Occurrence of ferredoxin:NAD+oxidoreductase activity and its ion specificity in several Gram-positive and Gram-negative bacteria

A ferredoxin:NAD+oxidoreductase was recently discovered as a redox-driven ion pump in the anaerobic, acetogenic bacteriumAcetobacterium woodii. The enzyme is assumed to be encoded by thernfgenes. Since these genes are present in the genomes of many bacteria, we tested for ferredoxin:NAD+oxidoreductase activity in cytoplasmic membranes from several different Gram-positive and Gram-negative bacteria that have annotatedrnfgenes. We found this activity inClostridium tetanomorphum,Clostridium ljungdahlii,Bacteroides fragilis, and Vibrio choleraebut not inEscherichia coliandRhodobacter capsulatus. As inA. woodii, the activity was Na+-dependent inC. tetanomorphumandB. fragilisbut Na+-independent inC. ljungdahliiandV. cholerae. We deleted thernfgenes fromB. fragilisand demonstrated that the mutant has greatly reduced ferredoxin:NAD+oxidoreductase activity. This is the first genetic proof that thernfgenes indeed encode the reduced ferredoxin:NAD+oxidoreductase activity.

Clostridium lundense sp. nov., a novel anaerobic lipolytic bacterium isolated from bovine rumen

A strictly anaerobic, mesophilic, endospore-forming, lipolytic bacterium, designated strain R1T, was isolated from bovine rumen fluid and characterized. Cells of this isolate were Gram-positive, non-motile rods that formed spherical terminal spores. The overall biochemical and physiological characteristics indicated that this strain should be placed in the genus Clostridium. The strain grew at temperatures between 25 and 47 °C (optimum, 37 °C), at pH between 5·0 and 8·5 (optimum pH 5·5–7·0) and in NaCl concentrations of 0–3 % (w/v). The isolate was not able to utilize glucose or other carbohydrates as carbon sources. The DNA G+C content was 31·2 mol%. Sequence analysis of the 16S rRNA gene of R1T revealed that it has the closest match (98 % similarity) with Clostridium tetanomorphum DSM 4474T. The highest levels of DNA–DNA relatedness of the isolate were 61·9 and 54·3 % with Clostridium pascui DSM 10365T and C. tetanomorphum DSM 4474T, respectively. Based on 16S rRNA gene sequence similarity, phylogenetic analysis, DNA G+C content, DNA–DNA hybridization data and distinct phenotypic characteristics, strain R1T (=DSM 17049T=CCUG 50446T) was classified in the genus Clostridium, as a member of a novel species, for which the name Clostridium lundense sp. nov. is proposed.