Algicidal activity of Morganella morganii against axenic and environmental strains of Microcystis aeruginosa: Compound combination effects.

Cyanobacterial harmful algal blooms (cyanoHABs) are a global problem with serious consequences for public health and many sectors of the economy. The use of algicidal bacteria as natural antagonists to control bloom-forming cyanobacteria is a topic of growing interest. However, there are still unresolved questions that need to be addressed to better understand their mode of action and to implement effective mitigation strategies. In this study, thirteen bacterial strains isolated from both scums and concentrated bloom samples exhibited algicidal activity on three Microcystis aeruginosa strains with different characteristics: the axenic microcystin (MC)-producing strain M. aeruginosa PCC7820 (MaPCC7820), and two environmental (non-axenic) M. aeruginosa strains isolated from two different water bodies in Poland, one MC-producer (MaSU) and another non-MC-producer (MaPN). The bacterial strain SU7S0818 exerted the highest average algicidal effect on the three cyanobacterial strains. This strain was identified as Morganella morganii (99.51% similarity) by the 16S rRNA gene analyses; hence, this is the first study that demonstrates the algicidal properties of these ubiquitous bacteria. Microscopic cell counting and qPCR analyses showed that M. morganii SU7S0818 removed 91%, 96%, and 98.5% of MaPCC7820, MaSU and MaPN cells after 6 days of co-culture, respectively. Interestingly, the ultra-high-performance liquid chromatography-tandem mass spectrometer (UHPLC-MS/MS) analyses showed that this bacterium was involved on the release of several substances with algicidal potential. It was remarkable how the profile of some compounds evolved over time, as in the case of cadaverine, tyramine, cyclo[Pro-Gly] and cyclo[Pro-Val]. These dynamic changes could be attributed to the action of M. morganii SU7S0818 and the presence of associated bacteria with environmental cyanobacterial strains. Therefore, this study sheds light on how algicidal bacteria may adapt their action on cyanobacterial cells by releasing a combination of compounds, which is a crucial insight to exploit them as effective biological tools in the control of cyanoHABs.

Environmental factors driving the occurrence of the invasive cyanobacterium Sphaerospermopsis aphanizomenoides (Nostocales) in temperate lakes.

Cyanobacterial blooms are an increasing threat worldwide. Invasions of certain cyanobacterial species, mainly towards higher latitudes, add to this concern as they enrich the pool of potential bloom-formers in the invaded region. Among the numerous causes of this escalating process, climate warming is commonly considered the most crucial factor, but empirical studies of this issue are lacking. The aim of our study was to identify physical, chemical and biological factors related to the occurrence of an invasive cyanobacterium at the northern border of its putative current range, and thus enabling its expansion. This study focuses on the relatively little studied species Sphaerospermopsis aphanizomenoides (Nostocales, Cyanobacteria; synonyms: Aphanizomenon aphanizomenoides, Anabaena aphanizomenoides), which is predicted to become one of the main nuisance species of the future. Forty-nine freshwater lakes located between latitudes 51° and 55°N were examined for the presence of S. aphanizomenoides, and environmental factors that could drive its occurrence were studied simultaneously. To identify factors correlated with the presence of the species, principal component analysis (PCA) and Mann-Whitney U test were performed. Water temperature did not differentiate lakes with or without S. aphanizomenoides, however the study was conducted in a particularly hot summer. Total phosphorus concentration was identified as the primary driving factor of the occurrence of S. aphanizomenoides. The species grew in poor light conditions and high phytoplankton biomass, mainly in shallow lakes. As shown by detrended correspondence analysis (DCA), the species accompanied shade tolerant, eutrophic species of native and invasive cyanobacteria as well as eukaryotic algae. Our results indicate that eutrophication may be the primary factor enabling the increasing occurrence of S. aphanizomenoides in temperate environments, and suggest that this process may stimulate expansion of cyanobacterial species towards high latitudes.