that Cladophora may control bacterial ABR depending on its life-cycle stage. Our results also show how spatially and temporally dynamic ABR is in nearshore aquatic bacteria, which warrants further research.

Taxon-specific C/N relative use efficiency for amino acids in an estuarine community

Microbial activity plays a critical role in determining the nutrient status of an ecosystem (i.e. N or C limitation). While the balance of C/N assimilation has been measured at the whole community scale, quantitative detection of N and C assimilation from a single substrate at the scale of individual taxa has not been carried out. We recently developed Chip-SIP, a microarray and NanoSIMS-based method for linking microbial phylogeny and function that allows simultaneous measurement of (15)N and (13)C incorporation. Here, we measured the relative incorporation of C and N from dual-labeled substrates by individual microbial taxa in bottle incubations of samples collected from an estuary. Incubation times < 24 h were sufficient to successfully detect active microbes incorporating (15)N ammonium. In subsequent experiments, we used the incorporation of labeled amino acids (AAs) as a proxy for heterotrophic activity and showed different levels of incorporation among different taxonomic groups. Taxon-specific differences in the net incorporation of AA-derived C and N indicate that the C/N relative use efficiency ranged from 0.8 to 1.4, where 1 reflects stoichiometric incorporation of C and N. Our results revealed that microbial organic matter processing is affected by taxon-specific physiological diversity, both in terms of general activity levels and in the ratio of assimilated C/N.

Bacterial production and growth rate estimation from [h]thymidine incorporation for attached and free-living bacteria in aquatic systems

Production and specific growth rates of attached and free-living bacteria were estimated in an oligotrophic marine system, La Salvaje Beach, Vizcaya, Spain, and in a freshwater system having a higher nutrient concentration, Butron River, Vizcaya, Spain. Production was calculated from [methyl-H]thymidine incorporation by estimating specific conversion factors (cells or micrograms of C produced per mole of thymidine incorporated) for attached and free-living bacteria, respectively, in each system. Conversion factors were not statistically different between attached and free-living bacteria: 6.812 x 10 and 8.678 x 10 mug of C mol for free-living and attached bacteria in the freshwater system, and 1.276 x 10 and 1.354 x 10 mug of C mol for free-living and attached bacteria in the marine system. Therefore, use of a unique conversion factor for the mixed bacterial population is well founded. However, conversion factors were higher in the freshwater system than in the marine system. This could be due to the different trophic conditions of the two systems. Free-living bacteria contributed the most to production in the two systems (85% in the marine system and 67% in the freshwater system) because of their greater contribution to total biomass. Specific growth rates calculated from production data and biomass data were similar for attached and free-living bacteria.

Impact of storms on heterotrophic activity of epilimnetic bacteria in a southwestern reservoir

The impact of storm conditions on the heterotrophic activity of planktonic bacteria in a southwestern reservoir was investigated. Storm events were considered as rainfall in excess of 2.5 cm in a 24-h period before sampling. Storm conditions stimulated heterotrophic activities and resulted in increased uptake rates and decreased turnover times of glutamate and acetate. Uptake rates were 45 to 75% faster immediately after storm conditions than they were during calm conditions. Activity levels appeared to return to prestorm levels within 48 h. Bacterial cell numbers did not change substantially during storm events. Cell-specific activity indicated that increases in heterotrophic activity were the result of increased activity of individual cells. Light penetration, levels of particulate organic carbon, K(t) + S(n) values, and population levels of attached bacteria suggest that immediate sediment loading of the reservoir or increased substrate levels could not account for abrupt increases in heterotrophic activities.

Electrolyte effects on attachment of an estuarine bacterium

The effect of electrolyte concentration on attachment of Vibrio alginolyticus to hydroxyapatite was determined. Bacterial affinity for attachment to the surface and surface capacity were derived from linearization of bacterial adsorption isotherms. At low concentrations (<0.1 M) the affinity of the bacteria for the surface increased with increasing ionic strength, in agreement with the D.L.V.O. theory of colloid interaction. At higher concentrations, bacterial affinity for the surface decreased with increasing concentration of cations and was not related to ionic strength changes in the medium. These results demonstrate a change in the mechanism by which salts affect bacterial attachment at salt concentrations above 0.1 M. The results are consistent with the relationship between the proportion of attached bacteria and salinity observed in previously published field studies. The results may also resolve differences between various attachment studies carried out in different ionic strength media, utilizing different bacteria, surfaces, and experimental methods.

Thymidine incorporation by free-living and particle-bound bacteria in a eutrophic dimictic lake

The percentage of [methyl-H]thymidine incorporated into samples from a dimictic eutrophic lake and retained on polycarbonate membranes of 3.0-, 1.0-, and 0.2-mum pore size was studied in a lake with filamentous cyanobacteria as the dominant phytoplankton type throughout the period of thermal stratification. Water samples were also examined by epifluorescence microscopy for evidence of algal senescence and bacterial colonization of intact and damaged cyanobacterial filaments. A small percentage (2 to 20%) of bacterial activity was retained by filters with pore sizes >/= 1 mum in epilimnetic samples. Epilimnetic samples also had a small percentage of cyanobacterial filaments, either intact or damaged, which were visibly colonized by bacteria in summer and fall samples. A significant proportion (20 to 35%) of bacterial activity was retained by filters with pore sizes >/= 1 mum in samples collected from the metalimnion and hypolimnion during late summer and fall. The proportion of damaged cyanobacterial filaments was higher in these samples than in those from the epilimnion or from those obtained early in the summer. Furthermore, the filaments in these samples were more heavily colonized by bacteria. Overall, particle-bound production accounted for only 2 to 19% of total bacterial production from April to August in all water layers. It appears that the supply of colonizable particles (damaged cyanobacterial filaments) is an important factor affecting the level of particle-bound bacterial activity in this lake.

The effects of adherence to silicone surfaces on antibiotic susceptibility in Staphylococcus aureus

Sensitivity of Staphylococcus aureus to the antibiotics tetracycline, benzylpenicillin and vancomycin was found to decrease by 2-10 fold when cells were grown adherent to silicone catheter surfaces. Sensitivity to rifampicin and fusidic acid was not significantly altered in adherent cells. Susceptibility further decreased with increased adherence time prior to antibiotic challenge. The resistance observed was not genotypic, or due to the presence of a specialized subpopulation of bacteria, as it disappeared when the bacteria were removed from the catheter, subcultured and retested. Also, adherent bacteria were found to grow more slowly than bacteria growing planktonically. It is concluded that the decrease in antibiotic susceptibility of adherent bacteria is a function of the physiological status of the individual cells rather than a function of biofilm formation or slime production. The decrease in growth rate of the adherent bacteria is a result of the adherence process rather than a result of nutrient depletion. The decrease in growth rate is implicated, but is not the sole factor, in the decreased antibiotic susceptibility of adherent bacteria.

Exopolymers: An ecological characteristic of a floc-attached, ammonia-oxidizing bacterium

A lithotrophic ammonia-oxidizing bacterium of the Nitrosomonas type was isolated from the lower River Elbe. Enrichment was attained from suspended particulate matter (SPM) of a water sample. At its natural environment, this species almost exclusively occurred attached to flocs, as demonstrated with the immunofluorescence technique. On the species level, the isolate was not related to any of the described Nitrosomonas species. The strain was characterized by strong production of exopolymeric substances (EPS) and was observed to occur self-flocculating in pure cultures. Low ammonia concentrations stimulated EPS production. The EPS revealed an extensive capacity for binding particulate and dissolved materials, as well as cells of other bacterial species. This capacity was affected by changing pH values or salt concentrations of the medium. The EPS appeared to function as a buffer against toxic compounds and against changing environmental conditions. Another Nitrosomonas strain isolated from the Elbe estuary, but lacking recognizable EPS production, was used for comparison.

Temporal variability of attached and free-living bacteria in coastal waters

The temporal variability of the abundance and the incorporation of (3)H-thymidine and (14)C-glucose by attached and free-living bacteria, as well as their relation with environmental factors, were analyzed in a coastal marine ecosystem during a year. Both communities were quantitatively very different. Attached bacteria represented only 6.8% of the total bacterial abundance, whereas free-living bacteria represented 93.2%. The environmental factors most closely linked to the abundance and activity of free-living bacteria were temperature and the concentration of dissolved nutrients. Moreover, the free-living community showed similar temporal variations in abundance and in activity, with lower values in the cold months (from October to May). The attached community did not present the same pattern of variation as the free-living one. The abundance of the attached bacteria was mainly correlated to the concentration of particulate material, whereas their activity was correlated to temperature. We did not find a significant correlation between the abundance and the activity of the attached community. On the other hand, the activity per cell of the two communities did not present a clear temporal variation. Attached bacteria were more active than free-living ones in the incorporation of radiolabeled substrates on a per cell basis (five times more in the case of glucose incorporation and twice as active in thymidine incorporation). However, both communities showed similar specific growth rates. The results suggest that the two aquatic bacterial communities must not be considered as being independent of each other. There appears to be a dynamic equilibrium between the two communities, regulated by the concentrations of particulate matter and nutrients and by other environmental factors.

Synergism between research and simulation models of estuarine microbial food webs

Construction of mathematical simulation models helps to organize current information and extend inferences from available data. During the past two decades, microbial ecology has undergone rapid developments in both quantity and quality of available data. In particular, considerable advances have been made in our knowledge of microbial food web dynamics in the Duplin River watershed at Sapelo Island, Georgia. Here we provide examples of how modeling and microbial ecology have interfaced. In the early 1970s, construction of a 14-compartment model of carbon flow through a salt marsh ecosystem aided in directing method development and field experiments on the sediment microbial community. In turn, the results of field experiments corroborated the model's postulated controls on the community. Also, during the past 12 years we have developed a series of simulation models reflecting the growing information on the aquatic microbial food web. Early models provided evidence for the microbial loop but illustrated the paucity of knowledge concerning controls for bacterial growth on detritus. Results from newer methods in microbial ecology and studies from the Duplin River have allowed us to construct a model which provides realistic simulations but is also highly sensitive to certain parameter value changes (e.g., in organic matter availability and grazing by protozoans). Thus improvements in model structure and corroboration of the models with extant data have been closely tied to methodological and conceptual advances in microbial ecology. The relationship is viewed as synergistic, as needs for model parameter values and equation forms have directed further development of methods, experimentation, and field observations.

Influence of an S-layer on surface properties of Bacillus stearothermophilus

Various aspects of surface properties of the S-layer-carrying Bacillus stearothermophilus PV72 and of an S-layer-deficient mutant (strain PV72/T5) have been tested by adsorption assays on solid surfaces, electrostatic interaction chromatography and hydrophobic interaction chromatography. The adsorption assays have shown that cell adhesion of the S-layer-carrying strain was less influenced by environmental changes than it was with the S-layer-deficient mutant. Electrostatic interaction chromatography indicated that both strains have positively and negatively charged groups exposed on the cell surface but the S-layer-carrying strain reveals more positively charged groups than does the S-layer-deficient mutant. Hydrophobic interaction chromatography showed that both strains have a hydrophilic surface but that the hydrophilic properties are more pronounced with the strain lacking an S-layer.

Growth and comparative physiology of Klebsiella oxytoca attached to granular activated carbon particles and in liquid media

Experiments were performed to evaluate the comparative growth and physiology of Klebsiella oxytoca grown attached to granular activated carbon particles (GAC) and in liquid medium. Laboratory studies showed that when this organism attached to GAC, the growth rate was enhanced more than 10 times in the presence of glutamate, a substrate that adsorbed to the surface. No differences were observed if the substrate was glucose, which did not adsorb to GAC. Cellular [3H]thymidine uptake was used to estimate DNA biosynthesis. Attached bacteria grown in a minimal nutrient medium containing 20.0 mg/liter glutamate took up 5 times more [3H]thymidine than cells grown in suspension. [3H]uridine was used as a measure of RNA turnover. Attached cells were shown to assimilate 11 times more [3H]uridine than cells in liquid media. Cell size measurements were performed by differential filtration. Cells grown in a minimal medium with 20.0 mg/liter glutamate decreased in size over time, with 62% of the total number passing through a 1.0 micron filter after 9 days incubation. In the same period, 39% of a cell population that was grown on GAC passed through a 1.0 micron filter. These studies indicate that GAC provides an interfacial environment for the enhanced growth of K. oxytoca when glutamate is the substrate.

Production and Turnover of Planktonic Bacteria in Two Southeastern Blackwater Rivers

Production by attached and free-living planktonic bacteria in two blackwater rivers in the Southeastern United States was measured over a period of 14 months by using the rate of incorporation of [ methyl - 3 H]thymidine into DNA. Production rates and biomass dynamics were compared to determine the potential for in situ production to supply planktonic biomass. Bacterial production in these rivers was moderate and varied seasonally. Rates varied from 0.058 to 2.120 mg of C m −3 h −1 in the Ogeechee River and from 0.002 to 2.418 mg of C m −3 h −1 in Black Creek. Regressions of growth rate on various environmental variables showed that temperature and total dissolved organic carbon concentration were the best predictors of growth. Although attached bacteria were <21% of the total biomass, they accounted for up to 53% of the total production. Turnover times for attached bacteria ranged from <1 day to >3 years depending on season. Turnover times of free-living bacteria varied from 4.4 days to 11.8 years. Comparisons of biomass with production indicated that during most seasons, the majority of bacterial biomass in these rivers was of allochthonous origin. During summer, when water temperatures were high, bacterial growth in the river may have supplied a greater percentage of the standing stock of bacteria than allochthonous inputs.

Effect of salinity gradients and heterotrophic microbial activity on biodegradation of nitrilotriacetic acid in laboratory simulations of the estuarine environment

The biodegradation of nitrilotriacetic acid (NTA), a synthetic replacement detergent builder, in the estuarine environment was examined by using a laboratory estuarine simulation. Two interdependent microcosms were used; each of five vessels was equilibrated with a saline gradient between 1.30 and 17.17%, with the final vessel subsequently being increased to a maximum salinity of 31.6%. Each microcosm was seeded simultaneously with heterotrophic bacteria from both fresh and saline sources. Viable counts demonstrated the ability of each microcosm to sustain a mixed heterotrophic bacterial community throughout the range of salinities for 183 days after a stabilization period. Isolation studies demonstrated that both systems contained four bacterial species, representatives of the genera Vibrio and Flavobacterium and members of the coryneform group and the family Enterobacteriaceae. Total bacterial numbers and species diversity decreased with increased salinity. NTA was administered at low and high concentrations, one concentration to each microcosm, initially with the least amount of saline. Removal of both concentrations of NTA occurred and was attributed to biodegradation after a period of bacterial acclimatization. Subsequent dosing of NTA to vessels of higher salinity demonstrated that biodegradation was incomplete at observed mean salinities of greater than 9.18% at low influent NTA concentrations and greater than 5.08% at high influent NTA concentrations. Therefore, acclimatization was dose dependent. It was concluded that NTA acclimatization at the higher salinities ceased because of salinity stress-induced failure of NTA catabolism and not the disappearance of a particular bacterial species.

Attached and Free-Floating Bacterioplankton in Howe Sound, British Columbia, a Coastal Marine Fjord-Embayment

Factors which influence the attachment of bacterioplankton to particles (including phytoplankton) were investigated by using (i) water samples removed from a coastal temperate fjord over an annual cycle and (ii) unialgal cultures of Prorocentrum minimum, Dunaliella tertiolecta , and Skeletonema costatum . Silt and salinity levels in this fjord seawater did not appear to influence bacterial attachment, but the percent attached bacteria was inversely related to both chlorophyll a concentrations and primary productivities. During periods of high primary productivities the percent attached bacteria was low, whereas during periods of low, increasing, and declining primary productivities the percent attached bacteria was high. A similar pattern of bacterial attachment was observed when the three phytoplankton were grown as batch cultures. The percent attached bacterial numbers increased upon the initiation of algal growth and after these cells stopped growing, but not while the algae were growing. We suggest that a major factor influencing the attachment of bacterioplankton is the physiological condition of their major nutrient source, the phytoplankton; mainly free-living bacteria are associated with growing phytoplankton, whereas a much greater proportion of the bacteria are attached among senescent phytoplankton populations.

Utilization of surface localized substrate by non-adhesive marine bacteria

Thirty-four marine bacteria were isolated from the eluate of seawater passed through a column of glass beads coated with stearic acid. Irreversible attachment of these isolates to stearic acid-coated glass surfaces ranged from 7.6-100% of the total attached population, with 7 isolates exhibiting less than 10% irreversible adhesion. All 14 isolates tested were able to utilize surface bound(14)C-stearic acid, even though some showed mostly reversible adhesion to the surface. More detailed studies were made comparing the reversibly adheringVibrio MH3 with the irreversibly adheringPseudomonas NCMB2021. MH3 cells were readily removed from the surface by a gentle shear force, and a significant degree of(14)C-labeling of MH3 cells, but not of NCMB2021 cells, in the bulk phase was observed. The ecological significance of nutrient scavenging at solid surfaces by reversibly attached bacteria is considered.

Specific uptake rates of amino acids by attached and free-living bacteria in a mesotrophic lake

Seasonal and spatial patterns of specific uptake rates of amino acids by bacteria in Lake Constance were studied. The total bacterial population was divided into small (0.2- to 1.0-micron) and large (1.0- to 3.0-micron) free-living bacteria and attached bacteria by fractionated filtration. Data for attached bacteria, received by retention on 3.0-micron-pore Nuclepore filters, were corrected for free-living bacteria in this fraction. Specific uptake rates based on autoradiography were also recorded. Specific uptake rates for attached bacteria ranged from 9.41 X 10(-11) to 6.11 X 10(-8) ng of C h-1 cell-1 and were therefore significantly greater than those for free-living bacteria during most time periods. However, they were not significantly different from those for cells proven to be active by autoradiography. Specific uptake rates for small free-living bacteria ranged between 7.68 X 10(-11) and 4.60 X 10(-9) ng of C h-1 cell-1. They were nearly in the same range of those for large free-living bacteria (5.10 X 10(-11) to 1.07 X 10(-8) ng of C h-1 cell-1), although both fractions exhibited pronounced differences in their seasonal and vertical distributions.

Distribution and activity of bacteria in the headwaters of the Rhode River Estuary, Maryland, USA

A transect along the axis of the headwaters of a tidal estuary was sampled for microbial, nutrient, and physical parameters. Chlorophylla averaged 42μg 1(-1) and phytoplankton comprised an estimated 80% of the total microbial biomass as determined by adenosine triphosphate (ATP). Bacterial concentrations ranged from 0.3-53.9×10(6) cells ml(-1) and comprised about 4% of the total living microbial biomass. Bacterial production, determined by(3)H-methyl-thymidine incorporation was about 0.05-2.09× 10(9) cells 1(-1) h(-1), with specific growth rates of 0.26-1.69 d(-1). Most bacterial production was retained on 0.2μm pore size filters, but passed through 1.0μm filters. Significant positive correlations were found between all biomass measures and most nutrient measures with the exception of dissolved inorganic nitrogen nutrients where correlations were negative. Seasonal variability was evident in all parameters and variability among the stations was evident in most. The results suggest that bacterial production requires a significant carbon input, likely derived from autotrophic production, and that microbial trophic interactions are important.

Size of Suspended Bacterial Cells and Association of Heterotrophic Activity with Size Fractions of Particles in Estuarine and Coastal Waters

The size of bacteria and the size distribution of heterotrophic activity were examined in estuarine, neritic, and coastal waters. The data indicated the small size of suspended marine bacteria and the predominance of free-living cells in numerical abundance and in the incorporation of dissolved amino acids. The average per-cell volume of suspended marine bacteria in all environments was less than 0.1 μm 3 . Cell volume ranged from 0.072 to 0.096 μm 3 at salinities of 0 to 34.3‰ in the Newport River estuary, N.C., and from 0.078 to 0.096 μm 3 in diverse areas of the Gulf of Mexico. Thus, the free-living bacteria were too small to be susceptible to predation by copepods. In the Newport River estuary, ca. 93 to 99% of the total number of cells and 75 to 97% of incorporated tritium (from 3 H-labeled mixed amino acids) retained by a 0.2-μm-pore-size filter passed through a 3.0-μm-pore-size filter. Although the amino acid turnover rate per cell was higher for the bacteria in the >3.0-μm size fraction than in the <3.0-μm size fraction, the small number of bacteria associated with the >3.0-μm size particles resulted in the low relative contribution of attached bacteria to total heterotrophic activity in the estuary. For coastal and neritic samples, collected off the coast of Georgia and northeast Florida and in the plume of the Mississippi River, 56 to 98% of incorporated label passed through a 3.0-μm-pore-size filter. The greatest activity in the >3.0-μm fraction in the Georgia Bight was at nearshore stations and in the bottom samples. Our data were consistent with the hypothesis that resuspension of bottom material is an important factor in influencing the proportion of heterotrophic activity attributable to particle-associated bacteria.

Effects of Inorganic Particles on Metabolism by a Periphytic Marine Bacterium

Measurements were made of adsorption of a periphytic marine bacterium, glucose, and glutamic acid to inorganic particles in seawater and defined bacterial growth medium. Measurements of the metabolism of bacteria were made in the presence and absence of particles by microcalorimetry and radiorespirometry. It was found that hydroxyapatite adsorbs glutamic acid, but not glucose, from the experimental medium. It was also found that hydroxyapatite adsorbs essentially all of the bacteria from the medium when the bacterial concentration is approximately 6 × 10 5 bacteria per ml. If the bacterial concentration is approximately 6 × 10 7 , then only a small fraction of cells become attached. It was therefore possible to select bacterial concentrations and organic nutrients so that bacterial attachment, organic nutrient adsorption, or both would occur in different experiments. In this experimental system the metabolism by attached and nonattached bacteria of adsorbing and nonadsorbing organic nutrients was measured. The results show that bacterial activity in this model system was not enhanced by the particles, regardless of whether the bacteria, the organic nutrient, or both were associated with the surface. In fact, the respiratory activity of the attached bacteria was diminished in comparison with that of free bacteria.