Author: Dirk Tischler

Publisher: Frontiers Media SA

Published: 2019-08-12

Total Pages: 236

ISBN-13: 2889459225

Actinobacteria (Actinomycetes) represent one of the largest and most diverse phyla among Bacteria. The remarkable diversity is displayed by various lifestyles, distinct morphologies, a wide spectrum of physiological and metabolic activities, as well as genetics. Interestingly, most Actinobacteria have a high GC-content (ranging from 51% to >70%) and belong to Gram-positive or Gram-variable type microbes. Many species are well known for large genomes which may be of linear style as in case of rhodococci or circular. Many of those harbor linear megaplasmids as a kind of genetic storage device. Frequently gene redundancy is reported and in most cases the evolutionary history or a functional role remains enigmatic. Nevertheless these large genomes and megaplasmids provide access to a number of potential (homologous) biocatalysts which await elucidation. Actinobacteria are well known for their biotechnological potential which is exemplarily described for amino acid producing Corynebacteria, secondary metabolite producing Streptomyces, pathogenic targets as Nocardia and Mycobacteria, carotenoid building Micrococcus strains, acid fermenting Propionibacteria, health and food related Bifidobacterium strains, rubber degrading Gordonia species, and organic pollutant degrading rhodococci among others. In many cases individual pathways or enzymes can be modified or recombinantly employed for biocatalysis. Even some genetic tools to work directly in those microbes have been successfully used as for example in Corynebacterium or in Rhodococcus species. During the last decade more and more genomes have been sequenced and made available for data mining and become accessible by state of the art genomic manipulation methods as minimal genomes, knock-out or artificial evolution. With respect to this large and ancient phylum many questions can be asked either from a scientific or industrial point of view. In order to provide some crystallization points we like to raise some examples as follows. How small can be an actinobacterial genome? What is the driving force to comprise large and repetitive genomes/megaplasmids? What is needed to generate an actinobacterial power house for industry? Can we annotate novel biocatalysts from scratch and improve functional annotation? What are common and different features with respect to other bacteria and/or fungi? How many novel antibiotics are hidden among Actinobacteria? Is there more potential among extremophile members or are they only specialized? Here especially the production of natural compounds is of high interest.