Biology subjects

Baker, L. J.

Publications and source records attributed to Baker, L. J..

3 recordsLinked to original sources

bioRxiv2025

Symbiotic bacteria support calcium carbonate precipitation in the Gulf toadfish (Opsanus beta)

Marine fish play a significant yet understudied role in the oceanic carbon cycle through the production of magnesium rich calcium carbonate (CaCO3) precipitates known as ichthyocarbonates. These deposits form in the gut of marine teleost fish in response to salinity, serving as part of their osmoregulation strategy. Through this, marine fish may contribute as much as 9.04 Pg of CaCO3 per year in global new carbonate production, being equivalent to or potentially higher than the production by coccolithophores and pelagic foraminifera. Despite their ecological relevance, the biological mechanisms driving ichthyocarbonate precipitation remain to be fully resolved. Intriguingly, bacteria are consistently found in intimate association with ichthyocarbonate precipitates. Given the widespread capacity of prokaryotes to mediate CaCO precipitation, this association points to a previously unexplored microbial contribution to the process. To investigate the potential role of bacteria in ichthyocarbonate production, we subjected Gulf toadfish (Opsanus beta) to a salinity challenge common to their native range and known to elicit elevated CaCO3 precipitation. To assess the respective contributions of the host and its microbiota to ichthyocarbonate formation in the gut, we characterized the microbiome across the toadfish gut and performed meta-transcriptomic analysis. Across the toadfish gut, we identify a high abundance of vibrios associated with ichthyocarbonates with the metabolic potential for CaCO3 precipitation. Specifically, we observe the expression of the transcriptional activator of urease (ureR) by Photobacterium damselae subsp. damselae, which can induce the precipitation of CaCO3 via the production of bicarbonate. We demonstrate that CaCO precipitation in marine fish may not solely be a host-driven process, but potentially the result of a functional symbiosis with gut-associated Vibrio bacteria. We hypothesize that just as photosymbionts enable corals to build reefs, fish hosts along with their microbial partners may synergistically contribute to oceanic carbonate production. This discovery, if confirmed, expands the role of symbiosis in marine biomineralization and underscores its broader influence on global biogeochemical cycles.

microbiology↗

bioRxiv2023

Genome evolution following an ecological shift in nectar-dwelling Acinetobacter

The bacterial genus Acinetobacter includes species found in environmental habitats like soil and water, as well as species adapted to be host-associated or pathogenic. High genetic diversity may allow for this habitat flexibility, but the specific genes underlying switches between habitats are poorly understood. One lineage of Acinetobacter has undergone a substantial habitat change by evolving from a presumed soil-dwelling ancestral state to thrive in floral nectar. Here we compared the genomes of floral-dwelling and pollinator-associated Acinetobacter, including newly described species, with genomes from relatives found in other environments to determine the genomic changes associated with this ecological shift. Following one evolutionary origin of floral nectar adaptation, nectar-dwelling Acinetobacter species have undergone reduction in genome size compared to relatives and have experienced dynamic gene gains and losses as they diversified. We found changes in gene content underlying carbohydrate metabolism and nitrogen metabolism, which we predict to be beneficial in nectar environments. Gene losses follow a pattern consistent with genome streamlining, whereas gains appear to result from both evolutionary divergence and horizontal gene transfer. Most notably, nectar-dwelling Acinetobacter acquired the ability to degrade pectin from plant pathogens and the genes underlying this ability have duplicated and are under selection within the clade. We hypothesize that this ability was a key trait for adaptation to floral nectar, as it could improve access to nutrients in the nutritionally unbalanced habitat of nectar. These results identify the genomic changes and traits coinciding with a dramatic habitat switch from soil to floral nectar.

microbiology↗

bioRxiv2021

The coral symbiont Candidatus Aquarickettsia is variably abundant in threatened Caribbean acroporids and transmitted horizontally.

The aquatic symbiont "Candidatus Aquarickettsia rohweri" infects a diversity of non-bilaterian metazoan phyla. In the threatened coral Acropora cervicornis, Aquarickettsia proliferates in response to increased nutrient exposure, resulting in suppressed growth and increased disease susceptibility and mortality. This study evaluated the extent, as well as the ecology and evolution of Aquarickettsia infecting the Caribbean corals: Ac. cervicornis and Ac. palmata and their hybrid ( Ac. prolifera). The bacterial parasite Aquarickettsia was found in all acroporids, with host and sampling location impacting infection magnitude. Phylogenomic and genome-wide single nucleotide variant analysis found Aquarickettsia clustering by region, not by coral taxon. Fixation analysis suggested within coral colonies, Aquarickettsia are genetically isolated to the extent that reinfection is unlikely. Relative to other Rickettsiales, Aquarickettsia is undergoing positive selection, with Florida populations experiencing greater positive selection relative to the other Caribbean locations. This may be due to Aquarickettsia response to increased nutrient stress in Florida, as indicated by greater in situ replication rates in these corals. Aquarickettsia did not significantly codiversify with either coral animal nor algal symbiont, and qPCR analysis of gametes and juveniles from susceptible coral genotypes indicated absence in early life stages. Thus, despite being an obligate parasite, Aquarickettsia must be horizontally transmitted via coral mucocytes, an unidentified secondary host, or a yet unexplored environmentally mediated mechanism. Importantly, the prevalence of Aquarickettsia in Ac. cervicornis and high abundance in Florida populations suggests that disease mitigation efforts in the US and Caribbean should focus on preventing early infection via horizontal transmission.

microbiology↗