# Fungal-Lactobacteria Consortia and Enzymatic Catalysis for Polylactic Acid Production
## 3 Results and Discussion
### LA Production from Glucose and Starch and the Effect of QSMs
Thus, these bacteria should cooperate with one of the fungi able to metabolize starch for a fruitful bioprocess. This was observed in co-cultures of _L. plantarum_ M9 MG6-B2 with _T. amestolkiae_ (TM) and of _L. plantarum_ WCFS1 with _R. oryzae_ (RW). In the latter case, the LA produced was higher than in pure cultures of the bacteria but smaller than in those of _Rlizopus_, which suggests that both microorganisms compete for the glucose released from starch by fungal amylases, causing a detrimental impact on LA production. The addition of QSMs resulted in different effects, as previously observed in cultures with glucose (Figure 2). Supplementation with dodecanol proved to be positive in six of the nine cultures, although the most striking effect on LA levels was noticed in the TM consortium (64%), tripling the value of its control without QSM and doubling those  
Figure 3: LA production (% of the theoretical maximum) in pure cultures or co-cultures of the microorganisms selected with pure commercial starch as carbon source (24 h, 200 rpm, 28 \({}^{\circ}\)C). Microorganisms: _R. oryzae_ (R), _T. amestolkiae_ (T), _O. picaea_ (O), _L. plantarum_ M9 MG6-B2 (M), _L. plantarum_ WCFS1 (W) and their combinations. Farnesol (FaOH), 3-oxo-C12-HSL (HS) or dodecanol (Dodec.) were added to the cultures and the LA produced was compared with that from untreated cultures (control). observed with farnesol and for _R. oryzae_ (R) with dodecanol or farnesol. It is also interesting to note that combinations of _R. oryzae_ and _T. amestolkiae_ with _L. plantarum_ M9 MG6-B2, which lacks amylase activity, generated higher production than with the amylolytic strain WCFS1. On the other hand, despite the fact that the presence of dodecanol has been described in the bioactive fraction of an isolate of _R. oryzae_[43], no significant effects of this or other QSMs were observed in cultures of this strain, confirming the data obtained in the medium with glucose. In the case of the combinations of _O. picaea_ with any of the LAB in glucose (Figure 2) and in some starch cultures (Figure 3), the LA yield seems to decrease compared to their controls. Thus, we can consider that these QSMs have an effect on _O. picaea_ that indirectly impacts LA production; however, we cannot affirm that quorum quenching occurs, as it is unclear whether the fitness of the community is affected. In fact, previous studies showed pro-biofilm effects of these three QSMs in _O. picaea_[21]. The effect of QSMs could influence the degradation of starch or the fermentation of glucose to LA by LAB, but comparison of the data obtained in glucose and starch did not reveal big differences to shed light on this matter. In the most suitable consortium among those studied in this work there is a clear cooperative relationship between partners, with _T. amestolkiae_ decomposing starch and _L. plantarum_ M9 MG6-B2 converting glucose into LA and, probably, releasing other substances that the fungus uses to grow. This cooperation is improved by the inductor effect in the microbial metabolism of farnesol in the case of glucose medium and dodecanol in the case of the medium with starch. According to our results, the addition of 3-oxo-C12-HSL had little impact on LA production. Previous studies with this molecule, typically associated with QS interactions in Gram-negative bacteria [44], demonstrated that the Gram-positive _L. plantarum_ WCFS1 is also responsive to it and reported the over-expression of several oxidative enzymes [19]. We have not observed this behavior, and our data also indicate that this QSM does not affect LA production by _L. plantarum_ M9 MG6-B2. There are not studies about the response of this strain to acyl-homoserine lactones. Regarding farnesol, it is known that this QSM affects yeast-hyphae transition, biofilm formation and enzyme secretion in some fungi, such as _Candida albicans_[45], _O. picaea_[18] and _T. amestolkiae_.