DigitUMa
Repositório Institucional da Universidade da Madeira
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Nutrient deprivation stimulates soluble extracellular polymeric substances: physiological and biochemical responses in the cyanobacterium Cyanocohniella rudolphia
Publication . Rodrigues, Filipa; Mendonça, Ivana; Faria, Marisa; Mougin, Karine; Gómez Pinchetti, Juan Luis; Ferreira, Artur; Cordeiro, Nereida; Gonçalves Rodrigues, Ana Filipa; Silva Mendonça, Ivana Rita da; Faria, Marisa Camacho Gonçalves; cordeiro, nereida
The effect of macro- and micronutrient deprivation on the cyanobacterium Cyanocohniella rudolphia (BEA 0786B)
over 180 days (without medium renewal) was evaluated to intensify the production of soluble extracellular
polymeric substances (S-EPS). Growth, pH, cell-free medium viscosity, S-EPS content (phenol‑sulfuric acid
assay), Alcian Blue staining, and biochemical/structural markers were monitored to assess EPS release and
extracellular matrix dynamics. Progressive nutrient depletion induced a shift from biomass growth toward
extracellular-matrix investment. Microcolony formation observed around day 45 preceded a sustained high-
production phase, with pronounced matrix densification evident by approximately day 75. Apparent viscosity
increased in parallel with S-EPS accumulation and showed a strong correlation with extracellular carbohydrate
concentration (R
2
= 0.86), supporting its use as an operational, non-destructive proxy for S-EPS. Alcian Blue
staining qualitatively confirmed the presence of acidic polysaccharides. Quantitatively, S-EPS concentrations
increased from 0.1 to 0.8 g L
1
, accompanied by an increase in apparent viscosity from 24.7 to 34.7 mPa⋅s.
Morphological and spectroscopic analyses indicated a predominantly carbohydrate-rich extracellular matrix with
an increasing protein contribution over time.
As an exploratory proof of concept, unprocessed S-EPS present in the spent culture medium enabled LAP-
initiated photochemical formation of Au and Ag nanoparticles at 365 nm, with S-EPS acting as a stabilising
and co-reducing matrix and conferring pH-responsive optical behaviour. This indicates a practical route toward
integration into EPS-rich matrices to engineer stimuli-responsive coatings and biomaterials. Overall, this study
demonstrates that prolonged nutrient deprivation without medium renewal is an effective strategy to intensify S-
EPS accumulation in C. rudolphia and that apparent viscosity provides a practical in-process parameter for
monitoring production and supporting direct valorisation of spent culture medium in saline bioprocesses.
Towards scalable production of bound extracellular polymeric substances (B-EPS): autoclave hydrothermal extraction coupled with solvent-free ultrafiltration
Publication . Mendonça, Ivana; Rodrigues, Filipa; Marisa Faria; Gómez Pinchetti, Juan L.; Ferreira, Artur; Cordeiro, Nereida; Silva Mendonça, Ivana Rita da; Gonçalves Rodrigues, Ana Filipa; Faria, Marisa Camacho Gonçalves; cordeiro, nereida
Bound extracellular polymeric substances (B-EPS) are extracellular polysaccharides tightly attached to
cyanobacterial and microalgal cell surfaces, representing a high-value class of biopolymers with industrial
potential. Selective extraction is technically challenging due to strong adhesion to the cell wall and poten
tial co-extraction of soluble EPS. Conventional methods can be chemically aggressive and may involve
high energy and/or solvent inputs, making solvent-free extraction routes desirable. In this work, four
hydrothermal extraction techniques (reflux, autoclave, ultrasonic bath, and microwave) were evaluated for
their ability to recover B-EPS from the marine cyanobacterium Chroococcus submarinus (BEA 1200B),
followed by a harmonised ultrafiltration step. Each method was assessed for extraction efficiency and its
impact on bulk descriptors (inorganic carry-over, ATR-FTIR, zeta potential, and thermal profiles) and mor
phology. Among the methods tested, autoclave extraction demonstrated the highest performance, yield
ing up to 2.5 times more B-EPS than the other methods and showing reduced inorganic carry-over after
purification. Across all methods, the purified B-EPS fractions exhibited broadly comparable bulk profiles
under the applied analytics. Response Surface Methodology (RSM) applied to the autoclave system ident
ified temperature and extraction time as key variables; optimal conditions (biomass-to-solvent ratio 1:20
(w/v), 130 °C, 16 min) enabled >90% recovery. Coupling autoclave extraction with solvent-free ultrafiltra
tion avoids solvent precipitation and the use of hazardous reagents, enabling desalting and removal of
low-molecular-weight components. Using a photosynthetic marine strain supports seawater cultivation
and biogenic CO2 uptake, aligning the workflow with carbon-mitigation goals.
On taxonomy construction by recursive generative logic
Publication . Constantine, Larry LeRoy
Abstract
A potentially novel formal, systematic approach for theory-informed taxonomy construction is presented based on maximizing qualitative differences among defined taxa through generative logic. A recursive-dialectic taxonomy is a special form of classification constructed through recursive application of a logical function based on narrowly defined formal operations of absolute antithesis and absolute synthesis. Recursive-dialectic taxonomies have features that may offer advantages from both theoretical and applied perspectives across many different disciplines. The generative approach ensures that taxa are maximally conceptually distinct within the underlying theoretical framework from which the taxonomy is constructed. Such a taxonomy is also quantitatively well-defined, as it maps straightforwardly into a
k
-simplex closed property space in which geometrically defined taxonomic differentiae and typological dimensions are derived from and conceptually linked directly to the underlying theoretical basis of the taxonomy. The resulting closed property space is an Aitchison space that can be treated as compositional data for purposes of statistical analysis in empirical research based on the taxonomy. The relationship of the taxonomic method to Belnap–Dunn logic of first-degree entailment is noted. An example of application of the method to construction of a taxonomy of human socio-cultural systems based on social coordination theory is illustrated.
Selective contraction
Publication . Garapa, Marco; Eduardo Fermé; Reis, Maurício D. L.; Garapa, Marco; Fermé, Eduardo; Reis, Maurício
Abstract
Selective revision
operators are well-known non-prioritized revision operators that allow for the acceptance of only part of the new information while rejecting the rest. In this paper, we introduce their contraction counterparts, which we refer to as
selective contraction
operators. These operators enable the removal of only part of the input information. As such, selective contractions can be viewed as a method for removing some of the beliefs that support the input belief without eliminating the belief itself. In this sense, selective contraction operators allow for a weakening of the input belief’s strength without discarding it. We provide representation theorems for various classes of selective contraction operators.
The role of mental toughness and academic satisfaction in suppressing first-year students’ intentions to dropout of university
Publication . Rodrigues, Nuno; Rebelo, Teresa; Delgado Rodríguez, Naira; Rodrigues, Nuno
Abstract
The urgent need to reduce the substantial and persistent incidence of higher education dropout, especially during the first academic year, calls for further research to identify the core predictors of students’ withdrawal intentions and actual behaviors. Specifically, more research is needed to assess whether and how students’ personal resources and academic attitudes interplay in shaping this phenomenon. This study addresses these questions by examining the unexplored joint role of students’ mental toughness and academic satisfaction in counteracting their intention to leave university at the end of the first year. Data from a sample of 187 first-year undergraduates at a non-residential public university, collected at three measurement points, supported the validity of both variables in predicting dropout intentions, after controlling for the effects of academic performance. The results also indicated that the effect of mental toughness in suppressing dropout intentions does not occur when students are dissatisfied with the university. The main implications of these findings are presented and discussed.