Microbial community structures and bacteria-Cylindrospermopsis raciborskii interactions in Yilong Lake.

Cylindrospermopsis raciborskii-dominated harmful algae blooms have been reported globally in recent years. However, our understanding of the ecology of C. raciborskii in natural conditions is still poor. In this study, we collected the water samples from a C. raciborskii-blooming lake, Yilong Lake, in Yunnan province, China, and used both culture-dependent and culture-independent approaches to investigate their microbial communities and the interactions between C. raciborskii and the other bacteria. The composition and diversity of microbial communities were revealed with 16S rRNA gene high-throughput sequencing data analysis. Microbial co-occurrences analysis suggests C. raciborskii may have complex associations with other bacteria. Based on co-inoculation tests, we obtained 14 strains of bacterial strains from the water samples that exhibited either algicidal or promoting effects on a strain of C. raciborskii. Two bacterial isolates exhibited a consistent performance between co-occurrence analysis and experimental results. Effects of these bacteria-algae interspecies interactions on the bloom event are discussed. All these results may provide new insights into the C. raciborskii-dominated blooms and how its interspecies relationships with other bacteria may influence the bloom events in eutrophic waters throughout the world.

Isolation and characterization of algicidal bacteria from freshwater aquatic environments in China.

Algicidal bacteria can inhibit the growth of algae or lyse algal cells, thus playing roles in shaping aquatic microbial communities and maintaining the functions of aquatic ecosystems. Nevertheless, our understanding of their diversities and distributions remains limited. In this study, we collected water samples from 17 freshwater sites in 14 cities in China and screened a total of 77 algicidal bacterial strains using several prokaryotic cyanobacteria and eukaryotic algae as target strains. According to their target-specificities, these strains were classified into three subgroups, cyanobacterial algicidal bacteria, algal algicidal bacteria, and broad-target algicidal bacteria, each displaying distinctive compositions and geographical distribution patterns. They are assigned to Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes bacterial phyla, of which Pseudomonas and Bacillus are the most abundant gram-negative and gram-positive genus, respectively. A number of bacterial strains, such as Inhella inkyongensis and Massilia eburnean, are suggested as new algicidal bacteria. The diverse taxonomies, algal-inhibiting abilities and distributions of these isolates have suggested that there are rich algicidal bacterial resources in these aquatic environments. Our results provide new microbial resources for algal-bacterial interaction studies, and shed new insights into how algicidal bacteria can be used in the control of harmful algal blooms, as well as in algal biotechnology.

Algicidal interaction between Paenibacillus polymyxa MEZ6 and microalgae.

AIMS: Algicidal bacteria can be used for control of harmful algal bloom and extraction of algal bioproducts based on their algae-lysing activities. This work investigated the algae-lysing activity of a newly isolated algicidal bacterium, Paenibacillus polymyxa strain MEZ6 and its possible mechanisms. METHODS AND RESULTS: Algicidal bacteria were isolated from soil samples collected at the university campus. Co-inoculation tests identified that one isolate, MEZ6, can rapidly kill eukaryotic algae including Chlamydomonas reinhardtii, Tribonema minus, Haematococcus pluvialis, and Chlorella ellipsoidea. The strain was determined as Paenibacillus polymyxa MEZ6 based on 16S rRNA gene sequence and genome comparisons. The algicidal activity was detected in both living cells and cell-free supernatant of spent culture medium, suggesting cell-cell contact is not required for algicidal activity. Strain MEZ6 was less active towards cyanobacterial strains compared to algae. Genomic sequence and comparative proteomic analyses were performed to explore the possible algicidal mechanisms of the strain. Differentially expressed protein analysis identified a number of proteins related to polysaccharides degradation and antimicrobial secondary metabolite biosynthesis that may be involved in the algicidal activity of MEZ6. CONCLUSION: Paenibacillus polymyxa MEZ6 is a newly discovered gram-positive algicidal bacterial strain with high lytic activity towards several algal species. SIGNIFICANCE AND IMPACT OF THE STUDY: Our study extends the understanding of the versatile characters of Paenibacillus polymyxa and sheds new insights into its application in algae biotechnology.

Removal of antibiotic thiamphenicol by bacterium Aeromonas hydrophila HS01.

Thiamphenicol (TAP) is an amphenicol antibiotic, which has a broad-spectrum inhibitory effect on both gram-positive and gram-negative bacteria. Since it is widely used in animals and aquaculture, its residues in environment may bring potential risk for human health and ecosystems. While TAP can be removed through conventional physical or chemical methods, its bioremediation using microorganisms is less studied. Here, we report the removal of TAP by a bacterial strain, Aeromonas hydrophila HS01, which can remove more than 90.0% of TAP in a living cell-dependent manner. Our results indicated that its removal efficiency can be greatly affected by the growth condition. Proteomics studies revealed a number of differentially expressed proteins of HS01 in the presence of TAP, which may play critical roles in the transportation and degradation of TAP. All these results indicate bacterial strain A. hydrophila HS01 is a new microbial resource for efficiently removing TAP, and may shed new insights in developing bioremediation approaches for TAP pollution.