Dynamics of Human Gut Microbiota and Short-Chain Fatty Acids in Response to Dietary Interventions with Three Fermentable Fibers.

Production of short-chain fatty acids (SCFAs), especially butyrate, in the gut microbiome is required for optimal health but is frequently limited by the lack of fermentable fiber in the diet. We attempted to increase butyrate production by supplementing the diets of 174 healthy young adults for 2 weeks with resistant starch from potatoes (RPS), resistant starch from maize (RMS), inulin from chicory root, or an accessible corn starch control. RPS resulted in the greatest increase in total SCFAs, including butyrate. Although the majority of microbiomes responded to RPS with increases in the relative abundance of bifidobacteria, those that responded with an increase in Ruminococcus bromii or Clostridium chartatabidum were more likely to yield higher butyrate concentrations, especially when their microbiota were replete with populations of the butyrate-producing species Eubacterium rectale RMS and inulin induced different changes in fecal communities, but they did not generate significant increases in fecal butyrate levels.IMPORTANCE These results reveal that not all fermentable fibers are equally capable of stimulating SCFA production, and they highlight the importance of the composition of an individual's microbiota in determining whether or not they respond to a specific dietary supplement. In particular, R. bromii or C. chartatabidum may be required for enhanced butyrate production in response to RS. Bifidobacteria, though proficient at degrading RS and inulin, may not contribute to the butyrogenic effect of those fermentable fibers in the short term.

Engineering of the spinosyn PKS: directing starter unit incorporation.

The spinosyns are a family of potent and highly selective insect control agents that display a favorable environmental profile. As some regions of the spinosyn molecule are recalcitrant to chemical modification, a targeted genetic approach was carried out to generate new analogues. The polyketide synthase (PKS) loading modules from the avermectin PKS of Streptomyces avermitilis and the erythromcyin PKS of Saccharopolyspora erythraea were each used to replace the spinosyn PKS loading module. Both of the resulting strains containing hybrid PKS pathways produced the anticipated spinosyn analogues. Supplementation of the culture media with a range of exogenous carboxylic acids led to the successful incorporation of these novel elements to yield further novel spinosyn molecules, some of which demonstrated potent and new insecticidal activities. Furthermore, it has been demonstrated that semisynthesis of such novel metabolites can then be used to generate active analogues, demonstrating the effectiveness of utilizing these complementary methods to search the chemical space around this template.

Butenyl-spinosyns, a natural example of genetic engineering of antibiotic biosynthetic genes.

Spinosyns, a novel class of insect active macrolides produced by Saccharopolyspora spinosa, are used for insect control in a number of commercial crops. Recently, a new class of spinosyns was discovered from S. pogona NRRL 30141. The butenyl-spinosyns, also called pogonins, are very similar to spinosyns, differing in the length of the side chain at C-21 and in the variety of novel minor factors. The butenyl-spinosyn biosynthetic genes (bus) were cloned on four cosmids covering a contiguous 110-kb region of the NRRL 30141 chromosome. Their function in butenyl-spinosyn biosynthesis was confirmed by a loss-of-function deletion, and subsequent complementation by cloned genes. The coding sequences of the butenyl-spinosyn biosynthetic genes and the spinosyn biosynthetic genes from S. spinosa were highly conserved. In particular, the PKS-coding genes from S. spinosa and S. pogona have 91-94% nucleic acid identity, with one notable exception. The butenyl-spinosyn gene sequence codes for one additional PKS module, which is responsible for the additional two carbons in the C-21 tail. The DNA sequence of spinosyn genes in this region suggested that the S. spinosa spnA gene could have been the result of an in-frame deletion of the S. pogona busA gene. Therefore, the butenyl-spinosyn genes represent the putative parental gene structure that was naturally engineered by deletion to create the spinosyn genes.

Engineered biosynthesis of novel spinosyns bearing altered deoxyhexose substituents.

Novel spinosyns have been prepared by biotransformation, using a genetically engineered strain of Saccharopolyspora erythraea, in which the beta-D-forosamine moiety in glycosidic linkage to the hydroxy group at C17 is replaced by alpha-L-mycarose.