In situmicrocosms deployed at the coast of British Columbia (Canada) to study dilbit weathering and associated microbial communities under marine conditions

Abstract

Douglas Channel and the adjacent Hecate Strait (British Columbia, Canada) are part of a proposed route to ship diluted bitumen (dilbit). This study presents how two types of dilbit naturally degrade in this environment by using an in situ microcosm design based on dilbit-coated beads. We show that dilbit-associated n-alkanes were microbially biodegraded with estimated half-lives of 57–69 days. n-Alkanes appeared to be primarily degraded using the aerobic alkB, ladA and CYP153 pathways. The loss of dilbit polycyclic aromatic hydrocarbons (PAHs) was slower than of n-alkanes, with half-lives of 89–439 days. A biodegradation of PAHs could not be conclusively determined, although a significant enrichment of the phnAc gene (a marker for aerobic PAH biodegradation) was observed. PAH degradation appeared to be slower in Hecate Strait than in Douglas Channel. Microcosm-associated microbial communities were shaped by the presence of dilbit, deployment location and incubation time but not by dilbit type. Metagenome-assembled genomes of putative dilbit-degraders were obtained and could be divided into populations of early, late and continuous degraders. The majority of the identified MAGs could be assigned to the orders Flavobacteriales, Methylococcales, Pseudomonadales and Rhodobacterales. A high proportion of the MAGs represent currently unknown lineages or lineages with currently no cultured representative.

Genome-resolved analyses show an extensive diversification in key aerobic hydrocarbon-degrading enzymes across bacteria and archaea

“…This genome also had six copies of alkB/M and was isolated from a PAH-contaminated site [ 44 ]. The high HC degradation potential of other members of this genus has also been reported in the marine ecosystem [ 45 , 46 ]. Rugosibacter aromaticivorans (containing 5, 2 and 2 copies of xylX, ndoB, and tmoA genes, respectively), Pseudoxanthomonas _A spadix _B (with 4, 2 and 2 copies of xylX, todC1 and bphA1 genes, respectively), Thauera sp002354895 (4), Pigmentiphaga sp002188635 (4) are other examples of genomes that have multiple copies of the xylX gene.…”

Genome-resolved analyses show an extensive diversification in key aerobic hydrocarbon-degrading enzymes across bacteria and archaea

“…This genome also had six copies of alkB/M and was isolated from a PAH-contaminated site [28]. The high HC degradation potential of other members of this genus has also been reported in the marine ecosystem [29] S7 and Supplementary Figure S7). On the other hand, Glutamicibacter mysorens (4), Enteractinococcus helveticum (4), and many other genomes from the Castellaniella, Kocuria, and Halomonas genera, had several pheA copies in their individual genomes.…”

“…This genome also had six copies of alkB/M and was isolated from a PAH-contaminated site [28]. The high HC degradation potential of other members of this genus has also been reported in the marine ecosystem [29][30]. Rugosibacter aromaticivorans (containing 5, 2 and 2 copies of xylX, ndoB, and tmoA genes, respectively), Pseudoxanthomonas A spadix B (with 4, 2 and 2 copies of xylX, todC1 and bphA1 genes, respectively), Thauera sp002354895 (4), Pigmentiphaga sp002188635 (4) are other examples of genomes that have multiple copies of the xylX gene.…”

Marine Microbiota Responses to Shipping Scrubber Effluent Assessed at Community Structure and Function Endpoints

“…Also, we cannot exclude the presence of microbes with unknown properties that could be involved in complex degradation mechanisms. Microcosm‐associated microbial communities responding to diluted petroleum products contained metagenome‐assembled genomes representing currently unknown lineages (Schreiber et al, 2021) with potentially novel functions and PAH‐degrading features. Furthermore, Louvado et al (2015) showed that the genomes of PAH‐degrading bacterial isolates from deep‐sea sediments carry potential novel orthologs with low sequence similarity to known genes involved in the initial activation step of xenobiotic degradation pathways.…”