Biology subjects

Spencer, N.

Publications and source records attributed to Spencer, N..

3 recordsLinked to original sources

bioRxiv2023

Persistent enrichment of multidrug resistant Klebsiella in oral and nasal communities during long-term starvation

The human oral and nasal cavities can act as reservoirs for opportunistic pathogens capable of causing acute infection. These microbes asymptomatically colonize the human oral and nasal cavities which facilitates transmission within human populations via the environment, and they routinely possess a clinically-significant antibiotic-resistance genes. Among these opportunistic pathogens, the Klebsiella genus stands out as a notable example, with its members frequently linked to nosocomial infections and multidrug resistance. As with many colonizing opportunistic pathogens, how Klebsiella transitions from an asymptomatic colonizer to a pathogen remains unclear. Here, we explored a possible explanation by investigating the ability of oral and nasal Klebsiella to outcompete their native microbial community members under in vitro starvation conditions, which could be analogous to external hospital environments. When Klebsiella was present within a healthy human oral or nasal sample, the bacterial community composition shifted dramatically under starvation conditions and typically became dominated by Klebsiella. Furthermore, introducing K. pneumoniae exogenously into a native microbial community lacking K. pneumoniae, even at low inoculum, led to repeated dominance under starvation. K.pneumoniae strains isolated from healthy individuals oral and nasal cavities also exhibited resistance to multiple classes of antibiotics and were genetically similar to clinical and gut isolates. In addition, we found that in the absence of Klebsiella, other understudied opportunistic pathogens, such as Peptostreptococcus, dominate under starvation conditions. Our findings establish an environmental circumstance that allows for the outgrowth of Klebsiella and other opportunistic pathogens. The ability to outcompete other commensal bacteria and to persist under harsh environmental conditions may contribute to the colonization-to-infection transition of these opportunistic pathogens.

microbiology↗

bioRxiv2023

No Transcriptional Compensation for Extreme Gene Dosage Imbalance in Fragmented Bacterial Endosymbionts of Cicadas

Bacteria that form long-term intracellular associations with host cells lose many genes, a process that often results in tiny, gene-dense, and stable genomes. Paradoxically, the same evolutionary processes that drive genome reduction and simplification may also sometimes cause genome expansion and complexification. A bacterial endosymbiont of cicadas, Hodgkinia cicadicola, exemplifies this paradox. In many cicada species, a single Hodgkinia lineage with a tiny, gene-dense genome has split into several interdependent cell and genome lineages. Each new Hodgkinia lineage encodes a unique subset of the ancestral unsplit genome in a complementary way, such that the collective gene contents of all lineages sum to the total found in the ancestral single genome. This splitting process creates genetically distinct Hodgkinia cells that must function together to carry out basic cellular processes, but also creates a gene dosage problem where some genes are encoded by only a small fraction of cells while others are much more abundant. Here, by sequencing DNA and RNA of Hodgkinia from different cicada species with different amounts of splitting - along with those of its structurally stable, unsplit partner endosymbiont Sulcia muelleri - we show that Hodgkinia does not transcriptionally compensate to rescue the wildly unbalanced gene and genome ratios that result from lineage splitting. We also find evidence that Hodgkinia has a reduced capacity for basic transcriptional control independent of the splitting process. Collectively, these findings reveal another layer of degeneration that further pushes the limits of canonical molecular and cell biology in Hodgkinia, and may in part explain its propensity to go extinct through symbiont replacement. SignificanceMany cicadas host two bacterial endosymbionts, Hodgkinia and Sulcia, which produce essential amino acids missing from the insects xylem sap diet. Following 100+ million years of strict host association, both bacteria have lost many genes and posses extremely tiny genomes. In some cicadas, Hodgkinia has split into multiple cell lineages, distributing its genes, with little respect to their function, among separate lineages present at (sometimes wildly) different abundances. We find no transcriptional response to this in Hodgkinia, resulting in similarly imbalanced mRNA abundances. We also find less control of transcription in Hodgkinia compared to Sulcia. Hodgkinias transcriptome embodies an extreme, even relative to other highly-reduced endosymbionts, and raises questions about how cell biology in multi-lineage Hodgkinia can function at all.

evolutionary biology↗

bioRxiv2020

Activation of MrgprA3 and MrgprC11 on bladder-innervating afferents induces peripheral and central hypersensitivity to bladder distension

Understanding the sensory mechanisms innervating the bladder is paramount to developing efficacious treatments for chronic bladder hypersensitivity conditions. The contribution of Mas-gene-related G protein-coupled receptors (Mrgpr) to bladder signalling is currently unknown. Here we show in mice with single-cell RT-PCR that sub-populations of dorsal root ganglion (DRG) neurons innervating the mouse bladder express MrgprA3 (14%) and MrgprC11 (38%), either individually or in combination, with high levels of co-expression with Trpv1 (81-89%). Calcium imaging studies demonstrated MrgprA3 and MrgprC11 agonists (chloroquine, BAM8-22 and neuropeptide FF) activated sub-populations of bladder-innervating DRG neurons, showing functional evidence of co-expression between MrgprA3, MrgprC11 and TRPV1. In ex vivo bladder-nerve preparations chloroquine, BAM8-22 and neuropeptide FF all evoked mechanical hypersensitivity in sub-populations (20-41%) of bladder afferents. These effects were absent in recordings from Mrgpr-cluster{Delta}-/- mice. In vitro whole-cell patch clamp recordings showed that application of an MrgprA3/C11 agonist cocktail induced neuronal hyper-excitability in 44% of bladder-innervating DRG neurons. Finally, in vivo instillation of an MrgprA3/C11 agonist cocktail into the bladder of wild-type mice induced a significant activation of dorsal horn neurons within the lumbosacral spinal cord, as quantified by pERK-immunoreactivity. This MrgprA3/C11 agonist-induced activation was particularly apparent within the superficial dorsal horn and the sacral parasympathetic nuclei of wild-type, but not Mrgpr-cluster{Delta}-/- mice. This study demonstrates, for the first time, functional expression of MrgprA3 and MrgprC11 in bladder afferents. Activation of these receptors is not required for normal bladder function but does trigger hypersensitivity to distension, a critically valuable factor for therapeutic target development. Significance statementDetermining how bladder afferents become sensitized is the first step in finding effective treatments for common urological disorders such as overactive bladder and interstitial cystitis/bladder pain syndrome. Here we show that two of the key receptors, MrgprA3 and MrgprC11, that mediate itch from the skin are also expressed on afferents innervating the bladder. Activation of these receptors results in sensitization of bladder afferents, resulting in sensory signals being sent into the spinal cord that prematurely indicate bladder fullness. Targeting bladder afferents expressing MrgprA3 or MrgprC11 and preventing their sensitisation may provide a novel approach for treating overactive bladder and interstitial cystitis/bladder pain syndrome.

neuroscience↗