Development of a Universal Fluorescent Probe for Gram‐Positive Bacteria

Growth and genome-based insights of Fe(III) reduction of the high-temperature and NaCl-tolerant Shewanella xiamenensis from Changqing oilfield of China

Introduction

A facultative anaerobe bacterium Shewanella xiamenensis CQ-Y1 was isolated from the wastewater of Changqing oilfield in Shaanxi Province of China. Shewanella is the important dissimilatory metal-reducing bacteria. It exhibited a well potential application in biodegradation and bioremediation.

Methods

Genome sequencing, assembling and functional annotation were conducted to explore the genome information of CQ-Y1. The effect of temperatures and NaCl concentrations on the CQ-Y1 growth and Fe(III) reduction were investigated by UV visible spectrophotometry, SEM and XRD.

Results

Genomic analysis revealed its complete genome was a circular chromosome of 4,710,887 bp with a GC content of 46.50% and 4,110 CDSs genes, 86 tRNAs and 26 rRNAs. It contains genes encoding for Na⁺/H⁺ antiporter, K⁺/Cl^- transporter, heat shock protein associated with NaCl and high-temperature resistance. The presence of genes related to flavin, Cytochrome c, siderophore, and other related proteins supported Fe(III) reduction. In addition, CQ-Y1 could survive at 10% NaCl (w/v) and 45°C, and temperature showed more pronounced effects than NaCl concentration on the bacterial growth. The maximum Fe(III) reduction ratio of CQ-Y1 reached 70.1% at 30°C without NaCl, and the reduction reaction remained active at 40°C with 3% NaCl (w/v). NaCl concentration was more effective than temperature on microbial Fe(III) reduction. And the reduction products under high temperature and high NaCl conditions were characterized as Fe₃(PO₄)₂, FeCl₂ and Fe(OH)₂.

Discussion

Accordingly, a Fe(III) reduction mechanism of CQ-Y1 mediated by Cytochrome c and flavin was hypothesised. These findings could provide information for a better understanding of the origin and evolution of genomic and metabolic diversity of S. xiamenensis.

Imitation-mussel fluorescent silicon quantum dots for selective labeling and imaging of bacteria and biofilms

Selective labeling of distinct bacteria and biofilm is poised for the fundamental understanding of bacterial activities, interactions, and coupled phenomena occurring at the microscale. However, a simple and effective way to achieve selective bacterial labeling is still lacking. Herein, we report a fluorescence probe with core-shell nanostructure that has polydopamine (PDA) coating on the surface of fluorescent silicon quantum dots (SiQDs@PDA). The surface of the SiQDs@PDA can be functionalized by various molecules (2-mercaptoethylamine hydrochloride, PEG, d-alanine, glucose amide) through different strategies (Michael addition, π-π interaction, and ion–ion interaction). Importantly, the d-alanine (D-Ala)- and gluconamide (Glc)-functionalized SiQDs@PDA fluorescence probes are capable of selectively labeling gram-positive and gram-negative bacteria, as well as their biofilms. The excellent performance in universal functionalization and selective labeling and imaging of bacteria and their biofilms demonstrate that SiQDs@PDA are a promising fluorescence tool in microbe research.