The release of black phosphorus (BP) nanosheets has raised concerns regarding potential ecological risks. Previous studies have confirmed their toxicity to bacteria, but discrepancies were observed between results obtained from the growth curve and colony forming unit (CFU) methods, indicating the possibility of bacterial cells entering a viable but non-culturable (VBNC) state induced by BP nanosheets. To accurately assess the risks, it is crucial to understand the underlying mechanisms. In this study, we investigated the effect of BP nanosheets on Bacillus tropicus, a Gram-positive bacterium, using transcriptome sequencing and biological assays. Our findings revealed that BP nanosheets caused minimal cell death but predominately induced the VBNC state in most cells. At the transcriptional level, we observed significant down-regulation of pathways associated with cellular metabolism and respiratory chain in response to BP nanosheet treatment. Bacterial cells in the VBNC state exhibited depressed respiration to maintain basal cellular activity. Additionally, the reduced cellular respiration and metabolic activity were associated with a decrease in antibiotic susceptibility of the bacteria. These results provide new insights into the antibacterial mechanisms of BP nanosheets and emphasize the necessity of employing appropriate approaches, beyond the traditional CFU method, to assess the bacterial toxicity of nanomaterials.

中文翻译：

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揭示黑磷纳米片诱导热带芽孢杆菌存活但不可培养状态的机制


黑磷（BP）纳米片的释放引起了人们对潜在生态风险的担忧。之前的研究已经证实了它们对细菌的毒性，但生长曲线和菌落形成单位（CFU）方法获得的结果之间存在差异，表明BP纳米片诱导细菌细胞进入存活但不可培养（VBNC）状态的可能性。为了准确评估风险，了解潜在机制至关重要。在这项研究中，我们利用转录组测序和生物测定研究了 BP 纳米片对热带芽孢杆菌（一种革兰氏阳性细菌）的影响。我们的研究结果表明，BP 纳米片引起的细胞死亡极少，但主要诱导大多数细胞进入 VBNC 状态。在转录水平上，我们观察到 BP 纳米片治疗后与细胞代谢和呼吸链相关的通路显着下调。 VBNC 状态下的细菌细胞表现出呼吸抑制，以维持基础细胞活性。此外，细胞呼吸和代谢活动的减少与细菌抗生素敏感性的降低有关。这些结果为BP纳米片的抗菌机制提供了新的见解，并强调了在传统CFU方法之外采用适当方法来评估纳米材料的细菌毒性的必要性。