Produce Safety and Microbiology Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Albany, California, United States of America.
PLoS One. 2011;6(10):e25553. doi: 10.1371/journal.pone.0025553. Epub 2011 Oct 7.
Salmonella cycles between host and nonhost environments, where it can become an active member of complex microbial communities. The role of fungi in the environmental adaptation of enteric pathogens remains relatively unexplored. We have discovered that S. enterica Typhimurium rapidly attaches to and forms biofilms on the hyphae of the common fungus, Aspergillus niger. Several Salmonella enterica serovars displayed a similar interaction, whereas other bacterial species were unable to bind to the fungus. Bacterial attachment to chitin, a major constituent of fungal cell walls, mirrored this specificity. Pre-incubation of S. Typhimurium with N-acetylglucosamine, the monomeric component of chitin, reduced binding to chitin beads by as much as 727-fold and inhibited attachment to A. niger hyphae considerably. A cellulose-deficient mutant of S. Typhimurium failed to attach to chitin beads and to the fungus. Complementation of this mutant with the cellulose operon restored binding to chitin beads to 79% of that of the parental strain and allowed for attachment and biofilm formation on A. niger, indicating that cellulose is involved in bacterial attachment to the fungus via the chitin component of its cell wall. In contrast to cellulose, S. Typhimurium curli fimbriae were not required for attachment and biofilm development on the hyphae but were critical for its stability. Our results suggest that cellulose-chitin interactions are required for the production of mixed Salmonella-A. niger biofilms, and support the hypothesis that encounters with chitinaceous alternate hosts may contribute to the ecological success of human pathogens.
沙门氏菌在宿主和非宿主环境之间循环，在这些环境中，它可以成为复杂微生物群落中的活跃成员。真菌在肠病原体的环境适应中的作用仍相对未知。我们发现，鼠伤寒沙门氏菌（Salmonella enterica Typhimurium）迅速附着在常见真菌黑曲霉（Aspergillus niger）的菌丝上并形成生物膜。几个沙门氏菌血清型表现出类似的相互作用，而其他细菌物种则无法与真菌结合。细菌与几丁质（真菌细胞壁的主要成分）的附着反映了这种特异性。用几丁质的单体成分 N-乙酰葡萄糖胺预先孵育 S. Typhimurium ，可使与几丁质珠的结合减少多达 727 倍，并大大抑制对黑曲霉菌丝的附着。鼠伤寒沙门氏菌的纤维素缺陷突变体无法附着在几丁质珠和真菌上。用纤维素操纵子互补该突变体，可使与几丁质珠的结合恢复到亲本菌株的 79％，并允许附着和生物膜形成于黑曲霉上，表明纤维素通过其细胞壁的几丁质成分参与细菌对真菌的附着。与纤维素相反，鼠伤寒沙门氏菌卷曲菌毛对于在菌丝上的附着和生物膜形成不是必需的，但对于其稳定性是关键的。我们的结果表明，纤维素-几丁质相互作用是产生混合沙门氏菌-黑曲霉生物膜所必需的，并支持这样的假设，即与含几丁质的替代宿主的接触可能有助于人类病原体的生态成功。
