Advancing Our Functional Understanding of Host-Microbiota Interactions: A Need for New Types of Studies

Four Novel Caudoviricetes Bacteriophages Isolated from Baltic Sea Water Infect Colonizers of Aurelia aurita

The moon jellyfish Aurelia aurita is associated with a highly diverse microbiota changing with provenance, tissue, and life stage. While the crucial relevance of bacteria to host fitness is well known, bacteriophages have often been neglected. Here, we aimed to isolate virulent phages targeting bacteria that are part of the A. aurita-associated microbiota. Four phages (Pseudomonas phage BSwM KMM1, Citrobacter phages BSwM KMM2-BSwM KMM4) were isolated from the Baltic Sea water column and characterized. Phages KMM2/3/4 infected representatives of Citrobacter, Shigella, and Escherichia (Enterobacteriaceae), whereas KMM1 showed a remarkably broad host range, infecting Gram-negative Pseudomonas as well as Gram-positive Staphylococcus. All phages showed an up to 99% adsorption to host cells within 5 min, short latent periods (around 30 min), large burst sizes (mean of 128 pfu/cell), and high efficiency of plating (EOP > 0.5), demonstrating decent virulence, efficiency, and infectivity. Transmission electron microscopy and viral genome analysis revealed that all phages are novel species and belong to the class of Caudoviricetes harboring a tail and linear double-stranded DNA (formerly known as Siphovirus-like (KMM3) and Myovirus-like (KMM1/2/4) bacteriophages) with genome sizes between 50 and 138 kbp. In the future, these isolates will allow manipulation of the A. aurita-associated microbiota and provide new insights into phage impact on the multicellular host.

Microbial Networks Reveal the Structure of Water Microbial Communities in Kalamaili Mountain Ungulate Nature Reserve

Water microorganisms contribute to the key components of ecosystems in dryland waters, which are extremely important for wildlife. However, the distribution patterns of water microbes across different basal water sources are still largely unknown. This study was conducted to compare microorganisms in the water bodies of different types of water sources in the Kalamaili Mountain Ungulate Nature Reserve in China. Bioinformatic analysis revealed that the undirected microbial co-existence network consisted of 15 main modules referring to different water sources, which indicated specific molecular co-existence relationships. It was found that the most dominant phyla (namely Proteobacteria, Patescibacteria, Firmicutes, Bacteroidota, and Actinobacteriota) of the molecular ecological network shared the same structures as the microbial community, which justified the construction of the network via a random network formation. Principal coordinate analysis (PCoA) based on Bray–Curtis distances revealed that there were still considerable variations among different habitats, showing separate sample clusters. Additionally, the different topological roles of subnetworks trimmed to a uniform size indicated different co-existence patterns in the microbiome. The artificially recharged water from concrete pond substrate (ARC) subnetworks had a relatively discrete co-occurrence, while the natural water sources (NRE) and artificially recharged water from earthen pond substrate (ARE) groups were more compact with giant modules. The NRE and ARE groups were also richer in microbial composition and had a higher number of species with low abundance. Consequently, concrete substrates may contribute to dysfunction in water microbiomes. Moreover, the functional diversity of the NRE and ARE groups is due to more intra-module connections and more inter-module connections, indirectly leading to a stable function resilient to external environmental influences. In conclusion, the microecology of the NRE was more stable than that of the concrete substrate, and artificial transportation had less effect on the microbial community.

Proinflammatory Cytokines: Possible Accomplices for the Systemic Effects of Clostridioides difficile Toxin B

Clostridioides difficile infection (CDI) has a serious impact on the healthcare system, and most of its pathogenic effects are mainly due to the activity of toxins A and B (TcdA and TcdB, respectively). The molecular mechanisms of their cytotoxic activity are well known, especially in the colon, where the infection occurs and normally remains localized. However, the mechanisms causing toxic effects on various systemic organs (extraintestinal manifestations) with frequent lethal outcomes in some patients affected by CDI are still poorly understood. Few studies are available that demonstrate low serum levels of Tcds in both experimental animal models and patients with CDI. Until now, it has remained unclear how low levels of circulating Tcds could lead to serious toxic effects. On the basis of our previous in vitro studies, in which the proinflammatory cytokines TNF-alpha and IFN-gamma strongly potentiated the toxic activity of low doses of TcdB, we hypothesize that the presence of both TcdB in the circulation and a systemic proinflammatory cytokine storm may be responsible for the selective severe effects of TcdB in some patients. This may occur in patients with severe CDI and systemic Tcds, in whom proinflammatory cytokines such as TNF-alpha and IFN-gamma reach a significant concentration in the circulation. This hypothesis could identify therapeutic interventions based on the reduction or neutralization of the indirect toxic action of these cytokines.