Betaine or glycine betaine, a trimethylated glycine derivative, is abundant in saline environments where it is accumulated in the growing microbial cells to counteract external osmotic pressure. Depending on the ambient ionic strength, betaine content in the biomass of halophilic and haloalkaliphilic bacteria may be rather high, e.g. up to 16% (w/w) of total dry cell mass (Sorokin et al., 2008). When betaine is released into the environment either by lifetime excretion or after dying off the cells, it becomes available as a substrate for further degradation by microorganisms having appropriate enzymes. Formation and breakdown of betaine in the microbial world has been intensively studied in the 80s and 90s of the past century (Hagemann, 2011, Oren, 2006, Ventosa et al., 1998, Zhilina and Zavarzin, 1990), and this topic still remains interesting in the context of biotechnological applications (Zou et al., 2016). From the ecological point of view, aerobic degradation of betaine is not as interesting as anaerobic one, because in the latter case betaine decomposing bacteria can split off betaine molecule incompletely and its parts may serve as substrates for other microorganisms, thus giving rise to the betaine-based trophic chain. Depending on particular species, typical products of microbially mediated betaine degradation are trimethylamine, acetate, and sometimes methylated derivatives of glycine (Oren, 1990). The first two are well known methanogenic precursors and electron donors for sulfate reduction. Degradation of the osmoprotector betaine in saline water bodies, where trimethylamine serves as the main substrate for methanogenesis, is a necessary link in the implementation of the methylotrophic pathway of methanogenesis specific for halophilic methanogens (Zhilina and Zavarzin, 1990). Moreover, methanogens themselves can utilize betaine (Ticak et al., 2015, Watkins et al., 2014). Apart from terrestrial hypersaline lakes this pathway was shown for microbial consortia in other habitats where betaine is significant; among these are deep-sea hypersaline anoxic lakes Medee (Mediterranean Sea) (Yakimov et al., 2013) and Orca Basin (Gulf of Mexico) (Nigro et al., 2016), 2.5-km-deep shale formations Marcellus and Utica (Pennsylvania, USA) (Daly et al., 2016), Stiffkey salt marsh in Norfolk (UK) (Jones et al., 2019), and an oil reservoir of the Hoover Field (Gulf of Mexico) (Christman et al., 2020). Although anaerobes are known to degrade betaine, there are very few halophiles among them, namely Maledivibacter halophilum (former Clostridium halophilum) (Fendrich et al., 1990); Acetohalobium arabaticum (Kanehisa et al., 2016, Zhilina and Zavarzin, 1990); Halanaerobium alcaliphilum (Tsai et al., 1995); Halanaerobacter salinarius (Mouné et al., 1999); Halanaerobacter lacunarum (La Cono et al., 2015), and ‘Oceanirhabdus seepicola’ (Li et al., 2021). Potentially, Halomonas magadiensis and adjacent strains can be attributed to this group, but the authors found this property in aerobic conditions and did not test the anaerobic growth on betaine with nitrate (Duckworth et al., 2000). Since the alkaline conditions of soda lakes are often accompanied by high, up to saturation, content of sodium, it would be logical to expect to find there anaerobic haloalkaliphiles that degrade betaine similar to the haloneutralophiles of saline environments with neutral pH. The haloalkaliphilic betaine degrading strains of Natroniella sp. ANB-GB1 at 2 M Na+ and pH 10 and Halalkaliarchaeum sp. AArc-GB at 4 M Na+ and pH 9.7 recently isolated from hypersaline soda lakes in Kulunda Steppe (Altai region, Russia) (Sorokin, 2021), became the first anaerobic alkaliphiles capable of betaine decomposition. We also succeeded to isolate an anaerobic, alkaliphilic bacterium, designated strain Z-7014T, involved in betaine degradation, from sediments near to the soda lake Tanatar III which is located in the same region. Here, we report on the isolation and characterization of this strain that formed a deep phyletic lineage within the order Halanaerobiales.
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