Off-shore and On-shore Macroalgae Cultivation and Wild Harvesting: an LCA-based Evaluation from Baltic Case Studies

Seaweeds are organisms with unique characteristics. They contain a broad spectrum of micro and macro elements (i.e., minerals, carbohydrates, proteins, lipids, pigments, and vitamins). Furthermore, they have a very high growth rate and are present in large quantities and species in nature. Therefore, they represent an ideal feedstock for a biorefinery concept. Historically, macroalgae used in biorefineries have been harvested directly from the sea or the shores (off-shore technique). However, recent studies are analysing the possibility of creating on-shore cultivation facilities. This research aims to perform a Life Cycle Assessment (LCA) study that analyses and compares the environmental impact of two seaweed cultivation and wild harvesting techniques in the Baltic conditions based on existing pre-commercial and commercial projects. Inventory data are collected directly from two macroalgae producers in the Baltic Sea region (one wild harvester and one on-shore), integrated with literature, and then normalized to the selected functional unit, i.e., 1 ton of harvested fresh macroalgae. The results, implemented with SimaPro 9.4 software, determine which of the two techniques has the highest environmental impact and which are the most sensitive environmental indicators. Furthermore, the results underline the critical parameters for the two cultivations (i.e., fuel consumption and electricity), contributing to identifying environmental benchmarks for further optimization strategies. The alternative scenarios analysis included in the study aims to explore and highlight the effect of the variation of selected input parameters or assumptions to provide a consistent assessment of the uncertainty of the model outputs and the main findings in terms of environmental impacts

Contribution of increased mutagenesis to the evolution of pollutants-degrading indigenous bacteria

<div><p>Bacteria can rapidly evolve mechanisms allowing them to use toxic environmental pollutants as a carbon source. In the current study we examined whether the survival and evolution of indigenous bacteria with the capacity to degrade organic pollutants could be connected with increased mutation frequency. The presence of constitutive and transient mutators was monitored among 53 pollutants-degrading indigenous bacterial strains. Only two strains expressed a moderate mutator phenotype and six were hypomutators, which implies that constitutively increased mutability has not been prevalent in the evolution of pollutants degrading bacteria. At the same time, a large proportion of the studied indigenous strains exhibited UV-irradiation-induced mutagenesis, indicating that these strains possess error-prone DNA polymerases which could elevate mutation frequency transiently under the conditions of DNA damage. A closer inspection of two <i>Pseudomonas fluorescens</i> strains PC20 and PC24 revealed that they harbour genes for ImuC (DnaE2) and more than one copy of genes for Pol V. Our results also revealed that availability of other nutrients in addition to aromatic pollutants in the growth environment of bacteria affects mutagenic effects of aromatic compounds. These results also implied that mutagenicity might be affected by a factor of how long bacteria have evolved to use a particular pollutant as a carbon source.</p></div

Contribution of increased mutagenesis to the evolution of pollutants-degrading indigenous bacteria - Fig 3

<p><b>The phylogenetic trees of RulA (A) and RulB (B) protein sequences. Underlining indicates the genes of proteins which are located on plasmids.</b> Sequences derived from <i>P</i>. <i>fluorescens</i> strains PC20 and PC24 are shown in boldface. Sequences were aligned with ClustalX2 and further visualised with TreeViewX. Numbers at branch nodes indicate bootstrapping values for 1000 bootstrap replicates. Values under 500 were removed. The identifiers of the aligned sequences are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182484#pone.0182484.s015" target="_blank">S7 Table</a>.</p

The comparison of spontaneous and UV-C irradiation (5 J/m²) induced Rif^r mutant frequencies.

<p>Each data represents the median value from three replicate UV-mutagenesis assays. Data were analysed using the Mann-Whiteny U test (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182484#pone.0182484.s017" target="_blank">S9 Table</a>).</p

Comparison of spontaneous and UV-induced Rif^r mutant frequencies.

<p>Presented are only the results with indigenous strains exhibiting statistically significantly increased mutation frequency (p<0.045) after the exposure to UV-C irradiation analysed with Mann-Whitney U test (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182484#pone.0182484.s014" target="_blank">S6 Table</a>).</p

Study of the effect of phenolic compounds on the frequency of Rif^r mutants in nutritiously rich growth medium.

<p>Phenol or <i>m</i>-cresol was supplemented into M9 glucose medium supplemented with CAA for the strains PaW85, PaWpheBA, PaWrulAB and PC24 at the following concentrations: phenol (5 mM), <i>m</i>-cresol (2.5 mM). These compounds were added in lower concentrations (2.5 mM phenol and 1.25 mM <i>m</i>-cresol) for the strain PC20 because of growth inhibiting effects at higher concentrations. Data were analysed using the Kruskal-Wallis test (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182484#pone.0182484.s018" target="_blank">S10 Table</a>). *** designates P<0.0001.</p

UV-C irradiation tolerance of indigenous strains.

<p>UV-C irradiation tolerance of indigenous strains.</p

Median values of the spontaneous Rif^r mutant frequencies of the indigenous strains and the laboratory reference strain PaW85.

<p>Presented are only the results for strains exhibiting the mutant frequency statistically significantly different from that of the reference strain PaW85 (the Kruskal-Wallis test, p<0.006; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182484#pone.0182484.s009" target="_blank">S1 Table</a>). Isolate D2RT is missing from the figure because the median value of the frequency of Rif^r mutants of this strain was 0 (the mean value of Rif^r frequency of this strain was 1.07 x 10⁻⁹).</p