Control of heterotrophic prokaryotic abundance and growth rate in hypersaline planktonic environments

Abstract

The factors controlling prokaryote abundance and activity along salinity gradients were investigated in the Bras del Port solar saltern system (Alacant, Spain) in May 1999. Specific growth rates were high and prokaryote abundance relatively low at the lowest (seawater) salinities; the opposite was found at higher salinities. Experiments were carried out in representative salterns at salinities of 4 to 37%, to test whether prokaryote abundance and growth rate were (1) limited by inorganic or organic nutrients (nutrient addition experiments), (2) limited by cell abundance (dilution experiments), or (3) affected by zooplankton cascading down to affect the prokaryote predators. Lowsalinity ponds were limited by organic nutrients, while high-salinity ponds responded slightly only to dilution. Zooplankton affected prokaryote growth rates particularly in the medium-salinity ponds. In the low salinity ponds, zooplankton effects were weak and probably indirect (through increased supply of organic matter). Neither organic matter limitation nor zooplankton predation pressure affected prokaryote development in the higher salinity ponds. We suggest that 3 types of functional communities occur in the same saltern system: (1) an active, substrate-limited community in the low salinity ponds; (2) an active, grazer-controlled community in the medium salinity ponds; and (3) a possibly dormant, probably substrate-limited, community in the high salinity ponds. However, the results at the highest salinities were equivocal, because the dilution manipulation had detrimental effects, artificially decreasing the contribution of the haloarchaea, which were essential contributors to the total activity in the saltern. Bacterial taxonomic community composition was also determined in these experiments by denaturing gradient gel electrophoresis (DGGE) analyses on 16S rRNA genes, and showed very small changes in community composition in the experimental manipulations. Together with the known microbial community structure and composition at differing salinities along the gradient, our results show that functional aspects of the microbial food web also vary between salterns.

From community approaches to single-cell genomics: the discovery of ubiquitous hyperhalophilic Bacteroidetes generalists

“…Although a common portion of CCAB community remained in both crystallizers, there were also crystallizer-specific phylotypes, such as Halorhabdus-related phylotypes that were detected at all sampling times in CR30 or HQR7 Haloquadratum and Salinibacter phylotype SR6 present only in Community dynamics in hypersaline environments M Gomariz et al CR41 samples (HQR7 from January to June and SR6 in all samples). In addition, CR41 harbored Cyanobacteria from September to November, which is noteworthy as normally this group of prokaryotes is absent from close-to-saturation hypersaline waters being the green alga Dunaliella the only photoautotroph (Estrada et al, 2004;Gasol et al, 2004).…”

Global ecological patterns in uncultured Archaea

“…Good examples are the Methanomicrobiales and Methanosarcinales (indicator groups for freshwater and marine sediments, respectively), well known as central components for anaerobic organic matter degradation coupled to methanogenesis in aquatic environments. Haloarchaeales also constitute the most active population for organic matter degradation in hyperhaline environments (for example, Gasol (2004)), whereas in hydrothermal vents chemolithoautotrophs members of the Archaeoglobales and the Thermoprotei are recognized as key primary producers under anaerobic conditions by coupling oxidation of hydrogen gas with sulfate reduction (Segerer et al, 1993 and references therein). Furthermore, from the recent cultivation of the autotrophic ammonia oxidizer Crenarchaeota Nitrosocaldus yellowstonii (de la Torre, 2008), we can hypothesize a significant role in the nitrogen cycle of Hdv by members of the 1.1g group.…”

Genome and physiology of a model Epsilonproteobacterium responsible for sulfide detoxification in marine oxygen depletion zones

“…Growth rate, temperature, sea salt requirements, and oxygen sensitivity were investigated, and alternative electron donors (sulfur compounds, hydrogen, organic substances) and electron acceptors (nitrite, fumarate, Hepes) were tested. Growth rates were calculated by measuring cell numbers during a 7-d incubation, as assessed by flow cytometry (35). Chemical analyses were performed as described previously (36)(37)(38)(39)(40).…”