Factor analysis of the impact of the environment on microbial communities in the tvärminne area, southern coast of Finland

Data already examined by regression analysis were subjected to factor analysis to scrutinize the effects of environmental factors on microbial populations in the brackish waters of the Tv?rminne archipelago on the southern coast of Finland. Water samples were collected from 1.0-m depth at one point in Tv?rminne Storfj?rd, 71 times over about 2 years. Twenty-six parameters were determined on each sample, 10 of environmental and 16 of microbiological type. The correlations between the parameters were factorized using the principal axis solution, and eight factors chosen for further consideration were rotated by the varimax method. The major part of the variance (about 90% of the total communality) of the microbiological parameters was covered by five factors, interpreted as phytoplankton blooms, the periods before and after the blooms, freshwater outflows, and water temperature. Wind variables were components in the factors interpreted as freshwater outflows. Rainfall played a minor part in the total variance of the microbial community, but it washed yeasts and proteolytic bacteria from the land into the study area. The eight factors selected covered about 60 to 98% of the variance of the microbiological parameters. The highest values (above 90%) were obtained for direct counts of bacteria, for plate counts of mesophilic and polymyxin-resistant bacteria, and for the two community respiration parameters; the lowest values (60 to 75%) were obtained for H(2)S-producing and proteolytic bacteria.     

Effects of Environmental Factors on Microbial Populations in Brackish Waters off the Southern Coast of Finland

The roles played by environmental factors in seasonal changes in microbial populations were investigated in the Tvärminne area, off the southern coast of Finland. Surface-layer samples were collected at 1- or 2-week intervals in 1976-78, and 14 microbiological and 10 environmental parameters were determined. Stepwise multiple regression analysis was used to explain seasonal variation in the microbiological parameters. Separate analyses were made of the data from the open-water and ice-cover periods. In analyses of data from both periods, the environmental factors included accounted for a significant proportion of the variation in the parameters for community respiration (90%) and bacterial spores (80%), and a smaller proportion (60 to 65%) of the variation in total counts of bacteria and plate counts of psychrophiles and yeasts. Lower values (40 to 55%) were obtained for the variation in the other microbiological parameters. The environmental factors with maximal contributions were organic matter, water temperature, chlorophyll a, and salinity, but rainfall and winds also explained part of the variation in some microbiological parameters. In the winter analysis the results differed from those obtained for the other seasons, the variation being governed by parameters indicating freshwater outflows, namely, humic matter, salinity, water temperature (positive regression coefficient), and rainfall (negative regression coefficient).     

Effects of freshwater outflows on microbial populations in the Tvärminne archipelago, southern Finland

The effects of freshwater outflows were evaluated in three ways: (1) microbial populations in the outflow area (mainly Tvärminne Storfjärd) were compared with populations outside the area, (2) direct counts were made at three sites to monitor the abundance of bacteria along the seaward course of the outflows, and (3) a survey was made of the distribution of microorganisms in the archipelago. The indices used for the presence of freshwater outflows in the archipelago were low salinity, increased amounts of humic matter, and increased temperatures in the winter.
In the outer archipelago, the effects of the outflows were most evident in the low-salinity surface layer below the ice and were also distinguishable in spring and late autumn, but were noted only sporadically in the summer. The outflows were traced as far seaward as the border of the sea zone. The outflows transported various types of bacteria, bacterial spores and yeasts, but did not significantly affect the community respiration. Many of the microorganisms flowing with the fresh water in the winter evidently originated from sewage. During the other seasons, the roles of outflows from the firth of Pojoviken and runoff from the land became evident, but their contributions could not be estimated because fresh water and sewage move together. However, most of the bacterial spores seemed to originate from the land.
The archipelago east of Tvärminne Storfjärd proved to be appropriate for inshore brackish-water investigations being undisturbed by freshwater outflows.     

Microbiological Parameters for Differentiating between Coastal and Open Waters in the Northern Baltic Proper and the Gulf of Finland

The abundance of selected types of micro-organisms was compared between seven sites in inshore and offshore areas in the northern Baltic proper and at the entrance to the Gulf of Finland. The aim was to find out which of the microbiological parameters indicate terrestrial and littoral influences on the sites investigated and which of them indicate offshore conditions. During four cruises in 1977–78, samples were collected from 1-0 m depth, within one or a few days, at five offshore and two inshore sites.
Microbial numbers decreased consistently with increasing distance from the shore. The influence of terrestrial runoff, outflows from littoral areas and sediments was clear in the two Tvärminne inshore areas but not in the Ajax area situated about 10 km seaward of the outermost skerries of the Tvärminne archipelago. The influence of these factors was most distinctly indicated by viable bacteria at 18°C and polymyxin-resistant bacteria, rods and bacterial spores. Offshore characteristics were indicated by vibrios and bacteria obviously in a starved state. Proteolytic bacteria and yeasts did not indicate either of these conditions.     

Grazing of bacteria and phytoplankton by heterotrophic nanoflagellates in a Baltic Sea sample

Grazing by heterotrophic nanoflagellates on bacteria and phytoplankton was studied in a laboratory experiment, using a natural pelagic community originating from the Tvärminne sea area off the southern coast of Finland. Water was prescreened to remove larger grazers. Four experimental treatments were used: light and dark, with and without added nutrients. The growth of the large heterotrophic flagellates was stimulated by increased production of < 3 m phytoplankton. Clearance rates for heterotrophic nanoflagellates were estimated and were found to be within the range of previously reported values.     

Blooms of Single Bacterial Species in a Coastal Lagoon of the Southwestern Atlantic Ocean

We investigated seasonal differences in community structure and activity (leucine incorporation) of the planktonic bacterial assemblage in the freshwater and brackish-water zones of a shallow coastal lagoon of the southwestern Atlantic Ocean. Alphaproteobacteria formed the dominant microbial group in both zones throughout the sampling period. After an intrusion of marine water, members of the SAR11 lineage became abundant in the brackish-water zone. These bacteria were apparently distributed over the lagoon during the following months until they constituted almost 30% of all prokaryotic cells at both sampling sites. At the first sampling date (March 2003) a single alphaproteobacterial species unrelated to SAR11, Sphingomonas echinoides, dominated the microbial assemblages in both zones of the lagoon concomitantly with a bloom of filamentous cyanobacteria. Pronounced maxima of leucine incorporation were observed once in each zone of the lagoon. In the freshwater zone, this highly active microbial assemblage was a mix of the typical bacteria lineages expected in aquatic systems. By contrast, a single bacterial genotype with >99% similarity to the facultative pathogen gammaproteobacterial species Stenotrophomonas maltophilia formed >90% of the bacterial assemblage (>10⁷ cell ml⁻¹) in the brackish-water zone at the time point of highest bacterial leucine incorporation. Moreover, these bacteria were equally dominant, albeit less active, in the freshwater zone. Thus, the pelagic zone of the studied lagoon harbored repeated short-term blooms of single bacterial species. This finding may have consequences for environmental protection.     

Can Volatile Organic Metabolites Be Used to Simultaneously Assess Microbial and Mite Contamination Level in Cereal Grains and Coffee Beans?

A novel approach based on headspace solid-phase microextraction (HS-SPME) combined with comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC×GC–ToFMS) was developed for the simultaneous screening of microbial and mite contamination level in cereals and coffee beans. The proposed approach emerges as a powerful tool for the rapid assessment of the microbial contamination level (ca. 70 min versus ca. 72 to 120 h for bacteria and fungi, respectively, using conventional plate counts), and mite contamination (ca. 70 min versus ca. 24 h). A full-factorial design was performed for optimization of the SPME experimental parameters. The methodology was applied to three types of rice (rough, brown, and white rice), oat, wheat, and green and roasted coffee beans. Simultaneously, microbiological analysis of the samples (total aerobic microorganisms, moulds, and yeasts) was performed by conventional plate counts. A set of 54 volatile markers was selected among all the compounds detected by GC×GC–ToFMS. Principal Component Analysis (PCA) was applied in order to establish a relationship between potential volatile markers and the level of microbial contamination. Methylbenzene, 3-octanone, 2-nonanone, 2-methyl-3-pentanol, 1-octen-3-ol, and 2-hexanone were associated to samples with higher microbial contamination level, especially in rough rice. Moreover, oat exhibited a high GC peak area of 2-hydroxy-6-methylbenzaldehyde, a sexual and alarm pheromone for adult mites, which in the other matrices appeared as a trace component. The number of mites detected in oat grains was correlated to the GC peak area of the pheromone. The HS-SPME/GC×GC–ToFMS methodology can be regarded as the basis for the development of a rapid and versatile method that can be applied in industry to the simultaneous assessment the level of microbiological contamination and for detection of mites in cereals grains and coffee beans.     

Microbial Flora of Pond-Reared Brown Shrimp (Penaeus aztecus)

Agar plate counts and microbial types are reported for brown shrimp reared in 2-acre natural marshland and in 0.5-acre artificial ponds during June to October 1970. Bacterial counts of pond-reared shrimp ranged from 5 × 10⁴ to 5.5 × 10⁶ per g. At final harvest in October, bacterial counts ranged from 2 × 10⁵ to 5.5 × 10⁶ per g. In marsh ponds, bacterial counts of shrimp and pond water were lowest in August when both water temperature and salinity were high. Coryneform bacteria and to a lesser extent Vibrio were the predominant isolates from fresh pond shrimp. Shrimp stored at 3 to 5 C for 7 days were acceptable as judged by appearance and odor. Between 7 and 14 days of refrigerated storage, bacterial counts increased sharply and about 50% of the samples became unacceptable. Refrigerated storage of pond shrimp caused increases in coryneform bacteria and micrococci and decreases in Vibrio, Flavobacterium, Moraxella, and Bacillus species. Pseudomonas species were not significant in fresh or stored pond shrimp. The microbial flora of pond water usually was dominated by coryneform bacteria, Flavobacterium, Moraxella, and Bacillus species.     

Novel Clostridium populations involved in the anaerobic degradation of Microcystis blooms

Understanding the microbial degradation of Microcystis biomass is crucial for determining the ecological consequences of Microcystis blooms in freshwater lakes. The purpose of this study was to identify bacteria involved in the anaerobic degradation of Microcystis blooms. Microcystis scum was anaerobically incubated for 90 days at three temperatures (15 °C, 25 °C and 35 °C). We used terminal restriction fragment length polymorphism (T-RFLP) analysis of bacterial 16S rRNA genes, followed by cloning and sequencing of selected samples, to reveal the community composition of bacteria and their dynamics during decomposition. Clostridium spp. were found to be the most dominant bacteria in the incubations, accounting for 72% of the sequenced clones. Eight new clusters or subclusters (designated CLOS.1–8) were identified in the Clostridium phylogenetic tree. The bacterial populations displayed distinct successions during Microcystis decomposition. Temperature had a strong effect on the dynamics of the bacterial populations. At 15 °C, the initial dominance of a 207-bp T-RF (Betaproteobacteria) was largely substituted by a 227-bp T-RF (Clostridium, new cluster CLOS.2) at 30 days. In contrast, at 25 °C and 35 °C, we observed an alternating succession of the 227-bp T-RF and a 231-bp T-RF (Clostridium, new cluster CLOS.1) that occurred more than four times; no one species dominated the flora for the entire experiment. Our study shows that novel Clostridium clusters and their diverse consortiums dominate the bacterial communities during anaerobic degradation of Microcystis, suggesting that these microbes'' function in the degradation process.     

A multiomics approach to study the microbiome response to phytoplankton blooms

Phytoplankton blooms are predictable features of marine and freshwater habitats. Despite a good knowledge base of the environmental factors controlling blooms, complex interactions between the bacterial and archaeal communities and phytoplankton bloom taxa are only now emerging. Here, the current research on bacterial community’s structural and functional response to phytoplankton blooms is reviewed and discussed and further research is proposed. More attention should be paid on structure and function of autotrophic bacteria and archaea during phytoplankton blooms. A multiomics integration approach is needed to investigate bacterial and archaeal communities’ diversity, metabolic diversity, and biogeochemical functions of microbial interactions during phytoplankton blooms.     

Bacterial Production and Growth Rate Estimation from [3H]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-³H]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 × 10¹¹ and 8.678 × 10¹¹ μg of C mol⁻¹ for free-living and attached bacteria in the freshwater system, and 1.276 × 10¹¹ and 1.354 × 10¹¹ μg of C mol⁻¹ 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.     

Variations in the microbial log reduction curves of irradiated cod fillets, shrimp, and their respective homogenates.

When cod (Gadus morhua morhua) and headless white shrimp (Penaeus setiferus) were gamma irradiated with a series of low-ionizing radiation doses, a "shoulder(s)" was observed in the graph (log microbial counts versus dose) in the approximate range of 25 to 75 krads. When the microbiological survivors were differentiated into total counts, proteolytic and pseudomonad-type bacteria, it was observed that the pseudomonad-type bacteria were rapidly destroyed by 25 krads and that proteolytic bacteria were destroyed at a faster rate than the rest of the microorganisms. When cod fillets and shrimp were compared with their respective homogenates and irradiated at doses of 0, 10, 20, 30, 40, 50, 60, 80, 100, 150, 200, and 300 krads, the homogenates did not exhibit the characteristic shoulders. A further experiment was designed to test surface versus uniform dispersion of microorganisms on/in gelatin disks subjects to low doses of irradiation. Differences were found that may explain the observed differences between solid food materials such as fish fillets and shrimp and their homogenates.     

Enumeration of Bacteriophages and Host Bacteria in Sewage and the Activated-Sludge Treatment Process

Bacteriophage populations in an activated-sludge sewage treatment plant were enumerated. A newly developed assay for quantitation of total phages, employing direct electron microscopic counts, was used in conjunction with the plaque assay. The total concentration of phages was significantly higher in reactor mixed liquor and effluent than in influent sewage, indicating a net production of phages within the reactor. Maximum total phage concentrations in the fluid phase of sewage, activated-sludge mixed liquor, and reactor effluent were 2.2 × 10⁷, 9.5 × 10⁷, and 8.4 × 10⁷/ml, respectively. Conditions were optimized for isolation of predominant heterotrophic aerobic bacteria from sewage and mixed liquor. Blending at ice water temperatures was superior to ultrasound or enzyme treatments for maximum release of viable bacteria from microbial floc. A solidified extract of mixed liquor was superior to standard media for cultivating maximum numbers of heterotrophic bacteria. The highest culture counts for sewage and mixed liquor were 1.4 × 10⁷ and 1.3 × 10⁹/ml, respectively, which represented only 3 and 6.8% of the total microscopic cell counts. Only 3 out of 48 dominant bacterial isolates from either mixed liquor or sewage were hosts for phages present in the system. The sum of phage populations infecting these three hosts accounted for, at best, 3.8% (sewage) and 0.2% (mixed liquor) of the total number of phages present. Generally, specific phage titers were lower in mixed liquor than in sewage, indicating that these hosts were not responsible for the net production of phages in the reactor. This study emphasizes the limitations of the plaque assay for ecological studies of phages, and it suggests that bacteria responsible for phage production in activated-sludge mixed liquor are either minor components of the heterotrophic population, floc-producing strains, or members of other physiological groups.     

Blooms of single bacterial species in a coastal lagoon of the southwestern Atlantic Ocean

We investigated seasonal differences in community structure and activity (leucine incorporation) of the planktonic bacterial assemblage in the freshwater and brackish-water zones of a shallow coastal lagoon of the southwestern Atlantic Ocean. Alphaproteobacteria formed the dominant microbial group in both zones throughout the sampling period. After an intrusion of marine water, members of the SAR11 lineage became abundant in the brackish-water zone. These bacteria were apparently distributed over the lagoon during the following months until they constituted almost 30% of all prokaryotic cells at both sampling sites. At the first sampling date (March 2003) a single alphaproteobacterial species unrelated to SAR11, Sphingomonas echinoides, dominated the microbial assemblages in both zones of the lagoon concomitantly with a bloom of filamentous cyanobacteria. Pronounced maxima of leucine incorporation were observed once in each zone of the lagoon. In the freshwater zone, this highly active microbial assemblage was a mix of the typical bacteria lineages expected in aquatic systems. By contrast, a single bacterial genotype with >99% similarity to the facultative pathogen gammaproteobacterial species Stenotrophomonas maltophilia formed >90% of the bacterial assemblage (>10(7) cell ml(-1)) in the brackish-water zone at the time point of highest bacterial leucine incorporation. Moreover, these bacteria were equally dominant, albeit less active, in the freshwater zone. Thus, the pelagic zone of the studied lagoon harbored repeated short-term blooms of single bacterial species. This finding may have consequences for environmental protection.     

Can Particulate Air Sampling Predict Microbial Load in Operating Theatres for Arthroplasty?

Several studies have proposed that the microbiological quality of the air in operating theatres be indirectly evaluated by means of particle counting, a technique derived from industrial clean-room technology standards, using airborne particle concentration as an index of microbial contamination. However, the relationship between particle counting and microbiological sampling has rarely been evaluated and demonstrated in operating theatres. The aim of the present study was to determine whether particle counting could predict microbiological contamination of the air in an operating theatre during 95 surgical arthroplasty procedures. This investigation was carried out over a period of three months in 2010 in an orthopedic operating theatre devoted exclusively to prosthetic surgery. During each procedure, the bacterial contamination of the air was determined by means of active sampling; at the same time, airborne particulate contamination was assessed throughout the entire procedure. On considering the total number of surgical operations, the mean value of the total bacterial load in the center of the operating theatre proved to be 35 CFU/m³; the mean particle count was 4,194,569 no./m³ for particles of diameter ≥0.5 µm and 13,519 no./m³ for particles of diameter ≥5 µm. No significant differences emerged between the median values of the airborne microbial load recorded during the two types of procedure monitored. Particulates with a diameter of ≥0.5 µm were detected in statistically higher concentrations (p<0.001) during knee-replacement procedures. By contrast, particulates with a diameter of ≥5 µm displayed a statistically higher concentration during hip-replacement procedures (p<0.05). The results did not reveal any statistically significant correlation between microbial loads and particle counts for either of the particle diameters considered (≥0.5 µm and ≥5 µm). Consequently, microbiological monitoring remains the most suitable method of evaluating the quality of air in operating theatres.     

Post-Sampling Changes in Microbial Community Composition and Activity in a Subsurface Paleosol

Abstract Laboratory storage of deep vadose zone sediments has previously resulted in an increase in the abundance of cultured microorganisms by as much as 10,000-fold, without concomitant increases in total microscopic counts. In the present study, factors contributing to the time-dependent stimulation of various microbiological parameters were examined during a 224 d post-sampling period, using a factorial-design experiment that partitioned the effects of storage time, sediment condition (intact blocks or homogenized) during storage, and O₂ concentration (0.5, 4.5, and 21%) during storage at 15°C. Stored samples were analyzed at selected intervals, to determine direct microscopic counts, viable biomass, lipid biomarker profiles, cultured aerobic heterotrophic microorganisms, and microbial activity. Time of storage prior to analysis of the samples was the most important factor affecting the microbiological response. Sediment condition influenced the stimulation response: microbial activity and the population of cultured microorganisms increased faster, and reached slightly higher values, in the homogenized samples, although maximum values were reached at similar times in the homogenized and intact samples. O₂ concentration also influenced the response, but was the least important of the factors evaluated. Total cells and viable biomass, measured as total phospholipid fatty acids, changed little during storage. Maximum cultured populations and activity were attained at 63 to 112 d, with culture counts approximating the total numbers of microscopically counted cells. At approximately the same time, unbalanced growth (evidenced by high ratios of polyhydroxybutyrate to phospholipid fatty acid) indicated that inorganic nutrients became limiting. Lipid biomarkers indicative of Gram-positive bacteria, including actinomycetes, became dominant components of the community profiles in samples maintained at 0.5% and 4.5% O₂. The shift in the microbial community from relatively inactive, predominantly uncultured microorganisms to metabolically active populations that were nearly all cultured highlights the need for rapid initiation of analyses after sample acquisition, if measurement of in situ microbiological properties is desired. The fact that these processes also occur in intact sediment blocks suggests that minor perturbations in the chemical or physical properties of subsurface sediments can result in major changes in the activity and composition of the microbial community. Revised: 22 October 1997; Accepted 20 November 1997     

Indirect Measurement of the Lag Time Distribution of Single Cells of Listeria innocua in Food

The distribution of log counts at a given time during the exponential growth phase of Listeria innocua measured in food samples inoculated with one cell each was applied to estimate the distribution of the single-cell lag times. Three replicate experiments in broth showed that the distribution of the log counts is a linear mapping of the distribution of the detection times measured by optical density. The detection time distribution reflects the lag time distribution but is shifted in time. The log count distribution was applied to estimate the distributions of the lag times in a liquid dairy product and in liver paté after different heat treatments. Two batches of ca. 100 samples of the dairy product were inoculated and heated at 55°C for 45 min or at 62°C for 2 min, and an unheated batch was incubated at 4°C. The final concentration of surviving bacteria was ca. 1 cell per sample. The unheated cells showed the shortest lag times with the smallest variance. The mean and the variance of the lag times of the surviving cells at 62°C were greater than those of the cells treated at 55°C. Three batches of paté samples were heated at 55°C for 25 min, 62°C for 81 s, or 65°C for 20 s. A control batch was inoculated but not heated. All paté samples were incubated at 15°C. The distribution of the lag times of the cells heated at 55°C was not significantly different from that of the unheated cells. However, at the higher temperatures, 62°C and 65°C, the lag duration was longer and its variance greater.     

Assessment of brown tide blooms, caused by Aureococcus anophagefferens, and contributing factors in New Jersey coastal bays: 2000–2002

A 3 year study (2000–2002) in Barnegat Bay-Little Egg Harbor (BB/LEH), New Jersey (USA), was conducted by the New Jersey Department of Environmental Protection, Division of Science Research and Technology (DSRT) in cooperation with several partners to assess brown tide blooms in coastal waters in NJ. Water samples were collected by boat and helicopter at coastal stations from 2000 to 2002 along with field measurements. Aureococcus anophagefferens were enumerated and associated environmental factors were analyzed. A. anophagefferens abundances were classified using the Brown Tide Bloom Index and mapped, along with salinity and temperature parameters, to their geo-referenced location using the ArcView GIS. The highest A. anophagefferens abundances (>10⁶ cells ml⁻¹), including category 3 blooms (≥200,000 cells ml⁻¹) and category 2 blooms (≥35,000 to ≤200,000 cells ml⁻¹), recurred during each of the 3 years of sampling and covered significant geographic areas of the estuary, especially in Little Egg Harbor. While category 3 blooms were generally associated with warmer water temperatures (>16 °C) and higher salinity (>25–26 ppt), these factors were not sufficient alone to explain the timing or distribution of A. anophagefferens blooms. There was no significant relationship between brown tide abundances and dissolved organic nitrogen measured in 2002 but this was consistent with other studies. Extended drought conditions, with corresponding low freshwater inputs and elevated bay water salinities, occurring during this time were conducive to blooms. A. anophagefferens abundances were well above the reported levels that have been reported to cause negative impacts on shellfish. It was shown that over 50% of the submerged aquatic vegetation (SAV) habitat located in Barnegat Bay/Little Egg Harbor was categorized as having a high frequency of category 2 or 3 blooms for all 3 years.     

Dominating Role of an Unusual Magnetotactic Bacterium in the Microaerobic Zone of a Freshwater Sediment

A combination of polymerase chain reaction-assisted rRNA sequence retrieval and fluorescent oligonucleotide probing was used to identify in situ a hitherto unculturable, big, magnetotactic, rod-shaped organism in freshwater sediment samples collected from Lake Chiemsee. Tentatively named “Magnetobacterium bavaricum,” this bacterium is evolutionarily distant from all other phylogenetically characterized magnetotactic bacteria and contains unusually high numbers of magnetosomes (up to 1,000 magnetosomes per cell). The spatial distribution in the sediment was studied, and up to 7 × 10⁵ active cells per cm³ were found in the microaerobic zone. Considering its average volume (25.8 ± 4.1 μm³) and relative abundance (0.64 ± 0.17%), “M. bavaricum” may account for approximately 30% of the microbial biovolume and may therefore be a dominant fraction of the microbial community in this layer. Its microhabitat and its high content of sulfur globules and magnetosomes suggest that this organism has an iron-dependent way of energy conservation which depends on balanced gradients of oxygen and sulfide.     

Comparison of microbial and meiofaunal community analyses for determining impact of heavy metal contamination

The impact of long-term heavy metal contamination on soil communities was assessed by a number of methods. These included plate counts of culturable bacteria, community level physiological profiling (CLPP) by analysis of the utilization of multiple carbon sources in BIOLOG plates, community fatty acid methyl ester (C-FAME) profiling and dehydrogenase enzyme activity measurements. These approaches were complemented with microscopic assessments of the diversity of the nematode community. Samples from two sites with different histories of heavy-metal input were assessed. Major differences in microbial and meiofaunal parameters were observed both between and within the sites. There was a large degree of congruence between each of the microbiological approaches. In particular, one sample appeared to be distinguished by a reduction in culturable bacteria (especially pseudomonads), limited response to carbon sources in CLPP, and major differences in extracted fatty acid profiles. The use of multivariate analysis to examine the relationship between microbial and physicochemical measurements revealed that CLPP and plate counts were useful for determining the gross effect of metals on soil microbial communities, whereas proportions of metal-resistant bacteria and dehydrogenase activity differentiated between the two sites. Copper and zinc concentrations and pH all showed significant correlation with the microbial parameters. Nematode community structure was affected to a greater extent by soil pH than by metal content, but the within-site rankings were the same as those achieved for microbiological analyses. The use of these methods for field evaluation of the impact of industrial pollution may be possible provided care is taken when interpreting the data.