Biology subjects

Schmalenberger, A.

Publications and source records attributed to Schmalenberger, A..

7 recordsLinked to original sources

bioRxiv2024

Cultivation conditions of leafy vegetables determine phyllosphere bacterial community structures and ultimately affect growth of L. monocytogenes post-harvest

Cultivation conditions including plant species, variety, cultivation method and seasonality are all at least co-factors of epiphytic growth of L. monocytogenes. Meanwhile, phyllosphere associated bacteria were found to influence colonisation of invading pathogens. Thus, the main objective of this study was to determine whether cultivation conditions are factors in the development of the bacterial phyllosphere community on leafy vegetables which consequently influences L. monocytogenes growth. Indeed, this study revealed that vegetable cultivation condition was a more influential determinant of phyllosphere development than plant species. Of the identified phyllosphere associated bacteria presence of Pseudomonadaceae had a positive correlation with L. monocytogenes populations on all tested produce. Yet, Pseudomonadaceae content appeared to be more important for L. monocytogenes growth on spinach F1 Trumpet. From day 7 to 9 of storage, Pseudomonadaceae increases on open field spinach F1 Trumpet were associated with L. monocytogenes largest increase (0.94 log10 cfu g-1), whereas Pseudomonadaceae content decreased for polytunnel spinach F1 Trumpet and the corresponding L. monocytogenes populations remained unchanged. Carnobacteriaceae were present on spinach F1 Trumpet from polytunnel but not on other spinach produce with higher associated L. monocytogenes growth. Pectobacteriaceae (genus Dickeya) increased for spinach F1 Trumpet polytunnel but decreased for other spinach produce with lower associated L. monocytogenes growth. Similarly, polytunnel rocket Esmee had an increasing relative abundance of Pectobacteriaceae whereas it remained constant for polytunnel rocket Buzz. Compared to summer spinach F1 Trumpet produce, winter produce had significantly greater Streptococcaceae content and was correlated with a decrease in L. monocytogenes growth. Finally, higher phyllosphere alpha diversity putatively limited L. monocytogenes growth. Ultimately, this study revealed that cultivation conditions determine bacterial phyllosphere community structure which consequently influences L. monocytogenes growth.

microbiology↗

bioRxiv2024

Bacterial community structure analysis on Listeria monocytogenes inoculated spinach leaves is affected by PCR based methods to exclude chloroplast co-amplification

Consumption of ready-to-eat leafy vegetables has increased in popularity due to their anticipated health benefits, but their consumption also poses a potential health risk in the form of foodborne pathogens. Listeria monocytogenes is a ubiquitous pathogen that has been regularly found on leafy vegetables including spinach. Growth determining factors go beyond plant species and cultivation practice and may include the phyllosphere bacteriome to affect the growth potential of L. monocytogenes. This study investigated the bacteriome of spinach leaves, stored under EURL challenge conditions for 9 days after inoculation with L. monocytogenes using two methods of excluding chloroplast co-amplification (COMPETE, BLOCK) at the PCR step as well as a post-PCR chloroplast sequence filter option (CONTROL). While all three approaches have demonstrated a change of bacterial communities over time, the pPNA based BLOCK approach resulted in greater diversity similarities to the CONTROL option. The COMPETE solution with a specifically designed primer to prevent chloroplast amplification had a strong underrepresentation of the Planctomycetota phylum and to a lesser extend underrepresentation of Chloroflexi and Verrucomicrobiota due to the inheritance of the selected primer region that allowed to deselect chloroplast co-amplification. However, the COMPETE approach had the lowest level of chloroplast co-amplification. Higher growth potential of L. monocytogenes from day 7 to 9 co-occurred with higher relative abundances of Pseudomonadaceae and lower numbers of Lactobacillales, suggesting that particular phylogenetic groups may support growth of L. monocytogenes. While chloroplast co-amplification with spinach in the present study was relatively modest and a purely filter based chloroplast removal was sufficient, other leafy vegetables may require one of the tested co-amplification prevention solutions. While the COMPETE solution in the present study was linked to some amplification bias, the approach may be useful when otherwise co-amplification is very high and the demonstrated BLOCK approach with pPNA is insufficient.

microbiology↗

bioRxiv2024

The impact of struvite and ash recycling-derived fertilizers on microbial phosphorus mobilization capabilities and community structure in a Lolium perenne field trial

Rock phosphate is a non-renewable primary source for mineral phosphorus (P) fertilizers that intensive agriculture is highly dependent on. To avoid P fertilizer shortages and limit negative environmental impacts, circular economy approaches are needed with recycling-derived fertilizer (RDF) applications such as struvites and ashese. Hence, a grassland field trial was conducted with four RDFs, two struvites (potato wastewater, municipal wastewater) and two ashes (poultry-litter ash, sewage-sludge ash) at a P application rate of 40 kg P ha-1 (n=5). The impact of the RDFs on the soil microbial P cycling community was compared to conventional mineral P-fertiliser and a P-free control. Topsoil samples were taken directly after Lolium perenne grass cuts at months three, fife and 15. Cultivable phosphonate and phytate utilizing bacteria, potential acid and alkaline phosphomonoesterase activity, and phoC and phoD copy numbers responded stronger to seasonal effects than treatment effects. No significant overall effect of the fertilizer application was detected in the beta diversity of the bacterial and fungal communities after 15 months, but individual phylogenetic groups were affected by the treatments. The ash treatments demonstrated some distinguishing results across the bacterial and fungal community, with significantly higher relative abundance of Firmicutes and Rokubacteria and lower relative abundance of Actinobacteriota. Sewage-sludge ash had significantly lowest abundances of genera Bacillus and Bradyrhizobium (month 15s) that are well known for their P cycling abilities. The struvite RDFs either positively influenced the P cycling microbial community or did not affect it at all, while demonstrating better tri-calcium phosphate solubilizing capabilities after the 3 months harvest. These findings indicate that struvites could be a suitable replacement for conventional P fertilizers in the future.

microbiology↗

bioRxiv2023

Short Term Impact of Recycling-Derived Fertilizers on Their P Supply for Perennial Ryegrass (Lolium perenne)

Phosphorus is a finite, essential macronutrient for agriculture. Various nutrient recycling technologies in waste streams management are currently under development in many European countries in order to alleviate the dependency of the EU on imports of non-renewable raw material for the production of mineral phosphorus fertilizers commonly used in agriculture. The resulting products such as struvites and ashes need to be assessed for their application as so-called recycling-derived fertilisers (RDF) in the agricultural sector prior to commercialisation. Albeit high phosphorus abundance in most soils, the phosphorus availability for plant growth promotion in the soil solution is usually low due to strong P sorption in soil and depends vastly on the microbial mobilisation capability of the soil. To investigate the impact of different phosphorus fertilizers on plant growth and the soil P cycling microbiota, a short-term pot trial was conducted over the period of 54 days. Lolium perenne (var. AberGreen) was grown with application of superphosphate (SP) as inorganic fertiliser, two ashes (poultry litter ash (PLA) and sewage sludge ash (SSA) and two struvites (municipal wastewater struvite (MWS) and commercial CrystalGreen(R) (CGS) in rates of 20 and 60 kg P ha-1 in four replicates. A P-free control (SP0) was also included in the trial. Post-harvest, a positive correlation between dry weight yield and struvite application was detected, struvite P also was higher readily available and ACP activity was significantly improved for struvites at the high P application rate. The ash RDFs showed a liming effect at 60 kg P ha-1, and PLA60 negatively affected ACP activity, while PLA20 had significantly lower phoD copy numbers. P mobilization from phosphonates and phytates was not affected, TCP solubilization was negatively affected by mineral SP fertilizer application at both P concentrations. Overall, the bacterial and phoD harbouring community were not strongly affected by the P fertilization in this study.

microbiology↗

bioRxiv2022

International spread of emerging multidrug-resistant Rhodococcus equi

The recently characterized multidrug-resistant clone of the animal and human zoonotic pathogen Rhodococcus equi, MDR-RE 2287, has been circulating among horse farms in the United States (US) since the early 2000s. Here, we report the first documented detection of the MDR-RE 2287 clone outside the US. The finding highlights the risk of MDR-RE spreading internationally with the movement of horses.

microbiology↗

bioRxiv2021

Linking plant growth promoting arbuscular mycorrhizal colonization with bacterial plant sulfur supply

Sulfur (S) exists in organically bound complexes ([~]95%), predominantly as sulfonates, and are not directly plant available. Specific soil bacteria can mobilise sulfonates but very little is known about these bacteria in the hyphosphere. Since mycorrhizal fungi support growth of the majority of land plants, hyphosphere desulfonating bacteria may be of substantial benefit to the plant host. This study analysed the effect of AM inoculation with Rhizophagus irregularis (former G. intraradices, Glomus) and a mix of six AM species (Mixed) on PGP, microbial communities and sulfonate mobilising bacteria with L. perenne, Agrostis stolonifera and Plantago lanceolata as plant hosts in bi-compartmental microcosms and A. stolonifera in PGP pot experiments. AM inoculation significantly increased plant growth, percentage root colonisation and the quantity of cultivable desulfonating bacteria in the hyphosphere over pre-inoculated soil for all plants. Community analysis via PCR-DGGE revealed significantly different bacterial and fungal communities post inoculation. Analysis of the sulfonate mobilising asfA gene revealed a significantly altered community and novel bacterial isolates with this important functional ability post-inoculation. The results demonstrate that AM inoculation increased plant biomass yield, AM root colonisation and altered bacterial and fungal community dynamics in the hyphosphere. AM inoculated microcosms had an increased abundance of desulfonating bacteria that may be beneficial for plant-S supply. Research highlightsO_LIInoculation with AM fungi was shown to promote plant growth and harbour larger populations of sulfonate mobilising bacteria. C_LIO_LIPost-inoculation hyphospheric bacterial and saprotrophic fungal communities were shown to differ significantly in composition and abundance. C_LIO_LIAnalysis of sulfonate mobilising bacteria revealed novel presumptive species in possession of the asfA gene associated with AM hyphae. C_LIO_LIAM inoculation was shown to significantly impact the asfA positive bacterial community composition. C_LI

microbiology↗

bioRxiv2021

The role of arbuscular mycorrhiza and organosulfur mobilizing bacteria in plant sulphur supply

AM fungi are enhancing growth and health of many land plants but only some of these beneficial mechanisms are well understood. This study aimed to uncover the role of bacteria colonising AM fungi in organically-bound sulfur (S) mobilisation, the dominant S pools in soil that are not directly available to plants. The effect of an intact AM symbiosis with access to stable isotope organo-34S enriched soils encased in 35 {micro}m mesh cores was tested in microcosms with Agrostis stolonifera and Plantago lanceolata. At 3 month intervals, the plant shoots were analysed for 34S uptake. After 9 months, hyphae and associated soil was picked from static (mycorrhizal) and rotating (severed hyphae) mesh cores and corresponding rhizosphere soil was sampled for bacterial analysis. AM symbiosis increased uptake of 34S from organo-34S enriched soil at early stages of plant growth when S demand appeared to be high. The static (mycorrhizal) treatments were shown to harbour larger populations of cultivable heterotrophs and sulfonate mobilising bacteria. Microbial communities were significantly different in the hyphosphere of mycorrhizal hyphae and hyphae not associated to plant hosts. Sulfate ester (arylsulfatase enzyme assay, atsA gene) and sulfonate mobilising activity (asfA gene) was altered by an intact AM symbiotic partnership which stimulated the genera Azospirillum, Burkholderia and Polaromonas. Illumina sequencing revealed that AM symbiosis led to community shifts, reduced diversity and dominance of the Planctomycetes and Proteobacteria. This study demonstrated that AM symbioses can promote organo-S mobilization and plant uptake through interaction with hyphospheric bacteria. Research highlightsO_LIAM hyphae enhanced uptake of organically bound 34S at early stages of growth. C_LIO_LIAM hyphosphere harboured a large population of organo-S desulfurizing bacteria. C_LIO_LIMicrobial communities significantly differed in rotating and static mesh cores. C_LIO_LIAM hyphae influenced bacterial sulfate ester and sulfonate mobilising activity. C_LIO_LIAM hyphae reduced bacterial diversity, increased Planctomycetes and Proteobacteria abundance. C_LI

microbiology↗