Populations Of Heterotrophic Bacteria Research Articles

Physiological diversity and adaptations of aerobic heterotrophic bacteria from different depths of hypersaline, heliothermal and meromictic Ekho Lake (East Antarctica)

The hypersaline and meromictic Ekho Lake provides, with increasing depth, a large variety of different habitats to microorganisms. Out of 250 isolates, 51 bacterial strains were studied for physiological adaptations to their environment (i.e. to the depth layer from which they were obtained). Their salinity and temperature tolerance ranges for growth reflected the very conditions that were measured in the samples of their origin collected in the summer of 1989/1990. These observations indicated that the isolates are capable of growth at the depth of their origin and that they conceivably were endemics. Additionally, a separation of physiologically different populations of heterotrophic bacteria was indicated with respect to the utilization of C-compounds: the uppermost 4 m of the oxylimnion (with frequent waiter turnover and more extreme temperature conditions) supported primarily sugar-utilizing and halotolerant α-Proteobacteria and Gram-positives. The deeper, hypersaline and heliothermally heated layers (>4-24 m) had more moderately halophilic and amino acid-utilizing γ-Proteobacteria possibly of marine origin.

Populations of heterotrophic bacteria in an experimental recirculating aquaculture system

The aim of this work was to identify the main viable heterotrophic bacteria in a marine fish farm with a recirculating water system and to study their growth dynamics. The experiments were performed with sea bass (Dicentrarchus labrax) in an experimental recirculating water system. The bacteria identified were typical of the marine environment: Pseudomonas, Oceanospirillum, Marinobacter, Paracoccus and Erythrobacter genus from Bergey’s group IV, two genus of Vibrionaceae, one strain of Vibrio and one strain of Aeromonas. These populations were stable when the ingested feed/replacement water ratio was kept constant. Fixed bacteria formed large biofilms, which released about 104 CFU ml−1 into the tank. The biological filter, with its large surface area, was the largest source of bacteria in the farm, but the UV disinfection unit kept the number of free bacteria stable. When properly managed, the majority of bacteria that grew on the biological filter were from Bergey’s group IV; no Vibrio were ever detected on it.

Mesoscale features of phytoplankton and planktonic bacteria in a coastal area as induced by external water masses

The effects of different water masses and their physical structures on phytoplankton and bacteria were investigated in a coastal area of the Mediterranean Sea, the Gulf of Naples (Italy) on 9 and 10 November 1995. A small eddy (8 km in diameter), generated from offshore waters. occupied the inner part of the Gulf at surface, while the Modified Atlantic Water (MAW) intruded between 60 and 80 m depth. Phytoplankton communities as identified by HPLC pigment analysis (total) and flow cytometry (ultraphytoplankton) showed peculiarities in the different subsystems. Cryptophytes domlnated by pigment biomass were everywhere, while diatoms were more abundant at the coast and nanoflagellates at offshore stations. In the MAW, a peculiar phytoplankton community, different to that in the other water masses, occurred, and 2 populations of prochlorophytes were distinguished based on scatter and red fluorescence observations. Total bacterial numbers were significantly correlated to chlorophyll a (chl a) concentrations. Different populations of heterotrophic bacteria were identified based on apparent DN.4 content. Percentages of 2 such populations were significantly correlated to total chl a. Therefore, phytoplankton appears to regulate not only bacterial quantity but also composition. Although our study area was characterized by a marked oligotrophy, heterotrophic bacterial biomass never exceeded autotrophic biomass, as derived using constant conversion factors of bacteria and chl a to C. Therefore, no inverted pyramid was observed and bacterial biomass was still controlled by phytoplankton biomass. Mesoscale variability is of great relevance for energy and matter budgrts of coastal areas and its study is therefore fundamental. For example, eddies can be very important in coastal areas, influencing distribution of nutrients and organisms. Our approach, couphng HPLC and flow cytometry, represents a valuable tool for obtaining information on both phytoplankton coniposition and ecophysiology on a large number of samples, necessary for a valid representation of the space scales involved.

Treatability Testing of Intrinsic Bioremediation, Biostimulation, And Bioaugmentation of Diesel-oil Contaminated Soil At 5 ° C

Abstract To support the remediation design for a diesel-oil pipeline break near a remote railway river crossing near the British Columbia and Alaska border, a treatability test was designed to assess the in-situ bioremediation potential under four conditions of soil amendments at 5 ° C. The four conditions were:intrinsic bioremediation, where the soil received only water;biostimulation with one application of slow-release fertilizer;bioaugmentation with one application of both fertilizer and a psychrotrophic (cold-adapted), hydrocarbon-degrading bacterial culture; andsurfactant enhanced bioavailability, where the soil received one application of fertilizer and treatment with a biodegradable surfactant solution. Tests were monitored by soil respiration and bacterial enumeration and total extractable hydrocarbon (TEH) content by GC/FID. After 40 days incubation under aerobic conditions, all tests showed significant reduction in diesel range (C7 - C30) THE contamination. The intrinsic control was least effective, but still showed 66% TEH reduction at 5 ° C. The biostimulated soil performed the best, allowing 86% TEH reduction. The bioaugmented soil and surfactant treated soil both allowed about 75% TEH reduction. The study concluded that simple biostimulation with slow-release fertilizers would be the most appropriate bioremediation approach for this site. Introduction A four-inch diameter petroleum pipeline, located adjacent to the rail tracks of the White Pass and Yukon Route Railroad, was broken by heavy equipment working in the area in October 1994. A significant quantity of Arctic diesel fuel leaked and immediate efforts were made to recover most of the product through the summer of 1995. Following site investigation in November 1995, a plume of diesel contamination was delineated in the gravelly cobbles and boulder fill supporting the railway bridge over the East Fork Skagway River. The plume had migrated downward through the fill to bedrock surface. Liquid product at the toe of the slope could discharge with shallow groundwater flow over ground surface into the river. The estimated 500 m3 of residual hydrocarboncontaminated fill supporting the railway bed required remediation to prevent continued contamination of the water passing through the contaminated area. Initial soil chemical and biological data indicated that active natural biodegradation of petroleum hydrocarbons may be occurring at the site, but appears limited by natural nutrient level and the indigenous bacterial population at the site. The gravelly soil near the toe of the slope contains between 1,000 and 5,000 mg/kg of total extractable hydrocarbons (TEH) and has an indigenous heterotrophic bacteria population of between 104 and 106 bacteria/ g of soil. Excavation of the slope and structural fill supporting the operating railway was not feasible; therefore, in-situ remediation options were considered. Because of the generally low volatility of some components of Arctic diesel and the lack of electrical power at the remote site, in-situ bioremediation was considered the most feasible option. To determine the optimal conditions for in-situ bioremediation of this hydrocarbon-contaminated soil, a laboratory-scale treatability study was carried out. Because of the cold climate near the Alaska-British Columbia border, it was imperative that the testing be performed at the expected ambient soil temperature of about 5 to 8 ° C.

Effects of acidification on the changes of microbial diversity in aquatic microcosms

In an artificial pH‐gradient batch culture system, the effects of acidification on the species composition of a heterotrophic bacterial community were analyzed. As a result of this study, it was found that total bacteria numbers were not affected by acidification and that the population of heterotrophic bacteria decreased as pH became lower. The heterotrophic bacteria isolated from the entire pH gradient were 12 genera and 22 species. Among them, 64% were gram negative and 36% were gram positive bacteria. As pH decreased, the distribution rate of gram negative bacteria increased while that of gram positive bacteria decreased. The diversity of genera decreased from 13 to 5 as pH decreased from 7 to 3. The G+C content of all of the 202 isolated strains varied from 22.8 to 77.0%, and increased in interspecies of same genus as pH decreased. As a result of clustering analysis, the diversity index of species ranged from 1.13 to 2.37, and it had lower indices as pH decreased. In order to evaluate the diversity of numbers of sample of different size, a rarefaction method was used to analyze the expected number of species appearance according to pH. The statistical significance of species diversity was verified by the fact that the number decreased at lower pH

The influence of extensification in grassland management on the populations of micro-organisms in the phyllosphere of grasses

Comparing different methods of grassland management, the microbial community of grasses was analysed throughout the growing season. The quantitative development of heterotrophic bacteria, yeasts, filamentous fungi, streptomycetes and Listeria has been investigated. Furthermore, the community structure of heterotrophic bacteria was analysed by identifying isolated strains by means of classical biochemical and morphological examination supported by an application of multitest systems based on enzymatic reactions (Biolog, API). The population of heterotrophic bacteria and filamentous fungi was influenced by the age of plant material as well as by the density in the field. Thus, bacteria and fungi reached significantly larger numbers on plants of the late cut utilization (first cut at the beginning of July) in comparison with the regrowth of conventional cutting in mid May. These higher densities of micro-organisms exceeded threshold values that has been fixed for feedstuff s and therefore suggest an affect on the forage quality of this material. The population of yeasts neither showed a continual development over the season nor seemed to be influenced by any kind of management. Streptomycetes were only determined in larger numbers at the beginning of sampling in April, followed by a sporadical occurrence in the following course of investigation. Species of the genera Listeria have not been found at any time of sampling. The community structure of heterotrophic bacteria was numerically predominated by the genera Pseudomonas, Stenotrophomonas, Pantoea, Clavibacter and Curtobacterium. Generally, the population was characterized by low diversity. An influence of management on the composition of bacteria did not become obvious.

Modelling the ecological impact of contaminated river sediments on wetlands

In many riverine marginal wetlands water management is a main goal for nature conservation. However, sediments contaminated by organic chemicals and heavy metals often pose a potential risk for the ecosystem. The framework for our study is the wetlands of the rivers Weiße Elster and Parthe near Leipzig (Germany). We developed a conceptual model that links processes of sediment transport and biodegradation. The hydrological processes are described by a simplified advection-diffusion equation. The submodel for biodegradation includes a logistic equation and a Michaelis-Menten-like approach. It characterizes the growth of heterotrophic bacteria populations degrading contaminants. Hydrological parameters greatly affect the growth of the bacteria as well as the spatial distribution of accumulated contaminants. The spatial pattern of the metabolites differs significantly from that of the contaminants. As metabolites are also suspected to be toxic, they cannot be neglected. We discuss strategies to minimize negative impacts of contaminated sediments influencing the spatial arrangement of the overall risk potential.

MICROENVIRONMENTAL CONTROL OF PHOTOSYNTHESIS AND PHOTOSYNTHESIS‐COUPLED RESPIRATION IN AN EPILITHIC CYANOBACTERIAL BIOFILM1

ABSTRACTThe photosynthetic performance of an epilithic cyano‐bacterial biofilm was studied in relation to the in situ light field by the use of combined microsensor measurements of O2, photosynthesis, and spectral scalar irradiance. The high density of the dominant filamentous cyanobacteria (Oscillatoria sp.) embedded in a matrix of exopolymers and bacteria resulted in a photic zone of < 0.7 mm. At the biofilm surface, the prevailing irradiance and spectral composition were significantly different from the incident light. Multiple scattering led to an intensity maximum for photic light (400–700 nm) of ca. 120% of incident quantum irradiance at the biofilm surface. At the bottom of the euphotic zone in the biofilm, light was attenuated strongly to < 5–10% of the incident surface irradiance. Strong spectral signals from chlorophyll a (440 and 675 nm) and phycobilins (phycoerythrin 540–570 nm, phycocyanin 615–625 nm) were observed as distinct maxima in the scalar irradiance attenuation spectra in the upper 0.0–0.5 mm of the biofilm. The action spectrum for photosynthesis in the cyanobacterial layer revealed peak photosynthetic activity at absorption wavelengths of phycobilins, whereas only low photosynthesis rates were induced by light absorption of carotenoids (450–550 nm).Respiration rates in light‐ and dark‐incubated biofilms were determined using simple flux calculations on measured O2 concentration profiles and photosynthetic rates. A significantly higher areal O2 consumption was found in illuminated biofilms than in dark‐incubated biofilms. Although photorespiration accounted for part of the increase, the enhanced areal O2 consumption of illuminated biofilms could also be ascribed to a deeper oxygen penetration in light as well as an enhanced volumetric O2 respiration in and below the photic zone. Gross photosynthesis was largely unaffected by increasing flow velocities, whereas the O2 flux out of the photic zone, that is, net photosynthesis, increased with flow velocity. Consequently, the amount of produced O2 consumed within the biofilm decreased with increasing flow velocity. Our data indicated a close coupling of photosynthesis and respiration in biofilms, where the dissolved inorganic carbon requirement of the photo‐synthetic population may largely be covered by the respiration of closely associated populations of heterotrophic bacteria consuming a significant part of the photosynthetically produced oxygen and organic carbon.

Abundances and distributions of picoplankton populations in the central equatorial Pacific from 12°N to 12°S, 140°W

Abundances and distributions of picoplankton were studied on two cross-equatorial transect cruises (12°N, 140°W-12°S, 135°W) during February–March (TT007) and August–September 1992 (TT011). Samples were collected in the upper 200 m from early-morning and late-afternoon hydrocasts at 15 stations on each cruise (60 depth profiles, 820 samples). Populations of heterotrophic bacteria, Prochlorococcus, Synechococcus and small autotrophic eukaryotes were enumerated by dual-beam flow cytometry. At the northern end of the transect (7–12°N), abundances and vertical distributions were similar to those reported for the oligotrophic North Pacific gyre, with Prochlorococcus and heterotrophic bacteria dominating in the upper euphotic zone, and Synechococcus and eukaryotes exhibiting peaks in cell abundance at depth. All populations were abundant throughout the euphotic zone close to the equator and at the southern end of the transect. Heterotrophic bacteria and Synechococcus were generally more abundant in late-afternoon hydrocasts. The diel enhancement followed the temporal pattern in beam c and suspended particulates, and was particularly strong in the equatorial upwelling region where it averaged 13.6% of the morning population for heterotrophic bacteria and 22.3% for Synechococcus. Conservative estimates of daily growth rates from these data are 0.25 and 0.40 day −1, respectively, for the two populations. Near-surface maxima in heterotrophic bacteria were symmetrical around the equator, centered around 5°S and 5°N. Prochlorococcus was most abundant during local summer conditions at the respective ends of the transect. A minimum occurred in association with a dense aggregation of buoyant diatoms at the convergent front of a tropical instability wave (2°N, TT011). The ratio of Prochlorococcus to total bacteria was generally in the range of 0.15-0.2 for the upper water column, but varied during TT011 from > 0.3 for the most northern stations to < 0.1 at the 2°N front. At higher latitudes, Synechococcus was more numerous during El Niño conditions (TT007) on both sides of the equator and at southern stations on both cruises. Autographic eukaryotes were more abundant during local winters at the ends of the transect and during the “cold tongue” conditions (TT011) at the equator. Picoplankton account for most of the chlorophyll biomass and primary production in the central equatorial Pacific. Nonetheless, their abundances and distributions are relatively stable and conservative while other populations, such as diatoms, respond more dramatically to environmental forcing.

Enhanced activity of oligotrophic endogenous bacteria in clay‐rich sediments by nutrient injection

A controlled field experiment was performed in which the microbiology and geochemistry of clay‐rich fluvial‐deltaic sediments were characterized both before and after nutrient injection into a shallow well. Acetate addition (with nitrogen and phosphate) initially increased the heterotrophic bacteria population in the groundwater within 21 days after nutrient addition. Consumption of oxygen and injected nutrient resulted in an expected stimulation of copiotrophic bacterial growth (31–48 days), then a noticeable “trough phase”; reflecting minimal or no bacterial growth followed by a secondary peak reflecting another bacterial population growth surge (62–85 days). This secondary surge was apparently supported by the nutrients generated by the decomposing biomass (initial population peak), and by oxygen replenishment supplied by continual ground water flow. During the intervening trough phase, bacterial counts by most‐probable‐number analysis of soil samples indicated that the denitrifying population increase...

Nutrient status of wastewater in a fertilizer-factory-waste discharge equalization basin

The characteristics of wastewaters from a fertilizer factory, producing NH 3, urea, diammonium phosphate (DAP) and nitrogen-phosphorus-potassium (N-P-K) fertilizer blends, were monitored in stages for 18 months to correspond with the various stages of production of the different fertilizer minerals. Analysis of physico-chemical parameters of the various wastewater categories gave the following results: temperature, 28·0–32·5°C; pH, 5·0–9·48; conductivity, 2·5–2900·0 μmhos/cm; turbidity, 2·8–17·0 NTU; colour, 5–45 platinum cobalt units; DO, 1·4–7·0 mg/l; BOD 5, 1·0–41·4 mg/l; TS, 1000–8640 mg/l; TDS, 800–7600 mg/l; TSS, 200–3480 mg/l; acidity, 3·0–1000·0 mgCaCO 3/l; alkalinity, 10–460 mgCaCO 3/l; chloride, 249–1779 mg/l; total hardness, 0·0–20·0 mgCaCO 3/l; salinity, 0·0–3·5‰; calcium, 0·0–18·0 mg/l; magnesium, 0·0–0·972 mg/l; potassium, 18·0–50·0 mg/l; sulphate, 0·0–6640 mg/l; orthophosphate, 5·0–64·0 mg/l; NO 3-N, 0·04–1·57 mg/l; NO 2-N, 0·0–0·09 μg/l; NH 3-N, 0·0–0·72 mg/l. Variable results were obtained for the total coliform and faecal coliform counts with a range from 0 to > 1100 MPN/100 ml. Culturable aerobic heterotrophic bacteria populations ranged from 0·53 to 3100 × 10 3 cfu/ml. The fluctuations in these parameters were attributed to seasonal variations, varying effluent volumes, due to increased production capacity of the fertilizer plant, and the type of fertilizer mineral produced. A review of the waste-treatment system in the fertilizer factory is suggested, in order to minimize the impact of the pollutant components of the effluents on the ecology of the receiving creek.

Factors affecting the oxidation of elemental sulfur in soils

The use of elemental sulfur (S0) to alleviate widespread S deficiencies in agricultural soils is limited by the unpredictability of its oxidation to plant available sulfate. Here we review the biological, fertilizer and soil-related factors that control S0 oxidation. Sulfur oxidation in soil is mediated primarily by microorganisms, and thus it is the size, composition and activity of the microbial community which dictate oxidation rates. Because S0 oxidation is a biological process, it is strongly influenced by factors directly affecting microbial activity including soil temperature, water potential, and aeration. In many soils these factors represent the primary constraints to S0 oxidation. Oxidation is also influenced by the effective surface area of the S exposed to microbial activity. Thus oxidation is favored by reducing the particle size and abundant populations of heterotrophic bacteria and fungi capable of oxidizing S0, thus the availability of organic substrates from residue additions or root exudates may also affect S oxidation. Previous application of S0 may increase oxidation rates in many soils, presumably by stimulating S0 oxidizing populations. The large number of factors that govern S0 oxidation account for the variability in oxidation rates among soils, climatic regions, and agronomic practices. Many of these factors are subject to agronomic control, however, and it should be possible to devise S fertilizer strategies that exploit the slow release characteristics of S0 to meet crop demands efficiently in a variety of conditions.

Soil microbial population and nitrogen-transforming bacteria from 11-year sorghum tillage plots

Soil tillage alters crop residue placement, soil moisture and soil physical properties, which in turn may affect soil chemical and microbial properties. The impact of tillage on microbial populations was investigated by studying soil microbiological, physical and chemical properties after 11 years of a tillage management experiment with continuous sorghum ( Sorghum bicolor L. Moench) on an Orelia sandy clay loam (fine-loamy, mixed, hyperthermic Typic Ochraqualf). Soil from 0–7.5 and 7.5–15 cm depths was sampled from four replications of moldboard plow (MB), conventional till (CT), minimum till (MT) and no-till (NT) treatments in March (before planting) and May (during the growing season), 1989. Heterotrophic bacteria (HB) and actinomycete populations differed among tillage treatments before planting. Soil microbial populations differed with soil depth among all tillage treatments before the growing season (when no plants were present), but were similar among tillage treatments when counts by soil depth were composited, indicating that, although microbial distribution differed, total populations were similar. During the growing season, actinomycetes were lower in NT treatments, while HB counts were not significantly different between treatments. The similarity between treatments was attributed to drier soil conditions and the effect of plant roots in all treatments, which may have stimulated microbes similarly in all treatments. Ammonium oxidizers were lowest and dentrifiers highest in the NT soil a the 0–7.5 cm depth before planting. The sample obtained during the growing season indicated that soil nitrifier populations were usually greater in MT and NT treatments. The MB and CT treatments had significantly larger amounts of soil moisture, clay and nitrate than the NT and MT treatments, indicating that soil physical properties and nitrate levels were altered by tillage treatment. Soil nitrate was significantly correlated with nitrogen-transforming bacteria in several instances, although there was no predictable effect from soil depth or sampling date. In some instances, nitrifier counts fell and denitrifier counts increased as soil nitrate increased. HB and actinomycete population levels were not significantly correlated with the soil physical or chemical properties measured in this study. Although there were tillage treatment differences in soil physical (moisture, bulk density and clay content), chemical (nitrate-nitrogen, NO 3N) and microbiological properties (HB, actinomycetes, and denitrifier, nitrifier and ammonium oxidizer activity), generalizations about tillage system effects on soil microbiological properties were difficult to confirm because of the temporal nature of these differences.

The seasonality of heterotrophic bacteria on sandstones of ancient monuments

The heterotrophic bacteria population occurring on decaying sandstone from ancient monuments has been examined. Quantitative and qualitative observations are presented for seasonal variation over a period of 1 year. The diversity of heterotrophs occurring on sandstone was assessed on a monthly basis using a range of isolation media. An increase in numbers of bacteria was seen during the winter months: with both Gram-negative and Gram-positive types present. Gram-positive bacteria, especially spore-formers of the genus Bacillus, were found exclusively in the dry summer months. Decay activity, reflecting the potential of natural mixed populations present on the stone, also showed seasonal variation and this was related to the pattern of change for the bacterial species observed.

Lithotrophic and Heterotrophic Bacteria in Deep Subsurface Sediments and Their Relation to Sediment Properties

Abstract Subsurface sediments obtained from three cores drilled to depths of 260 m below the surface in South Carolina were analyzed for heterotrophic bacteria; N2‐fixing microaerophiles; and nitrifying, sulfur‐oxidizing, and H2‐oxidizing lithotrophic bacteria. In addition, pore waters were extracted for chemical analysis of inorganic nitrogen species, sulfate, dissolved organic carbon, pH, and Eh. Autotroph populations were generally less than 103 most probable number (MPN) g‐1 dry sediment with sulfur‐oxidizing bacteria, detected in 60% of the sediment samples, being the most frequently encountered group. Nitrifying bacteria were detected mainly in sediments from one borehole (P28), and their populations in those sediments were correlated with pore‐water ammonium concentrations. Populations of heterotrophic bacteria in 60% of the sediments were greater than 106 colony forming units (CFU) g‐1 dry sediment and were typically lower in sediments of high clay content and low pH. Microaerophilic N2‐fixing bac...

A modified MPN method for counting oligotrophic bacteria by using naturally occurring organics.

A MPN method was modified to determine the number of oligotrophic bacteria in fresh water. A series of MPN media were prepared with natural lake water by either autoclaving or filter-sterili-zation, and with diluted peptone solution (0.5mg/l) as a reference. Bacterial growth-positive test tubes were judged directly by epifluorescence microscopic counting. The bacterial counts using the medium of filter-sterilized in situ lake water was significantly higher than those obtained by autoclaved in situ lake water or peptone media. The difference in counting values between auto-claving and filter-sterilization was much larger when natural lake water media were prepared after several days' incubation under light condition. In this period, the organic carbon concentration (as COD, chemical oxygen demand) increased more than twice, mainly due to the excretion by phytoplnakton. These results suggest that naturally occurring dissolved organic matter, which was much suitable for the growth of autochthonous bacteria (oligotrophs) in the corresponding period, becomes one of the best media for counting the number of oligotrophic bacteria. Seasonal fluctua-tion of bacterial counts obtained by the present method showed a good correlation to that of chl. a, suggesting that the natural population of heterotrophic bacteria was influenced by phytoplankton through its excreted organic carbon.

Effect of variable nutrient supply rates on the RNA level of a heterotrophic bacterial strain

The heterotrophic bacterial strain HIS 53 was grown in a continuous culture under chemostat conditions and at sinusoidal or stepwise variations of the dilution rate; aspartate, ammonium, and phosphate were the growth-limiting nutrients. Within a specific nutrient limitation the growth yield was constant and independent of the applied environmental conditions. Compared with the reference chemostat culture, sinusoidal variations of the dilution rate increased the cellular RNA level by 19%–53% dependent on the growth limitation; stepwise variations caused an increase of the RNA level by 28%–41%. It was hypothesized that under the variable environmental conditions in the natural habitat the physiological potential of the organism is enhanced by some such increase of the cellular RNA level. As a consequence these increased RNA levels influence the competition between heterotrophic bacteria and, as a result, also the composition of the population of heterotrophic bacteria.

Enumeration and identification of heterotrophic bacteria in groundwater and in a mountain stream

Populations of heterotrophic bacteria were enumerated from stream and groundwater samples taken from an undisturbed catchment basin in southwestern Alberta. Direct counts using epifluorescence microscopy were compared with total viable counts using standard plate count methods, the iodonitrotetrazolium formazan method (reduction of 2-(p-iodophenyl)-3-(p-nitro phenyl)-5-phenyl tetrazolium chloride to iodonitrotetrazolium formazan), the nalidixic acid method, and the slide culture method. The nalidixic acid method gave the highest results, with total viable counts as high as 34.6% of the total direct count. Attempts to enumerate bacteria on media made from decaying leaves and algal–bacterial slime gave lower values, approximately 10% of the numbers obtained on enriched media. Stream waters were found to be dominated by Pseudomonas spp. and groundwaters were dominated by Bacillus spp. No differences were found in either numbers or species identified between tryptone – glucose – yeast extract agar, brain–heart infusion agar, nutrient agar, or casein–peptone–starch agar.

Bacterial microflora associated with a coastal, marine fish-rearing unit

Populations of heterotrophic bacteria from a marine fish-rearing unit were estimated using a spread plate technique. Bacterial populations in winter were relatively low compared with counts in summer when the maximum water temperature was recorded. Almost 600 isolates were examined, and found mostly to be Gram-negative rods. The bacterial populations consisted of a diverse array of taxa, and the variations in total numbers were due to relative changes in the abundance of these. There were nine groups isolated exclusively from the surface of turbot, includingAlcaligenes faecalis, Bacillus firmus, Photobacterium Angustum, P. logei, Pseudomonas fluorescensand unidentified Gram-negative rods. In addition, pure culture growth ofAlteromonas haloplanktisand unidentified Gram-negative, budding bacteria were isolated from within the lesions of moribund turbot.

Diel relationships of microbial trophic groups and in situ dissolved carbohydrate dynamics in the caribbean sea

Dissolved total carbohydrate (TCHO), polysaccharide (PCHO), monosaccharide (MCHO) and organic carbon (DOC) were determined at 3-h intervals over 5 diel cycles in the mixed layer of the northwestern Caribbean Sea while following a drogued buoy. These data have been compared to populations of phototrophic (PNAN) and heterotrophic (HNAN) nanoplankton (2–20 μm diameter) and heterotrophic bacteria (HBAC) (0.2–2.0 μm diameter) estimated by epifluorescence counts, as well as to ΣCO2, phosphate, chlorophyll a and phaeopigment data determined simultaneously. Two different types of apparent diel dissolved carbohydrate (CHO) patterns were found. On 3 d when no sustained net ΣCO2 uptake was evident, TCHO and PCHO generally declined during the afternoon and early evening while MCHO tended to increase. On two other days when apparent sustained ΣCO2 uptake occurred during the day, there were large evening TCHO and PCHO peaks with constant or declining MCHO levels. These accumulations probably resulted from the release of recently produced PCHO from phototrophs. As was found earlier in the Sargasso Sea, PNAN populations were inversely related to PCHO concentrations. The sample to sample fluctuations of PNAN also were inversely related to the apparent rates of change of TCHO and PCHO, possibly due to an inverse relation between the rates of PNAN cell division and CHO excretion. Fluctuations in HBAC populations were inversely correlated with PCHO dynamics and directly related to MCHO variations, possibly due to extracellular hydrolysis of PCHO to MCHO during periods of rapid bacterial growth as well as to net heterotrophic PCHO uptake. A direct relationship between HNAN and TCHO fluctuations suggests the importance of HNAN excretion in the release of dissolved organics. The combined PNAN and HBAC fluctuations accounted for a more significant fraction of the variance in the apparent rates of change of PCHO than did any single population parameter indicating that intimate interactions between the microbial plankton groups are important in the in-situ regulation of CHO dynamics. Total system net TCHO release and uptake rates for 5 d averaged 56 and 53 μg C l-1 d-1 respectively, assuming that the observed fluctuations resulted from temporal planktonic processes in homogeneous water masses. While the data contain indications that this was the case, this assumption is not definitive.