Bacteria are primary agents of organic substrate metabolisation and elemental cycling in landfills. Two major bacterial groups, namely, Gram-positive (GP) and Gram-negative (GN), drive independent metabolic functions that contribute to waste stabilisation. There is a lack of explicit exploration of how these different bacterial guilds respond to changing carbon (C) availability and substrate depletion as landfills age and how landfill geochemistry regulates their distribution. This study investigated and compared the abundance and vertical distribution of GP and GN bacteria in 14- and 36-year-old municipal landfills and explored linkages among bacterial groups, nutrient elements, heavy metals and soil texture. We found higher GP bacteria in the 14-year-old landfill, while GN bacteria dominated the 36-year-old landfill. The non-metric multidimensional scaling (nMDS) analysis showed that dissimilarities in the relative abundance of the GP and GN bacteria were linked distinctly to landfill age, and not depth. In support of this inference, we further found that GP and GN bacteria were negatively correlated with heavy metals and essential nutrients in the 14- and 36-year-old landfills, respectively. Notably, the GP/GN ratio, an indicator of relative C available for bacterial mineralisation, was greater in the14-year-old landfill, suggesting greater C availability. Conversely, the C to N ratio was higher in the 36-year-old landfill, indicating lower N mineralisation. Collectively, the results of the study reveal key insights into how landfill ageing and stabilisation influence distinct functional shifts in the abundance of GP and GN bacteria, and these are mainly driven by changes in C and N bioavailability.

细菌是垃圾填埋场中有机底物代谢和元素循环的主要因素。两个主要的细菌群，即革兰氏阳性 (GP) 和革兰氏阴性 (GN)，驱动有助于废物稳定的独立代谢功能。随着垃圾填埋场的老化，这些不同的细菌群如何响应不断变化的碳 (C) 可用性和基质消耗，以及垃圾填埋场地球化学如何调节它们的分布，目前还缺乏明确的探索。本研究调查并比较了 14 年和 36 年城市垃圾填埋场中 GP 和 GN 细菌的丰度和垂直分布，并探讨了细菌群、营养元素、重金属和土壤质地之间的联系。我们在 14 年历史的垃圾填埋场中发现了较高的 GP 细菌，而 GN 细菌在 36 年历史的垃圾填埋场中占主导地位。非度量多维标度 (nMDS) 分析表明，GP 和 GN 细菌相对丰度的差异与垃圾填埋场年龄明显相关，而不是与深度相关。为了支持这一推论，我们进一步发现，GP 和 GN 细菌分别与 14 年和 36 年历史垃圾填埋场中的重金属和必需营养素呈负相关。值得注意的是，GP/GN 比率是细菌矿化可用的相对碳的指标，在​​ 14 年的垃圾填埋场中更高，表明碳的可用性更高。相反，36 年历史的垃圾填埋场的碳氮比较高，表明氮矿化程度较低。总的来说，研究结果揭示了垃圾填埋场老化和稳定如何影响 GP 和 GN 细菌丰度的不同功能变化的关键见解，