Shi W, Ngok F K, Zusman D R
Department of Molecular and Cell Biology, University of California, Berkeley 94720, USA.
Proc Natl Acad Sci U S A. 1996 Apr 30;93(9):4142-6. doi: 10.1073/pnas.93.9.4142.
Myxococcus xanthus is a Gram-negative bacterium that aggregates to form fruiting bodies when nutrients are limiting. Previous studies showed that the frz mutants that are defective in chemotaxis exhibited irregular and infrequent patterns of cellular reversal. In contrast, wild-type cells, when examined individually, reverse relatively frequently, about once every 6 min. It is not known how the change of reversal frequency effects cellular aggregation during fruiting body formation in M. xanthus. In this study, we stained cells with a tetrazolium dye so that we could track the reversal frequencies of single cells and cells in groups. We found that developmental cells in large groups reverse much less than cells in small groups or as single cells. This reduced cellular reversal frequency is related to the frz signal transduction system and correlated with the methylation of FrzCD (a methyl-accepting chemotaxis protein). Cells containing a mutation in the frz genes or in the genes required for social motility do not respond in this way. The reduction in cellular reversals as developmental cells accumulate in groups suggests a simple hypothesis for the aggregation of cells into discrete mounds during fruiting body formation. We also found that M. xanthus cells glide with equal frequency in the forward or reverse directions, indicating that cells do not contain a "head" or "tail."
黄色粘球菌是一种革兰氏阴性细菌，在营养物质有限时会聚集形成子实体。先前的研究表明，趋化性有缺陷的frz突变体表现出不规则且不频繁的细胞反转模式。相比之下，野生型细胞单独检查时，反转相对频繁，大约每6分钟一次。尚不清楚反转频率的变化如何影响黄色粘球菌子实体形成过程中的细胞聚集。在本研究中，我们用四唑染料对细胞进行染色，以便能够追踪单个细胞和细胞群体的反转频率。我们发现，大群体中的发育细胞反转次数比小群体或单个细胞中的细胞少得多。这种细胞反转频率的降低与frz信号转导系统有关，并与FrzCD（一种甲基接受趋化蛋白）的甲基化相关。在frz基因或社会运动所需基因中含有突变的细胞不会以这种方式做出反应。随着发育细胞在群体中积累，细胞反转次数的减少为子实体形成过程中细胞聚集成离散土堆提出了一个简单的假设。我们还发现，黄色粘球菌细胞向前或向后滑动的频率相同，这表明细胞没有“头”或“尾”。
