Effect of iron limitation and fur gene inactivation on the transcriptional profile of the strict anaerobe Clostridium acetobutylicum

Abstract

Iron is a nutrient of critical importance for the strict anaerobe Clostridium acetobutylicum, as it is involved in numerous basic cellular functions and metabolic pathways. A gene encoding a putative ferric uptake regulator (Fur) has been identified in the genome of C. acetobutylicum. In this work, we inactivated the fur gene by using insertional mutagenesis. The resultant mutant showed a slow-growing phenotype and enhanced sensitivity to oxidative stress, but essentially no dramatic change in its fermentation pattern. A unique feature of its physiology was the overflowing production of riboflavin. To gain further insights into the role of the Fur protein and the mechanisms for establishment of iron balance in C. acetobutylicum, we characterized and compared the gene-expression profile of the fur mutant and the iron-limitation stimulon of the parental strain. Not surprisingly, a repertoire of iron-transport systems was upregulated in both microarray datasets, suggesting that they are regulated by Fur according to the availability of iron. In addition, iron limitation and inactivation of fur affected the expression of several genes involved in energy metabolism. Among them, two genes, encoding a lactate dehydrogenase and a flavodoxin, were highly induced. In order to support the function of the latter, the ribDBAH operon responsible for riboflavin biosynthesis was also upregulated significantly. Furthermore, the iron-starvation response of C. acetobutylicum involved transcriptional modifications that were not detected in the fur mutant, suggesting that there exist additional mechanisms for adaptation to low-iron environments. Collectively, these results demonstrate that the strict anaerobe C. acetobutylicum senses and responds to availability of iron on multiple levels using a sophisticated system, and that Fur plays an important role in this process.

Control of Clostridium difficile Physiopathology in Response to Cysteine Availability

“…The ferric uptake regulator (Fur) protein is an iron response repressor that controls the expression of genes involved in iron transport in bacteria (61,62). The CD1287 protein shares 48% identity with the Fur protein of B. subtilis.…”

Coenzyme A-transferase-independent butyrate re-assimilation in Clostridium acetobutylicum—evidence from a mathematical model

“…It is speculated that the intracellular ATP and NADH pools play a crucial role in the clostridial adaptation to changing environmental condition including the pH level (Girbal and Soucaille 1994;Wietzke and Bahl 2012), nutritional composition (Bahl et al 1986;Girbal and Soucaille 1994), and further limitations (e.g. iron (Junelles et al 1988;Vasileva et al 2012)). …”

Comparative Proteomic Analysis of Streptomyces lividans Wild-Type andppkMutant Strains Reveals the Importance of Storage Lipids for Antibiotic Biosynthesis

“…Proteins annotated as involved in iron acquisition (SCO1925, SCO1623, SCO2270, and SCO7399) were less abundant in the ppk mutant strain. Under oxidative stress, iron is known to generate reactive free radicals by the Fenton reaction (55) that are damaging for cellular constituents (56)(57)(58). The downregulation of such genes in the ppk mutant might be necessary to limit the already high internal oxidative stress of this strain.…”