This paper aims at emphasizing the importance of a systemic approach together with new investigation tools provided by molecular biology to give new insights into microbial ecology. Through the presentation of four recently obtained results about the coexistence of species in competition on a single resource, it is argued that such an approach can have major impact on ecological problems. in the first example, we revisit the existing models of biotechnology and show how they can be updated in some sense to better describe the real world by taking into account the spatial heterogeneity in a very simple but effective way (in the sense that their qualitative predictions are in accordance with the observed data). In the second example, we show how an optimally designed biosystem may give insights to the understanding of the so-called barrier effect. The third example proposes a new explanation for coexistence, that we called "long run coexistence", in studying the transient behavior of a high dimensional system describing N species in competition on a single substrate. Finally, a last example presents the original concept of "biological control" which refers to the use of a particular species to globally stabilize an unstable biological process. (C) 2008 Elsevier Ltd. All rights reserved.