Bacterial cell shapes may be altered by the cell cycle, nutrient availability, environmental stress, and interactions with other organisms. The bean bug Riptortus pedestris possesses a symbiotic bacterium, Burkholderia insecticola, in its midgut crypts. This symbiont is a typical rod-shaped bacterium under in vitro culture conditions, but changes to a spherical shape inside the gut symbiotic organ of the host insect, suggesting the induction of morphological alterations in B. insecticola by host factors. The present study revealed that a deletion mutant of a peptidoglycan amidase gene (amiC), showing a filamentous chain form in vitro, adapted a swollen L-form-like cell shape in midgut crypts. Spatiotemporal observations of the ΔamiC mutant in midgut crypts revealed the induction of swollen cells, particularly prior to the molting of insects. To elucidate the mechanisms underlying in vivo-specific morphological alterations, the symbiont was cultured under 13 different conditions and its cell shape was examined. Swollen cells, similar to symbiont cells in midgut crypts, were induced when the mutant was treated with fosfomycin, an inhibitor of peptidoglycan precursor biosynthesis. Collectively, these results strongly suggest that the Burkholderia symbiont in midgut crypts is under the control of the host insect via a cell wall-attacking agent.

中文翻译：

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昆虫伯克霍尔德菌的肽聚糖酰胺酶突变体在豆虫Riptortus pedestris的肠道共生器官中适应 L 型形状

细菌细胞的形状可能会因细胞周期、营养供应、环境压力以及与其他生物的相互作用而改变。豆虫 Riptortus pedestris 在其中肠隐窝中拥有一种共生细菌 Burkholderia昆虫。这种共生体在体外培养条件下是一种典型的杆状细菌，但在宿主昆虫的肠道共生器官内变为球形，表明宿主因素诱导了 B.昆虫的形态学改变。本研究表明，在体外显示丝状链形式的肽聚糖酰胺酶基因 (amiC) 的缺失突变体适应了中肠隐窝中肿胀的 L 型细胞形状。中肠隐窝中 ΔamiC 突变体的时空观察揭示了肿胀细胞的诱导，特别是在昆虫蜕皮之前。为了阐明体内特异性形态改变的机制，共生体在 13 种不同条件下培养，并检查了其细胞形状。当用磷霉素（一种肽聚糖前体生物合成抑制剂）处理突变体时，会诱导肿胀细胞，类似于中肠隐窝中的共生细胞。总的来说，这些结果强烈表明中肠隐窝中的伯克霍尔德菌共生体受宿主昆虫通过细胞壁攻击剂的控制。