Novel insights regarding the sigmoidal pattern of resistance to neomycin conferred by the aphII gene, in Streptomyces lividans

Combinatorial biosynthesis of novel aminoglycoside antibiotics via pathway engineering

With the current spread of clinically relevant multidrug-resistant (MDR) pathogens, insufficient unearthing of new anti-infectives, and the high cost required for approval of new antimicrobial agents, a strong need for getting these agents via more economic and other alternative routes has emerged. With the discovery of the biosynthetic pathways of various antibiotics pointing out the role of each gene/protein in their antibiotic-producing strains, it became apparent that the biosynthetic gene clusters can be manipulated to produce modified antibiotics. This new approach is known as the combinatorial biosynthesis of new antibiotics which can be employed for obtaining novel derivatives of these valuable antibiotics using genetically modified antibiotic-producing strains (pathway engineering). In this review and based on the available biosynthetic gene clusters of the major aminoglycoside antibiotics (AGAs), the possible alterations or modifications that could be done by co-expression of certain gene(s) previously known to be involved in unique biosynthetic steps have been discussed. In this review defined novel examples of modified AGA using this approach were described and the information provided will act as a platform of researchers to get and develop new antibiotics by the antibiotic-producing bacterial strains such as Streptomyces, Micromonospora,…etc. This way, novel antibiotics with new biological activities could be isolated and used in the treatment of infectious diseases conferring resistance to existing antibiotics.

An Autobioluminescent Method for Evaluating In Vitro and In Vivo Growth of Rhodococcus equi

A previously reported method for evaluating the intracellular growth of Rhodococcus equi using enhanced green fluorescent protein is unsuitable for the quantitative evaluation of the entire sample because the signal can be detected only in the excitation region. Therefore, we created an autobioluminescent R. equi using luciferase (luxABCDE). First, we connected luxABCDE to the functional promoter P_aphII and introduced it into the chromosomes of ATCC33701 and ATCC33701_P-. Luminescence was detected in both transformants, and a correlation between the bacterial number and luminescence intensity in the logarithmic phase was observed, indicating that luxABCDE is functionally and quantitatively expressed in R. equi. The luminescence of ATCC33701 was significantly higher than that of ATCC33701_P- at 24 h after infection with J774A.1. Next, RNA-Seq analysis of ATCC33701 to search for endogenous high-expression promoters resulted in the upstream sequences of RS29370, RS41760, and vapA being selected as candidates. Luminescence was detected in each transformant expressing the luxABCDE using these upstream sequences. We examined the luminescence intensity by coexpressing the frp gene, an enhancer of the luciferase reaction, with luxABCDE. The luminescence intensity of the coexpressing transformant was significantly enhanced in J774A.1 compared with the non-coexpressing transformant. Finally, we examined the luminescence in vivo. The luminescence signals in the organs peaked on the third day following the administration of ATCC33701 derivatives in mice, but no luminescence signal was detected when the ATCC33701_P- derivative was administered. The autologous bioluminescent method described herein will enhance the in vitro and in vivo quantitative analysis of R. equi proliferation.

IMPORTANCE We established an autologous bioluminescent strain of R. equi and a method to evaluate its proliferation in vitro and in vivo quantitatively. This method overcomes the weakness of the fluorescence detection system that only measures the site of excitation light irradiation. It is expected to be used as an in vitro and in vivo growth evaluation method with excellent quantitative properties. In addition, it was suggested that the selection of a promoter that expresses luxABCDE could produce a luminescence with high intensity. Although this method needs further improvement, such as creating transformants that can maintain high luminescence intensity regardless of environmental changes such as temperature fluctuations, it is possible to observe bacterial growth over time in mice without killing them. Therefore, this method can be used to not only evaluate the pathogenicity of various wild and gene-deficient strains but also to screen preventive and therapeutic methods such as vaccines.