Bacteria control the length of their polysaccharides, which can control cell viability, physiology, virulence, and immune evasion. Polysaccharide chain length affects immunomodulation, but its impact on bacterial physiology and antibiotic susceptibility was unclear. We probed the consequences of truncating the mycobacterial galactan, an essential linear polysaccharide of about 30 residues. Galactan covalently bridges cell envelope layers, with the outermost cell wall linkage point occurring at residue 12. Reducing galactan chain length by approximately half compromises fitness, alters cell morphology, and increases the potency of hydrophobic antibiotics. Systematic variation of the galactan chain length revealed that it determines periplasm size. Thus, glycan chain length can directly affect cellular physiology and antibiotic activity, and mycobacterial glycans, not proteins, regulate periplasm size.

细菌控制其多糖的长度，从而控制细胞活力、生理、毒力和免疫逃避。多糖链长度影响免疫调节，但其对细菌生理学和抗生素敏感性的影响尚不清楚。我们探讨了截断分枝杆菌半乳聚糖的后果，这是一种约 30 个残基的必需线性多糖。半乳聚糖共价连接细胞包膜层，最外层的细胞壁连接点出现在残基 12 处。将半乳聚糖链长度减少大约一半会损害适应性，改变细胞形态，并增加疏水性抗生素的效力。半乳聚糖链长的系统变化表明它决定了周质大小。因此，聚糖链长可以直接影响细胞生理和抗生素活性，