Fig. 3.

Symbionts sense chitin oligosaccharides (COS) only in the mature light organ. (A) Catabolism of COS in the genus Vibrio. COS are derivatives of amino di- and monosaccharides that represent enzymatic products of chitin hydrolysis (green box). After the COS are transported into the cell as the phosphorylated form, the acetyl and amino groups are removed from the hexose core before it enters glycolysis. The last common step in COS catabolism is the deamination of glucosamine-P by the enzyme NagB. To define amino sugar and COS catabolism in V. fischeri, we tested the ability of the ∆nagB mutant to grow on several sugars as a sole source of carbon (data shown in Fig. S3A). GlcNAc, N-acetyl glucosamine; (GlcNAc)₂, N-acetylchitobiose; GlcN, glucosamine; out, extracellular or periplasmic space; in, intracellular space. (B) Growth of a ∆nagB V. fischeri mutant in seawater–tryptone medium (SWTO), either without (−) or with (+) the addition of 20 mM GlcNAc at the arrow. Error bars indicate SEM, n = 4. (C) Extent of colonization of the squid light organ at immature and mature stages of host development by wild type, ∆nagB, and an in cis complemented (∆nagB Tn7::nagB) strain. cfu, colony-forming units; error bars indicate SEM, n = 12; statistical tests on log-transformed data are as described in Fig. 2.