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Variation in genome content is a potent mechanism of microbial adaptation. The genomes of members of the cyanobacterial genus Acaryochloris vary greatly in gene content as a consequence of the idiosyncratic retention of both recent gene duplicates and plasmid-encoded genes acquired by horizontal transfer. For example, the genome of Acaryochloris strain MBIC11017, which was isolated from an iron-limited environment, is enriched in duplicated and novel genes involved in iron assimilation. Here, we took an integrative approach to characterize the adaptation of Acaryochloris MBIC11017 to low environmental iron availability and the relative contributions of the expression of duplicated versus novel genes. We observed that Acaryochloris MBIC11017 grew faster and to a higher yield in the presence of nanomolar concentrations of iron than did a closely related strain. These differences were associated with both a higher rate of iron assimilation and a greater abundance of iron assimilation transcripts. However, recently duplicated genes contributed little to increased transcript dosage; rather, the maintenance of these duplicates in the MBIC11017 genome is likely due to the sharing of ancestral dosage by expression reduction. Instead, novel, horizontally transferred genes are responsible for the differences in transcript abundance. The study provides insights on the mechanisms of adaptive genome evolution and gene expression in Acaryochloris. [ABSTRACT FROM AUTHOR]

Aphis gossypii Glover is a destructive pest of numerous crops throughout the world. Although the expansion of Bt cotton cultivation has helped to control some insect pests, the damage from cotton aphids has not been mitigated. The evolution of aphid resistance to imidacloprid has made its chemical control more difficult since its introduction in 1991. Field populations of A. gossypii that were collected from different transgenic (Bt) cotton planting areas of China in 2014 developed different levels of resistance to imidacloprid. The IMI_R strain has developed high resistance to imidacloprid with the resistance ratio > 1200-fold. Compared with the susceptible IMI_S strain, the IMI_R strain also developed a high level cross resistance to sulfoxaflor and acetamiprid. The limited synergism with either PBO or DEF suggests that resistance may be due to the site mutation of molecular target rather than to enhanced detoxification. Three target-site mutations within the nicotinic acetylcholine receptor (nAChR) β1 subunit were detected in the IMI_R strain. The R81T mutation has been reported to be responsible for imidacloprid resistance in A. gossypii and M. persicae . Both V62I and K264E were first detected in A. gossypii . These point mutations are also present in field populations, suggesting that they play a role in the resistance to imidacloprid. Furthermore, the expression level of transcripts encoding β1 subunit was decreased significantly in the IMI_R strain compared with the IMI_S strain, suggesting that both point mutations and the down-regulation of nAChR β1 subunit expression may be involved in the resistance mechanism for imidacloprid in A. gossypii . These results should be useful for the management of imidacloprid-resistant cotton aphids in Bt cotton fields in China. [ABSTRACT FROM AUTHOR]