Significance of Acetate as a Microbial Carbon and Energy Source in the Water Column of Gulf of Mexico: Implications for Marine Carbon Cycling

Abstract

Acetate is a key intermediate of organic matter mineralization, but its metabolism remains largely unconstrained in the pelagic ocean. We conducted an integrated biogeochemical study to investigate microbial acetate cycling in the northern Gulf of Mexico with the goal of elucidating the importance of acetate as a carbon and energy source. Acetate was used primarily as an energy source, as evidenced by observed oxidation rates (rate constant k: 0.06–0.22 day−1) that varied between 42% and 96% of total biological acetate uptake (i.e., assimilation + oxidation; k: 0.06–0.34 day−1). The assimilation of acetate into biomass (k: 0.01–0.20 day−1) illustrated the potential significance of acetate as a biomass carbon source, particularly in nutrient‐rich coastal waters. No relationship between acetate assimilation or oxidation and environmental factors, such as chlorophyll and nutrients, was observed. However, elevated acetate uptake in reduced oxygen waters characterized by particulate organic carbon mineralization suggests that acetate metabolism may be a good proxy for particulate organic carbon breakdown. Molecular genetic analysis revealed that SAR11 Alphaproteobacteria were the most abundant heterotrophic bacteria and suggest that they may utilize acetate. At some sites, acetate carbon may have accounted for up to 50.4% of the bacterial carbon production. These results suggest that acetate may serve as an important carbon and energy source for heterotrophic bacteria thus revealing a potentially significant role of acetate for dissolved organic carbon cycling in the ocean.

Genomic and enzymatic evidence of acetogenesis by anaerobic methanotrophic archaea

“…The genomic and enzymatic evidence provided by this study of acetate production by ANME-2a could explain the existence of the large heterotrophic communities in cold seep ecosystems, as acetate is a popular carbon source for marine ecosystems. In surface water, acetate has been identified not only as an energy source but also as an important carbon source incorporated into biomass (accounting for 58% of total uptake) by heterotrophic bacteria 32 . In anoxic sediments, acetate was found to be utilized primarily by non-methanogenic heterotrophs as an energy and carbon source, and approximately 10-76% was assimilated into biomass for cell growth 10,33 .…”

Prokaryotic Capability to Use Organic Substrates Across the Global Tropical and Subtropical Ocean

“…Although acetate is considered a fermentation product, rapid acetate uptake has been reported in several aquatic ecosystems, including surface oxic marine waters (Ho et al, 2002). Zhuang et al (2019) recently revealed the high relevance of acetate as a metabolic substrate in the water column of the Gulf of Mexico. Acetate is primarily used as an energy source (evidenced by its high oxidation rates) and shows significant levels of assimilation into biomass, illustrating the potential significance of acetate as a carbon source that supports microbial growth (Zhuang et al, 2019).…”

Arcobacter peruensis sp. nov., a Chemolithoheterotroph Isolated from Sulfide- and Organic-Rich Coastal Waters off Peru

“…Permanently sulfidic marine basins exhibit not only elevated rates of dark carbon fixation but also high rates of both acetate production and acetate assimilation (0.05 to 0.5 M day Ϫ1 ) (51). Acetate assimilation has been suggested to provide an important source of carbon for microbial growth on the highly productive northern Gulf of Mexico shelf (52). A. peruensis could assimilate acetate by converting it to acetyl-CoA using the combination of the high-affinity acetate permease (K m ϭ 5.4 M) and the acetyl-CoA synthetase (53,54) (Fig.…”