Study of marine bacteria inactivation by photochemical processes: disinfection kinetics and growth modeling after treatment

Assessing the effectiveness of filtration + UV-C radiation for the treatment of simulated ballast water at various holding times

In recent years, the issue of invasive alien species brought on by ballast water has drawn increasing attention, and advances in ballast water treatment technologies have been made. One of the most popular combined ballast water treatment technologies utilized in ballast water management systems (BWMSs) globally is filtration + UV-C radiation. During the actual voyage of the ship, ballast water is treated by the BWMS and then enters the dark ballast tanks until the ballast water is discharged. Marine organisms are able to complete DNA damage caused by UV radiation in dark ballast tanks. Therefore, the length of holding time affects the effectiveness of the BWMS in treating ballast water. The objective of this study was to examine the efficacy of filtration + UV-C irradiation treatment at different holding times for the removal or inactivation of phytoplankton and zooplankton populations during simulated ballast water treatment. Results indicate that the holding time after the filtration + UV-C radiation treatment increased the inactivating efficacy, especially for zooplankton in natural seawater. For phytoplanktons in ballast water, the strongest impact on the treatment efficacy was reached with a holding time of 24 h.

Inactivation of the waterborne marine pathogen Vibrio alginolyticus by photo-chemical processes driven by UV-A, UV-B, or UV-C LED combined with H2O2 or HSO5. WATER RESEARCH 2023;232:119686. [PMID: 36764105 DOI: 10.1016/j.watres.2023.119686]

Ultraviolet (UV) radiation is a well-implemented process for water disinfection. The development of emergent UV sources, such as light-emitting diodes (LEDs), has afforded new possibilities for advanced oxidation processes. The emission wavelength is considered to be an important factor for photo-chemical processes in terms of both biological damage and energetic efficiency, as the inactivation mechanisms and mode-of-action may differ according to the wavelength that is applied. In addition, these processes merit exploration for inactivating emerging pathogens, such as marine vibrios, that are important bacteria to control in maritime activities. The main goal of this study was to compare the disinfection efficacy of several UV-LED driven processes with different modes of action. First, the effect of UV-LEDs was assessed at different UV ranges (UV-A, UV-B, or UV-C). Second, the possible enhancement of a combination with hydrogen peroxide (H₂O₂) or peroxymonosulfate salt (HSO₅^-) was investigated under two different application strategies, i.e. simultaneous or sequential. The results obtained indicate a high sensitivity of Vibrio alginolyticus to UV radiation, especially under UV-B (k_obs = 0.24 cm²/mJ) and UV-C (k_obs = 1.47 cm²/mJ) irradiation. The highest inactivation rate constants were obtained for UV/HSO₅^- (k_obs (cm²/mJ)=0.0007 (UV-A); 0.39 (UV-B); 1.79 (UV-C)) with respect to UV/H₂O₂ (k_obs (cm²/mJ)=0.0006 (UV-A); 0.26 (UV-B); and 1.54 (UV-C)) processes, however, regrowth was avoided only with UV/H₂O₂. Additionally, the disinfection enhancement caused by a chemical addition was more evident in the order UV-A > UV-B > UV-C. By applying H₂O₂ (10 mg/L) or HSO₅^- (2.5 mg/L) in a sequential mode before the UV, negligible effects were obtained in comparison with the simultaneous application. Finally, promising electrical energy per order (EE_O) values were obtained as follows: UV/HSO₅^- (EE_O (kWh/m³)=1.68 (UV-A); 0.20 (UV-B); 0.04 (UV-C)) and UV/H₂O₂ (EE_O (kWh/m³)=2.15 (UV-A); 0.32 (UV-B); 0.04 (UV-C)), demonstrating the potential of UV-LEDs for disinfection in particular activities such as the aquaculture industry or maritime transport.

Identifying the mediators of intracellular E. coli inactivation under UVA light: The (photo) Fenton process and singlet oxygen

Solar disinfection (SODIS) was probed for its underlying mechanism. When Escherichia coli was exposed to UVA irradiation, the dominant solar fraction acting in SODIS process, cells exhibited a shoulder before death ensued. This profile resembles cell killing by hydrogen peroxide (H2O2). Indeed, the use of specialized strains revealed that UVA exposure triggers intracellular H2O2 formation. The resultant H2O2 stress was especially impactful because UVA also inactivated the processes that degrade H2O2-peroxidases through the suppression of metabolism, and catalases through direct enzyme damage. Cell killing was enhanced when water was replaced with D2O, suggesting that singlet oxygen plays a role, possibly as a precursor to H2O2 and/or as the mediator of catalase damage. UVA was especially toxic to mutants lacking miniferritin (dps) or recombinational DNA repair (recA) enzymes, indicating that reactions between ferrous iron and UVA-generated H2O2 lead to lethal DNA damage. Importantly, experiments showed that the intracellular accumulation of H2O2 alone is insufficient to kill cells; therefore, UVA must do something more to enable death. A possibility is that UVA stimulates the reduction of intracellular ferric iron to its ferrous form, either by stimulating O2•- formation or by generating photoexcited electron donors. These observations and methods open the door to follow-up experiments that can probe the mechanisms of H2O2 formation, catalase inactivation, and iron reduction. Of immediate utility, the data highlight the intracellular pathways formed under UVA light during SODIS, and that the presence of micromolar iron accelerates the rate at which radiation disinfects water.

On the Efficacy of H2O2 or S2O82- at Promoting the Inactivation of a Consortium of Cyanobacteria and Bacteria in Algae-Laden Water

Harmful algal blooms in coastal areas can significantly impact a water source. Microorganisms such as cyanobacteria and associated pathogenic bacteria may endanger an ecosystem and human health by causing significant eco-hazards. This study assesses the efficacy of two different reagents, H2O2 and S2O82−, as (pre-)treatment options for algae-laden waters. Anabaena sp. and Vibrio alginolyticus have been selected as target microorganisms. With the objective of activating H2O2 or S2O82−, additional experiments have been performed with the presence of small amounts of iron (18 µmol/L). For the cyanobacterial case, H2O2-based processes demonstrate greater efficiency over that of S2O82−, as Anabaena sp. is particularly affected by H2O2, for which >90% of growth inhibition has been achieved with 0.088 mmol/L of H2O2 (at 72 h of exposure). The response of Anabaena sp. as a co-culture with V. alginolyticus implies the use of major H2O2 amounts for its inactivation (0.29 mmol/L of H2O2), while the effects of H2O2/Fe(II) suggests an improvement of ~60% compared to single H2O2. These H2O2 doses are not sufficient for preventing the regrowth of V. alginolyticus after 24 h. The effects of S2O82− (+ Fe(II)) are moderate, reaching maximum inhibition growth of ~50% for Anabaena sp. at seven days of exposure. Nevertheless, doses of 3 mmol/L of S2O82− can prevent the regrowth of V. alginolyticus. These findings have implications for the mitigation of HABs but also for the associated bacteria that threaten many coastal ecosystems.

Recent progress and challenges facing ballast water treatment - A review

The transoceanic movement of non-indigenous microorganisms and organic and inorganic contaminants through the transfer of ballast water of ocean-going vessels can be considered highly likely. The introduction of contaminants and non-indigenous microorganisms can cause changes in indigenous microorganisms, marine species, and biota, which can create problems for the ecology, economy, environment, and human health. This paper compiles and presents ballast water treatment system concepts, principles of inactivation mechanisms used, and the advantages and challenges of the treatment technologies. In addition, the paper aims to draw attention to the relationship between various organisms and the individual mechanism to be inactivated, including the effect of external factors (e.g., pH, salinity, turbidity) on inactivation efficiency. This review can assist in the choice of a suitable ballast water treatment system, taking into account the water conditions (e.g., pH, temperature, salinity) and indigenous species of the maritime areas where the ships intend to operate. This review also provides information describing the responses of the various organisms to different treatment techniques.

Wild microorganism and plankton decay in ballast water treatments by solar disinfection (SODIS) and advanced oxidation processes

Ballast water (BW) is a dead weight used by ships to provide stability in their journeys. It poses health, economic and ecological problems. Since 2017, the International Maritime Organization-IMO mandated management of BW. This research compares plankton mortality and microorganism inactivation in different BW treatments to identify possible decay models. Treatments include solar radiation (Srad), UV, H₂O₂ and advanced oxidation processes (AOPs). In the wild populations, the disinfection capacity was measured in natural seawater pumped from the Santa Marta port zone in Colombia. AOPs showed different models and effectiveness according to the treatment and microorganism. Plankton larger than 50 μm was the most resistant; therefore, it must be removed first by a previous filter. Wild microorganisms showed log-linear and log-linear tail decay models for most AOPs in E. coli. For Vibrio, the models were log-lineal tail and biphasic models.

Bacterial Biodiversity of Extra Virgin Olive Oils and Their Potential Biotechnological Exploitation

Bacterial diversity of 15 extra virgin olive oils, obtained from different Italian varieties, including Frantoio, Coratina, Bosana, and Semidana, was analyzed in this study. All bacterial isolates were genotyped using RAPD and REP-PCR method and grouped by means of cluster analyses. Sequencing of 16S rDNA of 51 isolates, representative of 36 clusters, led to the identification of Bacillus spp., Brevibacillus spp., Micrococcus spp., Staphylococcus spp., Pantoea spp., Kocuria spp., Lysinbacillus spp., and Lactobacillus spp., most of which reported for first time in olive oils. Phenotypic characterization of the 51 isolates, some of which ascribed to potentially probiotic species, indicate that two of them have beta-glucosidase activity while 37% present lipolytic activity. Preliminary evaluation of probiotic potential indicates that 31% of the isolates show biofilm formation ability, 29% acidic pH resistance, and 25% bile salt resistance. Finally, 29% of the isolates were sensitive to antibiotics while the remaining 71%, that include bacterial species well-recognized for their ability to disseminate resistance genes in the environment, showed a variable pattern of antibiotic resistance. The results obtained underline that microbial diversity of extra virgin olive oils represents an unexpected sink of microbial diversity and poses safety issues on the possible biotechnological exploitation of this microbial biodiversity.

Application of persulfate salts for enhancing UV disinfection in marine waters

Over the years, industrial activities that generate high salinity effluents have been intensifying; this has relevant potential for causing organic and microbiological pollution which damages both human and ocean health. The development of new regulations, such as ballast water convention, encourage the development of treatment systems that can be feasible for treating seawater effluents. Accordingly, an approach based on the UV activation of persulfate salts has been assessed. In this scenario, two different persulfate sources (S₂O₈^2- and HSO₅^-) were evaluated under UV-C irradiation for disinfection purposes. An optimization process was performed with low chemical doses (<1 mM). In order to extensively examine the applicability on seawater, different water matrices were tested as well as different microorganisms including both fecal and marine bacteria. An enhancement of UV-inactivation with the addition of persulfate salts was achieved in all cases, kinetic rate constant has been accelerated by up to 79% in seawater. It implies a UV-dose saving up to 45% to achieve 4-log reductions. Best efficiencies were obtained with [HSO₅^-] = 0.005 mM and [S₂O₈^2-] = 0.5 mM. Higher effectiveness was obtained with the use of HSO₅^- due to its low stability and interaction with chloride. Also, different responses were obtained according to the specific microorganisms by achieving faster disinfection in Gram-negative than in Gram-positive bacteria, the sensitivity observed was Vibrio spp. > E. coli > E. faecalis ≈ Marine Heterotrophic Bacteria. With an evaluation of regrowth after treatment, greater cell damage was detected with the addition of persulfate salts. The major ability of regrowth for marine bacteria encourages the use of a residual disinfectant after disinfection processes.

An outbreak of acute disease and mortality in Atlantic salmon (Salmo salar) post-smolts in Norway caused by Tenacibaculum dicentrarchi

An outbreak of disease characterized by skin ulcers, fin rot and mortality was observed a few days after the transfer of Atlantic salmon (Salmo salar) from a freshwater smolt production facility to a land-based seawater post-smolt site. Dead and moribund fish had severe skin and muscle ulcers, often 2-6 cm wide, particularly caudal to the pectoral fins. Microscopic examination of smears from ulcers and head kidney identified long, slender Gram-negative rods. Histopathological analysis revealed abundance of long, slender Tenacibaculum-like bacteria in ulcers and affected fins. Genetic characterization using multilocus sequence analysis (MLSA) of seven housekeeping genes, including atpA, dnaK, glyA, gyrB, infB, rlmN and tgt, revealed that the isolates obtained during the outbreak were all clustered with the Tenacibaculum dicentrarchi-type strain (USC39/09^T ) from Spain. Two bath challenge experiments with Atlantic salmon and an isolate of T. dicentrarchi from the outbreak were performed. No disease or mortality was observed in the first trial. In the second trial with a higher challenge dose of T. dicentrarchi and longer challenge time, we got 100% mortality within 48 hr. This is the first reported outbreak of disease caused by T. dicentrarchi in Norwegian farmed Atlantic salmon.

Microorganisms in ballast water: Disinfection, community dynamics, and implications for management

Increasing concerns have accelerated the development of international regulations and methods for ballast water management to limit the introduction of non-indigenous species. The transport of microorganisms with ballast water has received scientific attention in recent years. However, few studies have focused on the importance of organisms smaller than 10 μm in diameter. In this work, we review the effects of ballast water transport, disinfection, and the release of microorganisms on ecosystem processes with a special focus on heterotrophic bacteria. It is important to evaluate both direct and indirect effects of ballast water treatment systems, such as the generation of easily degradable substrates and the subsequent regrowth of heterotrophic microorganisms in ballast tanks. Disinfection of water can alter the composition of bacterial communities through selective recolonization in the ballast water or the recipient water, and thereby affects bacterial driven functions that are important for the marine food web. Dissolved organic matter quality and quantity and the ecosystem status of the treated water can also be affected by the disinfection method used. These side effects of disinfection should be further investigated in a broader context and in different scales (laboratory studies, large-scale facilities, and on the ships).

Inactivation of marine heterotrophic bacteria in ballast water by an Electrochemical Advanced Oxidation Process

Seawater treatment is increasingly required due to industrial activities that use substantial volumes of seawater in their processes. The shipping industry and the associated management of a ship's ballast water are currently considered a global challenge for the seas. Related to that, the suitability of an Electrochemical Advanced Oxidation Process (EAOP) with Boron Doped Diamond (BDD) electrodes has been assessed on a laboratory scale for the disinfection of seawater. This technology can produce both reactive oxygen species and chlorine species (especially in seawater) that are responsible for inactivation. The EAOP was applied in a continuous-flow regime with real seawater. Natural marine heterotrophic bacteria (MHB) were used as an indicator of disinfection efficiency. A biphasic inactivation kinetic model was fitted on experimental points, achieving 4-Log reductions at 0.019 Ah L^-1. By assessing regrowth after treatment, results suggest that higher bacterial damages result from the EAOP when it is compared to chlorination. Furthermore, several issues lacking fundamental understanding were investigated such as recolonization capacity or bacterial community dynamics. It was concluded that, despite disinfection processes being effective, there is not only a possibility for regrowth after treatment but also a change on bacterial population diversity produced by the treatment. Finally, energy consumption was estimated and indicated that 0.264 kWh·m^-3 are needed for 4.8-Log reductions of MHB; otherwise, with 0.035 kWh·m^-3, less disinfection efficiency can be obtained (2.2-Log red). However, with a residual oxidant in the solution, total inactivation can be achieved in three days.

Implications in studies of environmental risk assessments: Does culture medium influence the results of toxicity tests of marine bacteria?

Two marine bacterial populations (Roseobacter sp. and Pseudomonas litoralis) were exposed to different concentrations of zinc (300, 625, 1250, 2000, 2500 and 5000 mg L^-1) and cadmium (75, 250, 340, 500 and 1000 mg L^-1) using two culture media (full nutrient Marine Broth 2216 "MB" and 1:10 (vol/vol) dilution with seawater of Marine Broth 2216 "MB_SW"), in order to assess population responses depending on the culture medium and also potential adverse effects associated with these two metals. Different responses were found depending on the culture medium (Bacterial abundance (cells·mL^-1), growth rates (μ, hours^-1), and production of Extracellular Polysaccharides Substances (EPS) (μg glucose·cells^-1). Results showed negative effects in both strains after the exposure to Zn treatments. Both strains showed highest metal sensitivity at low concentrations using both culture media. However, different results were found when exposing the bacterial populations to Cd treatments depending on the culture medium. Highest toxicity was observed using MB at low levels of Cd concentrations, whereas MB_SW showed toxicity to bacteria at higher concentrations of Cd. Results not only showed adverse effects on Roseobacter sp. and Pseudomonas litoralis associated with the concentration of Zn and Cd, but also confirm that depending on the culture medium results can differ. This work suggests MB_SW as an adequate culture medium to study metal toxicity bioassays in order to predict realistic effects on marine bacterial populations.