Thermophilic bacteria and their thermozymes in composting processes: a review

Abstract

In this review, the composting process of organic waste is discussed through an in-depth exploring of its thermophilic phase. It starts with the highlight on the thermodynamic evolution, which needs to be assessed when deciding to use reactors for composting, also in the context of energy generation. The composting process is mediated by different types of microorganisms, and the bacteria that play key roles are evaluated. The roles of the genera Bacillus and Thermus are considered, often described as the main components of the microbiota of compost. Due to their adaptation to the composting processes, they are candidates for technological purposes. Subsequentially, the focus is moved on the thermostable enzymes that can be isolated from them and their succession during the composting processes. Experimental examples of enzyme-related literature are reviewed, for example investigating proteases and ureases, which are found at the beginning of the process. In addition, cellulases, hemicellulases, lignin-modifying enzymes, and esterases have been described for their activities during the thermophilic phase, giving them great potential for biotechnological and industrial applications. Following, the composition of the microbial community is analyzed through the description of approaches of metagenomics. Despite it being a relatively new but fast-growing field within biology, it is intended to be a priority analysis to acquire knowledge on genomes of environmental microorganisms and communities. Finally, a space is dedicated to the description of the composting plant which treats olive oil wastes within the LIFE TIRSAV PLUS project (LIFE05 ENV/IT/00845). Through two plant solutions, being the Dynamic and the Static Composting, it provides a high-quality compost with an effective, flexible and economical process. Graphical Abstract

Application of Near-Infrared Spectroscopy for Monitoring and/or Control of Composting Processes

“…A prerequisite for good quality products during composting is the control of the aforementioned conditions [6]. An indication of microbial activities during the composting process is the change in temperature, which is justifiably considered a parameter that indicates the status of the process [15][16][17]. When the favorable conditions for the implementation of the composting process have been achieved, it will take place in several main stages, which we can follow according to the microorganisms that prevail in a certain stage [6].…”

Effects of composts obtained from hazelnut wastes on the cultivation of pepper (Capsicum annuum) seedlings

“…Measuring the temperature is one of the cheapest and easiest methods to observe the finalization of the bio-oxidative phase of composts 24 . The composting process includes mesophilic (10–42 °C), thermophilic (45–70 °C), mesophilic II (65–50 °C), and maturation (50–23 °C) stages 25 , 26 . The first three stages are known as the bio-oxidative phase.…”

Heterologous expression and structure prediction of a xylanase identified from a compost metagenomic library

“…A typical composting process involves four main phases, i.e., mesophilic, thermophilic, maturation, and curing. In the thermophilic phase, the compost piles reach high temperatures, above 45 °C, due to the intense microbial activity of thermophilic populations that release a wide range of thermostable enzymes able to degrade complex molecules, which are crucial for the lignocellulose degradation (Kukkar et al 2022 ; Finore et al 2023 ). The synergistic action of a cocktail of enzymes with diversified activities is required for a complete breakdown of lignocellulose into fermentable sugars.…”

“…Mining of novel enzymes with efficient catalytic activities through metagenomics can be performed using two types of approaches, namely sequence- and function-based metagenomics. The sequence-based approach allows the characterization of microbial communities in terms of taxonomy and the prediction of functional diversity by applying complex sequencing methods and databases (e.g., CAZy database) (Kukkar et al 2022 ; Santos-Pereira et al 2023 ; Finore et al 2023 ). On the other hand, function-based metagenomics is focused on the discovery of new metabolic pathways and genes encoding functional enzymes or other bioactive molecules of biotechnological relevance (Pabbathi et al 2021 ; Kukkar et al 2022 ).…”