Genetic Determinants of Reutericyclin Biosynthesis in Lactobacillus reuteri

Reutericyclin is a unique antimicrobial tetramic acid produced by some strains of Lactobacillus reuteri. This study aimed to identify the genetic determinants of reutericyclin biosynthesis. Comparisons of the genomes of reutericyclin-producing L. reuteri strains with those of non-reutericyclin-producing strains identified a genomic island of 14 open reading frames (ORFs) including genes coding for a nonribosomal peptide synthetase (NRPS), a polyketide synthase (PKS), homologues of PhlA, PhlB, and PhlC, and putative transport and regulatory proteins. The protein encoded by rtcN is composed of a condensation domain, an adenylation domain likely specific for d-leucine, and a thiolation domain. rtcK codes for a PKS that is composed of a ketosynthase domain, an acyl-carrier protein domain, and a thioesterase domain. The products of rtcA, rtcB, and rtcC are homologous to the diacetylphloroglucinol-biosynthetic proteins PhlABC and may acetylate the tetramic acid moiety produced by RtcN and RtcK, forming reutericyclin. Deletion of rtcN or rtcABC in L. reuteri TMW1.656 abrogated reutericyclin production but did not affect resistance to reutericyclin. Genes coding for transport and regulatory proteins could be deleted only in the reutericyclin-negative L. reuteri strain TMW1.656ΔrtcN, and these deletions eliminated reutericyclin resistance. The genomic analyses suggest that the reutericyclin genomic island was horizontally acquired from an unknown source during a unique event. The combination of PhlABC homologues with both an NRPS and a PKS has also been identified in the lactic acid bacteria Streptococcus mutans and Lactobacillus plantarum, suggesting that the genes in these organisms and those in L. reuteri share an evolutionary origin.     

The environmental and genetic determinants of chick telomere length in Tree Swallows (Tachycineta bicolor)

Conditions during early life can have dramatic effects on adult characteristics and fitness. However, we still know little about the mechanisms that mediate these relationships. Telomere shortening is one possibility. Telomeres are long sequences of DNA that protect the ends of chromosomes. They shorten naturally throughout an individual's life, and individuals with short telomeres tend to have poorer health and reduced survival. Given this connection between telomere length (TL) and fitness, natural selection should favor individuals that are able to retain longer telomeres for a greater portion of their lives. However, the ability of natural selection to act on TL depends on the extent to which genetic and environmental factors influence TL. In this study, we experimentally enlarged broods of Tree Swallows (Tachycineta bicolor) to test the effects of demanding early‐life conditions on TL, while simultaneously cross‐fostering chicks to estimate heritable genetic influences on TL. In addition, we estimated the effects of parental age and chick sex on chick TL. We found that TL is highly heritable in Tree Swallow chicks, and that the maternal genetic basis for TL is stronger than is the paternal genetic basis. In contrast, the experimental manipulation of brood size had only a weak effect on chick TL, suggesting that the role of environmental factors in influencing TL early in life is limited. There was no effect of chick sex or parental age on chick TL. While these results are consistent with those reported in some studies, they are in conflict with others. These disparate conclusions might be attributable to the inherent complexity of telomere dynamics playing out differently in different populations or to study‐specific variation in the age at which subjects were measured.