Microbial community of respiratory surfaces and features of tissue energy metabolism in the Black Sea bivalve mollusk Anadara kagoshimensis (Tokunaga, 1906) under conditions of acute hypoxia and hydrogen sulfide contaminationстатьяИсследовательская статья
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Аннотация:The phylogenetic composition of the microbiome from the respiratory surfaces of the bivalve mollusk Anadara kagoshimensis (Tokunaga, 1906) was studied for the first time with the use of high-throughput sequencing of 16S rRNA gene. The study revealed significant and rapid (within two days) alterations in the qualitative and quantitative composition of the microbial community. These alterations were influenced by the dissolved oxygen content and the presence of hydrogen sulfide in the environment. Furthermore, the observed alterations impacted metabolic pathways within A. kagoshimensis tissues. Under normoxic conditions (6.9–8.2 mg O2 l−1), the microbiome from the respiratory surfaces of ark shell was predominantly (85% of all 16S rRNA gene reads) composed of microorganisms belonging to the genus Stenotrophomonas (family Xanthomonadaceae), aerobic, catalase-positive, motile hydrolytic bacteria that actively consume oxygen. However, under normoxic conditions, the metabolism of ark shell gills was found to be anaerobic. This was evidenced by the highest lactate dehydrogenase (LDH) activity in relation to other tissues (foot, hepatopancreas), high lactate and low glucose content in this tissue. Under conditions of acute hypoxia (0.22–0.50 mg O2 l−1), the microbiome from the respiratory surfaces of A. kagoshimensis was found to be dominated by facultatively anaerobic microflora, predominantly consisting of bacteria from the genera Vibrio and Listonella. The main type of metabolism of these bacteria under anaerobic conditions is fermentation processes with the formation of various organic acid derivatives. Under conditions of acute hypoxia, glucose-lactate metabolism in A. kagoshimensis tissues was inhibited. The decrease in LDH and malate dehydrogenase (MDH) activities without any alteration in the content of pyruvate, lactate and glucose in the tissues when compared to the control group provides evidence for this. Hypoxia has been observed to induce an increase in succinate dehydrogenase (SDH) activity in all tissues, which may be explained by a decrease in the content of the SDH inhibitor, oxaloacetate. Exposure to hydrogen sulfide (6 mg S2⁻ l−1; 0.10–0.50 mg O2 l−1) resulted in the predominance of microaerophilic sulfide-oxidizing microorganisms in the respiratory tissues microbiome, consisting mainly of bacteria belonging to the family Arcobacteraceae (genera Pseudarcobacter, Halarcobacter and Arcobacter). The glucoselactate pathway of mollusk metabolism was completely suppressed under these conditions. The activity of SDH in the gills of A. kagoshimensis exposed to hydrogen sulfide did not change significantly in comparison with the control group. This finding suggests the protective role of microorganisms capable of oxidizing reduced sulfate compounds. Consequently, the functionality of the mitochondrial respiratory chain in mollusks exposed to hydrogen sulfide contamination becomes possible.
