Mycoalgae biofilm: development of a novel platform technology using algae and fungal cultures
Authors: Bo Hu
Aravindan Rajendran
Journal: Biotechnology for Biofuels (2016)
Discipline: BIOLOGY & BIOCHEMISTRY
Keywords: Bioprocessing; Co-culture; Filamentous fungi; Kinetics; Microalgae
Affiliations: Department of Bioproducts and Biosystems Engineering, University of Minnesota, Room: 219, BioAgEng, 1390 Eckles Ave, St. Paul, MN 55108-6005 USA., Department of Bioproducts and Biosystems Engineering, University of Minnesota, Room: 315, 1390 Eckles Ave, Saint Paul, MN 55108-6005 USA.

Abstract:  Background: Microalgae is considered a promising source for biofuel and bioenergy production, bio-remediation and production of high-value bioactive compounds, but harvesting microalgae is a major bottleneck in the algae based processes. The objective of this research is to mimic the growth of natural lichen and develop a novel biofilm platform technology using filamentous fungi and microalgae to form a lichen type of biofilm "mycoalgae" in a supporting polymer matrix. Results: The possibility of co-existence of Chlorella vulgaris with various fungal cultures was tested to identify the best strain combination for high algae harvest efficiency. The effect of different matrices for cell attachment and biofilm formation, cell surface characterization of mycoalgae biofilm, kinetics of the process with respect to the algae-fungi cell distribution and total biomass production was studied. Mycoalgae biofilm with algae attachment efficiency of 99.0 % and above was achieved in a polymer-cotton composite matrix with glucose concentration of 2 g/L in the growth medium and agitation intensity of 150 rpm at 27 °C. The total biomass in the co-culture with the selected strain combination (Mucor sp. and Chlorella sp.) was higher than the axenic cultures of fungi and algae at the conditions tested. Conclusions: The results show that algae can be grown with complete attachment to a bio-augmenting fungal surface and can be harvested readily as a biofilm for product extraction from biomass. Even though, interaction between heterotrophic fungi and phototrophic algae was investigated in solid media after prolonged contact in a report, this research is the first of its kind in developing an artificial lichen type biofilm called "mycoalgae" biofilm completely attached on a matrix in liquid cultures. The mycoalgae biofilm based processes, propounds the scope for exploring new avenues in the bio-production industry and bioremediation. 

Retracted: No

PubPeer comments:
 In the publication, ATR-FTIR is used to assess the surface changes of both organisms when they are cultivated together in form of biofilm. It is addressed in the discussion about a more detailed explanation of the FTIR spectra in **Additional file 2**. At first view, it was strange the assignation of band 1743cm-1: *- The peak at 1743 cm-1 (C=O ester stretching vibrations) is the main lipid band which could be derived from the ester linkage of the fatty acids (aliphatic monocarboxylic acids). This absorbance at 1743 cm-1 can be explained by the outer characteristics of the cell membrane being largely composed of lipopolysaccharide (LPS), which consists of a lipid and a polysaccharide joined by a covalent bond. Region 1 (Fig. S1) explains the fatty acid with 2851 and 2921 cm-1 being CH2 symmetric stretch and CH2 asymmetric stretch.* Even the work is base on a fungus and an algae, they explain that this peak is due to a large amount of LPS, which is a compound that mainly appears in the outer membrane of gram-negative bacteria being also a differentiating characteristic. This association doesn t make any sense, and seems to report that LPS is present in fungi and algae, although common phospholipids in membranes could fit with 1745cm-1 ester band. Since the FTIR acquisition and analysis was carried out in the Characterization Facility from the same university (University of Minnesota) is probable that authors were not aware well on this, which doesn t exclude a revision, followed by the one from the reviewers of the journal. Even that the interpretation is in supplementary information and the FTIR analysis is not an essential part of the whole study it should be notice since it can lead to misinterpretation in other works. ![file] , 
 ![file] This is a FTIR-ATR spectrum from the phospholipid phosphatidylcholine and belongs to the following publication: DOI 10.1007 s12155-010-9098-y Any other phospholipid on the membrane should have the same peak for ester group. Therefore, go so far assigning that band to LPS, like in gram-negative bacteria, doesn t make any sense. ,