Physiological adaptation of Desulfitobacterium hafniense strain TCE1 to tetrachloroethene respiration

Abstract

Desulfitobacterium spp. are ubiquitous organisms with a broad metabolic versatility, and some isolates have the ability to use tetrachloroethene (PCE) as terminal electron acceptor. In order to identify proteins involved in this organohalide respiration process, a comparative proteomic analysis was performed. Soluble and membrane-associated proteins obtained from cells of Desulfitobacterium hafniense strain TCE1 that were growing on different combinations of the electron donors lactate and hydrogen and the electron acceptors PCE and fumarate were analyzed. Among proteins increasingly expressed in the presence of PCE compared to fumarate as electron acceptor, a total of 57 proteins were identified by mass spectrometry analysis, revealing proteins involved in stress response and associated regulation pathways, such as PspA, GroEL, and CodY, and also proteins potentially participating in carbon and energy metabolism, such as proteins of the Wood-Ljungdahl pathway and electron transfer flavoproteins. These proteomic results suggest that D. hafniense strain TCE1 adapts its physiology to face the relative unfavorable growth conditions during an apparent opportunistic organohalide respiration.

Fig. 1.

Representative 2D gels of membrane protein fractions from D. hafniense strain TCE1 cultivated on lactate-PCE (A) and lactate-fumarate (B). The numbers in braces indicate the position of the isoforms of PCE reductive dehalogenase (PceA) ({1}) and a sulfur transferase ({2}), two examples of proteins increasingly expressed in the presence of PCE. MW, molecular weight in thousands.

Fig. 2.

Distribution of proteins whose expression was increased by PCE on the basis of the following functional categories: carbon metabolism and carbohydrate transport (CC), energy production and conversion (EC), transcription and translation (TT), secretion and transport (ST), cell wall and membrane metabolism (CM), amino acid metabolism (AA), posttranslational modification and chaperones (PC), replication and repair (RR), undefined function (UF), nucleotide metabolism (NT), coenzyme metabolism (CO), and defense mechanism (DM).

Fig. 3.

PCE dechlorination recovery of D. hafniense strain TCE1 after long-term cultivation on fumarate. (A) Growth and chloride release during growth on PCE; black triangles, absorbance at 600 nm of a culture routinely cultivated on PCE; black squares, absorbance at 600 nm of the recovering culture on PCE; white squares, concentration of chloride released in the recovering culture. (B) PCR product targeting the pceA gene amplified from 0.2 ng of DNA extracted from 4-day cultures routinely cultivated on fumarate and PCE and used as inocula (left panel) and from the recovering culture on PCE over time (right panel).