Lignin forms a large part of plant biomass. It is a highly heterogeneous polymer of 4-hydroxyphenylpropanoid units and is embedded within polysaccharide polymers forming lignocellulose. Lignin provides strength and rigidity to plants and is rather resilient towards degradation. To improve the (bio)processing of lignocellulosic feedstocks, more effective degradation methods of lignin are in demand. Nature has found ways to fully degrade lignin through the production of dedicated ligninolytic enzyme systems. While such enzymes have been well thoroughly studied for ligninolytic fungi, only in recent years biochemical studies on bacterial enzymes capable of lignin modification have intensified. This has revealed several types of enzymes available to bacteria that enable them to act on lignin. Two major classes of bacterial lignin-modifying enzymes are DyP-type peroxidases and laccases. Yet, recently also several other bacterial enzymes have been discovered that seem to play a role in lignin modifications. In the present review, we provide an overview of recent advances in the identification and use of bacterial enzymes acting on lignin or lignin-derived products.

Overusing non-degradable plastics causes a series of environmental issues, inferring a switch to biodegradable plastics. Polyhydroxyalkanoates (PHAs) are promising biodegradable plastics that can be produced by many microbes using various substrates from waste feedstock. However, the cost of PHAs production is higher compared to fossil-based plastics, impeding further industrial production and applications. To provide a guideline for reducing costs, the potential cheap waste feedstock for PHAs production have been summarized in this work. Besides, to increase the competitiveness of PHAs in the mainstream plastics economy, the influencing parameters of PHAs production have been discussed. The PHAs degradation has been reviewed related to the type of bacteria, their metabolic pathways/enzymes, and environmental conditions. Finally, the applications of PHAs in different fields have been presented and discussed to induce comprehension on the practical potentials of PHAs.

DyP peroxidases comprise a novel superfamily of heme-containing peroxidases, which is unrelated to the superfamilies of plant and animal peroxidases. These enzymes have so far been identified in the genomes of fungi, bacteria, as well as archaea, although their physiological function is still unclear. DyPs are bifunctional enzymes displaying not only oxidative activity but also hydrolytic activity. Moreover, these enzymes are able to oxidize a variety of organic compounds of which some are poorly converted by established peroxidases, including dyes, β-carotene, and aromatic sulfides. Interestingly, accumulating evidence shows that microbial DyP peroxidases play a key role in the degradation of lignin. Owing to their unique properties, these enzymes are potentially interesting for a variety of biocatalytic applications. In this review, we deal with the biochemical and structural features of DyP-type peroxidases as well as their promising biotechnological potential.