Chemolithotrophic haloalkaliphiles from soda lakes

Abstract

This paper summarizes recent data on the occurrence and properties of lithotrophic prokaryotes found in extremely alkaline, saline (soda) lakes. Among the chemolithotrophs found in these lakes the obligately autotrophic sulfur-oxidizing bacteria were the dominant, most diverse group, best adapted to haloalkaline conditions. The culturable forms are represented by three new genera, Thioalkalimicrobium, Thioalkalivibrio and Thioalkalispira in the Gammaproteobacteria. Among them, the genus Thioalkalivibrio was most metabolically diverse, including denitrifying, thiocyanate-oxidizing and facultatively alkaliphilic species. Culturable methane-oxidizing populations in the soda lakes belong to the type I methanotroph group in the Gammaproteobacteria, mostly in the genus Methylomicrobium. The nitrifying bacteria in hyposaline soda lakes were represented by a new species Nitrobacter alkalicus (Alphaproteobacteria), and by an alkaliphilic subspecies of Nitrosomonas halophila (Betaproteobacteria). Both belonged to the low salt-tolerant alkaliphiles. The facultatively autotrophic haloalkaliphilic isolates able to grow with hydrogen as electron donor were identified as representatives of the alpha-3 subclass of the Proteobacteria (aerobic) and of the Natronolimnicola - Alkalispirillum group in the gammaproteobacteria (nitrate-reducing). While all chemolithotrophic isolates from soda lakes belong to the alkaliphiles with a pH optimum for growth around 10, only the sulfur-oxidizing group included species able to grow under hypersaline conditions. This indicates that carbon and nitrogen cycles in the hypersaline alkaline lakes might not be closed.

Bacterial diversity and activity along a salinity gradient in soda lakes of the Kulunda Steppe (Altai, Russia)

“…autotrophic nitrification, methanogenesis and complete-oxidizer SRB, may not be able to deal with high salinities for thermodynamic reasons (Oren 1999). However, soda lakes are a specific type of saline lake in which NaHCO 3 /Na 2 CO 3 is the major salt in solution, a two times weaker electrolyte than sodium chloride, demanding approximately two times less energy to adapt to osmotic stress (Sorokin and Kuenen 2005b). Furthermore, at concentrations higher than 2 M total Na + , sodium carbonates are present only in their undissociated form, causing less stress than sodium chloride, which is fully dissociate up to saturation (5 M Na + ).…”

“…In the last decade, special attention has been given to the investigation of the microbial communities in soda lakes using both traditional isolation methods (Duckworth et al 1996;Sorokin et al 2004;Sorokin and Kuenen 2005b) and molecular biology techniques (Humayoun et al 2003;Rees et al 2004;Scholten et al 2005;Foti et al 2007). Few reviews (Zavarzin et al 1999;Jones et al 1998) summarize these results, showing that soda lakes contain representatives of the major trophic and phylogenetic groups of prokaryotes, and that they can be considered as autonomous systems, in which cycling of nutrients is close to complete.…”

“…In soda lakes sodium carbonate/ bicarbonate is the major salt in solution, which has different physical and chemical properties, such as being a two times weaker electrolyte than sodium chloride. For this, a less energetically expensive osmotic adaptation is needed than demanded for life in NaCl brines (Sorokin and Kuenen 2005b). Nevertheless, organisms inhabiting soda lakes have to deal with high alkaline conditions, which represent an extra stress factor.…”

CO2 uptake by a soil microcosm

“…These prokaryotes use inorganic substrates to derive energy for biosynthesis reactions via aerobic or anaerobic CO 2 assimilation (Alfreider et al, 2009). They are unique in their ability to derive energy from sources not related to solar activity and can be found in diverse locations both above and below the Earths crust (Waksman and Joffe, 1922;Starkey, 1935;Pedersen, 2000;Amend and Teske, 2005;Sorokin and Kuenen, 2005;Alfreider et al, 2009). Microbial uptake of atmospheric CO 2 via autotrophic processes is a well characterised biological phenomenon, but actual estimations of sequestration rates are rare in the literature .…”

Microbial Isobutyronitrile Utilization under Haloalkaline Conditions

“…These habitats harbor mostly haloalkaliphilic prokaryotic microbial communities (8,20,25). Recently, we have described the first example of a bacterium, Natronocella acetinitrilica, isolated from soda lake sediments, capable of growth with aceto-and propionitrile as carbon, energy, and nitrogen sources under haloalkaline conditions (21).…”