Recently, we have introduced a new bioeconomic indicator in order to avoid the difficulties in evaluating the process and technologies for sustainability. In this paper, we wish to improve this new indicator for the analysis of sustainability. Indeed, the indicator has been based on the exergy analysis of dissipation and irreversibility, and it was proven in some social and technical application. In this work, a more general definition has been introduced in order to use it in any evaluation of sustainability. In particular, it has been applied to improve the biofuel production obtained by microorganisms, starting from the biophysical behaviour of the microorganisms themselves. Indeed, in industrialised countries, the management of CO2emissions represents one of the present compelling issues. In this context, the improvement of the energy efficiency, and its rational use, can be considered a fundamental economic strategy for the sustainable development of the industrialised countries. Our indicator takes into account all these requests for the development and sustainability, resulting a very interesting thermoeconomic quantity to be used by decision makers. Moreover, it is used to prove that mutualism can represent a new approach for the optimisation of biofuels production.