Polyhydroxybutyrate-producing cyanobacteria from lampenflora: The case study of the "Stiffe" caves in Italy

Rihab Djebaili; Amedeo Mignini; Ilaria Vaccarelli; Marika Pellegrini; Daniela M Spera; Maddalena Del Gallo; Anna Maria D'Alessandro

doi:10.3389/fmicb.2022.933398

Polyhydroxybutyrate-producing cyanobacteria from lampenflora: The case study of the "Stiffe" caves in Italy

Front Microbiol. 2022 Jul 28:13:933398. doi: 10.3389/fmicb.2022.933398. eCollection 2022.

Authors

Rihab Djebaili¹, Amedeo Mignini¹, Ilaria Vaccarelli¹, Marika Pellegrini¹, Daniela M Spera², Maddalena Del Gallo¹, Anna Maria D'Alessandro¹

Affiliations

¹ Department of Life, Health and Environmental Sciences, University of L'Aquila, L'Aquila, Italy.
² Quality Engineering S.r.l., Pescara, Italy.

Abstract

This study aimed to estimate the green formation lampenflora of "Stiffe" caves in order to evaluate their suitability as an isolation source of cyanobacteria useful for the production of polyhydroxyalkanoates (PHAs). The cave system was chosen as the sampling site due to its touristic use and the presence of high-impact illuminations. The biofilms and the mats of the illuminated walls were sampled. Samples were investigated by 16S rRNA gene analysis and culturable cyanobacteria isolation. The isolated strains were then screened for the production of PHAs under typical culturing and nutritional starvation. Cultures were checked for PHA accumulation, poly-β-hydroxybutyrate (PHB) presence (infrared spectroscopy), and pigment production. The 16S rRNA gene metabarcoding. Highlighted a considerable extent of the pressure exerted by anthropogenic activities. However, the isolation yielded eleven cyanobacteria isolates with good PHA (mainly PHB)-producing abilities and interesting pigment production rates (chlorophyll a and carotenoids). Under normal conditions (BG11₀), the accumulation abilities ranged from 266 to 1,152 ng mg dry biomass^-1. The optimization of bioprocesses through nutritional starvation resulted in a 2.5-fold increase. Fourier transform infrared (FTIR) studies established the occurrence of PHB within PHAs extracted by cyanobacteria isolates. The comparison of results with standard strains underlined good production rates. For C2 and C8 strains, PHA accumulation rates under starvation were higher than Azospirillum brasilense and similar to Synechocystis cf. salina 192. This study broadened the knowledge of the microbial communities of mats and biofilms on the lightened walls of the caves. These findings suggested that these structures, which are common in tourist caves, could be used to isolate valuable strains before remediation measures are adopted.

Keywords: 16S rRNA gene metabarcoding; biopolymers; deep biosphere; microbial communities of caves; polyhydroxyalkanoates.