A Noncanonical Role for Yersiniabactin in Bacterial Copper Acquisition

Interspecific cross-talk: The catalyst driving microbial biosynthesis of secondary metabolites

Microorganisms co-exist and co-evolve in nature, forming intricate ecological communities. The interspecies cross-talk within these communities creates and sustains their great biosynthetic potential, making them an important source of natural medicines and high-value-added chemicals. However, conventional investigations into microbial metabolites are typically carried out in pure cultures, resulting in the absence of specific activating factors and consequently causing a substantial number of biosynthetic gene clusters to remain silent. This, in turn, hampers the in-depth exploration of microbial biosynthetic potential and frequently presents researchers with the challenge of rediscovering compounds. In response to this challenge, the coculture strategy has emerged to explore microbial biosynthetic capabilities and has shed light on the study of cross-talk mechanisms. These elucidated mechanisms will contribute to a better understanding of complex biosynthetic regulations and offer valuable insights to guide the mining of secondary metabolites. This review summarizes the research advances in microbial cross-talk mechanisms, with a particular focus on the mechanisms that activate the biosynthesis of secondary metabolites. Additionally, the instructive value of these mechanisms for developing strategies to activate biosynthetic pathways is discussed. Moreover, challenges and recommendations for conducting in-depth studies on the cross-talk mechanisms are presented.

A dual-emission polymer carbon nanoparticles for ratiometric and visual detection of pH value and bilirubin

Herein, we prepared a novel fluorescent polymer carbon nanoparticles by polymerizing dopamine (DA) and o-phenylenediamine (OPD) through oxidation of hydrogen peroxide. In a neutral environment, the synthesized fluorescent polymer carbon nanoparticles (PDA-OPD) exhibited two emission peaks at 460 nm and 540 nm with 400 nm excitation wavelength. In an acidic environment, the fluorescence emission peaks of PDA-OPD at 540 nm showed an obvious fluorescence quenching, and there existed a good linear relationship between the fluorescence ratio F₅₄₀/F₄₆₀ and environment pH value. In an alkaline environment, the fluorescence emission peak at 460 nm showed obvious fluorescence quenching after the addition of bilirubin, while a novel fluorescence emission peak at 560 nm emerged gradually. The PDA-OPD could be also used to detect bilirubin in the range of 0-400 μmol·L^-1.

Dual-purpose isocyanides produced by Aspergillus fumigatus contribute to cellular copper sufficiency and exhibit antimicrobial activity

The maintenance of sufficient but nontoxic pools of metal micronutrients is accomplished through diverse homeostasis mechanisms in fungi. Siderophores play a well established role for iron homeostasis; however, no copper-binding analogs have been found in fungi. Here we demonstrate that, in Aspergillus fumigatus, xanthocillin and other isocyanides derived from the xan biosynthetic gene cluster (BGC) bind copper, impact cellular copper content, and have significant metal-dependent antimicrobial properties. xan BGC-derived isocyanides are secreted and bind copper as visualized by a chrome azurol S (CAS) assay, and inductively coupled plasma mass spectrometry analysis of A. fumigatus intracellular copper pools demonstrated a role for xan cluster metabolites in the accumulation of copper. A. fumigatus coculture with a variety of human pathogenic fungi and bacteria established copper-dependent antimicrobial properties of xan BGC metabolites, including inhibition of laccase activity. Remediation of xanthocillin-treated Pseudomonas aeruginosa growth by copper supported the copper-chelating properties of xan BGC isocyanide products. The existence of the xan BGC in several filamentous fungi suggests a heretofore unknown role of eukaryotic natural products in copper homeostasis and mediation of interactions with competing microbes.

Antimicrobial Activity of Metals and Metalloids

Competition shapes evolution. Toxic metals and metalloids have exerted selective pressure on life since the rise of the first organisms on the Earth, which has led to the evolution and acquisition of resistance mechanisms against them, as well as mechanisms to weaponize them. Microorganisms exploit antimicrobial metals and metalloids to gain competitive advantage over other members of microbial communities. This exerts a strong selective pressure that drives evolution of resistance. This review describes, with a focus on arsenic and copper, how microorganisms exploit metals and metalloids for predation and how metal- and metalloid-dependent predation may have been a driving force for evolution of microbial resistance against metals and metalloids. Expected final online publication date for the Annual Review of Microbiology, Volume 75 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Fenton-like reaction driving the degradation and uptake of multi-walled carbon nanotubes mediated by bacterium

Carbon nanotubes (CNTs) have been widely studied because of their potential applications. The increasing applications of CNTs and less known of their environmental fates rise concerns about their safety. In this study, the biotransformation of multi-walled carbon nanotubes (MWCNTs) by Labrys sp. WJW was investigated. Within 16 days, qPCR analysis showed that cell numbers increased 4.92 ± 0.36 folds using 100 mg/L MWCNTs as the sole carbon source. The biotransformation of MWCNTs, which led to morphology and functional group change, was evidenced by transmission electron microscopy and X-ray photoelectron spectroscopy analyses. Raman spectra illustrated that more defects and disordered carbon appeared on MWCNTs during incubation. The underlying biotransformation mechanism of MWCNTs through an extracellular bacterial Fenton-like reaction was demonstrated. In this bacteria-mediated reaction, the OH production was induced by reduction of H₂O₂ involved a continuous cycle of Fe(II)/Fe(III). Bacterial biotransformation of MWCNTs will provide new insights into the understanding of CNTs bioremediation processes.

Copper Utilization, Regulation, and Acquisition by Aspergillus fumigatus

Copper is an essential micronutrient for the opportunistic human pathogen, Aspergillus fumigatus. Maintaining copper homeostasis is critical for survival and pathogenesis. Copper-responsive transcription factors, AceA and MacA, coordinate a complex network responsible for responding to copper in the environment and determining which response is necessary to maintain homeostasis. For example, A. fumigatus uses copper exporters to mitigate the toxic effects of copper while simultaneously encoding copper importers and small molecules to ensure proper supply of the metal for copper-dependent processes such a nitrogen acquisition and respiration. Small molecules called isocyanides recently found to be produced by A. fumigatus may bind copper and partake in copper homeostasis similarly to isocyanide copper chelators in bacteria. Considering that the host uses copper as a microbial toxin and copper availability fluctuates in various environmental niches, understanding how A. fumigatus maintains copper homeostasis will give insights into mechanisms that facilitate the development of invasive aspergillosis and its survival in nature.