Biology subjects

Mack, M. C.

Publications and source records attributed to Mack, M. C..

3 recordsLinked to original sources

bioRxiv2026

Moss Transplants in the Tundra Reveal Host-Specific Microbiomes and Nitrogen Fixation Responses

In tundra ecosystems, moss-associated microbes are a major source of new nitrogen, yet the relative contributions of environment, host identity, and microbiome composition to variation in nitrogen-fixation rates are difficult to disentangle. To test how environmental change alters moss microbiomes and nitrogen-fixation rates, we used a one-year reciprocal transplant experiment between two Alaskan tundra sites that differ by 5{degrees}C in mean annual temperature. Intact moss cores containing one of three moss species, Hylocomium splendens, Aulacomnium turgidum, and Pleurozium schreberi, were transplanted between sites or returned to their home site. After one year, we quantified nitrogen-fixation rates using 15N incubation and characterized bacterial communities using 16S rRNA gene amplicon sequencing. H. splendens showed consistently low nitrogen-fixation rates with little transplant response, whereas P. schreberi and A. turgidum home and transplant tundra cores generally exhibited higher rates at the cooler, more northern site regardless of origin. In contrast, bacterial community structure changed little following transplantation, with composition driven primarily by moss species. Only in cyanobacteria and some heterotrophic bacterial lineages did we find subtle ASV-level changes. The absence of an association between microbial composition and nitrogen fixation, together with the heterogeneity among moss species, suggests that over short timescales, host physiology and microenvironment play a larger role in the variation of nitrogen-fixation rates than community turnover. The fact that short-term shifts in moss-associated nitrogen-fixation rate are driven primarily by host species identity, rather than microbiome restructuring, has important implications for near-term predictions of nitrogen inputs under Arctic climate change.

microbiology↗

bioRxiv2021

The Functional Significance of Bacterial Predators

Predation structures food webs, influences energy flow, and alters rates and pathways of nutrient cycling through ecosystems, effects that are well documented for macroscopic predators. In the microbial world, predatory bacteria are common, yet little is known about their rates of growth and roles in energy flows through microbial food webs, in part because these are difficult to quantify. Here, we show that growth and carbon uptake were higher in predatory bacteria compared to non-predatory bacteria, a finding across 15 sites, synthesizing 82 experiments and over 100,000 taxon-specific measurements of element flow into newly synthesized bacterial DNA. Obligate predatory bacteria grew 36% faster and assimilated carbon at rates 211% higher than non-predatory bacteria. These differences were less pronounced for facultative predators (6% higher growth rates, 17% higher carbon assimilation rates), though high growth and carbon assimilation rates were observed for some facultative predators, such as members of the genera Lysobacter and Cytophaga, both capable of gliding motility and wolfpack hunting behavior. Added carbon substrates disproportionately stimulated growth of obligate predators, with responses 63% higher than non-predators for the Bdellovibrionales and 81% higher for the Vampirovibrionales, whereas responses of facultative predators to substrate addition were no different from non-predators. This finding supports ecological theory that higher productivity increases predator control of lower trophic levels. These findings also indicate that the functional significance of bacterial predators increases with energy flow, and that predatory bacteria influence element flow through microbial food webs.

ecology↗

bioRxiv2017

Novel bacterial lineages associated with boreal moss species

Mosses are critical components of boreal ecosystems where they typically account for a large proportion of net primary productivity and harbor diverse bacterial communities that can be the major source of biologically-fixed nitrogen in these ecosystems. Despite their ecological importance, we have limited understanding of how microbial communities vary across boreal moss species and the extent to which local environmental conditions may influence the composition of these bacterial communities. We used marker gene sequencing to analyze bacterial communities associated with eight boreal moss species collected near Fairbanks, AK USA. We found that host identity was more important than site in determining bacterial community composition and that mosses harbor diverse lineages of potential N2- fixers as well as an abundance of novel taxa assigned to understudied bacterial phyla (including candidate phylum WPS-2). We performed shotgun metagenomic sequencing to assemble genomes from the WPS-2 candidate phylum and found that these moss-associated bacteria are likely anoxygenic phototrophs capable of carbon fixation via RuBisCo with an ability to utilize byproducts of photorespiration from hosts via a glyoxylate shunt. These results give new insights into the metabolic capabilities of understudied bacterial lineages that associate with mosses and the importance of plant hosts in shaping their microbiomes.

microbiology↗