Wildfires affect soils in multiple ways, leading to numerous challenges for colonizing microorganisms. While it is thought that fire-adapted microorganisms lie at the forefront of postfire ecosystem recovery, the specific strategies that these organisms use to thrive in burned soils remain largely unknown. Through bioactivity screening of bacterial isolates from burned soils, we discovered that several Paraburkholderia spp. isolates produced a set of unusual rhamnolipid surfactants with a natural methyl ester modification. These rhamnolipid methyl esters (RLMEs) exhibited enhanced antimicrobial activity against other postfire microbial isolates, including pyrophilous Pyronema fungi and Amycolatopsis bacteria, compared to the typical rhamnolipids made by organisms such as Pseudomonas spp. RLMEs also showed enhanced surfactant properties and facilitated bacterial motility on agar surfaces. In vitro assays further demonstrated that RLMEs improved aqueous solubilization of polycyclic aromatic hydrocarbons, which are potential carbon sources found in char. Identification of the rhamnolipid biosynthesis genes in the postfire isolate, Paraburkholderia kirstenboschensis str. F3, led to the discovery of rhlM, whose gene product is responsible for the unique methylation of rhamnolipid substrates. RhlM is the first characterized bacterial representative of a large class of integral membrane methyltransferases that are widespread in bacteria. These results indicate multiple roles for RLMEs in the postfire lifestyle of Paraburkholderia isolates, including enhanced dispersal, solubilization of potential nutrients, and inhibition of competitors. Our findings shed new light on the chemical adaptations that bacteria employ to navigate, grow, and outcompete other soil community members in postfire environments.

中文翻译：

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表面活性抗生素生产作为火灾后微生物的多功能适应

野火以多种方式影响土壤，给微生物定殖带来诸多挑战。虽然人们认为适应火灾的微生物处于火灾后生态系统恢复的最前沿，但这些生物在烧毁的土壤中繁衍生息的具体策略仍然很大程度上未知。通过对烧毁土壤中分离的细菌进行生物活性筛选，我们发现了几种 Paraburkholderia spp。分离物产生了一组具有天然甲酯改性的不寻常的鼠李糖脂表面活性剂。与假单胞菌等生物体产生的典型鼠李糖脂相比，这些鼠李糖脂甲酯 (RLME) 对其他火灾后微生物分离株（包括嗜热火线菌属真菌和无枝酸菌细菌）表现出增强的抗菌活性。RLME 还表现出增强的表面活性剂特性并促进琼脂表面上的细菌运动。体外测定进一步表明，RLME 改善了多环芳烃的水溶解度，多环芳烃是在焦炭中发现的潜在碳源。火灾后分离株 Paraburkholderia kirstenboschensis str 中鼠李糖脂生物合成基因的鉴定。F3 导致了 rhlM 的发现，其基因产物负责鼠李糖脂底物的独特甲基化。RhlM 是细菌中广泛存在的一大类整合膜甲基转移酶的第一个特征细菌代表。这些结果表明 RLME 在 Paraburkholderia 分离株的火灾后生活方式中发挥多种作用，包括增强扩散、溶解潜在营养物质和抑制竞争者。我们的研究结果为细菌在火灾后环境中导航、生长和战胜其他土壤群落成员所采用的化学适应提供了新的线索。