Abstract
Chitin,
a highly insoluble polymer of GlcNAc, is produced in massive quantities
in the marine environment. Fortunately for survival of aquatic
ecosystems, chitin
is rapidly catabolized by marine bacteria. Here we describe a bacterial
two-component hybrid sensor/kinase (of the ArcB type) that rigorously
controls expression of approximately 50 genes, many involved in chitin degradation. The sensor gene, chiS, was identified in Vibrio furnissii and Vibrio cholerae
(predicted amino acid sequences, full-length: 84% identical, 93%
similar). Mutants of chiS grew normally on GlcNAc but did not express
extracellular chitinase, a specific chitoporin, or beta-hexosaminidases,
nor did they exhibit chemotaxis, transport, or growth on chitin
oligosaccharides such as (GlcNAc)(2). Expression of these systems
requires three components: wild-type chiS; a periplasmic high-affinity chitin oligosaccharide, (GlcNAc)(n) (n > 1), binding protein
(CBP); and the environmental signal, (GlcNAc)(n). Our data are
consistent with the following model. In the uninduced state, CBP binds
to the periplasmic domain of ChiS and "locks" it into the minus conformation. The environmental signal, (GlcNAc)(n), dissociates the complex by binding to CBP, releasing ChiS, yielding the plus phenotype (expression of chitinolytic genes). In V. cholerae,
a cluster of 10 contiguous genes (VC0620-VC0611) apparently comprise a
(GlcNAc)(2) catabolic operon. CBP is encoded by the first, VC0620,
whereas VC0619-VC0616 encode a (GlcNAc)(2) ABC-type permease. Regulation
of chiS requires expression of CBP but not (GlcNAc)(2) transport.
(GlcNAc)(n) is suggested to be essential for signaling these cells that chitin is in the microenvironment.
https://www.ncbi.nlm.nih.gov/pubmed/14983042
Global impact of Vibrio cholerae interactions with chitin.
(Arveltavaa on että vibrio hakeutuu sinne missä on kitiinikäsittelyä ja valmista ravinnetta mukoosassa - saattaa olla että vibrio kaappaa jonkin fysiologisen tien tärkeille ravinteilleen kiinnittymällä järjestelmän "kitiniä sitovaan periplasmisen domeenin" läheisyyteen jollain sillalla- olisi loogista.)
Abstract
The interaction of Vibrio cholerae with chitin
exemplifies for microbial ecology a successful bacteria-substrate
interaction with complex and significant influence on the lifestyle of
the bacterium. Chitin
is one of the most abundant polymers on earth and possibly the most
abundant in the aquatic environment, where its association with V. cholerae
has provided the microorganism with a number of advantages, including
food availability, adaptation to environmental nutrient gradients,
tolerance to stress and protection from predators. Emergent properties
of V. cholerae-chitin
interactions occur at multiple hierarchical levels in the environment
and include cell metabolic and physiological responses e.g. chemotaxis,
cell multiplication, induction of competence, biofilm formation,
commensal and symbiotic relationship with higher organisms, cycling of
nutrients, and pathogenicity for humans and aquatic animals. As factors
mediating virulence of V. cholerae
for humans and aquatic animals derive from mechanisms of adaptation to
its environment, at different levels of hierarchical scale, V. cholerae interactions with chitin
represent a useful model for examination of the role of primary habitat
selection in the development of traits that have been identified as
virulence factors in human disease.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4170974/
In aquatic environments, Vibrio cholerae colonizes mainly on the chitinous surface of copepods and utilizes chitin as the sole carbon and nitrogen source. Of the two extracellular chitinases essential for chitin utilization, the expression of chiA2 is maximally up-regulated in host intestine. Recent studies indicate that several bacterial chitinases may be involved in host pathogenesis. However, the role of V. cholerae chitinases in host infection is not yet known. In this study, we provide evidence to show that ChiA2 is important for V. cholerae survival in intestine as well as in pathogenesis. We demonstrate that ChiA2 de-glycosylates mucin and releases reducing sugars like GlcNAc and its oligomers. Deglycosylation of mucin corroborated with reduced uptake of alcian blue stain by ChiA2 treated mucin. Next, we show that V. cholerae could utilize mucin as a nutrient source. In comparison to the wild type strain, ΔchiA2 mutant was 60-fold less efficient in growth in mucin supplemented minimal media and was also ∼6-fold less competent to survive when grown in the presence of mucin-secreting human intestinal HT29 epithelial cells. Similar results were also obtained when the strains were infected in mice intestine. Infection with the ΔchiA2 mutant caused ∼50-fold less fluid accumulation in infant mice as well as in rabbit ileal loop compared to the wild type strain. To see if the difference in survival of the ΔchiA2 mutant and wild type V. cholerae was due to reduced adhesion of the mutant, we monitored binding of the strains on HT29 cells. The initial binding of the wild type and mutant strain was similar. Collectively these data suggest that ChiA2 secreted by V. cholerae in the intestine hydrolyzed intestinal mucin to release GlcNAc, and the released sugar is successfully utilized by V. cholerae for growth and survival in the host intestine.
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