Constitutive expression of the Type VI Secretion System carries no measurable fitness cost in Vibrio cholerae.

The Type VI Secretion System (T6SS) is a widespread and highly effective mechanism of microbial warfare; it confers the ability to efficiently kill susceptible cells within close proximity. Due to its large physical size, complexity, and ballistic basis for intoxication, it has widely been assumed to incur significant growth costs in the absence of improved competitive outcomes. In this study, we precisely examine the fitness costs of constitutive T6SS firing in the bacterium Vibrio cholerae. We find that, contrary to expectations, constitutive expression of the T6SS has a negligible impact on growth, reducing growth fitness by 0.025 ± 0.5% (95% CI) relative to a T6SS- control. Mathematical modeling of microbial populations demonstrates that, due to clonal interference, constitutive expression of the T6SS will often be neutral, with little impact on evolutionary outcomes. Our findings underscore the importance of precisely measuring the fitness costs of microbial social behaviors and help explain the prevalence of the T6SS across Gram-negative bacteria.

Spatial constraints and stochastic seeding subvert microbial arms race.

Surface attached communities of microbes grow in a wide variety of environments. Often, the size of these microbial community is constrained by their physical surroundings. However, little is known about how size constraints of a colony impact the outcome of microbial competitions. Here, we use individual-based models to simulate contact killing between two bacterial strains with different killing rates in a wide range of community sizes. We found that community size has a substantial impact on outcomes; in fact, in some competitions the identity of the most fit strain differs in large and small environments. Specifically, when at a numerical disadvantage, the strain with the slow killing rate is more successful in smaller environments than in large environments. The improved performance in small spaces comes from finite size effects; stochastic fluctuations in the initial relative abundance of each strain in small environments lead to dramatically different outcomes. However, when the slow killing strain has a numerical advantage, it performs better in large spaces than in small spaces, where stochastic fluctuations now aid the fast killing strain in small communities. Finally, we experimentally validate these results by confining contact killing strains of Vibrio cholerae in transmission electron microscopy grids. The outcomes of these experiments are consistent with our simulations. When rare, the slow killing strain does better in small environments; when common, the slow killing strain does better in large environments. Together, this work demonstrates that finite size effects can substantially modify antagonistic competitions, suggesting that colony size may, at least in part, subvert the microbial arms race.

Sociomicrobiology: Coexistence of conflict and cooperation in the squid light organ.

The Hawaiian bobtail squid's Vibrio fischeri symbionts use quorum sensing for both bioluminescence and to modulate antagonism. New research finds quorum sensing unexpectedly represses V. fischeri's type 6 secretion system, highlighting intricate connections between cooperative and competitive microbial behaviors.

PANX3 Channels Regulate Architecture, Adhesion, Barrier Function, and Inflammation in the Skin.

The channel-forming glycoprotein PANX3 functions in cutaneous wound healing and keratinocyte differentiation, but its role in maintaining skin homeostasis through aging is not yet understood. We found that PANX3 is absent in newborn skin but becomes upregulated with age. We characterized the skin of global Panx3-knockout (KO) mice and found that KO dorsal skin showed sex differences at different ages but generally had reduced dermal and hypodermal areas compared with age-matched controls. Transcriptomic analysis of the KO epidermis revealed reduced E-cadherin stabilization and Wnt signaling compared with that of wild-type, consistent with the inability of primary KO keratinocytes to adhere in culture and diminished epidermal barrier function in KO mice. We also observed increased inflammatory signaling in the KO epidermis and a higher incidence of dermatitis in aged KO mice compared with that in wild-type controls. These findings suggest that during skin aging, PANX3 is critical in the maintenance of dorsal skin architecture, keratinocyte cell-cell and cell-matrix adhesion, and inflammatory skin responses.

Pannexin 1 binds ß-catenin to modulate melanoma cell growth and metabolism.

Melanoma is the most aggressive skin malignancy with increasing incidence worldwide. Pannexin1 (PANX1), a member of the pannexin family of channel-forming glycoproteins, regulates cellular processes in melanoma cells including proliferation, migration, and invasion/metastasis. However, the mechanisms responsible for coordinating and regulating PANX1 function remain unclear. Here, we demonstrated a direct interaction between the C-terminal region of PANX1 and the N-terminal portion of ß-catenin, a key transcription factor in the Wnt pathway. At the protein level, ß-catenin was significantly decreased when PANX1 was either knocked down or inhibited by two PANX1 blockers, Probenecid and Spironolactone. Immunofluorescence imaging showed a disrupted pattern of ß-catenin localization at the cell membrane in PANX1-deficient cells, and transcription of several Wnt target genes, including MITF, was suppressed. In addition, a mitochondrial stress test revealed that the metabolism of PANX1-deficient cells was impaired, indicating a role for PANX1 in the regulation of the melanoma cell metabolic profile. Taken together, our data show that PANX1 directly interacts with ß-catenin to modulate growth and metabolism in melanoma cells. These findings provide mechanistic insight into PANX1-mediated melanoma progression and may be applicable to other contexts where PANX1 and ß-catenin interact as a potential new component of the Wnt signaling pathway.

A 6-Year Experience of Laser Treatments for Burn Scars in a Regional Burn Center-Safety, Efficacy, and Quality Improvement.

Laser treatments have long been used as a treatment method for burn scars. Since 2012, more than 1800 laser treatments were performed at Lehigh Valley Health Network Burn Center, far exceeding any previous cohort in studies exploring laser treatments for burn scars. Although previous research has looked at improving scar appearance and physiology with laser treatments, very few have focused on safety. The purpose of the study was to determine whether laser treatments are a safe treatment option for burn scars. Four hundred and fourteen patients who had undergone at least one laser treatment in the outpatient burn center since 2012 were analyzed. Electronic medical records (EPIC) were reviewed. The data were entered in REDCap and later exported to Microsoft Excel and R Studio for statistical analysis. Most of the complications found were related to the moderate sedation during the procedures and were mild, ie, nausea. The most common adverse effect was prolonged recovery time, which can affect practice flow. The overall postoperative complication rate for laser treatments with and without moderate sedation was minimal at 2.2% and 1.4%, respectively. Pain during and after the procedure averaged 3.9 and 1.7, respectively, on a 1 to 10 scale. The Vancouver Scar Scale showed modest improvement in scar appearance over time with an average improvement of 1.4. The high variability of the Vancouver Scar Scale observed in this series underlines its lack of sensitivity. The study results show that laser treatments for burn scars in the outpatient setting generally are safe for patients in need of burn scar intervention. Some practice flow adjustments need to be taken into consideration when offering these procedures in an outpatient setting.

An autoinhibitory mechanism controls RNA-binding activity of the nitrate-sensing protein NasR.

The ANTAR domain harnesses RNA-binding activity to promote transcription attenuation. Although several ANTAR proteins have been analyzed by high-resolution structural analyses, the residues involved in RNA-recognition and transcription attenuation have not been identified. Nor is it clear how signal-responsive domains are allosterically coupled with ANTAR domains for control of gene expression. Herein, we examined the sequence conservation of ANTAR domains to find residues that may associate with RNA. We subjected the corresponding positions of Klebsiella oxytoca NasR to site-directed alanine substitutions and measured RNA-binding activity. This revealed a functionally important patch of residues that forms amino acid pairing interactions with residues from NasR's nitrate-sensing NIT domain. We hypothesize these amino acid pairing interactions are part of an autoinhibitory mechanism that holds the structure in an "off" state in the absence of nitrate signal. Indeed, mutational disruption of these interactions resulted in constitutively active proteins, freed from autoinhibition and no longer influenced by nitrate. Moreover, sequence analyses suggested the autoinhibitory mechanism has been evolutionarily maintained by NasR proteins. These data reveal a molecular mechanism for how NasR couples its nitrate signal to RNA-binding activity, and generally show how signal-responsive domains of one-component regulatory proteins have evolved to exert control over RNA-binding ANTAR domains.

Overexpressed HSF1 cancer signature genes cluster in human chromosome 8q.

BACKGROUND: HSF1 (heat shock factor 1) is a transcription factor that is found to facilitate malignant cancer development and proliferation. In cancer cells, HSF1 mediates a set of genes distinct from heat shock that contributes to malignancy. This set of genes is known as the HSF1 Cancer Signature genes or simply HSF1-CanSig genes. HSF1-CanSig genes function and operate differently than typical cancer-causing genes, yet it is involved in fundamental oncogenic processes. RESULTS: By utilizing expression data from 9241 cancer patients, we identified that human chromosome 8q21-24 is a location hotspot for the most frequently overexpressed HSF1-CanSig genes. Intriguingly, the strength of the HSF1 cancer program correlates with the number of overexpressed HSF1-CanSig genes in 8q, illuminating the essential role of HSF1 in mediating gene expression in different cancers. Chromosome 8q21-24 is found under selective pressure in preserving gene order as it exhibits strong synteny among human, mouse, rat, and bovine, although the biological significance remains unknown. Statistical modeling, hierarchical clustering, and gene ontology-based pathway analyses indicate crosstalk between HSF1-mediated responses and pre-mRNA 3' processing in cancers. CONCLUSIONS: Our results confirm the unique role of chromosome 8q mediated by the master regulator HSF1 in cancer cases. Additionally, this study highlights the connection between cellular processes triggered by HSF1 and pre-mRNA 3' processing in cancers.