Unique organization and unprecedented diversity of the Bacteroides (Pseudobacteroides) cellulosolvens cellulosome system

Abstract

Background (Pseudo) Bacteroides cellulosolvens is an anaerobic, mesophilic, cellulolytic, cellulosome-producing clostridial bacterium capable of utilizing cellulose and cellobiose as carbon sources. Recently, we sequenced the B. cellulosolvens genome, and subsequent comprehensive bioinformatic analysis, herein reported, revealed an unprecedented number of cellulosome-related components, including 78 cohesin modules scattered among 31 scaffoldins and more than 200 dockerin-bearing ORFs. In terms of numbers, the B. cellulosolvens cellulosome system represents the most intricate, compositionally diverse cellulosome system yet known in nature.ResultsThe organization of the B. cellulosolvens cellulosome is unique compared to previously described cellulosome systems. In contrast to all other known cellulosomes, the cohesin types are reversed for all scaffoldins i.e., the type II cohesins are located on the enzyme-integrating primary scaffoldin, whereas the type I cohesins are located on the anchoring scaffoldins. Many of the type II dockerin-bearing ORFs include X60 modules, which are known to stabilize type II cohesin–dockerin interactions. In the present work, we focused on revealing the architectural arrangement of cellulosome structure in this bacterium by examining numerous interactions between the various cohesin and dockerin modules. In total, we cloned and expressed 43 representative cohesins and 27 dockerins. The results revealed various possible architectures of cell-anchored and cell-free cellulosomes, which serve to assemble distinctive cellulosome types via three distinct cohesin–dockerin specificities: type I, type II, and a novel-type designated R (distinct from type III interactions, predominant in ruminococcal cellulosomes).ConclusionsThe results of this study provide novel insight into the architecture and function of the most intricate and extensive cellulosomal system known today, thereby extending significantly our overall knowledge base of cellulosome systems and their components. The robust cellulosome system of B. cellulosolvens, with its unique binding specificities and reversal of cohesin–dockerin types, has served to amend our view of the cellulosome paradigm. Revealing new cellulosomal interactions and arrangements is critical for designing high-efficiency artificial cellulosomes for conversion of plant-derived cellulosic biomass towards improved production of biofuels.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0898-6) contains supplementary material, which is available to authorized users.

Pan-Cellulosomics of Mesophilic Clostridia: Variations on a Theme

“…Likewise, additional related cellulosome-producing mesophilic clostridia, such as Clostridium puniceum , Herbinix luporum , Clostridium hungatei , Clostridium roseum , etc., have not been included herein. Moreover, the contribution of additional, recently sequenced mesophilic, but complex, multi-scaffoldin cellulosome-producing bacteria, such as Clostridium alkalicellulosi and Bacteroides ( Pseudobacteroides ) cellulosolvens [ 19 ], will also shed light on the cellulosomal models of the mesophilic bacteria.…”

“…The major scaffoldin genes are clustered in the genome in a sca gene cluster , wherein the sca genes do not appear adjacent to the dockerin-bearing enzymes, as they do in the simple cellulosome-producing bacteria [ 16 ]. Complex cellulosomes have been observed in C. thermocellum [ 17 ], Bacteroides ( Pseudobacteroides ) cellulosolvens [ 18 , 19 ], Acetivibrio cellulolyticus [ 20 , 21 ], Ruminococcus flavefaciens [ 22 , 23 ], and C. clariflavum [ 24 , 25 ].…”

Inducing effects of cellulosic hydrolysate components of lignocellulose on cellulosome synthesis in Clostridium thermocellum

“…The method works well only when two following prerequisites are satisfied: (i) the cellulosome‐producing bacterium harbours single primary scaffoldin and (ii) the cellulosomes produced under different conditions contain the primary scaffoldin and similar enzymatic components at average level. The first prerequisite is obviously satisfied for C. thermocellum analysed in this study, but not for Acetivibrio cellulolyticus (Hamberg et al ., ), Pseudobacteroides cellulosolvens (Zhivin et al ., ), etc., which have more complex cellulosomal architectures. The second prerequisite is likely true in this study because both glucose and cellobiose are the hydrolysates of Avicel.…”

Isolation, biochemical characterization and phylogeny of a cellulose-degrading ruminal bacterium

“…Ruminococcus albus and R. flavefaciens use cellulosomes, pili proteins (Rakotoarivonina et al, 2005) and glicocalix containing extracellular polymeric substances (Weimer et al, 2006), and the catalytic part of the cellulosome includes cellulases, xylanases and pectinases that work synergistically to degrade the complex molecules of the cell wall (Artzi et al, 2016). Microorganisms with these characteristics have potential for the industry of cellulosic-biofuel production since the high cost of converting biomass to sugars is the main obstacle for developing this industry (Venkatesh, 2014;Zhivin et al, 2017).…”