Cyanobacterial blooms in oil-contaminated subtidal sediments revealed by integrated approaches

Inputs don't equal outputs: bacterial microbiomes of the ingesta, gut, and feces of the keystone deposit feeder Ilyanassa obsoleta

Bacteria drive energy fluxes and geochemical processes in estuarine sediments. Deposit-feeding invertebrates alter the structure and activity of microbial communities through sediment ingestion, gut passage, and defecation. The eastern mud snail, Ilyanassa obsoleta, is native to estuaries of the northwestern Atlantic, ranging from Nova Scotia, Canada, to Florida in the USA. Given extremely high densities, their deposit-feeding and locomotory activities exert ecological influence on other invertebrates and microbes. Our aim was to characterize the bacterial microbiome of this 'keystone species' and determine how its feeding alters the native bacterial microbiota. We gathered snails from both mudflat and sandflat habitats and collected their fresh fecal pellets in the laboratory. Dissection of these same snails allowed us to compare bacterial assemblages of ingested sediments, shell surfaces, gut sections (esophagus, stomach, intestine), and feces using DNA metabarcoding. Our findings indicate a diverse, resident gut microbiota. The stomach and intestines were dominated by bacteria of the genus Mycoplasma. Comparison of ingesta and feces revealed digestion of several bacterial taxa, introduction of gut residents during passage, in addition to unique bacterial taxa within the feces of unknown provenance. Our results demonstrate that I. obsoleta has the potential to modify microbial community structure in estuarine sediments.

Functional potential and assembly of microbes from sediments in a lake bay and adjoining river ecosystem for polycyclic aromatic hydrocarbon biodegradation

Lake and adjoining river ecosystems are ecologically and economically valuable and are heavily threatened by anthropogenic activities. Determining the inherent capacity of ecosystems for polycyclic aromatic hydrocarbon (PAH) biodegradation can help quantify environmental impacts on the functioning of ecosystems, especially on that of the microbial community. Here, PAH biodegradation potential was compared between sediments collected from a lake bay (LS) and an adjoining river (RS) ecosystem. Microbial community composition, function, and their co-occurrence patterns were also explored. In the RS, the biodegradation rates (K_D ) of pyrene or PAH were almost two orders of magnitude higher than those in the LS. Sediment functional community structure and network interactions were dramatically different between the LS and RS. Although PAH degradation genes (p450aro, quinoline, and qorl) were detected in the LS, the community activity of these genes needed to be biostimulated for accelerated bioremediation. In contrast, functional communities in the RS were capable of spontaneous natural attenuation of PAH. The degradation of PAH in the RS also required coordinated response of the complex functional community. Taken together, elucidating functions and network interactions in sediment microbial communities and their responses to environmental changes are very important for the bioremediation of anthropogenic toxic contaminants.

Impact of exogenous nitrogen on the cyanobacterial abundance and community in oil-contaminated sediment: A microcosm study

The pollution caused by oil spills is a global problem, and outbreaks of blue algae in oil-polluted areas are harmful to plankton in the ocean. The ocean is a barren environment limited by low availabilities of nitrogen and other nutrients, and further nitrogen limitation caused by oil contamination is considered one of the important factors leading to outbreaks of cyanobacteria, but the effects of nitrogen amendment in this situation are not well understood. Here, we present the results from nitrogen amendment experiments conducted in oil-contaminated microcosms. Green mats appeared on the sediment surface of each treatment group at different time points. The appearance of cyanobacterial blooms in the oil-contaminated group supplemented with nitrogen was significantly delayed compared with that in the oil-contaminated group without nitrogen addition. Moreover, oil promoted nitrogen fixation and stimulated the growth of nitrogen-fixing cyanobacteria in the oil-contaminated microcosms. Our results suggest that nitrogen limitation is a vital factor for the induction of cyanobacterial blooms in oil-contaminated environments, and the addition of nitrogen reduced the abundance of cyanobacteria by up to approximately 2.5-fold and slowed the bloom process.