Substrate-dependent competition and cooperation relationships between Geobacter and Dehalococcoides for their organohalide respiration

Abstract

Obligate and non-obligate organohalide-respiring bacteria (OHRB) play central roles in the geochemical cycling and environmental bioremediation of organohalides. Their coexistence and interactions may provide functional redundancy and community stability to assure organohalide respiration efficiency but, at the same time, complicate isolation and characterization of specific OHRB. Here, we employed a growth rate/yield tradeoff strategy to enrich and isolate a rare non-obligate tetrachloroethene (PCE)-respiring Geobacter from a Dehalococcoides-predominant microcosm, providing experimental evidence for the rate/yield tradeoff theory in population selection. Surprisingly, further physiological and genomic characterizations, together with co-culture experiments, revealed three unique interactions (i.e., free competition, conditional competition and syntrophic cooperation) between Geobacter and Dehalococcoides for their respiration of PCE and polychlorinated biphenyls (PCBs), depending on both the feeding electron donors (acetate/H2 vs. propionate) and electron acceptors (PCE vs. PCBs). This study provides the first insight into substrate-dependent interactions between obligate and non-obligate OHRB, as well as a new strategy to isolate fastidious microorganisms, for better understanding of the geochemical cycling and bioremediation of organohalides.

Geobacter sp. Strain IAE Dihaloeliminates 1,1,2-Trichloroethane and 1,2-Dichloroethane

“…As shown in Figure , the highest 16S rRNA gene sequence similarities of 98.9–99.0% exist with the tetrachloroethene (PCE)-dechlorinating species G. lovleyi, , which presumably also accommodates the 1,2-DCA-dechlorinating Geobacter sp. strain AY…”

“…To date, the capability to utilize chlorinated electron acceptors has been well characterized in G. lovleyi strains. , G. lovleyi strain SZ and the recently isolated strain LYY reduce PCE and trichloroethene (TCE) to cis -1,2-dichloroethene ( c DCE) via hydrogenolysis. , G.…”

“…lovleyi strains. , G. lovleyi strain SZ and the recently isolated strain LYY reduce PCE and trichloroethene (TCE) to cis -1,2-dichloroethene ( c DCE) via hydrogenolysis. , G. lovleyi strain SZ cannot dechlorinate 1,2-DCA and 1,1,2-TCA, and strain LYY’s ability to dechlorinate 1,2-DCA or 1,1,2-TCA has not been determined …”

Effects of Heavy Metal Ions on Microbial Reductive Dechlorination of 1, 2-Dichloroethane and Tetrachloroethene

“…For instance, Geobacter lovleyi strain SZ can fulfill the cobamide requirement of Dehalococcoides strains (Yan et al, 2012). Geobacter can also supply carbon source to Dehalococcoides strains by fermenting lactate to acetate (Liang et al, 2021). Also worth mentioning is that, without dynamic monitoring, the abundance and function of Geobacter may be underestimated since community structures were only analyzed at the completion of reductive dechlorination.…”

“…Geobacter and Dehalococcoides were the dominant OHRB genera in the second transferred enrichment cultures with relative abundances of 11.12% and 3.42%, respectively. Geobacter lovleyi strain SZ, isolated from Su-Zi Creek sediment of Korea in 2005, and Geobacter lovleyi strain LYY, isolated from black-odorous urban river sediment of China, are capable of PCE-to-cDCE dechlorination (Sung et al, 2006;Amos et al, 2007;Liang et al, 2021). This information suggested that the Geobacter population in the PCEdechlorinating enrichment was responsible for the reductive dechlorination of PCE to cDCE, which was futher dechlorinated to ethene by Dehalococcoides.…”