Ocean oligotrophication concurrent with warming weakens the capacity of marine primary producers to support marine food webs and act as a CO₂ sink, and is believed to result from reduced nutrient inputs associated to the stabilization of the thermocline. However, nutrient supply in the oligotrophic ocean is largely dependent on the recycling of organic matter. This involves hydrolytic processes catalyzed by extracellular enzymes released by bacteria, which temperature dependence has not yet been evaluated. Here, we report a global assessment of the temperature‐sensitivity, as represented by the activation energies (E_a), of extracellular β‐glucosidase (βG), leucine aminopeptidase (LAP) and alkaline phosphatase (AP) enzymatic activities, which enable the uptake by bacteria of substrates rich in carbon, nitrogen, and phosphorus, respectively. These E_a were calculated from two different approaches, temperature experimental manipulations and a space‐for‐time substitution approach, which generated congruent results. The three activities showed contrasting E_a in the subtropical and tropical ocean, with βG increasing the fastest with warming, followed by LAP, while AP showed the smallest increase. The estimated activation energies predict that the hydrolysis products under projected warming scenarios will have higher C:N, C:P and N:P molar ratios than those currently generated, and suggest that the warming of oceanic surface waters leads to a decline in the nutrient supply to the microbial heterotrophic community relative to that of carbon, particularly so for phosphorus, slowing down nutrient recycling and contributing to further ocean oligotrophication.

Summary: The microbial response to environmental changes in coastal waters of the eastern Cantabrian Sea was explored for four years by analysing a broad set of environmental variables along with bacterial community metabolism and composition. A recurrent seasonal cycle emerged, consisting of two stable periods, characterized by low bacterial metabolic activity (winter) from October to March, and high bacterial metabolic activity (summer) from May to August. These two contrasting periods were linked by short transition periods in April (T _A ) and September (T _S ). The phylogenetic groups Alphaproteobacteria and Bacteroidetes were dominant during winter and summer respectively, and their recurrent alternation was mainly driven by the bloom of eukaryotic phytoplankton before T _A and the bloom of prokaryotic phytoplankton before T _S . Bacterial growth efficiency remained high and stable during the winter and summer periods but dropped during the two short transition periods. Our results suggest that bacterial growth efficiency should be considered a very resilient property that reflects different stages in the adaptation of the bacterial community composition to the environmental changes occurring throughout the seasonal cycle in this coastal ecosystem.

In this study, we hypothesized that shifts in the kinetic parameters of extracellular hydrolytic enzymes may occur as a consequence of seasonal environmental disturbances and would reflect the level of adaptation of the bacterial community to the organic matter of the ecosystem. We measured the activities of enzymes that play a key role in the bacterial growth (leucine aminopeptidase, β‐ and α‐glucosidases) in surface coastal waters of the Eastern Cantabrian Sea and determined their kinetic parameters by computing kinetic models of distinct complexity. Our results revealed the existence of two clearly distinct enzymatic systems operating at different substrate concentrations: a high‐affinity system prevailing at low substrate concentrations and a low‐affinity system characteristic of high substrate concentrations. These findings could be the result of distinct functional bacterial assemblages growing concurrently under sharp gradients of high‐molecular‐weight compounds. We constructed an ecological network based on contemporaneous and time‐delayed correlations to explore the associations between the kinetic parameters and the environmental variables. The analysis revealed that the recurring phytoplankton blooms registered throughout the seasonal cycle trigger the wax and wane of those members of the bacterial community able to synthesize and secrete specific enzymes.

Mikroplastiko sintetikoak (≤ 5 mm) gero eta kantitate handiagoan aurkitzen diren ingurumen-kutsatzaileak dira, mundu osoko estuarioetan eta itsas sistemetan metatzen direnak ezin direlako era errazean degradatu. Mikroplastikoen ugaritasunak, tamaina txikiak eta dentsitate baxuak korronte ozeanikoen bidez sakabanatzen eta garraiatzen laguntzen diete. kutsatzaile horiek erabilera handiko produktuen isurketaren bidez hel daitezke ur-sistemetara, edota ingurumen-baldintza aldakorren pean (izozte-desizoztea, erradiazio ultramorea, ur-korronteak, eta abar) deskonposatzen diren hondar plastiko handiagoetatik sor daitezke itsasoan bertan. Plastiko horien mundu-mailako urteroko fabrikazioa asko handitu da azken hamarkadan, eta konponbide bat laster ez bada eskaintzen, itsasoko mikroplastikoen metaketak eta hedapenak handiagotzen jarraituko du, horrek dakartzan ondorio ekologikoekin eta toxikologikoekin. Alde batetik, mikroplastikoak mikroorganismoen kolonizaziorako aproposak diren gainazalak dira, komunitate naturalen aktibitatean eta konposizioan aldaketak sustatzen dituztenak, eta, ondorioz, ziklo biogeokimikoetan aldaketak ere eragiten dituztenak. Beste alde batetik, mikroplastikoak eta adsorbituta daramaten kutsatzaile kimikoak zein metal astunak ingeritzeko potentzial altua dute itsas animaliek, haien ehunetan eta organoetan metatzen baitira, eta harrezkero, sare trofikoetan zehar transferitu eta biohanditu. Gainera, mikroplastikoek patogenoen, biotoxinen eta antibiotikoekiko erresistenteak diren geneen sakabanaketan parte hartzen dute, eta osasun publikoan eragin zuzena izan dezakete. Naturan badaude entzimen bidez mikroplastikoak guztiz edo partzialki degradatzeko eta energia-iturri moduan erabiltzeko gai diren mikroorganismoak. Beraz, mikroplastikoak degrada ditzaketen mikroorganismoak identifikatzea etorkizun handiko estrategia da biodegradazio naturala errazteko eta ekosistema naturalen garbiketan laguntzeko, ingurumenaren aurkako inpakturik eragin gabe.

The rise of antimicrobial resistance is reducing the effectiveness of current therapies and highlights the need for new antimicrobial agents. Marine environments, rich in microorganisms adapted to extreme conditions, represent a promising reservoir of bioactive compounds. The marine bacterium Marinomonas mediterranea secretes, among others, lysine oxidase (LodA) and glycine oxidase (GoxA), enzymes that generate hydrogen peroxide and exhibit antibacterial activity. Based on this mechanism, we hypothesized that modifying specific experimental con-ditions could enhance the antimicrobial potential of the secreted enzymes and additional com-pounds, broadening their activity spectrum. In this study, culture conditions were optimized to promote the production of inhibitory molecules, and the antimicrobial activity of the M. medi-terranea secretome was assessed against clinically relevant microorganisms. The concentrated secretome obtained from growth in Marine Broth exhibited antimicrobial activity against the Gram-negative and Gram-positive bacteria analyzed and several pathogenic fungi, an effect at-tributable to some proteins present in it. Among them, LodA and GoxA, previously associated with bacterial growth inhibition, also appear to contribute to antifungal activity. Moreover, valyl-tRNA synthetase emerged as a potential new antimicrobial factor. These findings high-light the biotechnological potential of marine microorganisms and support further exploration of their secretomes for the development of new antimicrobial agents.

Ekialdeko Kantauriar Itsasoko kostaldeko partikula exopolimeriko gardenen (PEG) urtean zeharreko bilakaera produkzioaren informazio-fitxa