E coli MG1655 biofilm and planktonic gene expression

Bacteria growing as surface-adherent biofilms are better able to withstand chemical and physical stresses than their unattached, planktonic counterparts. Using transcriptional profiling and quantitative PCR, we observed a previously uncharacterized gene, yjfO, to be upregulated during Escherichia coli MG1655 biofilm growth in a chemostat on serine-limited defined medium. A yjfO mutant, developed through targeted insertion mutagenesis, and a yjfO-complemented strain, were obtained for further characterization. While bacterial surface colonization levels (CFU/cm2) were similar in all three strains, the mutant strain exhibited reduced microcolony formation when observed in flow cells, and greatly enhanced flagellar motility on soft (0.3%) agar. Complementation of yjfO restored microcolony formation and flagellar motility to wild type levels. Cell surface hydrophobicity and twitching motility were unaffected by the presence or absence of yjfO. In contrast to the parent strain, biofilms from the mutant strain were less able to resist acid and peroxide stresses. yjfO had no significant effect on E. coli biofilm susceptibility to alkali or heat stress. Planktonic cultures from all three strains showed similar responses to these stresses. Regardless of the presence of yjfO, planktonic E. coli withstood alkali stress better than biofilm populations. Complementation of yjfO restored viability following exposure to peroxide stress, but did not restore acid resistance. Based on its influence on biofilm formation, stress response, and effects on motility, we propose renaming the uncharacterized gene, yjfO, as bsmA (biofilm stress and motility). Transcriptional profiling of duplicate biofilm and planktonic cultures of E. coli MG1655 grown in serine-limited MOPS minimal media.

以表面黏附生物膜（biofilms）形式生长的细菌，相较于游离的浮游态（planktonic）菌体，能够更有效地抵御化学与物理胁迫。本研究通过转录组分析（transcriptional profiling）与定量PCR（quantitative PCR），在以丝氨酸限制型限定培养基（defined medium）培养的恒化器（chemostat）中，观察到大肠杆菌MG1655生物膜生长阶段，此前未被表征的基因yjfO出现上调表达。我们通过靶向插入诱变（targeted insertion mutagenesis）构建了yjfO突变株，并获得了yjfO互补菌株（yjfO-complemented strain），用于后续表征分析。尽管三株菌的细菌表面定植水平（菌落形成单位每平方厘米，CFU/cm²）无显著差异，但突变株在流动室（flow cells）中观察到的微菌落形成能力减弱，且在0.3%软琼脂（soft agar）上的鞭毛运动性（flagellar motility）显著增强。yjfO的互补回复可将微菌落形成能力与鞭毛运动性恢复至野生型水平。yjfO的存在与否对细胞表面疏水性（cell surface hydrophobicity）与抽动运动性（twitching motility）无显著影响。与亲本菌株相比，突变株的生物膜对酸胁迫（acid stress）与过氧化物胁迫（peroxide stress）的抵御能力显著下降，但yjfO对大肠杆菌生物膜的碱胁迫（alkali stress）与热胁迫（heat stress）敏感性无显著影响。三株菌的浮游培养物对上述各类胁迫的响应均无显著差异。无论是否存在yjfO，浮游态大肠杆菌对碱胁迫的耐受能力均优于生物膜种群。yjfO的互补回复可恢复过氧化物胁迫暴露后的细胞存活率（viability），但无法恢复其酸耐受能力。基于yjfO对生物膜形成、胁迫响应以及运动性的调控作用，我们建议将该未表征基因yjfO重命名为bsmA（生物膜胁迫与运动性，biofilm stress and motility）。本研究对在丝氨酸限制型MOPS最小培养基（MOPS minimal media）中培养的大肠杆菌MG1655的重复生物膜与浮游培养物进行了转录组分析。