Structure and function of natural sulphide-oxidizing microbial mats under dynamic input of light and chemical energy

Abstract

We studied the interaction between phototrophic and chemolithoautotrophic sulphide-oxidizing microorganisms in natural microbial mats forming in sulphidic streams. The structure of these mats varied between two end-members: one characterized by a layer dominated by large sulphur-oxidizing bacteria (SOB; mostly Beggiatoa-like) on top of a cyanobacterial layer (B/C mats) and the other with an inverted structure (C/B mats). C/B mats formed where the availability of oxygen from the water column was limited (o5 μM). Aerobic chemolithotrophic activity of the SOB depended entirely on oxygen produced locally by cyanobacteria during high light conditions. In contrast, B/C mats formed at locations where oxygen in the water column was comparatively abundant (445 μM) and continuously present. Here SOB were independent of the photosynthetic activity of cyanobacteria and outcompeted the cyanobacteria in the uppermost layer of the mat where energy sources for both functional groups were concentrated. Outcompetition of photosynthetic microbes in the presence of light was facilitated by the decoupling of aerobic chemolithotrophy and oxygenic phototrophy. Remarkably, the B/C mats conserved much less energy than the C/B mats, although similar amounts of light and chemical energy were available. Thus ecosystems do not necessarily develop towards optimal energy usage. Our data suggest that, when two independent sources of energy are available, the structure and activity of microbial communities is primarily determined by the continuous rather than the intermittent energy source, even if the time-integrated energy flux of the intermittent energy source is greater.

Cyanobacteria in Sulfidic Spring Microbial Mats Can Perform Oxygenic and Anoxygenic Photosynthesis Simultaneously during an Entire Diurnal Period

“…The cold, light-exposed sulfidic springs at Frasassi, Italy (Klatt et al, 2016), which harbor thin microbial mats inhabited by diverse anoxygenic, oxygenic and versatile phototrophs, are one example of such an environment. Our recent studies of cyanobacteria isolated from this system revealed two novel cyanobacterial adaptations to H 2 S. The first adaptation mechanism, observed for a versatile cyanobacterium Pseudoanabaena str.…”

“…Our recent studies of cyanobacteria isolated from this system revealed two novel cyanobacterial adaptations to H 2 S. The first adaptation mechanism, observed for a versatile cyanobacterium Pseudoanabaena str. FS39, included partitioning between AP and OP that is regulated kinetically by H 2 S through the apparent affinity of the electron transport components involved in AP [sulfide:quinone:reductase (SQR)] and OP [photosystem II (PSII)] toward plastoquinone, which is where both electron transport pathways intersect ( Figure 1 ; Klatt et al, 2016). OP in this cyanobacterial strain is active only when the electron transport chain is not fully used by AP, which occurs when H 2 S is limiting.…”

A submarine volcanic eruption leads to a novel microbial habitat

“…This is coherent with the high extracellular enzymatic activities observed on the filament, . None of the genomic bins identified contained genes associated with photosynthetic pathways, therefore excluding photosynthesis from the metabolism of Venus's hair filaments (including Candidatus Thiolava veneris) 27 . Bioinformatic analyses indicated that the assemblage associated with the Venus's hair filaments is completely different, and indeed segregated apart, from any other assemblage reported from hydrothermal systems or elsewhere to date (Supplementary Table 4 and Supplementary Fig.…”

“…molecular analyses revealed the presence of known nematode species (for example, Paracanthonchus) that are also found in hydrothermal vent systems 27,29 and arthropods ( Supplementary Fig. 6).…”

Spatially resolved capture of hydrogen sulfide from the water column and sedimentary pore waters for abundance and stable isotopic analysis

“…10 adjacent Sentino river, resulting in a complex microbial community dominated by sulfide oxidizers and cyanobacteria (Klatt et al, 2016). Films deployed in this system document abundant sulfide both in the sediments and in the flowing water column (Figure 5c).…”