Enrichment of bacteria and alginate lyase genes potentially involved in brown alga degradation in the gut of marine gastropods

Michihiro Ito,Kotaro Watanabe,Tetsushi Mori,Kentaro Niwa,Toru Maruyama,Seinen Chow,Haruko Takeyama

doi:10.1038/s41598-018-38356-y

Abstract

Gut bacteria of phytophagous and omnivorous marine invertebrates often possess alginate lyases (ALGs), which are key enzymes for utilizing macroalgae as carbon neutral biomass. We hypothesized that the exclusive feeding of a target alga to marine invertebrates would shift the gut bacterial diversity suitable for degrading the algal components. To test this hypothesis, we reared sea hare (Dolabella auricularia) and sea snail (Batillus cornutus) for two to four weeks with exclusive feeding of a brown alga (Ecklonia cava). Pyrosequencing analysis of the gut bacterial 16S rRNA genes revealed shifts in the gut microbiota after rearing, mainly due to a decrease in the variety of bacterial members. Significant increases in six and four 16S rRNA gene phylotypes were observed in the reared sea hares and sea snails, respectively, and some of them were phylogenetically close to known alginate-degrading bacteria. Clone library analysis of PL7 family ALG genes using newly designed degenerate primer sets detected a total of 50 ALG gene phylotypes based on 90% amino acid identity. The number of ALG gene phylotypes increased in the reared sea hare but decreased in reared sea snail samples, and no phylotype was shared between them. Out of the 50 phylotypes, 15 were detected only after the feeding procedure. Thus, controlled feeding strategy may be valid and useful for the efficient screening of genes suitable for target alga fermentation.

Highlights

There have been recent developments in the use of marine macroalgae for biofuel production because of their high productivity, high abundance in nations bordering the sea, and compatibility with food resources[1,2,3]
Several bacterial alginate degraders were found in the gut microbiota of brown algae-eating marine invertebrates such as sea snails[26], sea urchins[27], and abalones[28,29,30,31,32]
All individuals used for rearing experiment (seven for the sea hare (SH) D. auricularia and six for the sea snail (SS) B. cornutus) survived until the end of experiment

Summary

Introduction

There have been recent developments in the use of marine macroalgae for biofuel production because of their high productivity, high abundance in nations bordering the sea, and compatibility with food resources[1,2,3]. Brown algae have the highest productivity among marine macroalgae[7] They contain polysaccharides such as alginate, fucoidan, cellulose, laminaran, and mannitol, among which alginate is the predominant structural polysaccharide constituting 10‒40% of dry weight[8]. Several bacterial alginate degraders were found in the gut microbiota of brown algae-eating marine invertebrates such as sea snails[26], sea urchins[27], and abalones[28,29,30,31,32]. The gut microbiota of phytophagous or omnivorous marine invertebrates may be suitable gene resources for the degradation of macroalgae components. The procedure for rearing marine invertebrates with a brown alga could result in the gut microbiota that habour genes necessary for degradation of the algal alginate polymers

Methods

Results

Conclusion