Microbial endogenous response to acute inhibitory impact of antibiotics

Enhanced endogenous respiration was observed as the significant/main response of the aerobic microbial culture under pulse exposure to antibiotics: sulfamethoxazole, tetracycline and erythromycin. Peptone mixture and acetate were selected as organic substrates to compare the effect of complex and simple substrates. Experiments were conducted with microbial cultures acclimated to different sludge ages of 10 and 2 days, to visualize the effect of culture history. Evaluation relied on modeling of oxygen uptake rate profiles, reflecting the effect of all biochemical reactions associated with substrate utilization. Model calibration exhibited significant increase in values of endogenous respiration rate coefficient with all antibiotic doses. Enhancement of endogenous respiration was different with antibiotic type and initial dose. Results showed that both peptone mixture and acetate cultures harbored resistance genes against the tested antibiotics, which suggests that biomass spends cellular maintenance energy for activating the required antibiotic resistance mechanisms to survive, supporting higher endogenous decay rates. <b>Abbreviations:</b>: maximum growth rate for <i>X</i>_H (day⁻¹); <i>K</i>_S: half saturation constant for growth of <i>X</i>_H (mg COD/L); <i>b</i>_H: endogenous decay rate for <i>X</i>_H (day⁻¹); <i>k</i>_h: maximum hydrolysis rate for <i>S</i>_H1 (day⁻¹); <i>K</i>_X: hydrolysis half saturation constant for <i>S</i>_H1(mg COD/L); <i>k</i>_hx: maximum hydrolysis rate for <i>X</i>_S1 (day⁻¹); <i>K</i>_XX: hydrolysis half saturation constant for <i>X</i>_S1 (mg COD/L); <i>k</i>_STO: maximum storage rate of PHA by <i>X</i>_H (day⁻¹); : maximum growth rate on PHA for <i>X</i>_H (day⁻¹); <i>K</i>_STO: half saturation constant for storage of PHA by <i>X</i>_H (mg COD/L); <i>X</i>_H1: initial active biomass (mg COD/L)

本研究观察到，好氧微生物菌群在脉冲暴露于磺胺甲恶唑（sulfamethoxazole）、四环素（tetracycline）与红霉素（erythromycin）三种抗生素时，其核心响应为内源性呼吸作用增强。研究选取蛋白胨混合物与乙酸盐作为有机底物，用以对比复杂底物与简单底物的作用差异。实验采用分别适应了10天和2天两种不同污泥龄的微生物菌群开展，以明晰菌群驯化历史的影响效应。本研究通过对摄氧速率曲线进行建模开展评估，该曲线可反映与底物利用相关的全部生化反应的综合影响。模型校准结果显示，在所有受试抗生素剂量下，内源性呼吸速率系数均出现显著提升。内源性呼吸作用的增强幅度随抗生素种类与初始给药剂量的不同而存在显著差异。实验结果表明，无论是蛋白胨混合物驯化菌群还是乙酸盐驯化菌群，均携带针对受试抗生素的耐药基因。这意味着微生物菌体需要消耗细胞维持能量来激活所需的抗生素耐药机制以维持存活，进而支撑了更高的内源衰减速率。<b>缩写说明：</b><i>μ</i>_H：异养菌<i>X</i>_H的最大比生长速率（day⁻¹）；<i>K</i>_S：异养菌<i>X</i>_H生长的半饱和常数（mg COD/L）；<i>b</i>_H：异养菌<i>X</i>_H的内源衰减速率（day⁻¹）；<i>k</i>_h：颗粒性有机物<i>S</i>_H1的最大水解速率（day⁻¹）；<i>K</i>_X：颗粒性有机物<i>S</i>_H1水解的半饱和常数（mg COD/L）；<i>k</i>_hx：溶解性发酵产物<i>X</i>_S1的最大水解速率（day⁻¹）；<i>K</i>_XX：溶解性发酵产物<i>X</i>_S1水解的半饱和常数（mg COD/L）；<i>k</i>_STO：异养菌<i>X</i>_H储存聚羟基脂肪酸酯（PHA）的最大储存速率（day⁻¹）；<i>μ</i>_PHA：异养菌<i>X</i>_H以聚羟基脂肪酸酯（PHA）为底物的最大比生长速率（day⁻¹）；<i>K</i>_STO：异养菌<i>X</i>_H储存聚羟基脂肪酸酯（PHA）的半饱和常数（mg COD/L）；<i>X</i>_H1：初始活性生物量（mg COD/L）