Soda lakes is a unique type of inland highly alkaline and saline habitat dominated by a specialized group of haloalkaliphilic bacteria and archaea (Grant and Jones, 2016). Intensive microbiology and molecular ecology studies of the soda lakes in the past three decades uncovered functionally rich and taxonomically diverse prokaryotic communities (Haines et al., 2023; Sorokin et al., 2014; Sorokin et al., 2015; Sorokin, 2017; Vavourakis et al., 2016, Vavourakis et al., 2018, Vavourakis et al., 2019; Zhao et al., 2020; Zorz et al., 2019). One of the primary steps of the carbon-cycling microbial communities is polymer degradation, and cellulose is one of the major carbohydrate polymers produced by plants and algae. So far, little was known about the identity of haloalkaliphilic prokaryotes involved in mineralization of cellulose in soda lakes. Only recently it was discovered that in hypersaline soda lakes aerobic natronoarchaea can fulfill this function, in particular the genera Natronobiforma and Natronolimnobius (Sorokin et al., 2015, Sorokin et al., 2018), whose genomes encode multiple copies of endo-cellulases from the GH5 and GH9 families (Elcheninov et al., 2023). However, the identity of cellulose-mineralizing bacteria in moderately saline soda lakes remained unclear. The only example of such bacteria, known so far, is a moderately salt-tolerant, anaerobic, cellulosome-forming Clostridium alkalicellulosi (lately reclassified as Acetivibrio alkalicellulosi or Herbivorax alkalicellulosi according to the GTDB classification) from a soda lake Hadyn in Tuva (Russia) (Zhilina et al., 2005; Zvereva et al., 2006).

Our recent efforts in obtaining a better understanding of the bacterial cellulose mineralization in moderately saline soda lakes resulted in enrichment of three haloalkaliphilic anaerobic bacterial cultures capable of utilization of various forms of insoluble cellulose as growth substrate. The primary cellulotrophic bacteria in these cultures were represented by new members of the Clostridiales, Halanaerobiales and Fibrobacterota (Sorokin et al., 2024). In this work we present results of phenotypic, phylogenetic and functional genomic analyses of the cellulotrophic Fibrobacterota strain ANBcel5T, and propose to classify this bacterium in a a new genus and species in the family Chitinispirillaceae.