Filamentation and biofilm formation are regulated by the phase-separation capacity of network transcription factors in Candida albicans.

The ability of the fungus Candida albicans to filament and form biofilms contributes to its burden as a leading cause of hospital-acquired infections. Biofilm development involves an interconnected transcriptional regulatory network (TRN) consisting of nine transcription factors (TFs) that bind both to their own regulatory regions and to those of the other network TFs. Here, we show that seven of the nine TFs in the C. albicans biofilm network contain prion-like domains (PrLDs) that have been linked to the ability to form phase-separated condensates. Construction of PrLD mutants in four biofilm TFs reveals that these domains are essential for filamentation and biofilm formation in C. albicans. Moreover, biofilm PrLDs promote the formation of phase-separated condensates in the nuclei of live cells, and PrLD mutations that abolish phase separation (such as the removal of aromatic residues) also prevent biofilm formation. Biofilm TF condensates can selectively recruit other TFs through PrLD-PrLD interactions and can co-recruit RNA polymerase II, implicating condensate formation in the assembly of active transcriptional complexes. Finally, we show that PrLD mutations that block the phase separation of biofilm TFs also prevent filamentation in an in vivo model of gastrointestinal colonization. Together, these studies associate transcriptional condensates with the regulation of filamentation and biofilm formation in C. albicans, and highlight how targeting of PrLD-PrLD interactions could prevent pathogenesis by this species.

Genotoxic Agents Produce Stressor-Specific Spectra of Spectinomycin Resistance Mutations Based on Mechanism of Action and Selection in Bacillus subtilis.

Mutagenesis is integral for bacterial evolution and the development of antibiotic resistance. Environmental toxins and stressors are known to elevate the rate of mutagenesis through direct DNA toxicity, known as stress-associated mutagenesis, or via a more general stress-induced process that relies on intrinsic bacterial pathways. Here, we characterize the spectra of mutations induced by an array of different stressors using high-throughput sequencing to profile thousands of spectinomycin-resistant colonies of Bacillus subtilis. We found 69 unique mutations in the rpsE and rpsB genes, and that each stressor leads to a unique and specific spectrum of antibiotic-resistance mutations. While some mutations clearly reflected the DNA damage mechanism of the stress, others were likely the result of a more general stress-induced mechanism. To determine the relative fitness of these mutants under a range of antibiotic selection pressures, we used multistrain competitive fitness experiments and found an additional landscape of fitness and resistance. The data presented here support the idea that the environment in which the selection is applied (mutagenic stressors that are present), as well as changes in local drug concentration, can significantly alter the path to spectinomycin resistance in B. subtilis.

Synthesized Geopolymers Adsorb Bacterial Proteins, Toxins, and Cells.

Pore-forming and hemolytic toxins are bacterial cytotoxic proteins required for virulence in many pathogens, including staphylococci and streptococci, and are notably associated with clinical manifestations of disease. Inspired by adsorption properties of naturally occurring aluminosilicates, we engineered inexpensive, laboratory-synthesized, aluminosilicate geopolymers with controllable pore and surface characteristics to remove pathogenic or cytotoxic material from the surrounding environment. In this study, macroporous and mesoporous geopolymers were produced with and without stearic acid surface modifications. Geopolymer binding efficacies were assessed by measuring adsorption of methicillin-resistant Staphylococcus aureus (MRSA) culture filtrate proteins, α-hemolysin and streptolysin-O toxins, MRSA whole cells, and antibiotics. Macroporous and mesoporous geopolymers were strong non-selective adsorbents for bacterial protein, protein toxins, and bacteria. Although some geopolymers adsorbed antibiotics, these synthesized geopolymers could potentially be used in non-selective adsorptive applications and optimized for adsorption of specific biomolecules.

Superior ion release properties and antibacterial efficacy of nanostructured zeolites ion-exchanged with zinc, copper, and iron.

Antimicrobial zeolites ion-exchanged with inexpensive transition metal ions (such as zinc, copper, and iron) are critically important for a broader adoption of the materials for public health applications. Due to the high surface area and small particle sizes, nanozeolites are particularly promising in enhancing the efficacy of the zeolite-based antimicrobial materials. By using highly-crystalline nanostructured zeolites (FAU) with textural mesoporosity, we report a comprehensive study on the materials characteristics of zinc-, copper-, and iron-ion exchanged nanozeolites, the ion release properties, and antibacterial efficacy against methicillin-resistant Staphylococcus aureus (MRSA), as well as a comparison of the properties to those obtained for the corresponding microsized zeolites. Superior ion release properties were observed for both zinc and copper ion-exchanged nanostructured zeolite X, with ion release up to 73% for zinc and 36% for copper of their initial loadings, as compared to 50% and 12%, respectively, for the corresponding microsized zeolites, validating the importance of nanostructuring for enhanced ion diffusion through zeolite pore channels. The 2 hours minimum bactericidal concentration (MBC) in saline for the copper ion-exchanged nanostructured zeolite X was 32 µg mL-1, half the corresponding microsized zeolite X MBC of 64 µg mL-1. Our results established nanostructured zeolite X as a superior host material for metal ion-based antimicrobials, with the aforementioned improvements for copper-exchanged nanozeolites compared to previous studies.