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PubMed2006

In vitro degradation of the flavonol quercetin and of quercetin glycosides in the porcine hindgut.

The present study investigated the microbial degradation of the plant flavonol quercetin and its naturally occurring glycosides isoquercitrin and rutin in the porcine hindgut. The experiments were carried out with the semicontinuous colon-simulation technique. The fluid and particle phase of pig hindgut contents from freshly slaughtered animals were used for the in vitro incubations. Following a five-day equilibration period, quercetin, isoquercitrin or rutin were administered to fermentation vessels and their turnover rate was determined. None of the flavonols affected parameters of microbial fermentation like pH, redox potential or VFA production. The turnover rate for isoquercitrin was seven times higher than the turnover for the fermentation fluid. The turnover rates for quercetin and rutin were four and twofold higher than fluid turnover, respectively. After administration of isoquercitrin or rutin, their aglycone quercetin was detected as an intermediary metabolite. Under sterile conditions using autoclaved incubation fluids and hindgut contents, turnover rates for quercetin and rutin were still higher than the fluid turnover in the fermentation vessels. This indicates a certain chemical instability of the flavonols and/or adsorption to ingesta particles. Thus, flavonols are subjected to microbial metabolism in the porcine hindgut. The glycosidic structure strongly influences the rate of metabolism.

Adsorption↗
PubMed2001

Limitations of using delta 18O for the source identification of nitrate in agricultural soils.

The stable isotopic composition (delta 15N and delta 18O) of nitrate was analyzed in two lysimeter field experiments in order to identify the conditions under which the dual isotope approach can be applied to identify the main source of nitrate in agricultural soils. The first field experiment involved six lysimeters beneath fields that had been fertilized for 10 yr with the same type of fertilizer (NH4NO3; delta 15N = +1.2@1000, delta 18O = +18.6@1000). The isotope ratios of NO3- in the leachate (delta 15N approximately 0@1000; delta 18O approximately +2@1000) could not be interpreted in a conventional way with either fertilizer or soil organic nitrogen as main sources. These results provided clear evidence for the microbial immobilization and subsequent mineralization and nitrification to NO3- (mineralization-immobilization turnover concept). This process masked the original oxygen isotope ratio of the fertilizer source during the summer when microbial activity was high. A second experiment involving the application of Ca(NO3)2 to three lysimeters during the winter confirmed that the dual isotope approach remains valid for the source identification of nitrate under conditions of low microbial activity. The study reveals the limitation of the dual isotope approach to characterize nitrate sources under biologically active conditions and the ability to quantify microbial processes when the main sources can be controlled.

Agriculture↗
PubMed2006

Identification of bacterial micropredators distinctively active in a soil microbial food web.

The understanding of microbial interactions and trophic networks is a prerequisite for the elucidation of the turnover and transformation of organic materials in soils. To elucidate the incorporation of biomass carbon into a soil microbial food web, we added 13C-labeled Escherichia coli biomass to an agricultural soil and identified those indigenous microbes that were specifically active in its mineralization and carbon sequestration. rRNA stable isotope probing (SIP) revealed that uncultivated relatives of distinct groups of gliding bacterial micropredators (Lysobacter spp., Myxococcales, and the Bacteroidetes) lead carbon sequestration and mineralization from the added biomass. In addition, fungal populations within the Microascaceae were shown to respond to the added biomass after only 1 h of incubation and were thus surprisingly reactive to degradable labile carbon. This RNA-SIP study identifies indigenous microbes specifically active in the transformation of a nondefined complex carbon source, bacterial biomass, directly in a soil ecosystem.

Bacteria↗
PubMed1986

Influence of substrate and microbial interaction on efficiency of rumen microbial growth.

Microbial N produced in the rumen and flowing to the duodenum (Ni) is related to the total amount of OM fermented or apparently digested in the rumen (OMf). This relationship, best expressed as microbial N yield (gNi/kgOMf), is affected mainly by the physical and chemical properties of feed carbohydrates and the amounts ingested. These factors influence yields at three levels of increasing complexity: Bacterial fermentation within one compartment following the continuous culture model. Fermentation pattern as such does not seem to affect yields. High fermentation rates are associated with lactate production, low methane production and transient polysaccharide synthesis. These effects induce acidification and lower yields, partly compensated by faster growth. Protozoal action, determined by the presence of sequestration spaces provided mainly by roughage diets. The presence of protozoa depresses microbial N yield but allows more complete fibre digestion. Compartmentation and differential passage. With roughage diets, optimal microbial N yield seems to require well developed microbial compartmentation, involving a large proportion of microbes in a large-particle pool with a slow turnover, balanced by a small proportion in liquid, small-particle pools with a fast turnover. Such a situation is associated with long roughage feeding. It is hypothesized that microbial N yields in the rumen may vary between two extremes which are associated with the feeding of long roughage on the one hand or with concentrate (starch) feeding on the other.

Adenosine Triphosphate↗
PubMed2005

Soil resource availability impacts microbial response to organic carbon and inorganic nitrogen inputs.

Impacts of newly added organic carbon(C) and inorganic nitrogen (N) on the microbial utilization of soil organic matter are important in determining the future C balance of terrestrial ecosystems. We examined microbial responses to cellulose and ammonium nitrate additions in three soils with very different C and N availability. These soils included an organic soil (14.2% total organic C, with extremely high extractable N and low labile C), a forest soil (4.7% total organic C, with high labile C and extremely low extractable N), and a grassland soil (1.6% total organic C, with low extractable N and labile C). While cellulose addition alone significantly enhanced microbial respiration and biomass C and N in the organic and grassland soils, it accelerated only the microbial respiration in the highly-N limited forest soil. These results indicated that when N was not limited, C addition enhanced soil respiration by stimulating both microbial growth and their metabolic activity. New C inputs lead to elevated C release in all three soils, and the magnitude of the enhancement was higher in the organic and grassland soils than the forest soil. The addition of cellulose plus N to the forest and grassland soils initially increased the microbial biomass and respiration rates, but decreased the rates as time progressed. Compared to cellulose addition alone, cellulose plus N additions increased the total C-released in the grassland soil, but not in the forest soil. The enhancement of total C-released induced by C and N addition was less than 50% of the added-C in the forest soil after 96 d of incubation, in contrast to 87.5% and 89.0% in the organic and grassland soils. These results indicate that indigenous soil C and N availability substantially impacts the allocation of organic C for microbial biomass growth and/or respiration, potentially regulating the turnover rates of the new organic C inputs.

Analysis of Variance↗
PubMed1989

Microbial flora in the gastrointestinal tract abolishes cytostatic effects of alpha-difluoromethylornithine in vivo.

Although treatment with the ornithine decarboxylase inhibitor alpha-difluoromethylornithine (DFMO) leads to depletion of intracellular polyamines and to related growth inhibition in vitro, its cytostatic effects in vivo are disappointing. This may be due to abolition of DFMO-induced growth inhibition by polyamines released during normal body cell turnover, to dietary polyamines, or to putrescine synthesized by the microbial flora in the GI tract. We studied selectively (aerobic) and totally (aerobic + anaerobic) GI tract-decontaminated LI210-bearing mice fed with 3 types of diet differing in their polyamine and carbohydrate residue contents and treated with combinations of intraperitoneal DFMO and oral deuterium-labelled putrescine. Our data show that, irrespective of diet type, total decontamination markedly potentiates the moderate tumor growth inhibition that is caused by DFMO alone. During total decontamination, growth-inhibited L1210 cells accumulate in the G0/G1 phase of the cell cycle. Although orally administered deuterium-labelled putrescine gave rise to deuterium labelling of L1210 putrescine, spermidine and spermine, the polyamine levels in our diets played only a minor role.

Animals↗
PubMed2004

Phage community dynamics in hot springs.

In extreme thermal environments such as hot springs, phages are the only known microbial predators. Here we present the first study of prokaryotic and phage community dynamics in these environments. Phages were abundant in hot springs, reaching concentrations of a million viruses per milliliter. Hot spring phage particles were resistant to shifts to lower temperatures, possibly facilitating DNA transfer out of these extreme environments. The phages were actively produced, with a population turnover time of 1 to 2 days. Phage-mediated microbial mortality was significant, making phage lysis an important component of hot spring microbial food webs. Together, these results show that phages exert an important influence on microbial community structure and energy flow in extreme thermal environments.

Archaea↗
PubMedDate not supplied

Effects of local delayed hypersensitivity on the small intestine.

There are many T and B cells in the small intestinal mucosa and local T cell immunity could have a role both in protective immunity and as a cause of disease (i.e. hypersensitivity). This latter aspect has been investigated by using several animal models to assess the effects of local delayed hypersensitivity on the structure and function of the small intestine. Heterotopically transplanted grafts of fetal small intestine in mice (isografts and allografts) have been examined by conventional histology, scanning and transmission electron microscopy, by making direct measurements of villi, crypts, and lymphoid cell infiltrate, and by counting the number of mitoses per crypt. This cell-mediated immune reaction causes lymphocyte infiltration which is most marked in the lamina propria, hyperplasia of the crypts of Lieberkühn, increased cell loss with villous atrophy and a flat surface, but the individual enterocytes appear fairly normal. Graft-versus-host disease cause exactly the same changes in structure and in cell kinetics as does rejection. However, crypt hyperplasia has been found to precede villous atrophy by several days. Preliminary experiments on local contact hypersensitivity suggest that intraluminal injection of oxazolone in the gut of sensitized mice also produces villous atrophy and crypt hyperplasia. It is postulated that these effects are likely to be produced via lymphokines: by an 'enteropathic' factor which damages the lamina propria and basement membrane, and a factor which is mitogenic for crypt stem cells. In mice infected with Giardia lamblia, crypt hyperplasia and lymphocyte infiltration of the epithelium are present and there is accelerated epithelial cell turnover. In rats infected with Nippostrongylus brasiliensis, the flat mucosa has been shown to be due to the thymus-dependent immune response and not directly to the damage produced by the parasite itself. A common factor in the variety of conditions associated with villous atrophy and crypt hyperplasia may well be a local cell-mediated immune reaction to food, microbial, parasite or other antigens which causes changes in enterocyte turnover rate and malabsorption.

Animals↗
PubMed2004

Dynamics of a pasture soil microbial community after deposition of cattle urine amended with [13C]urea.

Within grazed pastures, urine patches are hot spots of nitrogen turnover, since dietary N surpluses are excreted mainly as urea in the urine. This short-term experiment investigated 13C uptake in microbial lipids after simulated deposition of cattle urine at 10.0 and 17.1 g of urea C m(-2). Confined field plots without or with cattle urine amendment were sampled after 4 and 14 days, and soil from 0- to 5-cm and 10- to 20-cm depths was analyzed for content and composition of phospholipid fatty acids (PLFAs) and for the distribution of urea-derived 13C among individual PLFAs. Carbon dioxide emissions were quantified, and the contributions derived from urea were assessed. Initial changes in PLFA composition were greater at the lower level of urea, as revealed by a principal-component analysis. At the higher urea level, osmotic stress was indicated by the dynamics of cyclopropane fatty acids and branched-chain fatty acids. Incorporation of 13C from [13C]urea was low but significant, and the largest amounts of urea-derived C were found in common fatty acids (i.e., 16:0, 16:1omega7c, and 18:1omega7) that would be consistent with growth of typical NH4(+)-oxidizing (Nitrosomonas) and NO2(-)-oxidizing (Nitrobacter) bacteria. Surprisingly, a 20 per thousand depletion of 13C in the cyclopropane fatty acid cy17:0 was observed after 4 days, which was replaced by a 10 to 20 per thousand depletion of that in cy19:0 after 14 days. Possible reasons for this pattern are discussed. Autotrophic nitrifiers could not be implicated in urea hydrolysis to any large extent, but PLFA dynamics and the incorporation of urea-derived 13C in PLFAs indicated a response of nitrifiers which differed between the two urea concentrations.

Animals↗
PubMed2026

Integrative machine learning models to unravel gut microbial dysbiosis and functional disruption in polycystic ovary syndrome.

OBJECTIVE: To study gut microbial diversity and metabolic pathway disruptions in women with PolyCystic Ovary Syndrome (PCOS) compared with healthy controls, and to evaluate the diagnostic potential of microbiome-driven machine learning models. DESIGN: Case-controlled metagenomic data analysis SUBJECTS: Gut metagenomic data from women diagnosed with PCOS and age-matched healthy female controls EXPOSURE: Presence of PCOS MAIN OUTCOME MEASURES: The primary outcome measures will include gut microbial alpha and beta diversity indices, microbial taxon abundance, functional pathway profiles, predicted metabolite levels, microbe-functional pathway-metabolite interaction networks, and the diagnostic accuracy of microbiome-based machine learning models. RESULTS: Alpha and beta diversity analyses revealed marked gut microbial dysbiosis in women with PCOS, despite comparable species richness to healthy controls. Differential abundance analysis identified 41 significantly altered microbial species, including enrichment of proinflammatory taxa, such as Bacteroides vulgatus and Ruminococcus gnavus, and depletion of beneficial commensals, including Roseburia hominis and Prevotella copri. These compositional shifts indicate a proinflammatory microbial community structure in PCOS. Functional profiling demonstrated the upregulation of pathways involved in nucleotide turnover, lipid and carbohydrate metabolism, and neurotransmitter synthesis, potentially contributing to metabolic and neuroendocrine disruption. Network analysis revealed fragmented and unstable microbial-metabolite associations in PCOS compared with cohesive networks in controls. Microbiome-based machine learning models achieved a diagnostic accuracy of 84.25% (area under the curve 0.93), underscoring their predictive potential. CONCLUSION: The gut microbiome in PCOS is characterized by a proinflammatory community structure and disrupted metabolic pathways. These findings demonstrate the diagnostic potential of microbiome-based models and underscore the gut microbiome as a promising target for therapeutic interventions in the management of PCOS.

Polycystic Ovary Syndrome↗
PubMed2026

Microbial decomposer diversity and metabolic function during the decomposition of brine shrimp carcasses in a saline lake.

BACKGROUND: Decomposition of brine shrimp carcasses has a crucial role in carbon cycling of saline lakes, yet the microbial dynamics remain poorly understood. RESULTS: Here we integrated metagenomics, metatranscriptomics, culturomics, metabolomics, and microcosm experiments to investigate microbial community succession and function during brine shrimp (Artemia sp.) carcass decomposition in Barkol Lake, a hypersaline lake in China. A total of 149 metagenome-assembled genomes (MAGs) and 77 pure culture genomes were recovered across 33 phyla, with 72.12% genomes representing species-level novel lineages. Our results reveal diverse bacterial and archaeal taxa, including novel lineages from CG03, T1Sed10-126 and rare archaeal taxa (Asgardarchaeota, Thermoplasmatota, Nanoarchaeota, and Halobacteriota), involved in degradation of biomacromolecules-proteins, carbohydrates, lipids, and nucleic acids-via extracellular hydrolysis, nutrient transport, and intracellular catabolism. These taxa exhibit substrate preferences, rapidly responding to the breakdown of polysaccharides and proteins, followed by lipids and nucleic acids. Hydrolyzed oligomers are further oxidized by various microbes through fermentation, sulfate reduction, and methanogenesis via metabolic handoffs. Additionally, viral auxiliary metabolic genes (AMGs) further enhance microbial host functions, contributing to key ecological processes such as carbon cycling and stress response. A temporally structured microbial decomposer network (MDN) was observed, driving mineralization cascades from fermentation to sulfate reduction and methanogenesis. CONCLUSIONS: This study reveals microbial metabolic handoffs and virus-mediated modulation as critical mechanisms for organic matter turnover, expanding the known diversity and function of decomposers in saline ecosystems. Our findings offer new insights into biogeochemical processes in saline lakes and highlight a synergistic microbial decomposer network involving bacteria, archaea, and viruses that collectively drive nutrient cycling during brine shrimp carcass decomposition. Video Abstract.

Animals↗
PubMed2005

Short term effects of ozone on the plant-rhizosphere-bulk soil system of young beech trees.

Plant growth largely depends on microbial community structure and function in the rhizosphere. In turn, microbial communities in the rhizosphere rely on carbohydrates provided by the host plant. This paper presents the first study on ozone effects in the plant-rhizosphere-bulk soil system of 4-year-old beech trees using outdoor lysimeters as a research platform. The lysimeters were filled with homogenized soil from the corresponding horizons of a forest site, thus minimizing field heterogeneity. Four lysimeters were treated with ambient ozone (1 x O3) and four with double ambient ozone concentrations (2 x O3; restricted to 150 ppb). In contrast to senescence, which was almost unaffected by ozone treatment, both the photochemical quantum yield of photosystem II (PSII) and leaf gas exchange were reduced (11 - 45 %) under the elevated O3 regime. However, due to large variation between the plants, no statistically significant O3 effect was found. Even though the amount of primary metabolites, such as sugar and starch, was not influenced by elevated O3 concentrations, the reduced photosynthetic performance was reflected in leaf biochemistry in the form of a reduction in soluble phenolic metabolites. The rhizosphere microbial community also responded to the O3 treatment. Both community structure and function were affected, with a tendency towards a lower diversity and a significant reduction in the potential nutrient turnover. In contrast, litter degradation was unaffected by the fumigation, indicating that in situ microbial functionality of the bulk soil did not change.

Carbohydrate Metabolism↗
PubMed2001

Long-term effects of intercropping and bio-litter recycling on soil biological activity and fertility status of sub-tropical soils.

On-farm field experiments were carried out at two sites having 38- and 10-year-old orchard cropping systems under sub-tropical climatic regions to evaluate changes in organic carbon accumulation and chemical and microbiological properties of the soils. Under a system of different intercropped fruit trees, the cultivation of coconut (Cocos nucifera L.) intercropped with guava (Psidium guajava L.) enhanced the soil microbial activity approximately 2-fold after 38 yrs over 10 yrs of the same intercropped system. Soil organic carbon increased from 3.4 to 7.8 and 2.4 to 6.2 g kg-1 after 38 and 10 yrs, respectively, following the establishment of orchards. The increase was attributed to greater recycling of bio-litters. Levels of dehydrogenase, phosphatase and soil microbial biomass under field conditions generally depended more on the nature of the cropping system than on soil types. Similarly, average carbon inputs of bio-litter to the soil in monocrop (0.98 Mg ha-1 yr-1) was less than intercropped fruit trees (2.07 Mg ha-1 yr-1). The average level of soil microbial biomass carbon was 1158 kg ha-1 (0-0.15 m depth) and the organic carbon turnover rate was 8.5 yr-1 after 38 yrs of intercropped fruit trees, which resulted in a lower ratio (1.81) of carbon inputs to soil microbial biomass carbon.

Agriculture↗
PubMed1995

Rates of elementary steps catalyzed by rat liver cytosolic and mitochondrial inorganic pyrophosphatases in both directions.

We have investigated kinetics of pyrophosphate synthesis and phosphate-water oxygen exchange catalyzed by rat liver cytosolic and mitochondrial pyrophosphatases in the presence of Mg2+ as cofactor. A common kinetic model derived for these reactions implies that they involve formation of enzyme-bound pyrophosphate and proceed through two parallel pathways: pathway I, utilizing two magnesium phosphate molecules, and pathway II, utilizing both magnesium phosphate and free phosphate. Pyrophosphate formation is greatly facilitated in the active sites of both pyrophosphatases ([E.PPi]/[E.2Pi] = 0.11-0.24) compared to solution. The rate constants for PPi binding/release, bound PPi hydrolysis/synthesis, and two Pi binding/release steps catalyzed by cytosolic and mitochondrial pyrophosphatases were enumerated for pathway I. There is no unique rate-limiting step for pathway I for both enzymes in either direction. A modulating effect of magnesium phosphate on the oxygen exchange is observed with the cytosolic pyrophosphatase, explicable in terms of an allosteric phosphate-binding site or random-order release of two phosphate molecules from the active site. A remarkable feature of these mammalian pyrophosphatases versus their microbial counterparts is their high efficiency in pyrophosphate synthesis. The turnover numbers in the direction of synthesis are 14 and 9.3 s-1 for the cytosolic and mitochondrial enzymes, respectively (9 and 16% relative to hydrolysis turnover numbers). The results demonstrate that the enzyme-catalyzed synthesis of pyrophosphate, the simplest high-energy polyphosphate, can proceed at a high rate in the absence of an external energy input, such as that provided by protonmotive force in membrane systems.

Animals↗
PubMed2005

Bacterial immobilization and remineralization of N at different growth rates and N concentrations.

An experiment was designed to resolve two largely unaddressed questions about the turnover of N in soils. One is the influence of microbial growth rate on mobilization and remineralization of cellular N. The other is to what extent heterotrophic immobilization of NO(3)(-) is controlled by the soil concentration of NH(4)(+). Bacteria were extracted from a deciduous forest soil and inoculated into an aqueous medium. Various N pool dilution/enrichment experiments were carried out to: (1) calculate the gross N immobilization and remineralization rates; (2) investigate their dependence on NH(4)(+)and NO(3)(-) concentrations; (3) establish the microbial preference for NH(4)(+)and NO(3)(-) depending on the NH(4)(+)/NO(3)(-) concentration ratio. Remineralization of microbial N occurred mainly at high growth rates and NH(4)(+) concentrations. There was a positive correlation between NH(4)(+) immobilization and remineralization rates, and intracellular recycling of N seemed to be an efficient way for bacteria to withstand low inorganic N concentrations. Thus, extensive remineralization of microbial N is likely to occur only when environmental conditions promote high growth rates. The results support previous observations of high NO(3)(-) immobilization rates, especially at low NH(4)(+) concentrations, but NO(3)(-) was also immobilized at high NH(4) concentrations. The latter can be understood if part of the microbial community has a preference for NO(3)(-) over NH(4)(+).

Bacteria↗
PubMed1964

INHIBITION OF PROTEIN SYNTHESIS IN MAMMALIAN CELL-FREE SYSTEMS BY CHLORAMPHENICOL.

Chloramphenicol can inhibit protein synthesis in mammalian cell-free systems as effectively as it inhibits protein synthesis in analogous microbial systems. Significant inhibition in mammalian systems was obtained only when protein synthesis was stimulated by the addition of template RNA to the system, there being comparatively little inhibition of protein synthesis by ribosomes in the absence of stimulatory RNA. It is postulated that chloramphenicol may inhibit the function of messenger or template RNA by successfully competing for ribosomal binding sites, thereby preventing the attachment of RNA to ribosomes. The apparent discrepancy in the sensitivity of mammalian and microbial cells to chloramphenicol may be related to differences in turnover or stability of ribosomal template RNA rather than to intrinsic differences in mechanism of protein synthesis. These observations are in accord with the suggestion that protein synthesis in intact mammalian cells may be susceptible to chloramphenicol inhibition only at the time that new messenger or template RNA is being deposited on ribosomes and that more mature cells may be resistant because informative RNA already deposited on ribosomes is not accessible to chloramphenicol inhibition. The inhibitory effect of chloramphenicol on protein synthesis in proliferating cells may be an important factor in hematologic toxicity attributable to chloramphenicol.

Animals↗
PubMed2001

Alpha- and beta-Proteobacteria control the consumption and release of amino acids on lake snow aggregates.

We analyzed the composition of aggregate (lake snow)-associated bacterial communities in Lake Constance from 1994 until 1996 between a depth of 25 m and the sediment surface at 110 m by fluorescent in situ hybridization with rRNA-targeted oligonucleotide probes of various specificity. In addition, we experimentally examined the turnover of dissolved amino acids and carbohydrates together with the microbial colonization of aggregates formed in rolling tanks in the lab. Generally, between 40 and more than 80% of the microbes enumerated by DAPI staining (4',6'-diamidino-2-phenylindole) were detected as Bacteria by the probe EUB338. At a depth of 25 m, 10.5% +/- 7.9% and 14.2% +/- 10.2% of the DAPI cell counts were detected by probes specific for alpha- and beta-Proteobacteria. These proportions increased to 12.0% +/- 3.3% and 54.0% +/- 5.9% at a depth of 50 m but decreased again at the sediment surface at 110 m to 2.7% +/- 1.4% and 41.1% +/- 8.4%, indicating a clear dominance of beta-Proteobacteria at depths of 50 and 110 m, where aggregates have an age of 3 to 5 and 8 to 11 days, respectively. From 50 m to the sediment surface, cells detected by a Cytophaga/Flavobacteria-specific probe (CF319a) comprised increasing proportions up to 18% of the DAPI cell counts. gamma-Proteobacteria always comprised minor proportions of the aggregate-associated bacterial community. Using only two probes highly specific for clusters of bacteria closely related to Sphingomonas species and Brevundimonas diminuta, we identified between 16 and 60% of the alpha-Proteobacteria. In addition, with three probes highly specific for close relatives of the beta-Proteobacteria Duganella zoogloeoides (formerly Zoogloea ramigera), Acidovorax facilis, and Hydrogenophaga palleroni, bacteria common in activated sludge, 42 to 70% of the beta-Proteobacteria were identified. In the early phase (<20 h) of 11 of the 15 experimental incubations of aggregates, dissolved amino acids were consumed by the aggregate-associated bacteria from the surrounding water. This stage was followed by a period of 1 to 3 days during which dissolved amino acids were released into the surrounding water, paralleled by an increasing dominance of beta-Proteobacteria. Hence, our results show that lake snow aggregates are inhabited by a community dominated by a limited number of alpha- and beta-Proteobacteria, which undergo a distinct succession. They successively decompose the amino acids bound in the aggregates and release substantial amounts into the surrounding water during aging and sinking.

Alphaproteobacteria↗