7th joint conference "Joint Microbiology & Infection Conference 2024" of the DGHM and VAAM

Chair

Prof. Dr.

Abstract: Legionella are natural inhabitants of building plumbing biofilms (e.g. shower hoses), where interactions with other microorganisms influence their survival, proliferation, and death. Their interactions with their surrounding microbiome remain poorly understood. Here, we investigated the associations of Legionella with prokaryotic and eukaryotic microbiomes in biofilm samples extracted from 85 shower hoses of a single residential building. We used specific ddPCR quantification as well as general 16S rRNA and 18S rRNA amplicon sequencing to characterize the shower hose microbiomes. Sequencing data revealed a complex prokaryotic and eukaryotic microbiome in all samples. Legionella spp. relative abundance in the biofilms ranged between 0 - 7.8%, of which only 0 - 0.46% was L. pneumophila. Our data suggests that some microbiome members were associated with high Legionella relative abundance (e.g., Chthonomonas, Vrihiamoeba), while others were associated with low Legionella relative abundance (e.g., Aquabacterium, Vannella). Interestingly, the data analysis also revealed high genetic variability in the 16S rRNA sequences assigned to the genus Legionella (30 unique Amplicon Sequence Variants detected).  The correlations of the different Legionella variants with microbiome members showed distinct patterns, suggesting separate ecological niches potentially occupied by different Legionella species. This study provides insights into the ecology of Legionella with respect to: 1) the colonization of a high number of real shower hoses biofilm samples; 2) the ecological meaning of associations between Legionella and co-occurring prokaryotic/eukaryotic organisms; 3) the presence of multiple species of Legionella in building plumbing systems, and the potential of 16S rRNA based detection of Legionella diversity in the environment.

Legionella relative abundance in shower hose biofilms is associated with specific microbiome members

Invited Speaker

Invited Talk

Abstract: Running cold and hot water in buildings is a widely established commodity. Except for legionellae, little attention has been given to the microbiology of domestic hot-water installations (DHWIs). In many countries, regulations consider hot water as heated drinking water that must comply (cold) drinking water (DW) standards. Only few reports exist on the microbiome in DHWIs. The lack of both, information and hygienic regulations, asks for a broad microbiological investigation of DHWI. Using flow cytometric (FCM) total cell count (TCC) determination, FCM-fingerprinting, and 16S rRNA-gene-based metagenomic analysis, the characteristics and composition of bacterial communities in hot water from associated boilers was studied in 14 inhouse DW installations in Switzerland and Austria. At all locations, 1.3 to 8-fold enhanced TCC were recorded in hot water compared to the cold DW. FCM-fingerprints of cold and corresponding hot water indicated different composition of cold- and hot-water microbiomes. Also, hot water in each boiler had its own individual FCM-fingerprint. 16S-rRNA-gene-based community analysis confirmed the marked differences in microbiome composition. Generally, bacterial diversity in cold DW was broad, that in hot water was restricted, with thermophilic strains from the families Hydrogenophilaceae, Nitrosomonadaceae and Thermaceae dominating. Batch growth assays, consisting of heated cold DW and inoculated with hot water, resulted in immediate cell growth, suggesting hot-water boilers as autonomously operating, thermophilic bioreactors. When cold DW was used as inoculum no significant growth was observed. The generation of assimilable organic carbon from dissolved organic carbon due to heating appeared to be the driver for growth of thermophilic microbial communities in hot-water systems. Despite consumers have been exposed to hot-water microbiota for a long time, with the exception of Legionella, no major pathogens have so far been associated with hot-water use. The role of harmless thermophiles and their interaction with potential human pathogens at elevated temperatures in DHWIs remains to be investigated (see Water Research 253 (2024): 121109).

Active thermophilic bacterial communities thrive in domestic hot-water boilers

Abstract: Our knowledge on bacteria in drinking water is mainly limited to cold water (potable water cold, PWC). Bacteria in hot water (potable water hot, PWH) are understudied as routine diagnostics does typically not include incubation of nutrient agar plates with PWH samples at elevated temperatures like e.g. 50°C or 60°C. These temperatures would however be needed to enable growth and detection of thermotolerant bacteria that do not form colonies at 22°C or 36°C. Recently the bacterial diversity of PWH received more attention. We established a flow cytometry-based method to rapidly assess the heat tolerance of bacteria subjected to a heat gradient. The indirect viability criteria comprised maintenance of (1) cellular integrity, (2) enzymatic activity and (3) intracellular homeostasis when challenged with an acidic pH. When applied to different Legionella species, results demonstrated that the group of Legionella is highly diverse and that different Legionella differ greatly in their heat resistance. Legionella micdadei or representatives of Legionella pneumophila displayed a substantially greater resistance to heat than for example Legionella anisa or Legionella dumoffii. When applied to real water samples, bacteria in the hot water circulation displayed much greater thermotolerance than bacteria contained in cold drinking water. Also, the passage of PWC through a tube reactor kept at 36°C markedly increased the number of bacteria resistant to elevated temperatures. Apart from quickly assessing the heat tolerance of individual species or entire water microbiomes, the method is useful as a diagnostic guide when performing thermal disinfection and when being challenged with the question which temperature is needed and how long it should be maintained to achieve a satisfactory disinfection result. 

Some like it hot: how much heat do different Legionella species and bacteria in drinking water actually tolerate?

Professor

<strong>The Hidden Virosphere likely drives the microbial community and their functions in the pristine groundwater</strong>

Microbial Ecology & Evolution

<p>The ocean contains 1010 virus-like particles (VLP) per liter, vastly outnumbering host cells. Viruses significantly affect nutrient cycling by lysing 20-40% of bacteria daily, reprogramming host cells and promoting horizontal gene transfer (1029 genes/day). Playing a vital role in carbon fluxes, including carbon transport to the deep sea, contributing to marine ecosystem stability amid climate change. Pristine groundwater is a vital drinking water source, yet we lack an understanding of its viral ecosystem. We examine virus diversity, ecological importance, and functional interactions in a two-year study of seven wells within a pristine groundwater system along a hillslope transect. From ~1.3 terabases of metagenomics data, we identified &gt;7 million virus contigs, resulting in 257,814 and 82,807 virus operational taxonomic units (vOTUs) of ≥5 kb or ≥10 kb, respectively, representing a ~22-fold increase compared to publicly available groundwater vOTUs (n=3,584, ≥10 kb). Taxonomic analysis revealed that 99% of Hainich groundwater viruses were species-level unique, even when compared to a global ocean dataset. Approximately 81% could be taxonomically classified, with 99% belonging to the Caudoviricetes class (tailed phages). Ecological analysis using read mapping demonstrated site-specific endemism in virus communities, evidenced by strong grouping based on the sampled groundwater wells (p-value &lt;0.001). Our host prediction analysis found that 88% of viruses infect 78% of microbes (1,275 MAGs) from the same sample, including ecologically important groups like Pastecibacteria (81%) and Proteobacteria (74%). Additionally, about 5% of viruses may reprogram ~38% of host pathways through auxiliary metabolic genes (5,883 AMGs found, 24 times more than the GOV v.1). For instance, GAPDH (K00134), which breaks down glucose for energy and carbon. Furthermore, additionally Nitrite Reductase (K15876) and Sulfate Adenylyltransferase (K00957) help groundwater microbes thrive in oxygen-depleted conditions. Overall, this research offers valuable insights into groundwater virus communities and the mitigation of human impacts on groundwater resources.</p>

Symposium
Microbial Dynamics in Drinking Water Supply

Appointment

Chair

Programme

SymposiumMicrobial Dynamics in Drinking Water Supply

Appointment

Chair

Programme

Symposium
Microbial Dynamics in Drinking Water Supply