The infant gut microbiota has a high abundance of antibiotic resistance genes (ARGs) compared to adults, even in the absence of antibiotic exposure. Here we study potential sources of infant gut ARGs by performing metagenomic sequencing of breast milk, as well as infant and maternal gut microbiomes. We find that fecal ARG and mobile genetic element (MGE) profiles of infants are more similar to those of their own mothers than to those of unrelated mothers. MGEs in mothers’ breast milk are also shared with their own infants. Termination of breastfeeding and intrapartum antibiotic prophylaxis of mothers, which have the potential to affect microbial community composition, are associated with higher abundances of specific ARGs, the composition of which is largely shaped by bacterial phylogeny in the infant gut. Our results suggest that infants inherit the legacy of past antibiotic consumption of their mothers via transmission of genes, but microbiota composition still strongly impacts the overall resistance load.

Cyanobacterial mass occurrences (water blooms) cause ecological, economic and health problems worldwide. Still, little is known about heterotrophic bacteria associated with cyanobacteria and the interactions between those organisms. We isolated 460 bacterial strains from more than 40 lakes and rivers (151 samples), Baltic Sea (32 samples) and treated drinking water of seven treatment plants (29 samples). The water bodies and the raw water of the treatment plants were frequently dominated by high numbers of cyanobacteria. Various growth media were used to isolate the strains. Analysis of partial 16S rRNA gene fragments (701-905 bp for 358 strains and 413-497 bp for 102 strains) classified the isolated bacteria as Proteobacteria, Bacteroidetes, Actinobacteria, Firmicutes and Deinococcus-Thermus. Some of these isolates represented possible new bacterial orders, families, genera or species. We isolated various potentially pathogenic bacteria, such as Aeromonas, Vibrio, Acinetobacter and Pseudomonas, that may cause adverse health effects in humans and animals and should be taken into consideration when assessing the risks caused by cyanobacterial blooms. Several strains also inhibited or enhanced the growth of cyanobacteria. Most of such strains had an enhancing effect on the cyanobacterial growth. Other isolates were affiliated with genera such as Sphingomonas or Flavobacterium, which include strains that are capable of degrading cyanobacterial toxins or other recalcitrant and problematic organic compounds. The isolated strains provide a large group of bacteria that could be used in assessing and controlling the harmful effects of cyanobacteria.

We studied the frequency and composition of potential microcystin (MC) producers in 70 Finnish lakes with general and genus-specific microcystin synthetase gene E (mcyE) PCR. Potential MC-producing Microcystis, Planktothrix and Anabaena spp. existed in 70%, 63%, and 37% of the lake samples, respectively. Approximately two-thirds of the lake samples contained one or two potential MC producers, while all three genera existed in 24% of the samples. In oligotrophic lakes, the occurrence of only one MC producer was most common. The combination of Microcystis and Planktothrix was slightly more prevalent than others in mesotrophic lakes, and the cooccurrence of all three MC producers was most widespread in both eutrophic and hypertrophic lakes. The proportion of the three-producer lakes increased with the trophic status of the lakes. In correlation analysis, the presence of multiple MC-producing genera was associated with higher cyanobacterial and phytoplankton biomass, pH, chlorophyll a, total nitrogen, and MC concentrations. Total nitrogen, pH, and the surface area of the lake predicted the occurrence probability of mcyE genes, whereas total phosphorus alone accounted for MC concentrations in the samples by logistic and linear regression analyses. In conclusion, the results suggested that eutrophication increased the cooccurrence of potentially MC-producing cyanobacterial genera, raising the risk of toxic-bloom formation.Cyanobacterial mass occurrences are a frequent phenomenon worldwide. A survey of the blooms in freshwaters has shown that on average, 59% contain toxins, with hepatotoxic blooms being more common than neurotoxic blooms (45). Toxic blooms expose water users to health risks and prevent the recreational use of water (19).Microcystins (MCs) are the most prevalent cyanobacterial hepatotoxins in freshwaters, where they are produced mainly by strains of the genera Anabaena, Microcystis, Planktothrix, and occasionally Nostoc (45). The toxicity of MCs is due to the inhibition of eukaryotic protein phosphatases 1 and 2A (11,25) in liver cells, where MCs enter via the bile acid transport system (1). MCs are cyclic heptapeptides with a general structure of cyclo(-D-Ala-X-D-erythro-␤-methylaspartic acid-ZAdda-D-Glu-N-methyldehydroalanine), where X and Z are various L-amino acids and Adda is 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid. D-Glu and Adda form the part of the molecule that interacts with the protein phosphatases and thus are the crucial amino acids for the toxicity of MCs (8).MCs are produced by nonribosomal enzyme complexes. Adda is synthesized and integrated into the MC molecule by the enzymes McyG, McyD, and McyE. McyE also incorporates D-Glu, the other crucial amino acid for toxicity. Microcystin synthetase (mcy) gene clusters that encode these biosynthetic enzymes have now been characterized from all the main MCproducing genera (2,30,43,48). The presence of biosynthetic genes has also been proven a prerequisite for MC production (5). Although intensively studied, only a few st...

Toxic and non-toxic cyanobacterial strains from Anabaena, Aphanizomenon, Calothrix, Cylindrospermum, Nostoc, Microcystis, Planktothrix (Oscillatoria agardhii), Oscillatoria and Synechococcus genera were examined by RFLP of PCR-amplified 16S rRNA genes and 16S rRNA gene sequencing. With both methods, high 16S rRNA gene similarity was found among planktic, anatoxin-aproducing Anabaena and non-toxic Aphanizomenon, microcystin-producing and non-toxic Microcystis, and microcystin-producing and non-toxic Planktothrix strains of different geographical origins. The respective sequence similarities were 999-100 %, 942-999 % and 993-100 %. Thus the morphological characteristics (e.g. Anabaena and Aphanizomenon), the physiological (toxicity) characteristics or the geographical origins did not reflect the level of 16S rRNA gene relatedness of the closely related strains studied. In addition, cyanobacterial strains were fingerprinted with repetitive extragenic palindromic ( Abbreviations : ERIC, enterobacterial repetitive intergenic consensus ; LTRR, long tandemly repeated sequence ; ML, maximum-likelihood ; MP, maximum-parsimony ; NJ, neighbour-joining ; REP, repetitive extragenic palindromic ; STRR, short tandemly repeated sequence ; UPGMA, unweighted pairs group method with averages.The GenBank/EMBL accession numbers for the cyanobacterial 16S rRNA gene sequences are AJ133151-AJ133154, AJ133156, AJ133157, AJ133159-AJ133170, AJ133172-AJ133176 and AJ133185 bacteria occur in a wide range of habitats. In eutrophic fresh and brackish waters cyanobacteria form toxic water blooms which have caused human and animal poisonings (Ressom et al., 1994 ; Kuiper-Goodman et al., 1999). The most frequently found toxins in cyanobacterial blooms worldwide are hepatotoxic cyclic peptides, microcystins and nodularins (Sivonen & Jones, 1999). Mass occurrences of cyanobacteria that contain neurotoxins [anatoxin-a, anatoxin-a(S) and saxitoxins] have been found in Australia, Europe and North America (Sivonen & Jones, 1999). Cyanobacteria are a morphologically diverse group of organisms ranging from unicellular to filamentous forms. Traditionally, the classification of cyanobacteria has been based on morphological characters, Asayama et al. (1996) ; 2, Giovannoni et al. (1988) ; 3, Herdman et al. (1979a) ; 4, Herdman et al. (1979b) ; 5, Kenyon et al. (1972) ; 6, Kondo et al. (2000) ; 7, Lachance (1981) ; 8, Leeuwangh et al. (1983) ; 9, Lehtima$ ki et al. (2000) ; 10, Lu et al. (1997) ; 11, Luukkainen et al. (1993) ; 12, Luukkainen et al. (1994) ; 13, Lyra et al. (1997) ; 14, Masephol et al. (1996) ; 15, Mazel et al. (1990) ; 16, Neilan et al. (1995) ; 17, Neilan et al. (1997a) ; 18, Neilan et al. (1997b) ; 19, Neilan et al. (1999) ; 20, Otsuka et al. (1999) ; 21, Rapala et al. (1993) ; 22, Rasmussen & Svenning (1998) ; 23, Rippka & Herdman (1992) ; 24, Rippka et al. (1979) ; 25, Rouhiainen et al. (1995) ; 26, Rudi & Jakobsen (1999) ; 27, Rudi et al. (1997) ; 28, Rudi et al., 1998 ; 29, Sivonen et al. (1989) ; 30, Sivonen et al. (1990) ;...