Cable bacteria that are capable of transporting electrons on centimeter scales have been found in a variety of sediment types, where their activity can strongly influence diagenetic reactions and elemental cycling. In this study, the patterns of spatial and temporal colonization of surficial sediment by cable bacteria were revealed in two-dimensions by planar pH and H2S optical sensors for the first time. The characteristic sediment surface pH maximum zones begin to develop from isolated micro-regions and spread horizontally within 5 days, with lateral spreading rates from 0.3 to ~ 1.2 cm day−1. Electrogenic anodic zones in the anoxic sediments are characterized by low pH, and the coupled pH minima also expand with time. H2S heterogeneities in accordance with electrogenic colonization are also observed. Cable bacteria cell abundance in oxic surface sediment (0–0.25 cm) kept almost constant during the colonization period; however, subsurface cell abundance apparently increased as electrogenic activity expanded across the entire surface. Changes in cell abundance are consistent with filament coiling and growth in the anodic zone (i.e., cathodic snorkels). The spreading mechanism for the sediment pH–H2S fingerprints and the cable bacteria abundance dynamics suggest that once favorable microenvironments are established, filamentous cable bacteria aggregate or locally activate electrogenic metabolism. Different development dynamics in otherwise similar sediment suggests that the accessibility of reductant (e.g., dissolved phase sulfide) is critical in controlling the growth of cable bacteria.
Biogenic structures and cable bacteria interactions: redox domain residence times and the generation of complex pH distributions
Cable bacteria are multicellular filamentous bacteria that conduct electrons nonlocally between anoxic and oxic sediment regions, creating characteristic electrogenic pH fingerprints. These microbes aggregate in 3D patterns near biogenic structures, and filament fragments are also dispersed throughout deposits. Utilizing pH-sensitive planar optodes to investigate the dynamic response of electrogenic pH fingerprints to sediment reworking, we found that mobile bioturbators like nereid polychaetes (ragworms) can disturb the pH signatures. Sudden sediment disturbance associated with burrows at sub- to multi-centimeter scales eliminates detection of pH signatures. However, electrogenic pH fingerprints can recover in as little as 13 h near abandoned, closed burrows. Sequential collapse and regeneration of electrogenic pH fingerprints are associated with occupied and dynamic burrow structures, with the response time positively related to the scale of disturbance. In the case of relatively stable tube structures, built by benthos like spionid polychaetes and extending mm to cm into deposits, the electrogenic pH fingerprint is evident around the subsurface tubes. Cable filaments clearly associate with subsurface regions of enhanced solute exchange (oxidant supply) and relatively stable biogenic structures, including individual tubes and patches of tubes (e.g. made by Sabaco , a bamboo worm). Physically stable environments, favorable redox gradients, and enhanced organic/inorganic substrate availability promote the activity of cable bacteria in the vicinity of tubes and burrows. These findings suggest complex interactions between electrogenic activity fingerprints and species-specific patterns of bioturbation at multiple spatial and temporal scales, and a substantial impact of electrogenic metabolism on subsurface pH and early diagenetic reaction distributions in bioturbated deposits.
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- Award ID(s):
- 1737749
- NSF-PAR ID:
- 10278356
- Date Published:
- Journal Name:
- Marine Ecology Progress Series
- Volume:
- 669
- ISSN:
- 0171-8630
- Page Range / eLocation ID:
- 51 to 63
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
Electrogenic cable bacteria can couple spatially separated redox reaction zones in marine sediments using multicellular filaments as electron conductors. Reported as generally absent from disturbed sediments, we have found subsurface cable aggregations associated with tubes of the parchment worm Chaetopterus variopedatus in otherwise intensely bioturbated deposits. Cable bacteria tap into tubes, which act as oxygenated conduits, creating a three-dimensional conducting network extending decimeters into sulfidic deposits. By elevating pH, promoting Mn, Fe-oxide precipitation in tube linings, and depleting S around tubes, they enhance tube preservation and favorable biogeochemical conditions within the tube. The presence of disseminated filaments a few cells in length away from oxygenated interfaces and the reported ability of cable bacteria to use a range of redox reaction couples suggest that these microbes are ubiquitous facultative opportunists and that long filaments are an end-member morphological adaptation to relatively stable redox domains.more » « less
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null (Ed.)The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is a coordinated, multiexpedition International Ocean Discovery Program (IODP) drilling project designed to investigate fault mechanics and seismogenesis along subduction megathrusts through direct sampling, in situ measurements, and long-term monitoring in conjunction with allied laboratory and numerical modeling studies. The fundamental scientific objectives of the NanTroSEIZE drilling project include characterizing the nature of fault slip and strain accumulation, fault and wall rock composition, fault architecture, and state variables throughout the active plate boundary system. IODP Expedition 365 is part of NanTroSEIZE Stage 3, with the following primary objectives: (1) retrieval of a temporary observatory at Site C0010 that has been monitoring temperature and pore pressure within the major splay thrust fault (termed the “megasplay”) at 400 meters below seafloor since November 2010 and (2) deployment of a complex long-term borehole monitoring system (LTBMS) that will be connected to the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) seafloor cabled observatory network postexpedition (anticipated June 2016). The LTBMS incorporates multilevel pore pressure sensing, a volumetric strainmeter, tiltmeter, geophone, broadband seismometer, accelerometer, and thermistor string. Together with an existing observatory at Integrated Ocean Drilling Program Site C0002 and a possible future installation near the trench, the Site C0010 observatory will allow monitoring within and above regions of contrasting behavior of the megasplay fault and the plate boundary as a whole. These include a site above the updip edge of the locked zone (Site C0002), a shallow site in the megasplay fault zone and its footwall (Site C0010), and a site at the tip of the accretionary prism (Integrated Ocean Drilling Program Site C0006). Together, this suite of observatories has the potential to capture deformation spanning a wide range of timescales (e.g., seismic and microseismic activity, slow slip, and interseismic strain accumulation) across a transect from near-trench to the seismogenic zone. Site C0010 is located 3.5 km along strike to the southwest of Integrated Ocean Drilling Program Site C0004. 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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3354/meps13722
