Microbial Processing of Sediment‐Derived Dissolved Organic Matter: Implications for Its Subsequent Biogeochemical Cycling in Overlying Seawater

Abstract

Coastal sediments contain a large amount of dissolved organic matter (DOM), which can be mobilized into the overlying water by natural and anthropogenic activities. The bioavailability and subsequent biogeochemical effects of this sediment-derived DOM are unclear. To investigate those, we collected a sediment pore-water DOM (SDOM) sample and its overlying seawater to conduct a bioassay experiment, which allowed tracking of both short-term and long-term microbial processes in the context of DOM transformations. Short-term incubation results show that the SDOM extract supported the growth of specific taxa. The microbial community composition changed dramatically and an approximately 50% of SDOM-derived carbon was consumed within the first 2 days. Viruses likely played a role in promoting bacterial community succession, further enhancing transformation of this SDOM. Long-term incubation results show that labile DOM was gradually consumed, while approximately 16% of the initial SDOM appeared to be recalcitrant to microbial utilization and remained at the end (after 110 days) of the incubation experiment. Despite the short-term drastic changes in microbial community composition, a highly diverse microbial community is similar to the control at the end of the incubation. It is suggested here that resuspension of coastal sediments weakens their role as a net sink of carbon, with most of the mobilized SDOM transformed by successive microbial communities in the overlying seawater and the remaining recalcitrant organic material becoming part of the long-lived DOM pool. Thus, the bioavailability of the coastal SDOM might influence the carbon budget in coastal oceans.

Impact of Viral Lysis on the Composition of Bacterial Communities and Dissolved Organic Matter in Deep-Sea Sediments

“…The main changes of the DOM molecular composition were observed along the time axis of the experiments (Figure 3). The decomposition of bulk organic compounds and molecules that were probably liberated by slurrying led to a gradual removal of bio-available components, accompanied by a relative accumulation of more refractory compounds [66,70]. Despite the clear alteration of the DOM composition by the slurry process, DOM analysis revealed that prophage induction had modified the chemical composition and character of the benthic DOM pool, which is in line with previous studies [12,20,71].…”

Microbial transformation of distinct exogenous substrates into analogous composition of recalcitrant dissolved organic matter

“…Increasing studies of microbial metabolism have explained the production of RDOM (Lechtenfeld et al ., 2015, Osterholz et al ., 2015, Jiao et al ., 2018, Koch et al ., 2014). At the ecological level, marine microbial communities have been observed following predictable patterns (or recurrent patterns), involving complex network interactions in natural environments (Fuhrman et al ., 2015, Teeling et al ., 2016) and playing an important role in mediating organic carbon from the labile state to the relatively recalcitrant (Cai et al ., 2019). In addition, it has been previously suggested that the RDOM production could be independent of its ultimate sources (Koch et al ., 2005, Rossel et al ., 2013).…”

Chemical Diversity and Biochemical Transformation of Biogenic Organic Sulfur in the Ocean

“…Organic sulfur is the second most important reduced sulfur pool in sedimentary environments. FT-ICR-MS has shown that organic sulfur in surficial sediments is composed of a heterogeneous mixture of sulfur compounds (Cai et al, 2019). These compounds are considerably different from sulfur compounds identified in seawater.…”

“…The most important biologically mediated processes regulating the long term storage of organic matter in the ocean are the biological carbon pump (Ducklow et al, 2001) and the microbial carbon pump (Jiao et al, 2010(Jiao et al, , 2014(Jiao et al, , 2018. After the long-term incubation (110 days) of a microbial community in natural seawater, more sulfur metabolites may be produced, suggesting that biotic process lead to the formation of refractory compounds (Figure 5A) (Cai et al, 2019). SQDG is efficiently removed as it sinks to the deep sea; in contrast, around 40 sulfur-containing lipids, likely produced by photoautotrophs in the upper ocean, are potentially important as deep-ocean carbon storage compounds (Schubotz et al, 2018).…”