Antimicrobial activity against Microcystis aeruginosa and degradation of microcystin-LR by bacteria isolated from Antarctica

Biodegradation of microcystins by microbiota of duckweed Spirodela polyrhiza

Cyanobacteria-produced allelochemicals, including hepatotoxic microcystins (MCs), exert an inhibitory effect on macrophyte growth. However, the role of macrophyte-associated bacteria and algae (macrophyte microbiota) in mitigating these immediate negative effects of cyanotoxins remains poorly understood. In this paper, we analyzed the biodegradation of microcystin-RR, MC-LR, and MC-LF by microbiota of the macrophyte Spirodela polyrhiza. The biodegradation of two MC variants was observed and LC-MS/MS analysis allowed identifying the degradation products of MC-RR (m/z 1011, 984, 969, 877, 862, 820, and 615) and MC-LR (m/z 968 and 653), including eight previously unreported products. No degradation products of MC-LF were detected, suggesting its stability and resistance under experimental conditions. NGS-based profiling of microbial consortia revealed no major differences in bacterial community composition across experimental treatments. Taxa previously reported as capable of MC degradation have been found in S. polyrhiza microbiota. Furthermore, the presence of genes encoding putative microcystinase homologues and the formation of new linear intermediates suggest a biochemical pathway that is similar, but not identical to previously reported. The ability of aquatic plant microbiota to biodegrade MCs holds environmental significance, and further studies in this field are required.

Bioprospecting the potential of the microbial community associated to Antarctic marine sediments for hydrocarbon bioremediation

Microorganisms that inhabit the cold Antarctic environment can produce ligninolytic enzymes potentially useful in bioremediation. Our study focused on characterizing Antarctic bacteria and fungi from marine sediment samples of King George and Deception Islands, maritime Antarctica, potentially affected by hydrocarbon influence, able to produce enzymes for use in bioremediation processes in environments impacted with petroleum derivatives. A total of 168 microorganism isolates were obtained: 56 from sediments of King George Island and 112 from Deception Island. Among them, five bacterial isolates were tolerant to cell growth in the presence of diesel oil and gasoline and seven fungal were able to discolor RBBR dye. In addition, 16 isolates (15 bacterial and one fungal) displayed enzymatic emulsifying activities. Two isolates were characterized taxonomically by showing better biotechnological results. Psychrobacter sp. BAD17 and Cladosporium sp. FAR18 showed pyrene tolerance (cell growth of 0.03 g mL-1 and 0.2 g mL-1) and laccase enzymatic activity (0.006 UL-1 and 0.10 UL-1), respectively. Our results indicate that bacteria and fungi living in sediments under potential effect of hydrocarbon pollution may represent a promising alternative to bioremediate cold environments contaminated with polluting compounds derived from petroleum such as polycyclic aromatic hydrocarbons and dyes.

Temporal dynamics of microcystins in two reservoirs with different trophic status during the early growth stage of cyanobacteria

Harmful cyanobacterial blooms are increasing in frequency and severity, which makes their toxic secondary metabolites of microcystins (MCs) have been widely studied, especially in their distribution and influence factors in different habitats. However, the distribution of MCs on the early growth stage of harmful cyanobacteria and its influence factors and risks are still largely unknown. Thus, in the present study, two reservoirs (Lutian Reservoir and Lake Haitang) with different trophic status in China have been studied weekly from March to May in 2018, when the cyanobacteria communities were just in the early growth stage, to investigate the variation of MCs concentration and the relationships between MCs and environmental parameters. During the investigation, Lutian Reservoir and Lake Haitang were found to be mesotrophic and light eutrophic, respectively. In Lutian Reservoir, the concentration of EMCs (extracellular MCs) was obviously higher than that of IMCs (intracellular MCs) with a mean value of 0.323 and 0.264 μg/L, respectively. Meanwhile, the concentration of EMCs also fluctuated more sharply than that of IMCs. Congeners of IMC-YR and EMC-LR were respectively dominant in total concentrations of IMCs and EMCs. Unsurprisingly, in Lake Haitang, the concentrations of IMC and EMC were both significantly higher than that in Lutian Reservoir with a mean concentration of 0.482 and 0.472 μg/L, respectively. Differently, the concentration of MC-YR was dominant in both IMCs and EMCs, followed by MC-LR. In correlation analysis, the IMCs were significantly and positively correlated with the density and biomass of phytoplankton phyla and potential MCs-producing cyanobacteria and the parameters of water temperature (WT), nutrients, and organic matters. Similar results were also observed for EMCs. While the different variations of MCs in the two reservoirs might be primarily caused by the differences in WT, nutrients (especially phosphorus), organic matters, and the composition of MCs-producing cyanobacteria. In addition, the coexistence of the dominant species of Pseudoanabaena sp., which can produce a taste-and-odor compound of 2-methylisoborneol (2-MIB), might have a significant impact on the concentration and toxicity of MCs. Our results suggested that the risks posed by MCs at the early growth stage of cyanobacteria should also deserve our attention, especially in mesotrophic water bodies.

Recent Advances in the Research on the Anticyanobacterial Effects and Biodegradation Mechanisms of Microcystis aeruginosa with Microorganisms

Harmful algal blooms (HABs) have attracted great attention around the world due to the numerous negative effects such as algal organic matters and cyanobacterial toxins in drinking water treatments. As an economic and environmentally friendly technology, microorganisms have been widely used for pollution control and remediation, especially in the inhibition/biodegradation of the toxic cyanobacterium Microcystis aeruginosa in eutrophic water; moreover, some certain anticyanobacterial microorganisms can degrade microcystins at the same time. Therefore, this review aims to provide information regarding the current status of M. aeruginosa inhibition/biodegradation microorganisms and the acute toxicities of anticyanobacterial substances secreted by microorganisms. Based on the available literature, the anticyanobacterial modes and mechanisms, as well as the in situ application of anticyanobacterial microorganisms are elucidated in this review. This review aims to enhance understanding the anticyanobacterial microorganisms and provides a rational approach towards the future applications.

Algicidal Bacteria: A Review of Current Knowledge and Applications to Control Harmful Algal Blooms

Interactions between bacteria and phytoplankton in aqueous ecosystems are both complex and dynamic, with associations that range from mutualism to parasitism. This review focuses on algicidal interactions, in which bacteria are capable of controlling algal growth through physical association or the production of algicidal compounds. While there is some evidence for bacterial control of algal growth in the field, our understanding of these interactions is largely based on laboratory culture experiments. Here, the range of these algicidal interactions is discussed, including specificity of bacterial control, mechanisms for activity, and insights into the chemical and biochemical analysis of these interactions. The development of algicidal bacteria or compounds derived from bacteria for control of harmful algal blooms is reviewed with a focus on environmentally friendly or sustainable methods of application. Potential avenues for future research and further development and application of bacterial algicides for the control of algal blooms are presented.