Experimental and molecular approximation to microbial niche: trophic interactions between oribatid mites and microfungi in an oligotrophic freshwater system

Abstract

Mite-fungal interactions play a key role in structuring core ecosystem processes such as nutrient dynamics. Despite their ecological relevance, these cross-kingdom interactions remain poorly understood particularly in extreme environments. Herein, we investigated feeding preferences of a novel genetic lineage of aquatic oribatids obtained from an oligotrophic freshwater system in the Cuatro Ciénegas Basin (CCB) within the Chihuahuan Desert, Mexico. During in vitro diet preference bioassays, transient aquatic microfungi (Aspergillus niger, Talaromyces sp., and Pleosporales sp.) recovered from the same mesocosm samples were offered individually and simultaneously to mites. Gut content was analyzed using classic plating and culture-independent direct PCR (focusing on the fungal barcoding region) methods. Our results indicated that oribatids fed on all tested fungal isolates, yet the profusely developing A. niger was preferentially consumed with all fungal components being digested. This feeding habit is particularly interesting since A. niger has been reported as an unsuitable dietary element for population growth, being consistently avoided by mites in previous laboratory experiments. It is possible that our mites from the CCB have adapted to exploit available resources within this oligotrophic site. This work confirms the trophic relationship between microfungi and mites, two rarely investigated major components of the microbial community, shedding light on the niche dynamics under low-nutrient conditions.

<p class="Body"><strong>A new species of <em>Trhypochthoniellus</em> (Acari: Oribatida: Trhypochthoniidae) from Cuatro Ciénegas, Coahuila, Mexico, and a key to the world species</strong></p><p class="Body"> </p>

“…We observed that T. churincensis sp. nov. reproduced differently on the three fungal species tested by Velez et al (2018), evident in the growth time of the different stages of development and the number of immature individuals in each of the treatments use. This fact, combined with its unspecialized feeding habits, may have allowed this species to endure through the extreme and fluctuating temperature and water chemistry conditions in the ponds and lagoons of the CCB.…”

“…Specimens of T. churincensis sp. nov. used in this study were obtained from several wood pine block submerged at the Laguna Intermedia of the Churince system in 2014-2015 (Cuatro Ciénegas Basin, Coahuila, Mexico; details see Velez et al 2018). Laboratory culture was started in November 2016 with 30 specimens for each block (total 5).…”

“…Observations on additional material from other two sites (La Becerra and Pozas Rojas) did not show broad biometric differences with those obtained from the Churince, and specimens show consistency in the absence of botridium and bothridial seta as well as number of genital setae. The molecular sequences obtained by Velez et al (2018) indicated that Trhypochthoniellus churincensis sp. nov., represent a novel genetic lineage within the Crotonioidea, close to Trhypochthonius cladonicolus (Willmann 1919).…”

“…In summary, mites belonging to T. churincensis sp. nov., have the ability to feed on the usually avoided and unsuitable Aspergillus niger (Velez et al 2018), and seem to be mostly opportunistic feeders 'choosy generalists' (Schneider & Maraun 2005), but with preferences, possibly for more nutrient-rich or less toxic food, as observed for Archegozetes longisetosus (Brückner et al 2018). Food preference imprinting may be not beneficial for a highly opportunistic/generalist oribatid mite species like T. churincensis sp.…”

Growth and Fatty Acid Profile of the Aspergillus terreus in Different Culture Media and Temperatures

“…Micronutrients, on the other hand, correspond to elements called trace elements such as calcium, copper, iron, manganese, and zinc (Martín et al, 2019). Some fungi are considered oligotrophic, that is, they can survive in environments with a very limited supply of nutrients, growing in inhospitable environments, with high acidity and at temperatures above 37 ºC, acting in the capture of small amounts of volatile organic compounds of the atmosphere (Velez et al, 2018). Chemotrophs are fungi that need fixed forms of organic compounds, ranging from simple hexoses such as glucose to some types of polysaccharides such as starch and cellulose, as a means of supplying carbon and energy (Meena and Siddhardha, 2019).…”