This study examined packing (pocketing or holding accepted food in the mouth) in 3 children who were failing to thrive or had inadequate weight gain due to insufficient caloric intake. The results of an analysis of texture indicated that total grams consumed were higher when lower textured foods were presented than when higher textured foods were presented. The gram intake was related directly to levels of packing. That is, high levels of packing were associated with higher textured foods and low gram intake, and low levels of packing were associated with lower textured foods and high gram intake. All participants gained weight when texture of foods was decreased. Packing remained low during follow-up for 2 participants even when the texture of food was increased gradually over time. These data are discussed in relation to avoidance, response effort, and skill deficit.

Sphingomonas elodea ATCC 31461 produces gellan, a capsular polysaccharide that is useful as a gelling agent for food and microbiological media. Complementation of nonmucoid S. elodea mutants with a gene library resulted in identification of genes essential for gellan biosynthesis. A cluster of 18 genes spanning 21 kb was isolated. These 18 genes are homologous to genes for synthesis of sphingan polysaccharide S-88 from Sphingomonas sp. ATCC 31554, with predicted amino acid identities varying from 61% to 98%. Both polysaccharides have the same tetrasaccharide repeat unit, comprised of [-->4)-alpha- l-rhamnose-(1-->3)-beta- d-glucose-(1-->4)-beta- d-glucuronic acid-(1-->4)-beta- d-glucose-(1-->]. Polysaccharide S-88, however, has mannose or rhamnose in the fourth position and has a rhamnosyl side chain, while gellan has no sugar side chain but is modified by glyceryl and acetyl substituents. Genes for synthesis of the precursor dTDP- l-rhamnose were highly conserved. The least conserved genes in this cluster encode putative glycosyl transferases III and IV and a gene of unknown function, gelF. Three genes ( gelI, gelM, and gelN) affected the amount and rheology of gellan produced. Four additional genes present in the S-88 sphingan biosynthetic gene cluster did not have homologs in the gene cluster for gellan biosynthesis. Three of these gene homologs, gelR, gelS, and gelG, were found in an operon unlinked to the main gellan biosynthetic gene cluster. In a third region, a gene possibly involved in positive regulation of gellan biosynthesis was identified.

No abstract

A cluster of genes for diutan polysaccharide synthesis was isolated from a library of Sphingomonas sp. ATCC 53159 genomic DNA by complementation of glucosyl-isoprenylphosphate transferase-deficient mutants of Sphingomonas elodea ATCC 31461 (producing gellan) and Xanthomonas campestris (producing xanthan). The synthesis of polysaccharide in these strains shares a common first step, transfer of glucose-1-phosphate from UDP-glucose to the isoprenylphosphate lipid. The cluster of 24 genes was compared to genes for biosynthesis of gellan, and S-88 sphingan from Sphingomonas sp. ATCC 31554. Diutan, gellan and S-88 sphingan have a common four-sugar backbone but different side chains, one rhamnose for S-88 sphingan, a two-rhamnose side chain for diutan and no side chain for gellan. The genes for biosynthesis of diutan, gellan and S-88 sphingan were similar in general organization but differed in location of some genes, in particular, dpsG (putative polymerase), dpsR (putative lyase) and dpsS (putative repeat unit transporter). An unidentified reading frame urf31, present in the gene clusters for diutan and S-88 sphingan but not gellan, had similarity to glycosyl transferase group 2 proteins, and was detrimental when cloned in Sphingomonas elodea producing gellan that lacks a side chain, but not in Sphingomonas ATCC 31554 producing S-88 sphingan with a rhamnose side chain. Gene urf31 could possibly encode a side-chain rhamnosyl transferase. Another gene urf31.4 was unique to the diutan gene cluster. A plasmid containing 20 of the 24 genes resulted in a slight increase in the amount of diutan produced, but a significant increase in the rheological properties of diutan.

No abstract