Acetobacter tropicalis

Classification

Introduction

Acetobacter tropicalis is a Gram-negative, rod-shaped bacterium that can be found in singles, chains, or pairs, with a size that ranges from 0.5-0.7 by 1.8-2.0 micrometers [1,2]. Similar to other species from the Acetobacter genus, A.tropicalis is an obligate aerobe that can oxidize ethanol to acetic acid; oxidize acetate and lactate into carbon dioxide and water; and produce acid from glucose. This bacteria best survives in places where sugar fermentation occurs (alcoholic ecological niches), in temperatures ranging from 20-37 degrees Celsius, and in pH levels of 3.5 to 8.0 [1].

In terms of the distinguishable features of this species,A.tropicalis is recognized as a benign microorganism that is present in multiple areas of the environment. The species gets its name because it is mainly found in tropical regions. The species was first found in Indonesia on coconut fruits [1,3]. Interestingly, this bacteria is also found to be symbiotically living with fruit flies and other insect model organisms [4]. Its colonies are positive for catalase activity [1, 2].

Morphology

Acetobacter tropicalis is a Gram-negative, rod-shaped bacterium that can be found in singles, chains, or pairs, with a size that ranges from 0.5-0.7 by 1.8-2.0 micrometers. From past studies conducted, it has been noted that these bacteria form colonies are circular, convex, glistening, and nonpigmented [5].

Genome

Wan et al. 2017 were able to isolate a strain of A. tropicalis from ''''Drosophila melanogaster'''' [5]. From these studies, the complete genome comprised a single chromosomal circle of 3,988,649 b, along with a 56% content of GC and a conjugative plasmid of 151,013 bp. At large, sequencing data available comprises 10 genome assemblies. The median total length of the genome is of 3.758 Mb, the median protein count is 3182, and the median GC% is of 55.55% [6, 7].

Metabolism

A. tropicalis is an obligate aerobe and therefore undergoes oxidative fermentation. Via the mechanisms of oxidative fermentation, an organism is capable of oxidizing a variety of carbohydrates to produce energy. In this process, lactic acid and ethanol can be converted into acetic acid [1,3,4]. This is usually a 2 step pathway, involving the change of ethanol to acetaldehyde and furthermore acetaldehyde into acetic acid [7].

Biochemical properties & distinguishable features

Acetic acid bacteria are known for their ability to spoil wines irreversibly [1] These bacteriums can be isolated from the industrial vinegar fermentation processes and are frequently used as fermentation starter cultures [2]. Beyond the food industry, some acetic acid bacteria are also used as biocatalysts for eco-friendly fermentation processes [1].

A. tropicalis can be distinguished from other species in multiple ways. It is found in a particular ecological niche and is most capable of surviving in particular temperature ranges (20-37 degrees Celsius) and pH levels (3.5 to 8.0.). [1,2] It can produce 2-Keto-D-gluconic acid from D-glucose. It can use maltose and glycerol as carbon sources but not methanol. Has positive catalase activity and it has between a 55.6-56.2 G+C content of DNA [1,4]. It is SO2 and DMDC sensitive, it can utilize sorbic acid [3,7].

Interaction with other organisms

It is important to note that contradictory results have been obtained regarding the role of microbiota in different organisms. This is mainly due to the fact that interactions and symbiotic associations between insects and their bacteria, protozoa, and fungi are complex. These relationships can shift from parasitism to mutualism and are formulated upon extracellular or intracellular interactions. At large, these interactions can have a strong influence on nutrition, physiology, or reproduction of the host [4].

A. tropicalis has mainly been found to live in insects on sugar-based diets, fruits, chocolate, and wine [1,2,3,6]. This may suggest that the presence of acetic acid bacteria has some sort of link to the insect sugar metabolism [4].

References

[1] Bartowski, Eveline and Henschke, Paul. “Acetic Acid Bacteria Spoilage of Bottled Red Wine – A Review.” Journal of Food Microbiology, June 2008, pages 60-70.

[2] Sievers, Martin, and Jean Swings. “Acetobacter.” Wiley Online Library, American Cancer Society, 14 Sept. 2015, onlinelibrary.wiley.com/doi/10.1002/9781118960608.gbm00876.

[3] Hakim, Samim. “Acetobacter Tropicalis.” Viticulture and Enology, 20 Mar. 2018, wineserver.ucdavis.edu/industry-info/enology/wine-microbiology/bacteria/acetobacter-tropicalis.

[4] Kounatidis, Ilias, et al. “Acetobacter Tropicalis Is a Major Symbiont of the Olive Fruit Fly (Bactrocera Oleae).” Applied and Environmental Microbiology, American Society for Microbiology, 15 May 2009, aem.asm.org/content/75/10/3281#sec-12.

[5] Wan, Kenneth H., et al. “Complete Genome Sequence of Acetobacter Tropicalis Oregon-R-ModENCODE Strain BDGP1, an Acetic Acid Bacterium Found in the Drosophila Melanogaster Gut.” Microbiology Resource Announcements, American Society for Microbiology, 16 Nov. 2017, mra.asm.org/content/5/46/e01020-17#ref-list-1.

[6] “Acetobacter Tropicalis (ID 10668).” National Center for Biotechnology Information, U.S. National Library of Medicine, www.ncbi.nlm.nih.gov/genome/?term=Acetobacter%2Btropicalis%5BOrganism%5D&cmd=DetailsSearch.

[7] “Acetobacter Tropicalis – Stiven Mita.” How Microbes Create Our Favorite Delicacies, 28 Nov. 2016, fermentationstations.wordpress.com/2016/11/01/acetobacter-tropicalis-stiven-mita/.