The Cellulosome Paradigm in An Extreme Alkaline Environment

Abstract

Rapid decomposition of plant biomass in soda lakes is associated with microbial activity of anaerobic cellulose-degrading communities. The alkaliphilic bacterium, Clostridium alkalicellulosi, is the single known isolate from a soda lake that demonstrates cellulolytic activity. This microorganism secretes cellulolytic enzymes that degrade cellulose under anaerobic and alkaliphilic conditions. A previous study indicated that the protein fraction of cellulose-grown cultures showed similarities in composition and size to known components of the archetypical cellulosome Clostridium thermocellum. Bioinformatic analysis of the C. alkalicellulosi draft genome sequence revealed 44 cohesins, organized into 22 different scaffoldins, and 142 dockerin-containing proteins. The modular organization of the scaffoldins shared similarities to those of C. thermocellum and Acetivibrio cellulolyticus, whereas some exhibited unconventional arrangements containing peptidases and oxidative enzymes. The binding interactions among cohesins and dockerins assessed by ELISA, revealed a complex network of cellulosome assemblies and suggested both cell-associated and cell-free systems. Based on these interactions, C. alkalicellulosi cellulosomal systems have the genetic potential to create elaborate complexes, which could integrate up to 105 enzymatic subunits. The alkalistable C. alkalicellulosi cellulosomal systems and their enzymes would be amenable to biotechnological processes, such as treatment of lignocellulosic biomass following prior alkaline pretreatment.

Abundant Taxa and Favorable Pathways in the Microbiome of Soda-Saline Lakes in Inner Mongolia

“…It is defined as “soda” type when the sum of bicarbonate and carbonate concentrations are the first in the rank of dominant ions, and is “soda-saline” type when the concentration of other ions is higher than that of bicarbonate/carbonate ( Boros and Kolpakova, 2018 ). In these saline and alkaline environments, microorganisms exhibit surprisingly high biodiversity ( Grant, 2006 ; Mesbah et al, 2007 ; Asao et al, 2011 ; Lanzen et al, 2013 ), relatively high primary productivity rates ( Melack and Kilham, 1974 ; Melack, 1981 ; Kompantseva et al, 2009 ; Antony et al, 2013 ; Zorz et al, 2019 ), vigorous oxidation and reduction reactions of sulfur ( Sorokin et al, 2010 , 2011 ; Stam et al, 2010 ; Tourova et al, 2013 ; Vavourakis et al, 2019 ), and elevated metabolic activity of cellulose, methane, nitrogen and arsenic ( Iversen et al, 1987 ; Carini and Joye, 2008 ; Oremland et al, 2017 ; Phitsuwan et al, 2019 ). High concentrations of inorganic ions, such as (bi)carbonate and phosphate provide adequate essential elements, while hydrogen sulfide exhibits low toxicity under alkaline conditions ( Sorokin et al, 2015 ).…”

Mapping the deformability of natural and designed cellulosomes in solution

“…Genome mining of cellulosome-producing bacteria has revealed a large variety of cellulosomal systems [ 60 ] that potentially are linked to the natural habitats of the micro-organisms [ 61 ]. The encountered diversity raises the question whether the composition and spatial organization follows a general rule, or if the diversity also reflects the need to vary the connected biophysical properties, to adapt to specific habitats or substrate sources.…”

Mapping the Deformability of Natural and Designed Cellulosomes in solution

“…Genome mining of cellulosome-producing bacteria has revealed a large variety of cellulosomal systems [89] that potentially are linked to the natural habitats of the microorganisms [90]. The encountered diversity raises the question whether the composition and spatial organization follows a general rule, or if the diversity also re ects the need to vary the connected biophysical properties, to adapt to speci c habitats or substrate sources.…”