BackgroundPectin is a rather complex and highly branched polysaccharide strengthening the plant cell wall. Thus, many different pectinases are required for an efficient microbial conversion of biomass waste streams with a high pectin content like citrus peel, apple pomace or sugar beet pulp. The screening and optimization of strains growing on pectic substrates requires both, quantification of the residual substrate and an accurate determination of the enzymatic activity. Galacturonic acid, the main sugar unit of pectin, is an uncommon substrate for microbial fermentations. Thus, growth and enzyme production of the applied strain has to be characterized in detail to understand the microbial system. An essential step to reach this goal is the development of online monitoring tools.ResultsIn this study, a method for the online determination of residual substrate was developed for the growth of the plant pathogenic fungus Ustilago maydis on pectic substrates such as galacturonic acid. To this end, an U. maydis strain was used that expressed a heterologous exo-polygalacturonase for growth on polygalacturonic acid. The growth behavior on galacturonic acid was analyzed by online measurement of the respiration activity. A method for the online prediction of the residual galacturonic acid concentration during the cultivation, based on the overall oxygen consumption, was developed and verified by offline sampling. This sensitive method was extended towards polygalacturonic acid, which is challenging to quantify via offline measurements. Finally, the enzymatic activity in the culture supernatant was calculated and the enzyme stability during the course of the cultivation was confirmed.ConclusionThe introduced method can reliably predict the residual (poly)galacturonic acid concentration based on the overall oxygen consumption. Based on this method, the enzymatic activity of the culture broth of an U. maydis strain expressing a heterologous exo-polygalacturonase could be calculated. It was demonstrated that the method is especially advantageous for determination of low enzymatic activities. In future, it will be applied to U. maydis strains in which the number of produced hydrolytic enzymes is increased for more efficient degradation.Electronic supplementary materialThe online version of this article (10.1186/s13036-018-0128-1) contains supplementary material, which is available to authorized users.

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Today, the cheosphere’s and biosphere’s compositions of the planet are changing faster than experienced during the past thousand years. CO2 emissions from fossil fuel combustion are rising dramatically, including those from processing, manufacturing and consuming everyday products; this rate of greenhouse gas emission (36.2 Giga-tons accumulated in 2022) is raising global temperatures and destabilizing the climate, which is one of the most influential forces on our planet. As our world warms up, our climate will enter a period of constant turbulence, affecting more than 85% of our ecosystems, including the delicate web of life on these systems and impacting socioeconomic networks. How do we deal with the green transition to minimize climate change and its impacts while we are facing these new realities? One of the solutions is to use renewable natural resources. Indeed, nature itself, through the working parts of its living systems, the enzymes, can significantly contribute to achieve climate neutrality and good ecological/biodiversity status. Annually they can help decreasing CO2 emissions by 1 to 2.5 Billion-tons, carbon demand by about 200 Million-tons, and chemical demand by about 90 Million-tons. With current climate change goals, we review the consequences of climate change at multiple scales and how enzymes can counteract or mitigate them. We then focus on how they mobilize sustainable and greener innovations in consumer products that have a high contribution to global carbon emissions. Finally, key innovations and challenges to be solved at the enzyme and product levels are discussed. LAY SUMMARY Accumulated greenhouse gas emissions are expected to increase from 36.2 Giga-tons (Gt) to 60 Gt over the next three decades. The global surface temperature has increased by + 1.09 °C since 2001, and might increase by + 2.2 °C in 2100, +3.6 °C in 2200 and +4.6 °C in 2500. These emissions and temperature rises cannot be reduced in their entirety, but they can be lowered by using enzymes. Enzymes are proteins that catalyze biochemical reactions that make life possible since 3.8 billion years ago. Scientists have been able to "domesticate" them in such a way that enzymes, and their engineered variants, are now key players of the circular economy. With a world production of 117 Kilo-tons and a trade of 14.5 Billion-dollars, they have the potential to annually decrease CO2 emissions by 1 to 2.5 Billion-tons (Bt), the carbon demand to synthesise chemicals by 200 Million tons (Mt), the amount of chemicals by 90 Mt, and the economic losses derived from global warming by 0.5%, while promoting biodiversity and our planet’s health. Our success to increase these benefits will depend on better integration of enzymatic solutions in different sectors.