Many biodegradation pathways, both aerobic and anaerobic, have already been characterised, and the phylogenetic relationships among catabolic genes within them have been studied. However, new biodegradation activities and their coding genes are continuously being reported, including those involved in the catabolism of emerging contaminants and those generally regarded as non-biodegradable. Gene regulation is also an important issue for the efficient biodegradation of contaminants. Specific induction by the substrate and over-imposed global regulatory networks adjust the expression of the biodegradation genes to meet bacterial physiological needs. New biodegradation pathways can be assembled in a particular strain or in a bacterial consortium by recruiting biodegradation genes from different origins through horizontal gene transfer. The abundance and diversity of biodegradation genes, analysed by either genomic or metagenomic approaches, constitute valuable indicators of the biodegradation potential of a particular environmental niche. This knowledge paves the way to systems metabolic engineering approaches to valorise biowaste for the production of value-added products.

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Repetitive DNA is ubiquitous in eukaryotic genomes, and, in many species, comprises the bulk of the genome. Repeats include transposable elements that can self-mobilize and disperse around the genome, and tandemly-repeated satellite DNAs that increase in copy number due to replication slippage and unequal crossing over. Despite their abundance, repetitive DNA is often ignored in genomic studies due to technical challenges in their identification, assembly, and quantification. New technologies and methods are now providing the unprecedented power to analyze repetitive DNAs across diverse taxa. Repetitive DNA is of particular interest because it can represent distinct modes of genome evolution. Some repetitive DNA forms essential genome structures, such as telomeres and centromeres, which are required for proper chromosome maintenance and segregation, whereas others form piRNA clusters that regulate transposable elements; thus, these elements are expected to evolve under purifying selection. In contrast, other repeats evolve selfishly and produce genetic conflicts with their host species that drive adaptive evolution of host defense systems. However, the majority of repeats likely accumulate in eukaryotes in the absence of selection due to mechanisms of transposition and unequal crossing over. Even these neutral repeats may indirectly influence genome evolution as they reach high abundance. In this Special Issue, the contributing authors explore these questions from a range of perspectives.

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Interest in the study of life in hot environments, both with respect to the inhabiting microorganisms and the enzymes they produce, is currently very high. The biological mechanisms responsible for the resistance to high temperatures are not yet fully understood, whereas thermostability is a highly required feature for industrial applications. In this e-book, the invited authors provide diverse evidence contributing to the understanding of such mechanisms and the unlocking of the biotechnological potential of thermophiles and thermozymes.

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