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Carrageenan catabolism is conferred by a complex regulon in marine heterotrophic bacteria

ABSTRACT: Macroalgae contribute substantially to primary production in coastal ecosystems. Their biomass, mainly consisting of polysaccharides, is cycled into the environment by marine heterotrophic bacteria (MHB), using largely uncharacterized mechanisms. In Zobellia galactanivorans, we discovered and characterized the complete catabolic pathway for carrageenans, major cell wall polysaccharides of red macroalgae, providing a model system for carrageenan utilization by MHB. We further demonstrate that carrageenan catabolism relies on a multifaceted carrageenan-induced regulon, including a non-canonical polysaccharide utilization locus (PUL) and several distal genes. The genetic structure of the carrageenan utilization system is well conserved in marine Bacteroidetes, but modified in other MHB phyla. The core system is completed by additional functions which can be assumed by non-orthologous genes in different species. This complex genetic structure is due to multiple evolutionary events including gene duplications and horizontal gene transfers. These results allow for an extension on the definition of bacterial PUL-mediated polysaccharide digestion.

ORGANISM(S): Zobellia galactanivorans

PROVIDER: GSE101142 | GEO | 2017/12/06

SECONDARY ACCESSION(S): PRJNA393796

REPOSITORIES: GEO

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Project description:The phylum Bacteroidetes is a major component of the human gut microbiota which has a broad impact on the development and physiology of its host, and a potential role in a wide range of disease syndromes1-3. The predominance of Bacteroidetes and the genus Bacteroides in the distal gut is due in large part to the expansion of paralogous gene clusters, termed Polysaccharide Utilization Loci (PULs), dedicated to the uptake and catabolism of host derived and dietary polysaccharides4,5. It is generally thought that the diversity of PULs is key to Bacteroides successful competition for nutrients in the gut environment6. The nutritive value of the available polysaccharides varies greatly and thus their utilization is hierarchical and strictly controlled. A typical PUL includes regulatory genes that control expression in response to the presence of specific glycan substrates. However the existence of additional regulatory mechanisms has been predicted to explain phenomena such as the hierarchical control, catabolite repression, and the fine tuning of gene expression to match catabolic activity7-9. Using Bacteroides fragilis as a model organism, this report describes a previously unknown layer of regulatory control in which cis-encoded antisense small RNAs (sRNA) act as repressors of the PULsâ catabolic genes. Nearly 30% of B. fragilis PULs are subject to this type of sRNA control and these PULs tend to be more closely linked to the utilization of host-derived glycans than dietary polysaccharides. The findings described here indicate the presence of a global control mechanism that underlies the known regulatory circuits which modulate PUL expression in response to substrate availability, and hence provide novel insight into regulation of the gut Bacteroidetes physiology. This is a 4 chip study with 8 technical replicates on each chip. This was an in vitro, exploratory study to determine if mutation or overexpression of a sRNA associated with the Don locus would affect gene expression. In vitro cultures were grown in defined media with mucin glycans as the sole carbon source. The two chips representing growth of the wild type strain (638R) on mucin glycans were also used in a related study GSE53883 (GSM1303101 and GSM1303102).

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Carrageenan catabolism is conferred by a complex regulon in marine heterotrophic bacteria

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