Total Bacterial Biomass Research Articles

Growth and distribution patterns of Roseobacter/Rhodobacter, SAR11, and Bacteroidetes lineages in the Southern Ocean

Roseobacter/Rhodobacter and SAR11, affiliated with Alphaproteobacteria, and the phylum Bacteroidetes constitute a large proportion of marine planktonic bacteria, but information about their growth and distribution patterns in the Southern Ocean is scarce. The aim of the present study is to determine patterns in the biomass and productivity of Roseobacter/Rhodobacter, SAR11, and Bacteroidetes groups along the steep temperature, salinity, and organic matter gradients in the Southern Ocean by using catalyzed reporter deposition-fluorescence in situ hybridization and bromodeoxyuridine (BrdU) immunocytochemistry FISH. We found that Roseobacter/Rhodobacter, SAR11, and Bacteroidetes are prominent contributors to total bacterial biomass and production. SAR11 bacteria were the predominant lineage, but their biomass was low in the coldest regions. In contrast, the biomasses of Roseobacter/Rhodobacter and Bacteroidetes lineages were positively correlated with organic matter concentrations. The Roseobacter/Rhodobacter had the highest proportion of BrdU-positive (i.e., actively growing) cells among the three phylotypes at all stations, despite their low abundance. The relative contribution of Bacteroidetes to the total bacterial productivity (number of active cells) was negatively correlated with temperature. These results suggest that the growth and distribution patterns of Roseobacter/Rhodobacter, SAR11, and Bacteroidetes were determined by different environmental gradients (e.g., organic matter concentrations or temperature) in the Southern Ocean.

The phylogenetic structure of microbial biofilms and free-living bacteria in a small stream

The phylogenetic composition, bacterial biomass, and biovolume of both planktonic and biofilm communities were studied in a low-order Bystřice stream near Olomouc City, in the Czech Republic. The aim of the study was to compare the microbial communities colonizing different biofilm substrata (stream aggregates, stream sediment, underwater tree roots, stream stones, and aquatic macrophytes) to those of free-living bacteria. The phylogenetic composition was analyzed using fluorescence in situ hybridization for main phylogenetic groups. All phylogenetic groups studied were detected in all sample types. The stream stone was the substratum where nearly all phylogenetic groups were the most abundant, while the lowest proportion to the DAPI-stained cells was found for free-living bacteria. The probe specific for the domain Bacteria detected 20.6 to 45.8% of DAPI-stained cells while the probe specific for the domain Archaea detected 4.3 to 17.9%. The most abundant group of Proteobacteria was Alphaproteobacteria with a mean of 14.2%, and the least abundant was Betaproteobacteria with a mean of 11.4%. The average value of the Cytophaga-Flavobacteria group was 10.5%. Total cell numbers and bacterial biomass were highest in sediment and root biofilm. The value of cell biovolume was highest in stone biofilm and lowest in sediment. Overall, this study revealed relevant differences in phylogenetic composition, bacterial biomass, and biovolume between different stream biofilms and free-living bacteria.

Effect of temperature on organic matter transformation in a different ambient nutrient availability

We experimentally manipulated the thermal environment in laboratory mesocosms to evaluate the effect of temperature on organic matter transformation in two systems of lower and higher ambient nutrient availability. We used a system of 6 mesocosms, equipped with heating and cooling systems; 3 were filled with water from a mesotrophic lake and 3 with water from a eutrophic lake. Each of the 3 mesocosms were maintained at different temperatures: ambient lake temperature (10°C and 20°C), ambient +5°C, and ambient +10°C and the experiment was replicated in twice, in the spring and summer seasons. We measured rates of physicochemical and bacteriological parameters changes over a 2-day period. Results of the study demonstrated that, irrespective of nutrient concentration, an increase in temperature resulted in enhanced the level of labile organic matter, indicated by significantly elevated concentrations of dissolved organic carbon (DOC) and low values of SUVA (specific UV absorbance=Abs 260·1000/DOC). The effect of temperature was stronger in the lower nutrient concentration in the spring experiment treatments elevated by 5°C. The increase in temperature was additionally accompanied by significant increased total bacterial counts (TBC), biomass (BB) and heterogeneity of bacterioplankton. In the higher nutrient concentration, the increase in temperature exerted a greater influence on the dynamics of concentration of heteromorphic organic matter, shown by the negative correlation between particulate organic carbon (POC) and DOC content and TBC value. The accumulation of considerable quantities of refractory DOC and POC and low bacterioplankton activity may intensify the rate of degradation of eutrophic lake ecosystems.

Fungal and bacterial denitrification are differently affected by long-term pH amendment and cultivation of arable soil

Bacteria are considered as playing a predominant role in the production of nitrous oxide (N2O) in arable soil. Despite the knowledge that fungi are able to denitrify their contribution to denitrifier N2O production from arable soil is uncertain. Here, we assess the capability of fungi and bacteria to contribute to N2O emission from arable soil by measuring potential denitrification rates (PDR) as N2O production, after application of selective inhibitors aimed at distinguishing between fungal and bacterial denitrification, and related PDR to characteristics of the soil microbial community. Soil was sampled from a long-term crop rotation maintained since 1961 at seven different pH levels, ranging in 0.5 increments from pH 4.5 to 7.5, and along a cultivation gradient from freshly ploughed soil to three years under ley grass. Over both pH and cultivation gradients, bacteria contributed up to 54% and fungi contributed to 18% of the PDR. Residual N2O production that was not targeted by the selective inhibitors and hence could not be attributed to fungi or bacteria might be due to pre-synthesised enzymes or resistant organisms. The PDR of the bacterial community responded positively to increase in soil pH with the lowest PDR at pH 4.2 and the highest around pH 5.9. In contrast, fungal denitrification was not influenced by soil pH. Changes in ester linked fatty acids (ELFA) concentrations showed that whilst total bacterial biomass decreased with increasing pH fungal biomass was not significantly influenced by pH, driving an increase in the ratio of fungal–bacterial biomass. Both fungal biomass and bacterial biomass, and the PDR from the control treatment (no inhibitor application) across the pH gradient were greatest under long-term ley. Concentrations of fatty acids a15:0, 16:1ω7 and 17:1ω8 of microbial origin were positively correlated with the proportion of denitrification activity that was repressed by bacterial inhibitors. This suggests that there is a relationship between organisms that possess the fatty acids a15:0, 16:1ω7 and 17:1ω8, and the function of denitrification. Our results demonstrate that both fungal and bacterial denitrification were occurring in this arable soil. That management for pH and cultivation had differing effects on the potential contribution of fungal and bacterial denitrification to N2O production has implications for the development of appropriate management practices for mitigation of this greenhouse gas.

Effect of calco-magnesian amendment on the mineral weathering abilities of bacterial communities in acidic and silicate-rich soils

Liming of forest ecosystem is recognized to increase nutrients availability in soil and water and to enhance the biomass and bacterial activities in soil. However, little studies have investigated on change induced on bacterial ability to alter silicate mineral after soil liming. Thus, this study is carried out in experimental conditions using podzol collected in the winter (2007), spring and summer (2008) in small forest catchments in Vosges Mountains amended in 2003 by dolostone and limestone. Bacterial communities, extracted from various horizons of these soils amended or not, were put in contact with a phyllosilicate (phlogopite as sole source of Mg and Fe) in miniaturized bioassays in aerobic conditions. A weathering phenotype was determined through the quantification of (i) protons and organic acids released in assay solution by bacteria (ii) iron leached from phlogopite lattice into solution by bacteria and (iii) the carbon source consumption (i.e. glucose). These results were then compared to empirical model based on chemical leaching experiments realized in the same conditions in order to simulate the processes involved. In parallel, the carbon source utilization patterns of bacteria were investigated in order to discriminate the bacterial communities from amended and non-amended soil horizons. The results indicate that (1) the total bacterial biomass was unaffected by the Ca–Mg amendment, whereas the cultivable bacterial biomass increased after the amendment, and (2) the weathering and the carbon source utilization patterns of bacterial communities differs from one soil horizon to another and among soil types. The metabolic profiles analyzed indicated significant differences in organic C substrate usage depending on season and Ca–Mg amendment. Bacterial communities, extracted from the amended soil, are enable greater iron leaching compared to those found in the control soil, suggesting a greater release of organic acids and/or a more highly chelating organic acid release. The process developed by bacteria to alter the phillosilicate is complexolysis. We conclude that the Ca–Mg amendment had a positive effect on the functional richness of bacterial communities extracted from soil and on their potential to weather minerals that was present after several years.

Warming and increased precipitation frequency on the Colorado Plateau: implications for biological soil crusts and soil processes

Changes in temperature and precipitation are expected to influence ecosystem processes worldwide. Despite their globally large extent, few studies to date have examined the effects of climate change in desert ecosystems, where biological soil crusts are key nutrient cycling components. The goal of this work was to assess how increased temperature and frequency of summertime precipitation affect the contributions of crust organisms to soil processes. With a combination of experimental 2°C warming and altered summer precipitation frequency applied over 2 years, we measured soil nutrient cycling and the structure and function of crust communities. We saw no change in crust cover, composition, or other measures of crust function in response to 2°C warming and no effects on any measure of soil chemistry. In contrast, crust cover and function responded to increased frequency of summer precipitation, shifting from moss to cyanobacteria-dominated crusts; however, in the short timeframe we measured, there was no accompanying change in soil chemistry. Total bacterial and fungal biomass was also reduced in watered plots, while the activity of two enzymes increased, indicating a functional change in the microbial community. Taken together, our results highlight the limited effects of warming alone on biological soil crust communities and soil chemistry, but demonstrate the substantially larger effects of altered summertime precipitation.

Changes in enzyme activities and in the functional diversity of actinomycetes due to long term agricultural management

AbstractLong-term agricultural management alters soil organic matter, nutrient status, and potentially the decomposer community. We measured the abundance and activity of cellulose, chitin, and protease degrading bacteria, and total soil extra-cellular enzyme activity for cellulose (β-glucosidase), chitinase (N-acetyl-glucosaminidase), xylosidase, and phosphatase activity. By combining these methods, we could determine how bacterial decomposer abundance and function were altered by long-term management, and how the bacterial decomposer community relates to overall soil enzyme activity. We also measured microbial total fungal and bacterial biomass, soil organic carbon pools, and extractable nitrogen for supplementary comparisons. Soil samples were taken in June of 2010 from the Bad Lauchstädt field station’s Static Fertilization Experiment, under treatment for 108 years. Treatments include mineral (NPK) fertilizer (none or added at 140, 60, and 230 kg ha-1 yr-1) and manure addition (none, 20 T ha-1 2yr-1, and 30 T ha-1 2yr-1) in a full factorial experiment. We found that total cellulase activity and the abundance of cellulase degrading bacteria were higher in plots with manure addition. We observed the same pattern for total phosphatase activity, total chitinase activity, and the abundance of chitin degrading bacteria, although the trend was not statistically significant for total chitinase activity. These results suggest that long-term management does alter decomposition and that total soil enzyme activity reflects the abundance of decomposer bacteria.

Potential and limitations of ozone for the removal of ammonia, nitrite, and yellow substances in marine recirculating aquaculture systems

The high levels of water-reuse in intensive recirculating aquaculture systems (RAS) require an effective water treatment in order to maintain good water quality. In order to reveal the potential and limitations of ozonation for water quality improvement in marine RAS, we tested ozone's ability to remove nitrite, ammonia, yellow substances and total bacterial biomass in seawater, considering aspects such as efficiency, pH-dependency as well as the formation of toxic ozone-produced oxidants (OPO). Our results demonstrate that ozone can be efficiently utilized to simultaneously remove nitrite and yellow substances from process water in RAS without risking the formation of toxic OPO concentrations. Contemporaneously, an effective reduction of bacterial biomass was achieved by ozonation in combination with foam fractionation. In contrast, ammonia is not oxidized by ozone so long as nitrite and yellow substances are present in the water, as the dominant reaction of the ozone-based ammonia-oxidation in seawater requires the previous formation of OPO as intermediates. The oxidation of ammonia in seawater by ozone is basically a bromide-catalyzed reaction with nitrogen gas as end product, enabling an almost complete removal of ammonia-nitrogen from the aquaculture system. Results further show that pH has no effect on the ozone-based ammonia oxidation in seawater. Unlike in freshwater, an effective removal of ammonia even at pH-values as low as 6.5 has been shown to be feasible in seawater. However, as the predominant reaction pathway involves an initial accumulation of OPO to toxic amounts, we consider the ozone-based removal of ammonia in marine RAS as risky for animal health and economically unviable.

Effect of Extracellular DNA Destruction by DNase I on Characteristics of Forming Biofilms

Biofilm formation plays a crucial role in the development of different infections. This study was designed to examine the effects of extracellular DNA destruction by DNase I on characteristics of forming bacterial biofilms. We have found that extracellular matrix of biofilms formed in the presence of DNase I contains extracellular DNA fragments of about 30 kb. These data support the idea that cell-free DNA is constantly released to the extracellular matrix of bacterial biofilms. Our results indicate that extracellular DNA plays an important role in the properties of forming biofilms. Biofilms formed in the presence of DNase I (5.0 microg/mL) displayed reduced biofilm biomass, total bacterial biomass, decreased viability of bacteria, and decreased tolerance to antibiotics. The fact that destruction of extracellular DNA in forming biofilms by DNase I leads to the formation of an altered microbial community with decreased tolerance to environmental factors suggests the possibility to change the characteristics of forming biofilms by modifying cell-free DNA.

Metagenomic analysis reveals a marked divergence in the structure of belowground microbial communities at elevated CO2

Understanding the responses of biological communities to elevated CO2 (eCO2) is a central issue in ecology, but little is known about the influence of eCO2 on the structure and functioning (and consequent feedbacks to plant productivity) of the belowground microbial community. Here, using metagenomic technologies, we showed that 10 years of field exposure of a grassland ecosystem to eCO2 dramatically altered the structure and functional potential of soil microbial communities. Total microbial and bacterial biomass were significantly increased at eCO2, but fungal biomass was unaffected. The structure of microbial communities was markedly different between ambient CO2 (aCO2) and eCO2 as indicated by detrended correspondence analysis (DCA) of gene-based pyrosequencing data and functional gene array data. While the abundance of genes involved in decomposing recalcitrant C remained unchanged, those involved in labile C degradation and C and N fixation were significantly increased under eCO2. Changes in microbial structure were significantly correlated with soil C and N contents and plant productivity. This study provides insights into potential activity of microbial community and associated feedback responses of terrestrial ecosystems to eCO2.

Soil life in reconstructed ecosystems: Initial soil food web responses after rebuilding a forest soil profile for a climate change experiment

Disrupting ecosystem components, while transferring and reconstructing them for experiments can produce myriad responses. Establishing the extent of these biological responses as the system approaches a new equilibrium allows us more reliably to emulate comparable native systems. That is, the sensitivity of analyzing ecosystem processes in a reconstructed system is improved by excluding the period when observed phenomena are primarily responses caused by establishing the experiment rather than effects of imposed treatments; achieved by determining the extent of any pulse of activity caused by preparatory procedures. A native forest soil was physically disrupted when it was collected, sieved, and then rebuilt in lysimeters in a controlled-environment study evaluating the influence of elevated atmospheric CO 2 concentration and elevated atmospheric temperature on the reconstructed soil that was planted with Douglas-fir ( Pseudotsuga menziesii Mirb. Franco) seedlings. Generally, soil food web populations responded in two phases during the exposure as indicated by preliminary evaluation of the 4.5-year dataset. Also, previous work indicated that relatively elevated soil CO 2 effluxes occurred during the first phase, suggesting that food web populations may have responded to carbon sources made available when the soil was harvested and its profile reconstructed in the lysimeters. Results are presented for bacterial and fungal biomass, numbers of protozoa and nematodes to gain insight on whether the first phase responses are attributable to the acute stress of physically disrupting the soil. We found clear relationships between changes in predator and prey populations. A prominent spike for many of the food web populations occurred the year after the climate exposures began. Except for total bacterial biomass and total fungal-hyphae biomass, overall food web responses generally were unrelated to treatments. It appears that initial food web population responses were related to increased availability of soil carbon caused by establishing the experiment. Our results provide insights into determining the length of time to maintain reconstructed forest ecosystems before responses are observed related to experimental treatments. It appears that as long as 3 years elapsed before the soil food web appeared to recover from the acute physical disturbance; 1 year of recovery prior to commencing the climate exposures to allow the soil to rest after it was reconstructed, plus approximately the first 2 years of maintaining the climate treatments. Accounting for consequences of such periods of adjustment is critical for forecasting whether comparable natural ecosystems will be net sources or sinks of elevated concentrations of atmospheric CO 2.

Spatiotemporal distribution and activity patterns of bacteria from three phylogenetic groups in an oligomesotrophic lake

We explored the seasonal and vertical patterns of cell numbers, biomass, and amino acid incorporation of three major phylogenetic groups of the bacterioplankton in an oligomesotrophic alpine lake. Throughout the year the numerically dominant bacteria in the oxygenated epilimnion were small Actinobacteria. The timing and vertical location of their spring peak coincided with that of the heterotrophic flagellates (HNF). A second maximum of the relative proportions of Actinobacteria occurred during an autumn bloom of the diatom Asterionella formosa. Betaproteobacteria were negatively related to HNF abundances and formed maximal numbers and biomass during the summer stratification in the increasingly oxygen‐depleted hypolimnion. Members of the Cytophaga‐Flavobacteria subclade (CF) of Bacteroidetes preferably inhabited the completely anoxic zone of the hypolimnion. The numerically dominant Actinobacteria contributed only little to total bacterial biomass, whereas Betaproteobacteria and the comparatively rare (albeit large) CF represented the bulk of the bacterial carbon pool. Amino acid incorporation was mainly observed in Actinobacteria and Betaproteobacteria. Actinobacteria showed a clear preference for amino acids other than leucine. These bacteria represented the most active biomass (with respect to amino acid uptake), whereas the opposite was the case for CF. The contrasting vertical and seasonal patterns suggest that the three phylogenetic groups to some extent represent different functional compartments of the bacterioplankton.

Spatiotemporal distribution and activity patterns of bacteria from three phylogenetic groups in an oligomesotrophic lake

We explored the seasonal and vertical patterns of cell numbers, biomass, and amino acid incorporation of three major phylogenetic groups of the bacterioplankton in an oligomesotrophic alpine lake. Throughout the year the numerically dominant bacteria in the oxygenated epilimnion were small Actinobacteria. The timing and vertical location of their spring peak coincided with that of the heterotrophic flagellates (HNF). A second maximum of the relative proportions of Actinobacteria occurred during an autumn bloom of the diatom Asterionella formosa. Betaproteobacteria were negatively related to HNF abundances and formed maximal numbers and biomass during the summer stratification in the increasingly oxygen-depleted hypolimnion. Members of the Cytophaga-Flavobacteria subclade (CF) of Bacteroidetes preferably inhabited the completely anoxic zone of the hypolimnion. The numerically dominant Actinobacteria contributed only little to total bacterial biomass, whereas Betaproteobacteria and the comparatively rare (albeit large) CF represented the bulk of the bacterial carbon pool. Amino acid incorporation was mainly observed in Actinobacteria and Betaproteobacteria. Actinobacteria showed a clear preference for amino acids other than leucine. These bacteria represented the most active biomass (with respect to amino acid uptake), whereas the opposite was the case for CF. The contrasting vertical and seasonal patterns suggest that the three phylogenetic groups to some extent represent different functional compartments of the bacterioplankton.

Abundance, production and stabilization of microbial biomass under conventional and reduced tillage

Soil tillage practices affect the soil microbial community in various ways, with possible consequences for nitrogen (N) losses, plant growth and soil organic carbon (C) sequestration. As microbes affect soil organic matter (SOM) dynamics largely through their activity, their impact may not be deduced from biomass measurements alone. Moreover, residual microbial tissue is thought to facilitate SOM stabilization, and to provide a long term integrated measure of effects on the microorganisms. In this study, we therefore compared the effect of reduced (RT) and conventional tillage (CT) on the biomass, growth rate and residues of the major microbial decomposer groups fungi and bacteria. Soil samples were collected at two depths (0–5 cm and 5–20 cm) from plots in an Irish winter wheat field that were exposed to either conventional or shallow non-inversion tillage for 7 growing seasons. Total soil fungal and bacterial biomasses were estimated using epifluorescence microscopy. To separate between biomass of saprophytic fungi and arbuscular mycorrhizae, samples were analyzed for ergosterol and phospholipid fatty acid (PLFA) biomarkers. Growth rates of saprophytic fungi were determined by [ 14C]acetate-in-ergosterol incorporation, whereas bacterial growth rates were determined by the incorporation of 3H-leucine in bacterial proteins. Finally, soil contents of fungal and bacterial residues were estimated by quantifying microbial derived amino sugars. Reduced tillage increased the total biomass of both bacteria and fungi in the 0–5 cm soil layer to a similar extent. Both ergosterol and PLFA analyses indicated that RT increased biomass of saprophytic fungi in the 0–5 cm soil layer. In contrast, RT increased the biomass of arbuscular mycorrhizae as well as its contribution to the total fungal biomass across the whole plough layer. Growth rates of both saprotrophic fungi and bacteria on the other hand were not affected by soil tillage, possibly indicating a decreased turnover rate of soil microbial biomass under RT. Moreover, RT did not affect the proportion of microbial residues that were derived from fungi. In summary, our results suggest that RT can promote soil C storage without increasing the role of saprophytic fungi in SOM dynamics relative to that of bacteria.

New image analysis tool to study biomass and morphotypes of three major bacterioplankton groups in an alpine lake

We present an image analysis routine to de- termine the contribution of distinct morphotypes to the total abundance and biomass (carbon) of freshwater bac- terioplankton and to the fraction of cells detected by fluorescence in situ hybridization via catalyzed reporter deposition (CARD-FISH). The method was tested on bacterial assemblages from an alpine lake (Piburger See, Austria) at characteristic time points during the lim- nological year. Although on average 51% of 4',6'-di- amidino-2-phenylindole (DAPI)-stained objects were hy- bridized with the oligonucleotide probe EUB I-III, we detected on average 80% of total biomass determined from DAPI staining. The assemblage was numerically dominated by cocci and rods <0.6 µm (mean cell volume = 0.024 µm 3 ). Only a minor part of these morphotypes could be hybridized (18 and 50%, respectively). In con- trast, larger rods (0.087 µm 3 ), cocci (0.155 µm 3 ) and vibrio-shaped cells (0.073 µm 3 ) showed much higher probabilities to be detected by CARD-FISH. These mor- photypes per se formed the highest contribution to total biomass, which explained the high detection efficiency of biomass with CARD-FISH. In addition, we determined the seasonal dynamics of morphotype distributions within 3 distinct phylogenetic lineages. Actinobacteria were predominately small rods and cocci, whereas bac- teria from the Cytophaga -Flavobacterium-Bacteroides group formed mainly large rods, cocci and filaments. Be- taproteobacteria showed the highest morphological vari- ability. Within all lineages, distinct spatio-temporal dy- namics of dominant morphotypes were observed. Thus, the approach presented here will allow for more detailed studies of the amount of carbon bound by different bac- terial taxa. This is of relevance as distinct lineages can contribute much more to total bacterial biomass than to total bacterioplankton abundance.

Transformation of nitrogen compounds and dynamics of microbial biomass in fresh casts of Aporrectodea caliginosa

A comparative assessment of the contents of total nitrogen, ammonium, nitrates, and fungal and bacterial biomasses and of the activity of nitrogen transformation in fresh casts of Aporrectodea caliginosa and in a soddy-podzolic soil was performed. The total content of nitrogen in the casts was similar to or slightly higher than that in the soil; the content of inorganic forms of nitrogen in the casts was significantly higher than in the soil. The intensities of ammonification, nitrification, and denitrification and the pool of microbial biomass with a predominance of fungi during the 1.5-week-long incubation were also significantly higher in the casts. The activity of nitrogen fixation in the casts was lower than that in the soil. In the course of the incubation, the values of these parameters in the casts became closer to those in the soil. The inhibition of fungi in the casts with cycloheximide resulted in an increasing content of inorganic nitrogen and a higher activity of denitrification. In our opinion, this phenomenon is related to the fact that limitation of the fungal growth decreases the intensity of immobilization of nitrates and the fungal competition with denitrifying bacteria for available carbon. It was supposed that the activation of the fungal growth via application of plant substrates into the soil with a high population density of earthworms could suppress the emission of gaseous nitrogen compounds. The soil processing by earthworms had a positive effect on the soil properties.

Disruption of biofilms from sewage pipes under physical and chemical conditioning

Biofilms grown inside two sewage collecting pipes located in industrial and residential areas are studied. Bacterial biomass inside three layers of biofilms was evaluated. Biofilm cohesion under different mixing rate and ionic strength was also investigated. Effects of physical and chemical parameters in the biofilms were evaluated by monitoring turbidity, chemical and biochemical oxygen demands. Extracted organic matter from biofilms was partitioned to polar, aromatic and saturated fractions using activated silica column chromatography. Results revealed that bacterial biomass growth depending on biofilm thickness and stratification. The most loaded stratum in bacterial biomass was the sewage-biofilm interface stratum that represented 51% of the total bacterial biomass. Stirring rate and ionic strength of mono- and bivalent salts showed a major influence in biofilm disruption. The stirring time enhanced the exchange dynamic and matter capture between biofilm fragments at the critical stirring rate 90 r/min. Sodium chloride showed the dispersing effect on biofilms in suspension, and decreased the BOD5 (biochemical oxygen demand) beyond the physiological salt concentration.

Seasonal to hour variation scales in abundance and production of total and particle-attached bacteria in the open NW Mediterranean Sea (0–1000 m)

Abstract. We present the vertical and temporal dynamics of total vs. particle-attached bacterial abundance and activity over a 5 week period under summer to autumn transition in NW Mediterranean Sea. At a weekly time scale, total bacterial biomass and production in the euphotic layers was significantly correlated with phytoplanktonic biomass. At an hourly time scale, total bacterial biomass responded very rapidly to chlorophyll a fluctuations, suggesting a tight coupling between phytoplankton and bacteria for resource partitioning during the summer-autumn transition. In contrast, no influence of diel changes on bacterial parameters was detected. Episodic events such as coastal water intrusions had a significant positive effect on total bacterial abundance and production, whereas we could not detect any influence of short wind events whatever the magnitude. Finally, we show that particle-attached bacteria can represent a large proportion (up to 49%) of the total bacterial activity in the euphotic layer but display rapid and sporadic changes at hourly time scales. In the mesopelagic layers, bacterial abundance and production linearly decreased with depth, except some production peaks at 400–750 m. This study underlines the value of large datasets covering different temporal scales to clarify the biogeochemical role of bacteria in the cycling of organic matter in open seawater.

Soil carbon sequestration and changes in fungal and bacterial biomass following incorporation of forest residues

Sequestering carbon (C) in forest soils can benefit site fertility and help offset greenhouse gas emissions. However, identifying soil conditions and forest management practices which best promote C accumulation remains a challenging task. We tested whether soil incorporation of masticated woody residues alters short-term C storage at forested sites in western and southeastern USA. Our hypothesis was that woody residues would preferentially stimulate soil fungal biomass, resulting in improved C use efficiency and greater soil C storage. Harvest slash at loblolly pine sites in South Carolina was masticated (chipped) and either (1) retained on the soil surface, (2) tilled to a soil depth of 40 cm, or (3) tilled using at least twice the mass of organics. At comparative sites in California, live woody fuels in ponderosa pine stands were (1) masticated and surface applied, (2) masticated and tilled, or (3) left untreated. Sites with clayey and sandy soils were compared in each region, with residue additions ranging from 20 to 207 Mg ha −1. Total and active fungal biomass were not strongly affected by residue incorporation despite the high input of organics. Limited response was also found for total and active bacterial biomass. As a consequence, fungal:bacterial (F:B) biomass ratios were similar among treatments at each site. Total soil C was elevated at one California site following residue incorporation, yet was significantly lower compared to surface-applied residues at both loblolly pine sites, presumably due to the oxidative effects of tilling on soil organic matter. The findings demonstrated an inconsequential effect of residue incorporation on fungal and bacterial biomass and suggest a limited potential of such practices to enhance long-term soil C storage in these forests.

Bactérias em sedimentos da região entre-marés da Baía de Guaratuba, Paraná, Brasil

Bacteria in sea sediments play a fundamental role in organic matter decomposition, in several geochemistries transformations, in nutrient regeneration and as a nutritious source for the benthic fauna. Bacterial studies, in sediments of coastal environments, are important due to the intense anthropic activity in these areas. The objectives of the present research were to study in sediments of intertidal areas (sandy beaches and mangroves), of Guaratuba Bay: the variation of total heterotrophic bacteria, bacterial biomass, halophilic and halophobic heterotrophic bacteria, total coliforms, Escherichia coli, and the interrelation between biotic and abiotic factors. High values of total heterothrophic bacteria, bacterial biomass, total coliforms and E. coli were observed in two stations of sandy sediment intensely impacted, located close to the oldest area of Guaratuba city. In the inner stations, located in mangrove areas, high values of halophilic and halophobic aerobic cultivable bacteria, total coliforms and E. coli were also observed. The results show that high values, mainly of total heterothrophic bacteria, total coliforms and E. coli can also be found in polluted sandy sediments. Therefore, we suggest that microbiological analyses of sediments to be mandatory in the legislation for monitoring balneability and/or for the cultivation of organisms that may be subject of raw consumption.