Environmental Microbiology Reports

Despite decades of research, the factors determining the sinking velocity of marine biogenic particles remain poorly constrained, and growing evidence suggests that particle composition and morphology are as important as size in determining particle fate. We compared characteristics of suspended and sinking particles at three depths below the mixed layer and within the layer of maximal flux attenuation during the decline of a Phaeocystis pouchetii bloom in the Labrador Sea using marine snow catchers. Biochemical and morphological characteristics of suspended and sinking particles always differed, with differences depending primarily on bloom stage, and depth accounting for comparatively less variation. Exopolymer particles played a key role, with the relative concentrations of transparent exopolymer particles consistently higher in the suspended than in the sinking particle fraction. In contrast, the partitioning of coomassie-stainable particles changed with the bloom stage, as a function of the Phaeocystis life cycle. Ballast minerals played a negligible role during the late-bloom and bloom-decline stages, and their relative importance increased during the non-bloom stage. The C:N ratio was lower in suspended than sinking particles, with differences in morphological measures depending on bloom stage. Our findings emphasize that export potential is driven not only by particle size, but also by bloom stage, which is closely linked to plankton community composition and plays a key role in the timing and magnitude of carbon flux in the upper mesopelagic. Further, this work highlights the important and diverse roles of exopolymers in regulating carbon flux.

Plant-associated bacteria can promote plant growth under saline conditions, but salinity-dependent changes in bacterial physiological traits remain insufficiently understood. Here, we isolated bacteria from seedlings of quinoa (Chenopodium quinoa Willd.) lines maintained under laboratory propagation for more than 30 years and evaluated their activity under saline conditions. A quinoa-associated Pantoea isolate, strain 6PN, promoted primary root elongation and whole-plant dry weight of Arabidopsis thaliana under salt stress, whereas no significant effect was observed under non-saline conditions. Comparative analyses with reference Pantoea agglomerans strains showed that strain 6PN exhibited salinity-responsive indole-3-acetic acid (IAA) production. Genome analysis identified a putative ipdC gene and additional genes related to stress responses, nutrient acquisition, polysaccharide biosynthesis and export, flagellar biosynthesis, and chemotaxis. Phylogenomic analysis indicated that strain 6PN was genomically distinct from representative Pantoea species examined here. In an Arabidopsis trench-plate assay, GFP-labeled strain 6PN was recovered from spatially separated plant tissues at higher levels than a GFP-labeled reference strain under saline conditions. These results identify strain 6PN as a quinoa-associated Pantoea isolate with salinity-responsive IAA production and plant growth-promoting activity under defined salt-stress conditions.

Syngas fermentation by carbon monoxide (CO)-utilising acetogens offers a sustainable route for converting gasified waste materials into value-added chemicals. In this study, we isolated a novel thermophilic CO-utilising bacterium, strain AZ2, from marine hydrothermal sediment collected on the island of Sao Miguel, Azores, Portugal. Strain AZ2 is an obligately anaerobic, spore-forming bacterium. Average nucleotide identity (ANI; 78.4-86.7%) and digital DNA-DNA hybridization (dDDH; 23.4-32.5 %) analyses indicate that strain AZ2 represents a novel species within a previously uncharacterised lineage represented by the GTDB placeholder genus UBA2545 in the Neomoorellaceae family. Strain AZ2 was able to grow fermentatively on CO, producing acetate. We further demonstrated that its closest isolated relatives - Thermanaeromonas toyohensis, T. burensis, and Thermanaeromonas sp. strain 9S - are capable of growing on CO, producing either acetate or hydrogen gas (H2). Additionally, we unveiled the genomic potential for CO utilisation within other members of the GTDB placeholder class DSM-521 (previously Moorellia) to which our isolate belongs, expanding the list of possible thermophilic CO-utilising acetogens. We propose that strain AZ2T represents the type strain of a novel genus and species, named Thermobium azorense gen. nov., sp. nov. (= DSM 121889T = JCM 39698T).

The present-day martian surface is generally considered inhospitable to life because of low atmospheric pressure, intense surface radiation, global desiccation, and oxidizing chemistry which has been increasing since the late Noachian. However, shallow martian subsurface regions where mineralogy has shown groundwater movement may include localized hypersaline environments capable of retaining liquid water and supporting microbial metabolism. Haloferax volcanii, a model halophilic archaeon, has previously been shown to survive under low-pressure martian conditions (24 mbar) and to grow anaerobically supported by the Mars-relevant oxyanions nitrate and perchlorate under high-salinity conditions. Here, we investigated whether H. volcanii could actively grow under a combination of environmental and chemical conditions relevant to potentially habitable shallow subsurface martian lacustrine settings. Cultures were incubated for 160 days under anoxic, CO2-enriched, low-pressure conditions (24 mbar) in hypersaline liquid media supplemented with nitrate or perchlorate. Growth was observed in all low-pressure treatments and was confirmed by increases in optical density and biological reduction of nitrate and perchlorate. Scanning electron microscopy revealed extensive biofilm formation in low-pressure cultures, and Raman spectroscopy demonstrated the persistence of carotenoid biosignatures after prolonged incubation under martian conditions. Water loss remained below 4% across all treatments, indicating long-term stability of hypersaline brines throughout the experiment. These results demonstrate for the first time that a halophilic archaeon is capable of active growth and metabolism under a Mars-relevant combination of low pressure, high salinity, anoxia, and oxidizing chemistry, providing experimental support for the potential habitability of localized shallow subsurface martian environments. ImportanceThe search for cellular life is a major objective of future Mars exploration. While many studies have examined whether microorganisms can survive under martian conditions, far fewer have demonstrated active growth and metabolism. Here, we document Haloferax volcanii as the first halophilic archaeon capable of active growth under a defined combination of Mars-relevant low atmospheric pressure, high salinity, anoxia, and oxidizing chemical conditions. These findings expand the current understanding of the environmental limits of microbial growth and provide experimental evidence that localized brine environments in the shallow martian subsurface could support active microbial metabolism, if suitable organics and liquid water are present. In addition, this study establishes a practical framework for cultivating halophilic microorganisms under low-pressure martian conditions and may help guide future efforts to detect, cultivate, and characterize potential extant life on Mars.

From Brazilian limestone caves, we isolated 29 bacteria utilizing phenol (23 bacteria), toluene (all bacteria), and/or benzene (all bacteria) as sole carbon sources. One isolate showed phosphate solubilization, while lipase/esterase activity occurred in two isolates; no amylase activity was detected, but 16 isolates ([~]55%) exhibited protease activity. Among them, Nocardioides sp. SF1 was selected for whole-genome sequencing due to its aromatic compound tolerance and protease activity. Additionally, catechol cleavage assays yielded unexpected purple pigmentation, suggesting non-canonical aromatic metabolism. Its high-quality draft genome (4.25 Mbp, 16 contigs, N50 of 887 kb) lacks canonical phenol hydroxylase but encodes alternative oxidation systems, phenylacetyl-CoA pathway, besides, desferrioxamine siderophore, biosurfactants, and phosphate solubilization, key adaptations for oligotrophic caves and biotechnologically interesting activities. Whole-genome comparisons (TYGS/GGDC, OrthoANI and k-mer) suggest potential new species. Lacks acquired antimicrobial resistance genes (ResFinder) and pathogenicity potential (PathogenFinder). Nocardioides sp. SF1 emerges as a non-pathogenic candidate for aromatic bioremediation and plant growth promotion in contaminated, nutrient-poor environments, highlighting cave actinobacterias unexplored biotechnological potential.

Streptomyces are abundant soil inhabitants with extensive secondary metabolism and antibiotic resistance traits. Yet, their ecological role in shaping soil antibiotic resistome dynamics remains understudied. Here, we investigated how two different bio-based fertilizers harbouring Streptomyces shaped soil resistome and mobilome by combining genome analysis of eight Streptomyces isolates to metagenomic profiling of soils before fertilization, within 48 hours after fertilizer application, and six weeks after. Streptomyces genomes showed linkages among antibiotic resistance genes, carbohydrate-active enzymes, and antibiotic-production-associated biosynthetic gene clusters, connecting resistance and biosynthesis to broader metabolic strategies. Relationships between carbon degradation and biosynthesis associated with specific enzyme families, indicating that carbon availability shapes secondary metabolism. We confirmed experimentally that antibacterial potential varied with carbon source, suggesting that microbial activity during manufacturing of the bio-based fertilizers may create localized selection pressures before fertilizers enter the soil. Fertilization with the studied materials induced modest but consistent shifts in resistome and mobilome without major changes in dominant taxa or overall bacterial abundances, indicating functional reorganization within soil communities. Diversity of antibiotic resistance genes and mobile genetic elements increased, whereas abundance changes were small. Mobile genetic element composition showed stronger responses that were associated with fertilizer inputs, Streptomyces abundance, and taxa linked to faecal and resistance sources. Together, our results show that bio-based fertilizers shape soil resistome primarily through ecological restructuring of resident soil communities, while carbon-dependent microbial activity within fertilizers may enrich resistance. These factors should be considered in manufacturing of bio-based fertilizer as well as in designing agricultural practices.

The contribution of predation between bacteria to microbial community dynamics in agricultural fields has hardly been investigated. Here. dynamics of general prokaryotes (GEP) and of the predators Bdellovibrionales (Bd) and Bacteriovoracales (Bac) (Bdellovibrio-and-Like Organisms, BALOs) were studied in two agricultural fields differing in organic and mineral input regimes, for one year. Season, but not fertilization, affected absolute sizes of GEP and of BALO communities. 16S rRNA gene community analysis identified numerous novel Bd and Bac lineages, with none of the dominant BALOs related to characterized isolates. A few dominant BALO amplicon sequence variants (ASVs) persisted year-round, whereas others showed seasonal- or treatment specific responses. GEP, Bd, and Bac ASV a-diversity was mostly influenced by season, with some changes due to fertilization in Bd, and Bac communities. Seasonal changes, site, and fertilization regimes influenced {beta}-diversity of GEP, Bd and Bac communities and determined the structure of BALO-gram-negative bacteria interaction networks, signaling that niche segregation acts at the microbiome-BALO interface. Accordingly, we suggest that shifts in GEP community structure triggered by environmental changes and agricultural practices cascade to BALO predators, in turn affecting BALO-microbiome interactions. These dynamics may be harnessed to manipulate the soil microbiome to benefit sustainable environmental and agricultural outcomes.

Endosymbiosis is widespread throughout the tree of life. Understanding how the transition of a bacterial endosymbiont from facultative to host-dependent obligate life occurs is an important question for defining the origin of endosymbiosis. A novel gram-positive bacillus, Brevibacillus sp. TJ4 was isolated from the nitrogen-fixing yeast Rhodotorula mucilaginosa JGTA-S1, which houses several endobacteria within its cells. TJ4 can survive independently of yeast but exhibits genomic and metabolic features characteristic of an evolving endosymbiont, slowly assuming a host-dependent, obligate lifestyle. The TJ4 genome contains several incomplete pathways for carbohydrate, amino acid, vitamin, and cofactor metabolism, which is reflected in its increased reliance on host-derived nutrients and auxotrophy compared with that of other Brevibacillus spp. Comparative genomics revealed widespread genome rearrangements, loss of synteny, and multiple cross-genus and inter-kingdom horizontal gene transfer (HGT) events in TJ4 compared to other Brevibacillus spp. These HGTs include the acquisition of genes from bacteriophages and co-resident endobacteria of JGTA-S1. One such horizontally acquired gene, Type II 3-dehydroquinate dehydratase (AroQ), appears to have originated from the Rhodotorula host itself. This acquisition functionally restores the shikimate pathway in strain TJ4, as evidenced by the phylogenetic placement of AroQ from TJ4 within the clade of fungal AroQ homologs. Potential exploitation of the host JGTA-S1 appears to be a probable mode of endosymbiosis of TJ4, an evolving endosymbiont that we named Brevibacillus rhodotorulae sp. nov.

Profiling microbiomes is an important way to understand the function and composition of communities in the wild, but natural microbiomes are often highly complex and often unamendable to experimentation to reveal cause and effect relationships. By using a small group of cultivable strains to represent those found in the wild, synthetic communities are one solution to this problem. Here we describe the MAize Rhizosphere Synthetic Community (MARSc), a genome-enabled 31-member bacterial community representative of the diversity found on the roots of maize grown in Iowa soils. This community is built around Pseudomonas putida KT2440, a model maize rhizosphere colonist and synthetic biology chassis. We characterized microbe-microbe interactions and biofilm formation of MARSc members in a variety of environmental contexts, finding that both behaviors are broadly controlled by nutrient levels. Genomic analysis and microbiome profiling of these organisms revealed that annotated biofilm genes (such as surface attachment and exopolysaccharide production) correlated to rhizosphere colonization, but neither trait correlated to in vitro biofilm formation. In vitro interactions assay findings were surprisingly consistent with co-correlations of rhizosphere abundance amongst MARSc members on roots. Finally, we found that when applied to the roots, MARSc can increase maize growth under nitrogen-limiting conditions. Altogether, MARSc is a useful tool for identifying some of the factors influencing rhizosphere microbiome assembly and will be a strong foundation for further work in this area.

Evidence from the Cassini mission confirmed that Saturn's moon Enceladus hosts a subsurface alkaline ocean where rock-water reactions may generate redox disequilibria capable of supporting microbial metabolisms. To investigate potential microbial survival under simulated Enceladus ocean conditions, we used thermodynamic modeling to develop a salt formulation consistent with one possible Enceladus ocean composition and supplemented it with putative microbial energy sources to create a growth medium. The medium was inoculated with samples from diverse ocean world analog environments on Earth to determine which microorganisms could persist under Enceladus-like conditions. The microorganisms persisting in this geochemically bounded medium were heterotrophic, metabolically versatile bacteria with low carbon requirements. Genomic and physiological analyses further showed the presence of multiple stress-response pathways, sodium- based bioenergetic systems, osmoregulation strategies, and other adaptations consistent with survival in alkaline, low-nutrient settings. These results suggest that some stress-tolerant heterotrophic bacteria may serve as useful model organisms for life in Enceladus' subsurface ocean. These findings demonstrate the value of geochemically modeled media as a framework for constraining habitability, identifying relevant biosignatures, and probing potential microbial survival strategies beyond Earth.

The soil priming effect plays an important role in the global carbon cycle. Although well-studied, the mechanisms behind it remain elusive. So far, studies measured the phenomenon at the bulk soil scale, neglecting that it arises from spatially explicit processes that take place at the microscale. Here, we present a novel approach using a microfluidic device to directly assess the response of soil microbes living on a patch of complex substrate to a pulse of easily available substrate. Using time-resolved fluorescence microscopy, we tracked motility, position, shape characteristics and attached biomass of green fluorescent protein expressing Bacillus subtilis cells living on a transparent carboxymethylcellulose substrate patch exposed to a pulse of growth medium with differing concentrations. Assessing CMC decomposition via Congo-Red staining after 42 days of incubations with constant observation, we observed increased decomposition upon addition of enough labile substrate, resembling a priming effect. The pulse triggered a transient increase in bacterial motility, indicating the formation of exploring and growing subpopulations respectively. We observed a concentration-dependent growth response, resulting in different behaviors. High concentrations led to high biomass and decomposition of CMC, however growth was quickly limited, possibly by depletion of necessary nutrients and waste accumulation. Intermediate concentration, however, resulted in a more sustained attached biomass, that showed evidence of spatial self-organization, leading to similar decomposition. We present a novel experimental model system to study the behavior of soil microbes decomposing complex substrate and provide a unique view into the response of such a population to a labile substrate pulse.

Lake Constance is a pre-Alpine, monomictic, oligotrophic lake situated at the southern end of Germany composed of two main water bodies: deep, oligotrophic Upper Lake Constance (ULC) and the shallow, more mesotrophic Lower Lake Constance (LLC). To date, no sequencing-based study exists of the seasonal succession of the microbial plankton in Lake Constance. Over one-year, microbial plankton communities were sampled biweekly from the top 20 m of the water column in both sites and separated into nanoplankton (NP) and picoplankton (PP). Communities were analysed using rDNA amplicon sequencing: NP samples were analysed by 18S rDNA, and PP samples by 18S and 16S rDNA sequencing. Temporal community diversity was compared between sites and the effect of two major environmental perturbations, winter vertical mixing in ULC and oxygen depletion of the bottom-water layer in LLC, on the community was examined. Despite strong environmental contrasts, microbial plankton communities exhibited conserved seasonal temporal dynamics across basins. In contrast, pronounced compositional shifts occurred during mixing and oxygen depletion events. Approximately 20% of detected taxa were positively associated with these events, with log fold changes reaching 9.82, reflecting rare or undetectable taxa outside these periods. Taxa favoured by these perturbations commonly exhibited high metabolic flexibility, including mixotrophy, fermentation, or anaerobic respiration, or possessed functional traits conferring tolerance to altered redox and mixing regimes. Our results suggest that the temporal dynamics of freshwater microbial plankton communities are driven by deterministic processes and highlight the profound impact of large, and less known, environmental changes on these communities.

Nutritional symbionts can be essential for their animal hosts. The bacterial symbiont of the leaffooted bug, Leptoglossus zonatus, Caballeronia, is acquired from the environment each generation in the 2nd instar. The symbiont is critical for L. zonatus: aposymbiotic bugs are unable to reproduce. We hypothesized that symbiotic bugs excrete Caballeronia where juveniles might find and consume them. We inoculated L. zonatus with GFP-labelled Caballeronia and examined feces of each life stage. We found that Caballeronia is excreted almost exclusively in the adult stage. We then asked if 2nd instar nymphs could acquire Caballeronia from feces. Nymphs were provided with a) feces from adults fed GFP-labelled Caballeronia, b) GFP-Caballeronia in culture, or c) water only. We found that feces-fed bugs had similar rates of symbiont acquisition to those fed Caballeronia in culture, indicating that feces can be a source of Caballeronia for L. zonatus. However, compared to culture fed individuals, bugs fed feces had reduced survivorship and required longer to develop, and surviving adults had reduced mass. Bacterial motility assays showed that in contrast to cultured Caballeronia cells, Caballeronia in feces were non-motile. These results show suggest that feces can be a source of Caballeronia, at least in some environments, however transmission mode can influence success of the offspring.

In marine ecosystems, phytoplankton growth is frequently limited by iron, a micronutrient, due to its poor solubility from major sources such as atmospheric dust. Many phytoplankton cannot access dust-bound iron independently, and processes that solubilize this iron remain poorly understood. Here, we investigated whether bacterial partners can enhance phytoplankton growth under iron-limited conditions by facilitating utilization of dust-bound iron. Our study focused on Phaeodactylum tricornutum, a model diatom that is adapted to low iron growth conditions, grown in co-culture with bacteria isolated from its phycosphere. In iron-limited experiments using mineral dust as the sole iron source, the addition of Marinobacter significantly enhanced diatom growth compared to axenic controls, whereas Stappia significantly suppressed it. However, under iron-replete conditions, neither bacterium affected growth. These results indicated that under low-iron conditions, Marinobacter actively alleviates iron deficiency. Co-cultured bacterial cell abundances remained at least an order of magnitude lower than diatom cells. Marinobacter also enhanced algal growth within days of dust addition to established Fe-limited co-cultures, indicating its beneficial effect on P. tricornutum was not unique to a system in which it was newly introduced. Exometabolomic profiling comparing the axenic diatom and co-cultures revealed a suite of condensed aromatic organosulfur and peptide-like compounds associated with bacterial presence, as well as compounds that appeared to be unique to each co-culture, hinting at a molecular underpinning of each strains impact. Our findings demonstrate that low-abundance members of the phycosphere community can have a significant impact on host growth by modulating the accessibility of dust-bound Fe.

Freshwater salinization is of increasing concern for integrity and functioning of freshwater habitats worldwide. Experiments so far often have studied drastic salt additions, while gradient designs have been performed less commonly. We tested the effect of freshwater salinization in a mesocosm exposing the plankton community of the oligotrophic Lake Lunz, Austria, to a four-fold salinization gradient (control, 0.2, 1, a 5 ppt salt). Salinity was manipulated in a factorial design with enrichment, with 10 g L-1 and 30 g L-1 phosphorus, resulting in 8 treatments with 3 replicates each. We followed the effects of salinization on diversity, community composition and resource use over 36 days. Community composition was assessed by amplicon sequencing, Diversity loss and community turnover followed upon salt addition. All levels of salinization caused pronounced changes in community composition, with 5 ppt causing the most drastic changes. Salinization caused trophic downgrading by kicking out especially protistan consumers and rotifers, while some green algae and chrysophytes were especially tolerant, resulting in reduced phylogenetic and functional diversity with increasing salinization. In line with reduced top down control, salinization affected temporal variability in chlorophyll-a (chl-a) and resource use (RUE), with higher salinity causing more extreme fluctuations in chl-a and RUE. Enrichment overall aggravated salinization, enhancing temporal turnover and temporal fluctuations in resource use.

Microbial fuel cells (MFCs) technology offers sustainable electricity production. Current research largely focuses on few select model organisms, therefore the true prevalence of exoelectrogenesis amongst bacteria remaining largely unknown. We present a broad-scale survey of monomicrobial electricity production among environmental bacterial isolates inoculated in MFCs, using model organism Shewanella oneidensis MR-1 as a benchmark. Of the assessed taxa, 11-22% displayed exoelectrogenic activity, exceeding current predictions and identifying a further three novel exoelectrogenic species. Phylogenetic analysis based on the 16S sequences enabled the evolutionary relationship between isolates to be visualised, revealing that exoelectrogenesis is non-randomly distributed and phylogenetically conserved. Polarisation studies were implemented, revealing that numerous electron transfer mechanism were being utilised to perform exoelectrogenesis. The results of this study imply that bacterial electricity production is more widespread amongst culturable bacteria than previously estimated, with implications for bioprospecting novel exoelectrogens and predicting electrogenic activity in diverse microbial communities.

Although the roles of host-associated microbiomes in animal health are increasingly recognised, the factors influencing their variation remain understudied. The relatively simple microbiome of honey bees is a relevant system to address this gap. In particular, the relationship between variations in microbiome composition and the ectoparasite Varroa destructor, the main threat to honey bee health worldwide, is poorly established. In this study, we used metagenomic and statistical analyses of 1442 European honey bee colonies to investigate the relationships between the honey bee microbiome, temporality, location, V. destructor load, and behavioural response to its infestation by the host. While season, year, and location were identified as the main drivers of microbiome variation, V. destructor load emerged as a significant factor associated with microbiome variation. Notably, we identify several pathogens and opportunists that correlated positively with V. destructor load, while the core symbiont Bombilactobacillus correlated negatively. This is compatible with a shift in the microbiome toward dysbiosis, which may be driven by or promote V. destructor parasitism. By contrast, we found only limited evidence of an association between the microbiome and resistance behaviours of the host against this parasite. While the study cannot establish causal relationships, we present the largest metagenomic analysis of honey bee microbiomes to date, providing robust, generalisable evidence about the factors driving variation in the microbiome composition of this ecologically and economically important pollinator. These findings may serve as additional markers in selective breeding programs targeting V. destructor resistance, which could ultimately improve honey bee health.

Crop species may shape soil chemical properties and root-associated microbiota, but direct comparisons between contrasting crops remain limited. We compared soils and root-associated bacterial communities of Welsh onion (Allium fistulosum) and sweet potato (Ipomoea batatas) under the same field context. Sweet potato soil showed significantly lower electrical conductivity, inorganic nitrogen, and Mg saturation than control soil. Root-associated communities differed between crops, whereas alpha diversity did not. Proteobacteria-related taxa were more represented in Welsh onion roots, whereas Actinomycetia-related taxa were more represented in sweet potato roots, providing a basis for future studies on crop-specific soil microbial management.

Pelagibacterales gMED is the dominant epipelagic genomospecies in the western Mediterranean Sea. We used the O-chain biosynthesis gene clusters, OBCs, as clonal barcodes to analyse strain-level population structure. In total, 385 OBC-defined clonal lineages were tracked across Mediterranean metagenomes spanning 14 years and depths from 5 to 90 m within the photic zone, with between 128 and 336 detected per metagenome. The relative conservation of dominant OBC types across years, seasons, and geographic locations indicated a persistently high and stable clonal diversity.

Soil harbours a wide diversity of microbes responsible for essential functions, such as depolymerizing the C and N in organic matter through the production of exoenzymes. Some of these exoenzymes are universal, whereas others are specific to certain microbes. We hypothesized that higher microbial alpha diversity is associated with greater depolymerization capacity, specifically for protein and cellulose depolymerization, which will result in more N being mineralized. We therefore diluted two soil microbial communities, one from a forest soil and one from an agricultural soil, to create a diversity gradient. After nine weeks, we transferred these communities to a synthetic soil in which microbial necromass was the only nitrogen source. Before the transfer and two weeks after, we quantified protease, deaminase and {beta}-glucosidase potential activity, characterized the bacterial and fungal communities, and measured the quantity of nitrogen mineralized. The dilution had very little effect on the processes measured, with no clear trend. For identical alpha diversity values, some communities had high process rates, while other not. It appeared that these communities varied widely, a side effect of the dilution approach, and that this variation was significantly linked to process rates. This shows that community composition (beta diversity) is more strongly related to enzymatic potential and mineralization than species richness (alpha diversity) following necromass addition. In conclusion, the relationship between diversity and depolymerization of microbial necromass is not simply a matter of a linear decrease along with diversity but is rather linked to how reduced diversity results in more stochastic microbial communities. Highlights- Community composition (beta diversity) influence more microbial necromass depolymerization than species richness - Abundance of specific microbes explained ammonification and nitrification processes - Mineralization rates is different between crop and forest soil