**1. Introduction**

#### **1.1 Overview of** *Lactobacillus* **as a genus**

The genus *Lactobacillus* spp. are members of lactic acid bacteria (LAB) belonging to the family Lactobacillaceae, order Lactobacillales, class Bacilli, and phylum Firmicutes. For the past decades, the *Lactobacillus* genera have been revised and new genus names were assigned. From a taxonomic point of view, the genus *Lactobacillus* comprises 261 species (at March 2020) that are extremely diverse at phenotypic, ecological, and genotypic levels [1]. More than any genera of LAB, the genus *Lactobacillus* is generally regarded as safe (GRAS) and finds application in the food, dairy, cosmetic and pharmaceutical industries. The genus *Lactobacillus* is non-spore-forming, catalase-negative or pseudocatalase, oxidase negative, obligate saccharolytic rods or coccobacilli generally characterized by a low guanine and cytosine (GC) content

of the genome although the upper limit of GC content reaches 59.2 mol % [2]. The availability of 16S rRNA gene sequence and genome data has ultimately unlocked the frontiers of knowledge into the evolutionary relationships of *Lactobacillus* species.

Based on the type of sugar fermentation pathway, lactobacilli can be categorized into three groups, (i) obligatelyhomofermentative, that produce only lactic acid from glucose as an end product of carbohydrate metabolism through the glycolysis or Embden-Meyerhof- Parnas (EMP) pathway; (ii) facultativelyheterofermentative, that produce a mixture of lactic and acetic acid, diacetyl, acetoin, and carbon dioxide as end products of carbohydrate metabolism via the glycolysis or the phosphoketolase pathway, and; (iii) obligatelyheterofermentative, that produce lactic and acetic acid, or ethanol, and CO2 as end products of carbohydrate metabolism via the phosphoketolase (6-phosphogluconate) pathway [3].

The lactobacilli have varied resistance to different NaCl concentrations, antibiotics, and temperature or pH range mostly due to cellular fatty acids, isoprenoidquinones, and other characteristics of their cell wall composition [4].

Until recent times, most studies on lactobacilli were focused on their application in food fermentation and formed the greater percentage of probiotics in current use. However, the production of exopolysaccharides biopolymers has added a new dimension to the usefulness of lactobacilli.

This book chapter aims to critically look at *Lactobacillus* EPS, its inherent properties, potential pharmaceutical and industrial applications, and how to harness it in line with the 3rd and 9th components of the United Nations Sustainable Development Goals which include the establishment of good health and wellbeing and to promote industrialization, innovation, and infrastructure respectively.
