Leucine incorporation by aerobic anoxygenic phototrophic bacteria in the Delaware estuary

Abstract

Aerobic anoxygenic phototrophic (AAP) bacteria are well known to be abundant in estuaries, coastal regions and in the open ocean, but little is known about their activity in any aquatic ecosystem. To explore the activity of AAP bacteria in the Delaware estuary and coastal waters, single-cell 3 H-leucine incorporation by these bacteria was examined with a new approach that combines infrared epifluorescence microscopy and microautoradiography. The approach was used on samples from the Delaware coast from August through December and on transects through the Delaware estuary in August and November 2011. The percent of active AAP bacteria was up to twofold higher than the percentage of active cells in the rest of the bacterial community in the estuary. Likewise, the silver grain area around active AAP bacteria in microautoradiography preparations was larger than the area around cells in the rest of the bacterial community, indicating higher rates of leucine consumption by AAP bacteria. The cell size of AAP bacteria was 50% bigger than the size of other bacteria, about the same difference on average as measured for activity. The abundance of AAP bacteria was negatively correlated and their activity positively correlated with light availability in the water column, although light did not affect 3 H-leucine incorporation in light-dark experiments. Our results suggest that AAP bacteria are bigger and more active than other bacteria, and likely contribute more to organic carbon fluxes than indicated by their abundance.

Single-cell activity of freshwater aerobic anoxygenic phototrophic bacteria and their contribution to biomass production

“…In addition, the average specific rate of leucine uptake, based on the SGA around individual cells, was almost twofold higher for active AAP bacteria than for the average active bacterial cell in the community. This difference was slightly higher than that of the two previous MAR-AAP studies (1.6-and 1.4-fold, Kirchman et al, 2014;Stegman et al, 2014), and is also in agreement with previous studies showing that AAP bacteria tend to grow faster than the bulk bacterial community across a diverse range in aquatic habitats (Koblízek et al, 2007;Liu et al, 2010;Ferrera et al, 2011). We have further shown that AAP bacteria were on average larger than the average cell size in the community, a pattern that has been reported before (Sieracki et al, 2006;Lamy et al, 2011;Fauteux et al, 2015).…”

“…It is not clear, however, whether these higher apparent growth rates and potential competitiveness of AAP bacteria can be directly attributed to a light-driven effect. Recently, Stegman et al (2014) developed an approach that combines infrared epifluorescence microscopy with microautoradiography (AAP-MAR) in order to directly assess the activity of AAP bacteria from natural communities by measuring the incorporation of radioactive substrates by individual AAP cells. Recent studies using this approach in the Delaware estuary and the coastal waters of the West Antarctic Peninsula Stegman et al, 2014) confirmed that AAP cells were on average more active in substrate uptake than bulk bacterial cells, although there were large spatial and seasonal variations in the percentage of active AAP bacteria.…”

“…Recently, Stegman et al (2014) developed an approach that combines infrared epifluorescence microscopy with microautoradiography (AAP-MAR) in order to directly assess the activity of AAP bacteria from natural communities by measuring the incorporation of radioactive substrates by individual AAP cells. Recent studies using this approach in the Delaware estuary and the coastal waters of the West Antarctic Peninsula Stegman et al, 2014) confirmed that AAP cells were on average more active in substrate uptake than bulk bacterial cells, although there were large spatial and seasonal variations in the percentage of active AAP bacteria. Moreover, contrary to expectations, light did not enhance AAP single-cell activity in leucine incorporation in experimental incubations relative to dark controls, although AAP activity was positively correlated with light availability in the water column.…”

“…Using the AAP-MAR approach developed by Stegman et al (2014), we investigated how the proportion of active AAP bacteria and their single-cell activity in leucine incorporation vary among lakes, and how they compare with activity patterns of the bulk bacterial community. In addition, we explored the role of light in regulating the heterotrophic activity of bulk and AAP bacteria by exposing lake samples to artificial photosynthetically active radiation (PAR).…”

Geographic Impact on Genomic Divergence as Revealed by Comparison of Nine Citromicrobial Genomes

“…A erobic anoxygenic phototrophic bacteria (AAPB) are a widespread functional microbial group in the euphotic zone of the ocean and are thought to play important roles in the cycling of marine carbon and energy (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). AAPB can harvest light using bacteriochlorophyll a (BChl a) and various carotenoids to form a transmembrane proton gradient for the generation of ATP (1,11).…”